Make traits public to allow PCC to use formatting traits

Co-authored-by: Jędrzej Stuczyński <jedrzej.stuczynski@gmail.com>

Cargo.lock

@@ -396,7 +396,10 @@ version = "0.2.17"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ba3569f383e8f1598449f1a423e72e99569137b47740b1da11ef19af3d5c3223"
 dependencies = [
+ "lazy_static",
  "memchr",
+ "regex-automata",
+ "serde",
 ]
 
 [[package]]
@@ -468,6 +471,15 @@ dependencies = [
  "system-deps 3.2.0",
 ]
 
+[[package]]
+name = "cast"
+version = "0.2.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4c24dab4283a142afa2fdca129b80ad2c6284e073930f964c3a1293c225ee39a"
+dependencies = [
+ "rustc_version 0.4.0",
+]
+
 [[package]]
 name = "cc"
 version = "1.0.70"
@@ -631,30 +643,11 @@ dependencies = [
 name = "coconut-interface"
 version = "0.1.0"
 dependencies = [
- "coconut-rs",
  "getset",
+ "nymcoconut",
  "serde",
 ]
 
-[[package]]
-name = "coconut-rs"
-version = "0.5.0"
-source = "git+https://github.com/nymtech/coconut.git?branch=0.5.0#a1b72d51aa2a67b73b9f58d707030ae6dc70af7f"
-dependencies = [
- "bls12_381",
- "bs58",
- "digest 0.9.0",
- "ff",
- "getrandom 0.2.3",
- "group",
- "itertools",
- "rand 0.8.4",
- "serde",
- "serde_derive",
- "sha2",
- "thiserror",
-]
-
 [[package]]
 name = "colored"
 version = "2.0.0"
@@ -948,6 +941,42 @@ dependencies = [
  "validator-client",
 ]
 
+[[package]]
+name = "criterion"
+version = "0.3.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1604dafd25fba2fe2d5895a9da139f8dc9b319a5fe5354ca137cbbce4e178d10"
+dependencies = [
+ "atty",
+ "cast",
+ "clap",
+ "criterion-plot",
+ "csv",
+ "itertools",
+ "lazy_static",
+ "num-traits",
+ "oorandom",
+ "plotters",
+ "rayon",
+ "regex",
+ "serde",
+ "serde_cbor",
+ "serde_derive",
+ "serde_json",
+ "tinytemplate",
+ "walkdir",
+]
+
+[[package]]
+name = "criterion-plot"
+version = "0.4.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d00996de9f2f7559f7f4dc286073197f83e92256a59ed395f9aac01fe717da57"
+dependencies = [
+ "cast",
+ "itertools",
+]
+
 [[package]]
 name = "crossbeam-channel"
 version = "0.5.1"
@@ -1087,6 +1116,28 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "csv"
+version = "1.1.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "22813a6dc45b335f9bade10bf7271dc477e81113e89eb251a0bc2a8a81c536e1"
+dependencies = [
+ "bstr",
+ "csv-core",
+ "itoa",
+ "ryu",
+ "serde",
+]
+
+[[package]]
+name = "csv-core"
+version = "0.1.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2b2466559f260f48ad25fe6317b3c8dac77b5bdb5763ac7d9d6103530663bc90"
+dependencies = [
+ "memchr",
+]
+
 [[package]]
 name = "ct-logs"
 version = "0.8.0"
@@ -2271,6 +2322,12 @@ dependencies = [
  "tracing",
 ]
 
+[[package]]
+name = "half"
+version = "1.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "62aca2aba2d62b4a7f5b33f3712cb1b0692779a56fb510499d5c0aa594daeaf3"
+
 [[package]]
 name = "handlebars"
 version = "3.5.5"
@@ -3454,6 +3511,27 @@ dependencies = [
  "version-checker",
 ]
 
+[[package]]
+name = "nymcoconut"
+version = "0.5.0"
+dependencies = [
+ "bincode",
+ "bls12_381",
+ "bs58",
+ "criterion",
+ "digest 0.9.0",
+ "doc-comment",
+ "ff",
+ "getrandom 0.2.3",
+ "group",
+ "itertools",
+ "rand 0.8.4",
+ "serde",
+ "serde_derive",
+ "sha2",
+ "thiserror",
+]
+
 [[package]]
 name = "nymsphinx"
 version = "0.1.0"
@@ -3618,6 +3696,12 @@ version = "1.8.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "692fcb63b64b1758029e0a96ee63e049ce8c5948587f2f7208df04625e5f6b56"
 
+[[package]]
+name = "oorandom"
+version = "11.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0ab1bc2a289d34bd04a330323ac98a1b4bc82c9d9fcb1e66b63caa84da26b575"
+
 [[package]]
 name = "opaque-debug"
 version = "0.2.3"
@@ -4022,6 +4106,34 @@ version = "0.3.20"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7c9b1041b4387893b91ee6746cddfc28516aff326a3519fb2adf820932c5e6cb"
 
+[[package]]
+name = "plotters"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "32a3fd9ec30b9749ce28cd91f255d569591cdf937fe280c312143e3c4bad6f2a"
+dependencies = [
+ "num-traits",
+ "plotters-backend",
+ "plotters-svg",
+ "wasm-bindgen",
+ "web-sys",
+]
+
+[[package]]
+name = "plotters-backend"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d88417318da0eaf0fdcdb51a0ee6c3bed624333bff8f946733049380be67ac1c"
+
+[[package]]
+name = "plotters-svg"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "521fa9638fa597e1dc53e9412a4f9cefb01187ee1f7413076f9e6749e2885ba9"
+dependencies = [
+ "plotters-backend",
+]
+
 [[package]]
 name = "pmutil"
 version = "0.5.3"
@@ -4549,6 +4661,12 @@ dependencies = [
  "regex-syntax",
 ]
 
+[[package]]
+name = "regex-automata"
+version = "0.1.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6c230d73fb8d8c1b9c0b3135c5142a8acee3a0558fb8db5cf1cb65f8d7862132"
+
 [[package]]
 name = "regex-syntax"
 version = "0.6.25"
@@ -4814,6 +4932,15 @@ dependencies = [
  "semver 0.11.0",
 ]
 
+[[package]]
+name = "rustc_version"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bfa0f585226d2e68097d4f95d113b15b83a82e819ab25717ec0590d9584ef366"
+dependencies = [
+ "semver 1.0.4",
+]
+
 [[package]]
 name = "rustls"
 version = "0.19.1"
@@ -5035,6 +5162,16 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "serde_cbor"
+version = "0.11.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2bef2ebfde456fb76bbcf9f59315333decc4fda0b2b44b420243c11e0f5ec1f5"
+dependencies = [
+ "half",
+ "serde",
+]
+
 [[package]]
 name = "serde_derive"
 version = "1.0.130"
@@ -6283,6 +6420,16 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "tinytemplate"
+version = "1.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "be4d6b5f19ff7664e8c98d03e2139cb510db9b0a60b55f8e8709b689d939b6bc"
+dependencies = [
+ "serde",
+ "serde_json",
+]
+
 [[package]]
 name = "tokio"
 version = "1.12.0"

Cargo.toml

@@ -29,6 +29,7 @@ members = [
     "common/mixnode-common",
     "common/network-defaults",
     "common/nonexhaustive-delayqueue",
+    "common/nymcoconut",
     "common/nymsphinx",
     "common/nymsphinx/acknowledgements",
     "common/nymsphinx/addressing",

clients/native/src/client/mod.rs

@@ -1,8 +1,10 @@
 // Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0
 
-use crate::client::config::{Config, SocketType};
-use crate::websocket;
+use futures::channel::mpsc;
+use log::*;
+use tokio::runtime::Runtime;
+
 use client_core::client::cover_traffic_stream::LoopCoverTrafficStream;
 use client_core::client::inbound_messages::{
     InputMessage, InputMessageReceiver, InputMessageSender,
@@ -22,23 +24,26 @@ use client_core::client::topology_control::{
     TopologyAccessor, TopologyRefresher, TopologyRefresherConfig,
 };
 use client_core::config::persistence::key_pathfinder::ClientKeyPathfinder;
+#[cfg(feature = "coconut")]
+use coconut_interface::{hash_to_scalar, Credential, Parameters};
+#[cfg(feature = "coconut")]
+use credentials::bandwidth::{
+    prepare_for_spending, BandwidthVoucherAttributes, BANDWIDTH_VALUE, TOTAL_ATTRIBUTES,
+};
+#[cfg(feature = "coconut")]
+use credentials::obtain_aggregate_verification_key;
 use crypto::asymmetric::identity;
-use futures::channel::mpsc;
 use gateway_client::{
     AcknowledgementReceiver, AcknowledgementSender, GatewayClient, MixnetMessageReceiver,
     MixnetMessageSender,
 };
-use log::*;
 use nymsphinx::addressing::clients::Recipient;
 use nymsphinx::addressing::nodes::NodeIdentity;
 use nymsphinx::anonymous_replies::ReplySurb;
 use nymsphinx::receiver::ReconstructedMessage;
-use tokio::runtime::Runtime;
 
-#[cfg(feature = "coconut")]
-use coconut_interface::Credential;
-#[cfg(feature = "coconut")]
-use credentials::{bandwidth::prepare_for_spending, obtain_aggregate_verification_key};
+use crate::client::config::{Config, SocketType};
+use crate::websocket;
 
 pub(crate) mod config;
 
@@ -176,8 +181,17 @@ impl NymClient {
         .await
         .expect("could not obtain aggregate verification key of validators");
 
+        let params = Parameters::new(TOTAL_ATTRIBUTES).unwrap();
+        let bandwidth_credential_attributes = BandwidthVoucherAttributes {
+            serial_number: params.random_scalar(),
+            binding_number: params.random_scalar(),
+            voucher_value: hash_to_scalar(BANDWIDTH_VALUE.to_be_bytes()),
+            voucher_info: hash_to_scalar(String::from("BandwidthVoucher").as_bytes()),
+        };
+
         let bandwidth_credential = credentials::bandwidth::obtain_signature(
-            &self.key_manager.identity_keypair().public_key().to_bytes(),
+            &params,
+            &bandwidth_credential_attributes,
             &self.config.get_base().get_validator_api_endpoints(),
         )
         .await
@@ -188,6 +202,7 @@ impl NymClient {
         prepare_for_spending(
             &self.key_manager.identity_keypair().public_key().to_bytes(),
             &bandwidth_credential,
+            &bandwidth_credential_attributes,
             &verification_key,
         )
         .expect("could not prepare out bandwidth credential for spending")

clients/native/src/commands/init.rs

@@ -1,25 +1,36 @@
 // Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0
 
-use crate::client::config::Config;
-use crate::commands::override_config;
+use std::convert::TryInto;
+use std::sync::Arc;
+use std::time::Duration;
+
 use clap::{App, Arg, ArgMatches};
+use rand::rngs::OsRng;
+use rand::seq::SliceRandom;
+use rand::thread_rng;
+use url::Url;
+
 use client_core::client::key_manager::KeyManager;
 use client_core::config::persistence::key_pathfinder::ClientKeyPathfinder;
+#[cfg(feature = "coconut")]
+use coconut_interface::{hash_to_scalar, Credential, Parameters};
 use config::NymConfig;
+#[cfg(feature = "coconut")]
+use credentials::bandwidth::{
+    prepare_for_spending, BandwidthVoucherAttributes, BANDWIDTH_VALUE, TOTAL_ATTRIBUTES,
+};
+#[cfg(feature = "coconut")]
+use credentials::obtain_aggregate_verification_key;
 use crypto::asymmetric::{encryption, identity};
 use gateway_client::GatewayClient;
 use gateway_requests::registration::handshake::SharedKeys;
 use nymsphinx::addressing::clients::Recipient;
 use nymsphinx::addressing::nodes::NodeIdentity;
-use rand::rngs::OsRng;
-use rand::seq::SliceRandom;
-use rand::thread_rng;
-use std::convert::TryInto;
-use std::sync::Arc;
-use std::time::Duration;
 use topology::{filter::VersionFilterable, gateway};
-use url::Url;
+
+use crate::client::config::Config;
+use crate::commands::override_config;
 
 pub fn command_args<'a, 'b>() -> clap::App<'a, 'b> {
     App::new("init")
@@ -36,9 +47,9 @@ pub fn command_args<'a, 'b>() -> clap::App<'a, 'b> {
             .takes_value(true)
         )
         .arg(Arg::with_name("validators")
-                .long("validators")
-                .help("Comma separated list of rest endpoints of the validators")
-                .takes_value(true),
+                 .long("validators")
+                 .help("Comma separated list of rest endpoints of the validators")
+                 .takes_value(true),
         )
         .arg(Arg::with_name("disable-socket")
             .long("disable-socket")
@@ -57,6 +68,39 @@ pub fn command_args<'a, 'b>() -> clap::App<'a, 'b> {
         )
 }
 
+// this behaviour should definitely be changed, we shouldn't
+// need to get bandwidth credential for registration
+#[cfg(feature = "coconut")]
+async fn _prepare_temporary_credential(validators: &[Url], raw_identity: &[u8]) -> Credential {
+    let verification_key = obtain_aggregate_verification_key(validators)
+        .await
+        .expect("could not obtain aggregate verification key of validators");
+
+    let params = Parameters::new(TOTAL_ATTRIBUTES).unwrap();
+    let bandwidth_credential_attributes = BandwidthVoucherAttributes {
+        serial_number: params.random_scalar(),
+        binding_number: params.random_scalar(),
+        voucher_value: hash_to_scalar(BANDWIDTH_VALUE.to_be_bytes()),
+        voucher_info: hash_to_scalar(String::from("BandwidthVoucher").as_bytes()),
+    };
+
+    let bandwidth_credential = credentials::bandwidth::obtain_signature(
+        &params,
+        &bandwidth_credential_attributes,
+        validators,
+    )
+    .await
+    .expect("could not obtain bandwidth credential");
+
+    prepare_for_spending(
+        raw_identity,
+        &bandwidth_credential,
+        &bandwidth_credential_attributes,
+        &verification_key,
+    )
+    .expect("could not prepare out bandwidth credential for spending")
+}
+
 async fn register_with_gateway(
     gateway: &gateway::Node,
     our_identity: Arc<identity::KeyPair>,

clients/socks5/src/client/mod.rs

@@ -1,11 +1,10 @@
 // Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0
 
-use crate::client::config::Config;
-use crate::socks::{
-    authentication::{AuthenticationMethods, Authenticator, User},
-    server::SphinxSocksServer,
-};
+use futures::channel::mpsc;
+use log::*;
+use tokio::runtime::Runtime;
+
 use client_core::client::cover_traffic_stream::LoopCoverTrafficStream;
 use client_core::client::inbound_messages::{
     InputMessage, InputMessageReceiver, InputMessageSender,
@@ -23,21 +22,27 @@ use client_core::client::topology_control::{
     TopologyAccessor, TopologyRefresher, TopologyRefresherConfig,
 };
 use client_core::config::persistence::key_pathfinder::ClientKeyPathfinder;
+#[cfg(feature = "coconut")]
+use coconut_interface::{hash_to_scalar, Credential, Parameters};
+#[cfg(feature = "coconut")]
+use credentials::bandwidth::{
+    prepare_for_spending, BandwidthVoucherAttributes, BANDWIDTH_VALUE, TOTAL_ATTRIBUTES,
+};
+#[cfg(feature = "coconut")]
+use credentials::obtain_aggregate_verification_key;
 use crypto::asymmetric::identity;
-use futures::channel::mpsc;
 use gateway_client::{
     AcknowledgementReceiver, AcknowledgementSender, GatewayClient, MixnetMessageReceiver,
     MixnetMessageSender,
 };
-use log::*;
 use nymsphinx::addressing::clients::Recipient;
 use nymsphinx::addressing::nodes::NodeIdentity;
-use tokio::runtime::Runtime;
 
-#[cfg(feature = "coconut")]
-use coconut_interface::Credential;
-#[cfg(feature = "coconut")]
-use credentials::{bandwidth::prepare_for_spending, obtain_aggregate_verification_key};
+use crate::client::config::Config;
+use crate::socks::{
+    authentication::{AuthenticationMethods, Authenticator, User},
+    server::SphinxSocksServer,
+};
 
 pub(crate) mod config;
 
@@ -164,8 +169,17 @@ impl NymClient {
         .await
         .expect("could not obtain aggregate verification key of validators");
 
+        let params = Parameters::new(TOTAL_ATTRIBUTES).unwrap();
+        let bandwidth_credential_attributes = BandwidthVoucherAttributes {
+            serial_number: params.random_scalar(),
+            binding_number: params.random_scalar(),
+            voucher_value: hash_to_scalar(BANDWIDTH_VALUE.to_be_bytes()),
+            voucher_info: hash_to_scalar(String::from("BandwidthVoucher").as_bytes()),
+        };
+
         let bandwidth_credential = credentials::bandwidth::obtain_signature(
-            &self.key_manager.identity_keypair().public_key().to_bytes(),
+            &params,
+            &bandwidth_credential_attributes,
             &self.config.get_base().get_validator_api_endpoints(),
         )
         .await
@@ -176,6 +190,7 @@ impl NymClient {
         prepare_for_spending(
             &self.key_manager.identity_keypair().public_key().to_bytes(),
             &bandwidth_credential,
+            &bandwidth_credential_attributes,
             &verification_key,
         )
         .expect("could not prepare out bandwidth credential for spending")

clients/socks5/src/commands/init.rs

@@ -1,23 +1,34 @@
 // Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0
 
-use crate::client::config::Config;
-use crate::commands::override_config;
+use std::convert::TryInto;
+use std::sync::Arc;
+use std::time::Duration;
+
 use clap::{App, Arg, ArgMatches};
+use rand::{prelude::SliceRandom, rngs::OsRng, thread_rng};
+use url::Url;
+
 use client_core::client::key_manager::KeyManager;
 use client_core::config::persistence::key_pathfinder::ClientKeyPathfinder;
+#[cfg(feature = "coconut")]
+use coconut_interface::{hash_to_scalar, Credential, Parameters};
 use config::NymConfig;
+#[cfg(feature = "coconut")]
+use credentials::bandwidth::{
+    prepare_for_spending, BandwidthVoucherAttributes, BANDWIDTH_VALUE, TOTAL_ATTRIBUTES,
+};
+#[cfg(feature = "coconut")]
+use credentials::obtain_aggregate_verification_key;
 use crypto::asymmetric::{encryption, identity};
 use gateway_client::GatewayClient;
 use gateway_requests::registration::handshake::SharedKeys;
 use nymsphinx::addressing::clients::Recipient;
 use nymsphinx::addressing::nodes::NodeIdentity;
-use rand::{prelude::SliceRandom, rngs::OsRng, thread_rng};
-use std::convert::TryInto;
-use std::sync::Arc;
-use std::time::Duration;
 use topology::{filter::VersionFilterable, gateway};
-use url::Url;
+
+use crate::client::config::Config;
+use crate::commands::override_config;
 
 pub fn command_args<'a, 'b>() -> clap::App<'a, 'b> {
     App::new("init")
@@ -40,9 +51,9 @@ pub fn command_args<'a, 'b>() -> clap::App<'a, 'b> {
             .takes_value(true)
         )
         .arg(Arg::with_name("validators")
-                .long("validators")
-                .help("Comma separated list of rest endpoints of the validators")
-                .takes_value(true),
+                 .long("validators")
+                 .help("Comma separated list of rest endpoints of the validators")
+                 .takes_value(true),
         )
         .arg(Arg::with_name("port")
             .short("p")
@@ -57,6 +68,39 @@ pub fn command_args<'a, 'b>() -> clap::App<'a, 'b> {
         )
 }
 
+// this behaviour should definitely be changed, we shouldn't
+// need to get bandwidth credential for registration
+#[cfg(feature = "coconut")]
+async fn _prepare_temporary_credential(validators: &[Url], raw_identity: &[u8]) -> Credential {
+    let verification_key = obtain_aggregate_verification_key(validators)
+        .await
+        .expect("could not obtain aggregate verification key of validators");
+
+    let params = Parameters::new(TOTAL_ATTRIBUTES).unwrap();
+    let bandwidth_credential_attributes = BandwidthVoucherAttributes {
+        serial_number: params.random_scalar(),
+        binding_number: params.random_scalar(),
+        voucher_value: hash_to_scalar(BANDWIDTH_VALUE.to_be_bytes()),
+        voucher_info: hash_to_scalar("BandwidthVoucher"),
+    };
+
+    let bandwidth_credential = credentials::bandwidth::obtain_signature(
+        &params,
+        &bandwidth_credential_attributes,
+        validators,
+    )
+    .await
+    .expect("could not obtain bandwidth credential");
+
+    prepare_for_spending(
+        raw_identity,
+        &bandwidth_credential,
+        &bandwidth_credential_attributes,
+        &verification_key,
+    )
+    .expect("could not prepare out bandwidth credential for spending")
+}
+
 async fn register_with_gateway(
     gateway: &gateway::Node,
     our_identity: Arc<identity::KeyPair>,

clients/tauri-client/src-tauri/src/main.rs

@@ -3,21 +3,24 @@
   windows_subsystem = "windows"
 )]
 
+use std::sync::Arc;
+
+use tokio::sync::RwLock;
+use url::Url;
+
 use coconut_interface::{
   self, hash_to_scalar, Attribute, Credential, Parameters, Signature, Theta, VerificationKey,
 };
 use credentials::{obtain_aggregate_signature, obtain_aggregate_verification_key};
-use std::sync::Arc;
-use tokio::sync::RwLock;
-use url::Url;
 
 struct State {
   signatures: Vec<Signature>,
   n_attributes: u32,
   params: Parameters,
-  public_attributes_bytes: Vec<Vec<u8>>,
-  public_attributes: Vec<Attribute>,
-  private_attributes: Vec<Attribute>,
+  serial_number: Attribute,
+  binding_number: Attribute,
+  voucher_value: Attribute,
+  voucher_info: Attribute,
   aggregated_verification_key: Option<VerificationKey>,
 }
 
@@ -37,9 +40,10 @@ impl State {
       signatures: Vec::new(),
       n_attributes,
       params,
-      public_attributes_bytes,
-      public_attributes,
-      private_attributes,
+      serial_number: private_attributes[0],
+      binding_number: private_attributes[1],
+      voucher_value: public_attributes[0],
+      voucher_info: public_attributes[1],
       aggregated_verification_key: None,
     }
   }
@@ -63,8 +67,8 @@ async fn randomise_credential(
 ) -> Result<Vec<Signature>, String> {
   let mut state = state.write().await;
   let signature = state.signatures.remove(idx);
-  let new = signature.randomise(&state.params);
-  state.signatures.insert(idx, new);
+  let (new_signature, _) = signature.randomise(&state.params);
+  state.signatures.insert(idx, new_signature);
   Ok(state.signatures.clone())
 }
 
@@ -117,14 +121,15 @@ async fn prove_credential(
   let state = state.read().await;
 
   if let Some(signature) = state.signatures.get(idx) {
-    match coconut_interface::prove_credential(
+    match coconut_interface::prove_bandwidth_credential(
       &state.params,
       &verification_key,
       signature,
-      &state.private_attributes,
+      state.serial_number,
+      state.binding_number,
     ) {
       Ok(theta) => Ok(theta),
-      Err(e) => Err(format!("{}", e)),
+      Err(e) => Err(format!("{:?}", e)),
     }
   } else {
     Err("Got invalid Signature idx".to_string())
@@ -144,10 +149,15 @@ async fn verify_credential(
 
   let state = state.read().await;
 
+  let public_attributes_bytes = vec![
+    state.voucher_value.to_bytes().to_vec(),
+    state.voucher_info.to_bytes().to_vec(),
+  ];
+
   let credential = Credential::new(
     state.n_attributes,
     theta,
-    state.public_attributes_bytes.clone(),
+    public_attributes_bytes,
     state
       .signatures
       .get(idx)
@@ -164,11 +174,13 @@ async fn get_credential(
 ) -> Result<Vec<Signature>, String> {
   let guard = state.read().await;
   let parsed_urls = parse_url_validators(&validator_urls)?;
+  let public_attributes = vec![guard.voucher_value, guard.voucher_info];
+  let private_attributes = vec![guard.serial_number, guard.binding_number];
 
   let signature = obtain_aggregate_signature(
     &guard.params,
-    &guard.public_attributes,
-    &guard.private_attributes,
+    &public_attributes,
+    &private_attributes,
     &parsed_urls,
   )
   .await

clients/webassembly/src/client/mod.rs

@@ -1,26 +1,31 @@
 // Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0
 
-use crypto::asymmetric::{encryption, identity};
-use futures::channel::mpsc;
-use gateway_client::GatewayClient;
-use nymsphinx::acknowledgements::AckKey;
-use nymsphinx::addressing::clients::Recipient;
-use nymsphinx::preparer::MessagePreparer;
-use rand::rngs::OsRng;
-use received_processor::ReceivedMessagesProcessor;
 use std::sync::Arc;
 use std::time::Duration;
-use topology::{gateway, nym_topology_from_bonds, NymTopology};
+
+use futures::channel::mpsc;
+use rand::rngs::OsRng;
 use url::Url;
 use wasm_bindgen::prelude::*;
 use wasm_bindgen_futures::spawn_local;
-use wasm_utils::{console_log, console_warn};
 
 #[cfg(feature = "coconut")]
 use coconut_interface::Credential;
 #[cfg(feature = "coconut")]
+use coconut_interface::{hash_to_scalar, Parameters};
+#[cfg(feature = "coconut")]
+use credentials::bandwidth::{BandwidthVoucherAttributes, BANDWIDTH_VALUE, TOTAL_ATTRIBUTES};
+#[cfg(feature = "coconut")]
 use credentials::{bandwidth::prepare_for_spending, obtain_aggregate_verification_key};
+use crypto::asymmetric::{encryption, identity};
+use gateway_client::GatewayClient;
+use nymsphinx::acknowledgements::AckKey;
+use nymsphinx::addressing::clients::Recipient;
+use nymsphinx::preparer::MessagePreparer;
+use received_processor::ReceivedMessagesProcessor;
+use topology::{gateway, nym_topology_from_bonds, NymTopology};
+use wasm_utils::{console_log, console_warn};
 
 pub(crate) mod received_processor;
 
@@ -109,15 +114,31 @@ impl NymClient {
             .await
             .expect("could not obtain aggregate verification key of validators");
 
-        let bandwidth_credential =
-            credentials::bandwidth::obtain_signature(identity_bytes, validators)
-                .await
-                .expect("could not obtain bandwidth credential");
+        let params = Parameters::new(TOTAL_ATTRIBUTES).unwrap();
+        let bandwidth_credential_attributes = BandwidthVoucherAttributes {
+            serial_number: params.random_scalar(),
+            binding_number: params.random_scalar(),
+            voucher_value: hash_to_scalar(BANDWIDTH_VALUE.to_be_bytes()),
+            voucher_info: hash_to_scalar(String::from("BandwidthVoucher").as_bytes()),
+        };
+
+        let bandwidth_credential = credentials::bandwidth::obtain_signature(
+            &params,
+            &bandwidth_credential_attributes,
+            validators,
+        )
+        .await
+        .expect("could not obtain bandwidth credential");
         // the above would presumably be loaded from a file
 
         // the below would only be executed once we know where we want to spend it (i.e. which gateway and stuff)
-        prepare_for_spending(identity_bytes, &bandwidth_credential, &verification_key)
-            .expect("could not prepare out bandwidth credential for spending")
+        prepare_for_spending(
+            identity_bytes,
+            &bandwidth_credential,
+            &bandwidth_credential_attributes,
+            &verification_key,
+        )
+        .expect("could not prepare out bandwidth credential for spending")
     }
 
     // Right now it's impossible to have async exported functions to take `&self` rather than self
@@ -275,7 +296,7 @@ impl NymClient {
         let validator_client = validator_client::ApiClient::new(self.validator_server.clone());
 
         let mixnodes = match validator_client.get_cached_active_mixnodes().await {
-            Err(err) => panic!("{}", err),
+            Err(err) => panic!("{:?}", err),
             Ok(mixes) => mixes,
         };
 

common/coconut-interface/Cargo.toml

@@ -8,4 +8,4 @@ description = "Crutch library until there is proper SerDe support for coconut st
 serde = { version = "1.0", features = ["derive"] }
 getset = "0.1.1"
 
-coconut-rs = { git = "https://github.com/nymtech/coconut.git", branch = "0.5.0" }
+nymcoconut = {path = "../nymcoconut" }

common/coconut-interface/src/lib.rs

@@ -4,7 +4,7 @@
 use getset::{CopyGetters, Getters};
 use serde::{Deserialize, Serialize};
 
-pub use coconut_rs::*;
+pub use nymcoconut::*;
 
 #[derive(Serialize, Deserialize, Getters, CopyGetters, Clone)]
 pub struct Credential {
@@ -42,7 +42,7 @@ impl Credential {
             .iter()
             .map(hash_to_scalar)
             .collect::<Vec<Attribute>>();
-        coconut_rs::verify_credential(&params, verification_key, &self.theta, &public_attributes)
+        nymcoconut::verify_credential(&params, verification_key, &self.theta, &public_attributes)
     }
 }
 
@@ -84,7 +84,7 @@ pub struct BlindSignRequestBody {
     #[getset(get = "pub")]
     blind_sign_request: BlindSignRequest,
     #[getset(get = "pub")]
-    public_key: coconut_rs::PublicKey,
+    public_key: nymcoconut::PublicKey,
     public_attributes: Vec<String>,
     #[getset(get = "pub")]
     total_params: u32,
@@ -92,13 +92,13 @@ pub struct BlindSignRequestBody {
 
 impl BlindSignRequestBody {
     pub fn new(
-        blind_sign_request: BlindSignRequest,
-        public_key: &coconut_rs::PublicKey,
+        blind_sign_request: &BlindSignRequest,
+        public_key: &nymcoconut::PublicKey,
         public_attributes: &[Attribute],
         total_params: u32,
     ) -> BlindSignRequestBody {
         BlindSignRequestBody {
-            blind_sign_request,
+            blind_sign_request: blind_sign_request.clone(),
             public_key: public_key.clone(),
             public_attributes: public_attributes
                 .iter()

common/credentials/src/bandwidth.rs

@@ -8,40 +8,74 @@
 
 use url::Url;
 
+use coconut_interface::{
+    Credential, Parameters, PrivateAttribute, PublicAttribute, Signature, VerificationKey,
+};
+
 use crate::error::Error;
 use crate::utils::{obtain_aggregate_signature, prepare_credential_for_spending};
-use coconut_interface::{hash_to_scalar, Credential, Parameters, Signature, VerificationKey};
 
-const BANDWIDTH_VALUE: u64 = 10 * 1024 * 1024 * 1024; // 10 GB
+pub const BANDWIDTH_VALUE: u64 = 10 * 1024 * 1024 * 1024; // 10 GB
 
-pub const PUBLIC_ATTRIBUTES: u32 = 1;
-pub const PRIVATE_ATTRIBUTES: u32 = 1;
+pub const PUBLIC_ATTRIBUTES: u32 = 2;
+pub const PRIVATE_ATTRIBUTES: u32 = 2;
 pub const TOTAL_ATTRIBUTES: u32 = PUBLIC_ATTRIBUTES + PRIVATE_ATTRIBUTES;
 
+pub const SERIAL_NUMBER_LEN: usize = 47;
+pub const BINDING_NUMBER_LEN: usize = 47;
+pub const VOUCHER_INFO_LEN: usize = 47;
+
+pub struct BandwidthVoucherAttributes {
+    // a random secret value generated by the client used for double-spending detection
+    pub serial_number: PrivateAttribute,
+    // a random secret value generated by the client used to bind multiple credentials together
+    pub binding_number: PrivateAttribute,
+    // the value (e.g., bandwidth) encoded in this voucher
+    pub voucher_value: PublicAttribute,
+    // a field with public information, e.g., type of voucher, epoch etc.
+    pub voucher_info: PublicAttribute,
+}
+
+impl BandwidthVoucherAttributes {
+    pub fn get_public_attributes(&self) -> Vec<PublicAttribute> {
+        vec![self.voucher_value, self.voucher_info]
+    }
+
+    pub fn get_private_attributes(&self) -> Vec<PrivateAttribute> {
+        vec![self.serial_number, self.binding_number]
+    }
+}
+
 // TODO: this definitely has to be moved somewhere else. It's just a temporary solution
-pub async fn obtain_signature(raw_identity: &[u8], validators: &[Url]) -> Result<Signature, Error> {
-    let public_attributes = vec![hash_to_scalar(BANDWIDTH_VALUE.to_be_bytes())];
-    let private_attributes = vec![hash_to_scalar(raw_identity)];
+pub async fn obtain_signature(
+    params: &Parameters,
+    attributes: &BandwidthVoucherAttributes,
+    validators: &[Url],
+) -> Result<Signature, Error> {
+    let public_attributes = attributes.get_public_attributes();
+    let private_attributes = attributes.get_private_attributes();
 
-    let params = Parameters::new(TOTAL_ATTRIBUTES)?;
-
-    obtain_aggregate_signature(&params, &public_attributes, &private_attributes, validators).await
+    obtain_aggregate_signature(params, &public_attributes, &private_attributes, validators).await
 }
 
 pub fn prepare_for_spending(
     raw_identity: &[u8],
     signature: &Signature,
+    attributes: &BandwidthVoucherAttributes,
     verification_key: &VerificationKey,
 ) -> Result<Credential, Error> {
-    let public_attributes = vec![BANDWIDTH_VALUE.to_be_bytes().to_vec()];
-    let private_attributes = vec![raw_identity.to_vec()];
+    let public_attributes = vec![
+        raw_identity.to_vec(),
+        BANDWIDTH_VALUE.to_be_bytes().to_vec(),
+    ];
 
     let params = Parameters::new(TOTAL_ATTRIBUTES)?;
 
     prepare_credential_for_spending(
         &params,
         public_attributes,
-        private_attributes,
+        attributes.serial_number,
+        attributes.binding_number,
         signature,
         verification_key,
     )

common/credentials/src/lib.rs

@@ -5,4 +5,7 @@ pub mod bandwidth;
 pub mod error;
 mod utils;
 
-pub use utils::{obtain_aggregate_signature, obtain_aggregate_verification_key};
+pub use utils::{
+    blind_sign_partial_credential, create_aggregate_verification_key, get_verification_keys,
+    obtain_aggregate_signature, obtain_aggregate_verification_key,
+};

common/credentials/src/utils.rs

@@ -1,14 +1,17 @@
 // Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0
 
-use crate::error::Error;
 use coconut_interface::{
-    aggregate_signature_shares, aggregate_verification_keys, hash_to_scalar, prepare_blind_sign,
-    prove_credential, Attribute, BlindSignRequestBody, Credential, Parameters, Signature,
-    SignatureShare, VerificationKey,
+    aggregate_signature_shares, aggregate_verification_keys, prepare_blind_sign,
+    prove_bandwidth_credential, Attribute, BlindSignRequest, BlindSignRequestBody,
+    BlindedSignature, Credential, ElGamalKeyPair, Parameters, Signature, SignatureShare,
+    VerificationKey,
 };
 use url::Url;
 
+use crate::bandwidth::PRIVATE_ATTRIBUTES;
+use crate::error::Error;
+
 /// Contacts all provided validators and then aggregate their verification keys.
 ///
 /// # Arguments
@@ -32,6 +35,43 @@ use url::Url;
 ///     Ok(())
 /// }
 /// ```
+pub async fn get_verification_keys(validators: &[Url]) -> Result<Vec<VerificationKey>, Error> {
+    if validators.is_empty() {
+        return Err(Error::NoValidatorsAvailable);
+    }
+
+    let mut shares = Vec::with_capacity(validators.len());
+
+    let mut client = validator_client::ApiClient::new(validators[0].clone());
+    let response = client.get_coconut_verification_key().await?;
+
+    shares.push(response.key);
+
+    for validator_url in validators.iter().enumerate().skip(1) {
+        client.change_validator_api(validator_url.1.clone());
+        let response = client.get_coconut_verification_key().await?;
+        shares.push(response.key);
+    }
+
+    Ok(shares)
+}
+
+pub fn create_aggregate_verification_key(
+    verification_keys: &Vec<VerificationKey>,
+) -> Result<VerificationKey, Error> {
+    if verification_keys.is_empty() {
+        return Err(Error::NoValidatorsAvailable);
+    }
+
+    // creates a vec of [1, 2, .. n] where n is length of verification_keys, e.g. [1,2,3] for 3 keys
+    let indices: Vec<u64> = (1u64..(verification_keys.len() + 1) as u64).collect();
+
+    Ok(aggregate_verification_keys(
+        &verification_keys,
+        Some(&indices.as_slice()),
+    )?)
+}
+
 pub async fn obtain_aggregate_verification_key(
     validators: &[Url],
 ) -> Result<VerificationKey, Error> {
@@ -58,22 +98,45 @@ pub async fn obtain_aggregate_verification_key(
     Ok(aggregate_verification_keys(&shares, Some(&indices))?)
 }
 
+pub async fn blind_sign_partial_credential(
+    validator_url: &Url,
+    elgamal_keypair: &ElGamalKeyPair,
+    blind_sign_request: &BlindSignRequest,
+    public_attributes: &[Attribute],
+    total_params: u32,
+) -> Result<BlindedSignature, Error> {
+    let client = validator_client::ApiClient::new(validator_url.clone());
+
+    let blind_sign_request_body = BlindSignRequestBody::new(
+        &blind_sign_request,
+        elgamal_keypair.public_key(),
+        public_attributes,
+        total_params,
+    );
+
+    Ok(client
+        .blind_sign(&blind_sign_request_body)
+        .await?
+        .blinded_signature)
+}
+
 async fn obtain_partial_credential(
     params: &Parameters,
     public_attributes: &[Attribute],
     private_attributes: &[Attribute],
     client: &validator_client::ApiClient,
+    validator_vk: &VerificationKey,
 ) -> Result<Signature, Error> {
     let elgamal_keypair = coconut_interface::elgamal_keygen(params);
     let blind_sign_request = prepare_blind_sign(
         params,
-        elgamal_keypair.public_key(),
+        &elgamal_keypair,
         private_attributes,
         public_attributes,
     )?;
 
     let blind_sign_request_body = BlindSignRequestBody::new(
-        blind_sign_request,
+        &blind_sign_request,
         elgamal_keypair.public_key(),
         public_attributes,
         (public_attributes.len() + private_attributes.len()) as u32,
@@ -83,7 +146,16 @@ async fn obtain_partial_credential(
         .blind_sign(&blind_sign_request_body)
         .await?
         .blinded_signature;
-    Ok(blinded_signature.unblind(elgamal_keypair.private_key()))
+    Ok(blinded_signature
+        .unblind(
+            params,
+            elgamal_keypair.private_key(),
+            validator_vk,
+            private_attributes,
+            public_attributes,
+            &blind_sign_request.get_commitment_hash(),
+        )
+        .unwrap())
 }
 
 pub async fn obtain_aggregate_signature(
@@ -97,40 +169,75 @@ pub async fn obtain_aggregate_signature(
     }
 
     let mut shares = Vec::with_capacity(validators.len());
+    let mut validators_partial_vks: Vec<VerificationKey> = Vec::with_capacity(validators.len());
 
     let mut client = validator_client::ApiClient::new(validators[0].clone());
-    let first =
-        obtain_partial_credential(params, public_attributes, private_attributes, &client).await?;
+    let validator_partial_vk = client.get_coconut_verification_key().await?;
+    validators_partial_vks.push(validator_partial_vk.key.clone());
+
+    let first = obtain_partial_credential(
+        params,
+        public_attributes,
+        private_attributes,
+        &client,
+        &validator_partial_vk.key,
+    )
+    .await?;
     shares.push(SignatureShare::new(first, 0));
 
     for (id, validator_url) in validators.iter().enumerate().skip(1) {
         client.change_validator_api(validator_url.clone());
-        let signature =
-            obtain_partial_credential(params, public_attributes, private_attributes, &client)
-                .await?;
+        let validator_partial_vk = client.get_coconut_verification_key().await?;
+        validators_partial_vks.push(validator_partial_vk.key.clone());
+        let signature = obtain_partial_credential(
+            params,
+            public_attributes,
+            private_attributes,
+            &client,
+            &validator_partial_vk.key,
+        )
+        .await?;
         let share = SignatureShare::new(signature, id as u64);
         shares.push(share)
     }
 
-    Ok(aggregate_signature_shares(&shares)?)
+    let mut attributes = Vec::with_capacity(private_attributes.len() + public_attributes.len());
+    attributes.extend_from_slice(private_attributes);
+    attributes.extend_from_slice(public_attributes);
+
+    let mut indices: Vec<u64> = Vec::with_capacity(validators_partial_vks.len());
+    for i in 1..validators_partial_vks.len() {
+        indices.push(i as u64);
+    }
+    let verification_key =
+        aggregate_verification_keys(&validators_partial_vks, Some(indices.as_ref())).unwrap();
+    Ok(aggregate_signature_shares(
+        params,
+        &verification_key,
+        &attributes,
+        &shares,
+    )?)
 }
 
 // TODO: better type flow
 pub fn prepare_credential_for_spending(
     params: &Parameters,
     public_attributes: Vec<Vec<u8>>,
-    private_attributes: Vec<Vec<u8>>,
+    serial_number: Attribute,
+    binding_number: Attribute,
     signature: &Signature,
     verification_key: &VerificationKey,
 ) -> Result<Credential, Error> {
-    let private_attributes = private_attributes
-        .iter()
-        .map(hash_to_scalar)
-        .collect::<Vec<Attribute>>();
-    let theta = prove_credential(params, verification_key, signature, &private_attributes)?;
+    let theta = prove_bandwidth_credential(
+        params,
+        verification_key,
+        signature,
+        serial_number,
+        binding_number,
+    )?;
 
     Ok(Credential::new(
-        (public_attributes.len() + private_attributes.len()) as u32,
+        (public_attributes.len() + PRIVATE_ATTRIBUTES as usize) as u32,
         theta,
         public_attributes,
         signature,

common/nymcoconut/Cargo.toml

@@ -0,0 +1,43 @@
+[package]
+name = "nymcoconut"
+version = "0.5.0"
+authors = ["Jedrzej Stuczynski <andrew@nymtech.net>", "Ania Piotrowska <ania@nymtech.net>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+bls12_381 = { version = "0.5", default-features = false, features = ["pairings", "alloc", "experimental"] }
+itertools = "0.10"
+digest = "0.9"
+rand = "0.8"
+thiserror = "1.0"
+serde = "1.0"
+serde_derive = "1.0"
+bs58 = "0.4.0"
+sha2 = "0.9"
+
+[dependencies.ff]
+version = "0.10"
+default-features = false
+
+[dependencies.group]
+version = "0.10"
+default-features = false
+
+[dev-dependencies]
+criterion = { version="0.3", features=["html_reports"] }
+doc-comment = "0.3"
+
+[dev-dependencies.bincode]
+version = "1"
+
+#[[bench]]
+#name = "benchmarks"
+#harness = false
+
+[features]
+default = []
+
+[target.'cfg(target_env = "wasm32-unknown-unknown")'.dependencies]
+getrandom = { version="0.2", features=["js"] }

common/nymcoconut/src/elgamal.rs

@@ -0,0 +1,333 @@
+// Copyright 2021 Nym Technologies SA
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use core::ops::{Deref, Mul};
+use std::convert::TryFrom;
+use std::convert::TryInto;
+
+use bls12_381::{G1Projective, Scalar};
+use group::Curve;
+use serde_derive::{Deserialize, Serialize};
+
+use crate::error::{CoconutError, Result};
+use crate::scheme::setup::Parameters;
+use crate::traits::{Base58, Bytable};
+use crate::utils::{try_deserialize_g1_projective, try_deserialize_scalar};
+
+/// Type alias for the ephemeral key generated during ElGamal encryption
+pub type EphemeralKey = Scalar;
+
+/// Two G1 points representing ElGamal ciphertext
+#[derive(Debug)]
+#[cfg_attr(test, derive(PartialEq))]
+pub struct Ciphertext(pub(crate) G1Projective, pub(crate) G1Projective);
+
+impl TryFrom<&[u8]> for Ciphertext {
+    type Error = CoconutError;
+
+    fn try_from(bytes: &[u8]) -> Result<Ciphertext> {
+        if bytes.len() != 96 {
+            return Err(CoconutError::Deserialization(format!(
+                "Ciphertext must be exactly 96 bytes, got {}",
+                bytes.len()
+            )));
+        }
+
+        let c1_bytes: &[u8; 48] = &bytes[..48].try_into().unwrap();
+        let c2_bytes: &[u8; 48] = &bytes[48..].try_into().unwrap();
+
+        let c1 = try_deserialize_g1_projective(
+            c1_bytes,
+            CoconutError::Deserialization("Failed to deserialize compressed c1".to_string()),
+        )?;
+        let c2 = try_deserialize_g1_projective(
+            c2_bytes,
+            CoconutError::Deserialization("Failed to deserialize compressed c2".to_string()),
+        )?;
+
+        Ok(Ciphertext(c1, c2))
+    }
+}
+
+impl Ciphertext {
+    pub fn c1(&self) -> &G1Projective {
+        &self.0
+    }
+
+    pub fn c2(&self) -> &G1Projective {
+        &self.1
+    }
+
+    pub fn to_bytes(&self) -> [u8; 96] {
+        let mut bytes = [0u8; 96];
+        bytes[..48].copy_from_slice(&self.0.to_affine().to_compressed());
+        bytes[48..].copy_from_slice(&self.1.to_affine().to_compressed());
+        bytes
+    }
+
+    pub fn from_bytes(bytes: &[u8]) -> Result<Ciphertext> {
+        Ciphertext::try_from(bytes)
+    }
+}
+
+/// PrivateKey used in the ElGamal encryption scheme to recover the plaintext
+#[derive(Debug)]
+#[cfg_attr(test, derive(PartialEq))]
+pub struct PrivateKey(pub(crate) Scalar);
+
+impl PrivateKey {
+    /// Decrypt takes the ElGamal encryption of a message and returns a point on the G1 curve
+    /// that represents original h^m.
+    pub fn decrypt(&self, ciphertext: &Ciphertext) -> G1Projective {
+        let (c1, c2) = &(ciphertext.0, ciphertext.1);
+
+        // (gamma^k * h^m) / (g1^{d * k})   |   note: gamma = g1^d
+        c2 - c1 * self.0
+    }
+
+    pub fn public_key(&self, params: &Parameters) -> PublicKey {
+        PublicKey(params.gen1() * self.0)
+    }
+
+    pub fn to_bytes(&self) -> [u8; 32] {
+        self.0.to_bytes()
+    }
+
+    pub fn from_bytes(bytes: &[u8; 32]) -> Result<PrivateKey> {
+        try_deserialize_scalar(
+            bytes,
+            CoconutError::Deserialization(
+                "Failed to deserialize ElGamal private key - it was not in the canonical form"
+                    .to_string(),
+            ),
+        )
+        .map(PrivateKey)
+    }
+}
+
+impl Bytable for PrivateKey {
+    fn to_byte_vec(&self) -> Vec<u8> {
+        self.to_bytes().to_vec()
+    }
+
+    fn try_from_byte_slice(slice: &[u8]) -> Result<Self> {
+        PrivateKey::from_bytes(slice.try_into().unwrap())
+    }
+}
+
+impl Base58 for PrivateKey {}
+
+// TODO: perhaps be more explicit and apart from gamma also store generator and group order?
+/// PublicKey used in the ElGamal encryption scheme to produce the ciphertext
+#[derive(Debug, Clone)]
+#[cfg_attr(test, derive(PartialEq))]
+pub struct PublicKey(G1Projective);
+
+impl PublicKey {
+    /// Encrypt encrypts the given message in the form of h^m,
+    /// where h is a point on the G1 curve using the given public key.
+    /// The random k is returned alongside the encryption
+    /// as it is required by the Coconut Scheme to create proofs of knowledge.
+    pub fn encrypt(
+        &self,
+        params: &Parameters,
+        h: &G1Projective,
+        msg: &Scalar,
+    ) -> (Ciphertext, EphemeralKey) {
+        let k = params.random_scalar();
+        // c1 = g1^k
+        let c1 = params.gen1() * k;
+        // c2 = gamma^k * h^m
+        let c2 = self.0 * k + h * msg;
+
+        (Ciphertext(c1, c2), k)
+    }
+
+    pub fn to_bytes(&self) -> [u8; 48] {
+        self.to_byte_vec().try_into().unwrap()
+    }
+
+    pub fn from_bytes(bytes: &[u8; 48]) -> Result<PublicKey> {
+        Ok(PublicKey::try_from(bytes.to_vec().as_slice()).unwrap())
+    }
+}
+
+impl Bytable for PublicKey {
+    fn to_byte_vec(&self) -> Vec<u8> {
+        self.0.to_affine().to_compressed().into()
+    }
+
+    fn try_from_byte_slice(slice: &[u8]) -> Result<Self> {
+        Ok(PublicKey::from_bytes(slice.try_into().unwrap()).unwrap())
+    }
+}
+
+impl TryFrom<&[u8]> for PublicKey {
+    type Error = CoconutError;
+
+    fn try_from(slice: &[u8]) -> Result<PublicKey> {
+        try_deserialize_g1_projective(
+            slice.try_into().unwrap(),
+            CoconutError::Deserialization(
+                "Failed to deserialize compressed ElGamal public key".to_string(),
+            ),
+        )
+        .map(PublicKey)
+    }
+}
+
+impl Base58 for PublicKey {}
+
+impl Deref for PublicKey {
+    type Target = G1Projective;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl<'a, 'b> Mul<&'b Scalar> for &'a PublicKey {
+    type Output = G1Projective;
+
+    fn mul(self, rhs: &'b Scalar) -> Self::Output {
+        self.0 * rhs
+    }
+}
+
+#[derive(Serialize, Deserialize)]
+/// A convenient wrapper for both keys of the ElGamal keypair
+pub struct ElGamalKeyPair {
+    private_key: PrivateKey,
+    public_key: PublicKey,
+}
+
+impl ElGamalKeyPair {
+    pub fn public_key(&self) -> &PublicKey {
+        &self.public_key
+    }
+
+    pub fn private_key(&self) -> &PrivateKey {
+        &self.private_key
+    }
+}
+
+/// Generate a fresh ElGamal keypair using the group generator specified by the provided [Parameters]
+pub fn elgamal_keygen(params: &Parameters) -> ElGamalKeyPair {
+    let private_key = params.random_scalar();
+    let gamma = params.gen1() * private_key;
+
+    ElGamalKeyPair {
+        private_key: PrivateKey(private_key),
+        public_key: PublicKey(gamma),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn keygen() {
+        let params = Parameters::default();
+        let keypair = super::elgamal_keygen(&params);
+
+        let expected = params.gen1() * keypair.private_key.0;
+        let gamma = keypair.public_key.0;
+        assert_eq!(
+            expected, gamma,
+            "Public key, gamma, should be equal to g1^d, where d is the private key"
+        );
+    }
+
+    #[test]
+    fn encryption() {
+        let params = Parameters::default();
+        let keypair = super::elgamal_keygen(&params);
+
+        let r = params.random_scalar();
+        let h = params.gen1() * r;
+        let m = params.random_scalar();
+
+        let (ciphertext, ephemeral_key) = keypair.public_key.encrypt(&params, &h, &m);
+
+        let expected_c1 = params.gen1() * ephemeral_key;
+        assert_eq!(expected_c1, ciphertext.0, "c1 should be equal to g1^k");
+
+        let expected_c2 = keypair.public_key.0 * ephemeral_key + h * m;
+        assert_eq!(
+            expected_c2, ciphertext.1,
+            "c2 should be equal to gamma^k * h^m"
+        );
+    }
+
+    #[test]
+    fn decryption() {
+        let params = Parameters::default();
+        let keypair = super::elgamal_keygen(&params);
+
+        let r = params.random_scalar();
+        let h = params.gen1() * r;
+        let m = params.random_scalar();
+
+        let (ciphertext, _) = keypair.public_key.encrypt(&params, &h, &m);
+        let dec = keypair.private_key.decrypt(&ciphertext);
+
+        let expected = h * m;
+        assert_eq!(
+            expected, dec,
+            "after ElGamal decryption, original h^m should be obtained"
+        );
+    }
+
+    #[test]
+    fn private_key_bytes_roundtrip() {
+        let params = Parameters::default();
+        let private_key = PrivateKey(params.random_scalar());
+        let bytes = private_key.to_bytes();
+
+        // also make sure it is equivalent to the internal scalar's bytes
+        assert_eq!(private_key.0.to_bytes(), bytes);
+        assert_eq!(private_key, PrivateKey::from_bytes(&bytes).unwrap())
+    }
+
+    #[test]
+    fn public_key_bytes_roundtrip() {
+        let params = Parameters::default();
+        let r = params.random_scalar();
+        let public_key = PublicKey(params.gen1() * r);
+        let bytes = public_key.to_bytes();
+
+        // also make sure it is equivalent to the internal g1 compressed bytes
+        assert_eq!(public_key.0.to_affine().to_compressed(), bytes);
+        assert_eq!(public_key, PublicKey::from_bytes(&bytes).unwrap())
+    }
+
+    #[test]
+    fn ciphertext_bytes_roundtrip() {
+        let params = Parameters::default();
+        let r = params.random_scalar();
+        let s = params.random_scalar();
+        let ciphertext = Ciphertext(params.gen1() * r, params.gen1() * s);
+        let bytes = ciphertext.to_bytes();
+
+        // also make sure it is equivalent to the internal g1 compressed bytes concatenated
+        let expected_bytes = [
+            ciphertext.0.to_affine().to_compressed(),
+            ciphertext.1.to_affine().to_compressed(),
+        ]
+        .concat();
+        assert_eq!(expected_bytes, bytes);
+        assert_eq!(ciphertext, Ciphertext::try_from(&bytes[..]).unwrap())
+    }
+}

common/nymcoconut/src/error.rs

@@ -0,0 +1,64 @@
+// Copyright 2021 Nym Technologies SA
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use thiserror::Error;
+
+/// A `Result` alias where the `Err` case is `coconut_rs::Error`.
+pub type Result<T> = std::result::Result<T, CoconutError>;
+
+#[derive(Error, Debug)]
+pub enum CoconutError {
+    #[error("Setup error: {0}")]
+    Setup(String),
+
+    #[error("encountered error during keygen")]
+    Keygen,
+
+    #[error("Issuance related error: {0}")]
+    Issuance(String),
+
+    #[error("Tried to prepare blind sign request for higher than specified number of attributes (max: {}, requested: {})", max, requested)]
+    IssuanceMaxAttributes { max: usize, requested: usize },
+
+    #[error("Interpolation error: {0}")]
+    Interpolation(String),
+
+    #[error("Aggregation error: {0}")]
+    Aggregation(String),
+
+    #[error("Unblind error: {0}")]
+    Unblind(String),
+
+    #[error("Verification error: {0}")]
+    Verification(String),
+
+    #[error("Deserialization error: {0}")]
+    Deserialization(String),
+
+    #[error(
+        "Deserailization error, expected at least {} bytes, got {}",
+        min,
+        actual
+    )]
+    DeserializationMinLength { min: usize, actual: usize },
+
+    #[error("Tried to deserialize {object} with bytes of invalid length. Expected {actual} < {} or {modulus_target} % {modulus} == 0")]
+    DeserializationInvalidLength {
+        actual: usize,
+        target: usize,
+        modulus_target: usize,
+        modulus: usize,
+        object: String,
+    },
+}

common/nymcoconut/src/impls/clone.rs

@@ -0,0 +1,15 @@
+use crate::{BlindSignRequest, BlindedSignature, Bytable, Theta};
+
+macro_rules! impl_clone {
+    ($struct:ident) => {
+        impl Clone for $struct {
+            fn clone(&self) -> Self {
+                Self::try_from_byte_slice(&self.to_byte_vec()).unwrap()
+            }
+        }
+    };
+}
+
+impl_clone!(BlindSignRequest);
+impl_clone!(BlindedSignature);
+impl_clone!(Theta);

common/nymcoconut/src/impls/mod.rs

@@ -0,0 +1,2 @@
+mod clone;
+mod serde;

common/nymcoconut/src/impls/serde.rs

@@ -0,0 +1,56 @@
+use crate::elgamal::PrivateKey;
+use crate::scheme::SecretKey;
+use crate::{
+    Base58, BlindSignRequest, BlindedSignature, PublicKey, Signature, Theta, VerificationKey,
+};
+use serde::de::Unexpected;
+use serde::{de::Error, de::Visitor, Deserialize, Deserializer, Serialize, Serializer};
+use std::fmt;
+
+macro_rules! impl_serde {
+    ($struct:ident, $visitor:ident) => {
+        pub struct $visitor {}
+
+        impl Serialize for $struct {
+            fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+            where
+                S: Serializer,
+            {
+                serializer.serialize_str(&self.to_bs58())
+            }
+        }
+
+        impl<'de> Visitor<'de> for $visitor {
+            type Value = $struct;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                write!(formatter, "A base58 encoded struct")
+            }
+
+            fn visit_str<E: Error>(self, s: &str) -> Result<Self::Value, E> {
+                match $struct::try_from_bs58(s) {
+                    Ok(x) => Ok(x),
+                    Err(_) => Err(Error::invalid_value(Unexpected::Str(s), &self)),
+                }
+            }
+        }
+
+        impl<'de> Deserialize<'de> for $struct {
+            fn deserialize<D>(deserializer: D) -> Result<$struct, D::Error>
+            where
+                D: Deserializer<'de>,
+            {
+                deserializer.deserialize_str($visitor {})
+            }
+        }
+    };
+}
+
+impl_serde!(SecretKey, V1);
+impl_serde!(VerificationKey, V2);
+impl_serde!(PublicKey, V3);
+impl_serde!(PrivateKey, V4);
+impl_serde!(BlindSignRequest, V5);
+impl_serde!(BlindedSignature, V6);
+impl_serde!(Signature, V7);
+impl_serde!(Theta, V8);

common/nymcoconut/src/lib.rs

@@ -0,0 +1,68 @@
+// Copyright 2021 Nym Technologies SA
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use std::convert::TryInto;
+
+use bls12_381::Scalar;
+
+pub use elgamal::elgamal_keygen;
+pub use elgamal::ElGamalKeyPair;
+pub use elgamal::PublicKey;
+pub use error::CoconutError;
+pub use scheme::aggregation::aggregate_signature_shares;
+pub use scheme::aggregation::aggregate_verification_keys;
+pub use scheme::issuance::blind_sign;
+pub use scheme::issuance::prepare_blind_sign;
+pub use scheme::issuance::BlindSignRequest;
+pub use scheme::keygen::ttp_keygen;
+pub use scheme::keygen::KeyPair;
+pub use scheme::keygen::VerificationKey;
+pub use scheme::setup::setup;
+pub use scheme::setup::Parameters;
+pub use scheme::verification::prove_bandwidth_credential;
+pub use scheme::verification::verify_credential;
+pub use scheme::verification::Theta;
+pub use scheme::BlindedSignature;
+pub use scheme::Signature;
+pub use scheme::SignatureShare;
+pub use traits::Base58;
+pub use utils::hash_to_scalar;
+
+use crate::traits::Bytable;
+
+pub mod elgamal;
+mod error;
+mod impls;
+pub mod proofs;
+pub mod scheme;
+#[cfg(test)]
+mod tests;
+pub mod traits;
+mod utils;
+
+pub type Attribute = Scalar;
+pub type PrivateAttribute = Attribute;
+pub type PublicAttribute = Attribute;
+
+impl Bytable for Attribute {
+    fn to_byte_vec(&self) -> Vec<u8> {
+        self.to_bytes().to_vec()
+    }
+
+    fn try_from_byte_slice(slice: &[u8]) -> Result<Self, CoconutError> {
+        Ok(Attribute::from_bytes(slice.try_into().unwrap()).unwrap())
+    }
+}
+
+impl Base58 for Attribute {}

common/nymcoconut/src/proofs/mod.rs

@@ -0,0 +1,836 @@
+// Copyright 2021 Nym Technologies SA
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// TODO: look at https://crates.io/crates/merlin to perhaps use it instead?
+
+use std::borrow::Borrow;
+use std::convert::TryInto;
+
+use bls12_381::{G1Projective, G2Projective, Scalar};
+use digest::generic_array::typenum::Unsigned;
+use digest::Digest;
+use group::GroupEncoding;
+use itertools::izip;
+use sha2::Sha256;
+
+use crate::elgamal::Ciphertext;
+use crate::error::{CoconutError, Result};
+use crate::scheme::setup::Parameters;
+use crate::scheme::VerificationKey;
+use crate::utils::{hash_g1, try_deserialize_scalar, try_deserialize_scalar_vec};
+use crate::{elgamal, Attribute, ElGamalKeyPair};
+
+// as per the reference python implementation
+type ChallengeDigest = Sha256;
+
+#[derive(Debug)]
+#[cfg_attr(test, derive(PartialEq))]
+pub struct ProofCmCs {
+    challenge: Scalar,
+    response_opening: Scalar,
+    response_private_elgamal_key: Scalar,
+    response_keys: Vec<Scalar>,
+    response_attributes: Vec<Scalar>,
+}
+
+// note: this is slightly different from the reference python implementation
+// as we omit the unnecessary string conversion. Instead we concatenate byte
+// representations together and hash that.
+// note2: G1 and G2 elements are using their compressed representations
+// and as per the bls12-381 library all elements are using big-endian form
+/// Generates a Scalar [or Fp] challenge by hashing a number of elliptic curve points.
+fn compute_challenge<D, I, B>(iter: I) -> Scalar
+where
+    D: Digest,
+    I: Iterator<Item = B>,
+    B: AsRef<[u8]>,
+{
+    let mut h = D::new();
+    for point_representation in iter {
+        h.update(point_representation);
+    }
+    let digest = h.finalize();
+
+    // TODO: I don't like the 0 padding here (though it's what we've been using before,
+    // but we never had a security audit anyway...)
+    // instead we could maybe use the `from_bytes` variant and adding some suffix
+    // when computing the digest until we produce a valid scalar.
+    let mut bytes = [0u8; 64];
+    let pad_size = 64usize
+        .checked_sub(D::OutputSize::to_usize())
+        .unwrap_or_default();
+
+    bytes[pad_size..].copy_from_slice(&digest);
+
+    Scalar::from_bytes_wide(&bytes)
+}
+
+fn produce_response(witness: &Scalar, challenge: &Scalar, secret: &Scalar) -> Scalar {
+    witness - challenge * secret
+}
+
+// note: it's caller's responsibility to ensure witnesses.len() = secrets.len()
+fn produce_responses<S>(witnesses: &[Scalar], challenge: &Scalar, secrets: &[S]) -> Vec<Scalar>
+where
+    S: Borrow<Scalar>,
+{
+    debug_assert_eq!(witnesses.len(), secrets.len());
+
+    witnesses
+        .iter()
+        .zip(secrets.iter())
+        .map(|(w, x)| produce_response(w, challenge, x.borrow()))
+        .collect()
+}
+
+impl ProofCmCs {
+    /// Construct non-interactive zero-knowledge proof of correctness of the ciphertexts and the commitment
+    /// using the Fiat-Shamir heuristic.
+    pub(crate) fn construct(
+        params: &Parameters,
+        elgamal_keypair: &ElGamalKeyPair,
+        ephemeral_keys: &[elgamal::EphemeralKey],
+        commitment: &G1Projective,
+        commitment_opening: &Scalar,
+        private_attributes: &[Attribute],
+        priv_attributes_ciphertexts: &[Ciphertext],
+    ) -> Self {
+        // note: this is only called from `prepare_blind_sign` that already checks
+        // whether private attributes are non-empty and whether we don't have too many
+        // attributes in total to sign.
+        // we also know, due to the single call place, that ephemeral_keys.len() == private_attributes.len()
+
+        // witness creation
+
+        let witness_commitment_opening = params.random_scalar();
+        let witness_private_elgamal_key = params.random_scalar();
+        let witness_keys = params.n_random_scalars(ephemeral_keys.len());
+        let witness_attributes = params.n_random_scalars(private_attributes.len());
+
+        // recompute h
+        let h = hash_g1(commitment.to_bytes());
+        let hs_bytes = params
+            .gen_hs()
+            .iter()
+            .map(|h| h.to_bytes())
+            .collect::<Vec<_>>();
+
+        let g1 = params.gen1();
+
+        // compute commitments
+        let commitment_private_key_elgamal = g1 * witness_private_elgamal_key;
+
+        // Aw[i] = (wk[i] * g1)
+        let commitment_keys1_bytes = witness_keys
+            .iter()
+            .map(|wk_i| g1 * wk_i)
+            .map(|witness| witness.to_bytes())
+            .collect::<Vec<_>>();
+
+        // Bw[i] = (wm[i] * h) + (wk[i] * gamma)
+        let commitment_keys2_bytes = witness_keys
+            .iter()
+            .zip(witness_attributes.iter())
+            .map(|(wk_i, wm_i)| elgamal_keypair.public_key() * wk_i + h * wm_i)
+            .map(|witness| witness.to_bytes())
+            .collect::<Vec<_>>();
+
+        // zkp commitment for the attributes commitment cm
+        // Ccm = (wr * g1) + (wm[0] * hs[0]) + ... + (wm[i] * hs[i])
+        let commitment_attributes = g1 * witness_commitment_opening
+            + witness_attributes
+                .iter()
+                .zip(params.gen_hs().iter())
+                .map(|(wm_i, hs_i)| hs_i * wm_i)
+                .sum::<G1Projective>();
+
+        let ciphertexts_bytes = priv_attributes_ciphertexts
+            .iter()
+            .map(|c| c.to_bytes())
+            .collect::<Vec<_>>();
+
+        // compute challenge
+        let challenge = compute_challenge::<ChallengeDigest, _, _>(
+            std::iter::once(params.gen1().to_bytes().as_ref())
+                .chain(hs_bytes.iter().map(|hs| hs.as_ref()))
+                .chain(std::iter::once(h.to_bytes().as_ref()))
+                .chain(std::iter::once(
+                    elgamal_keypair.public_key().to_bytes().as_ref(),
+                ))
+                .chain(std::iter::once(commitment.to_bytes().as_ref()))
+                .chain(std::iter::once(commitment_attributes.to_bytes().as_ref()))
+                .chain(std::iter::once(
+                    commitment_private_key_elgamal.to_bytes().as_ref(),
+                ))
+                .chain(commitment_keys1_bytes.iter().map(|aw| aw.as_ref()))
+                .chain(commitment_keys2_bytes.iter().map(|bw| bw.as_ref()))
+                .chain(ciphertexts_bytes.iter().map(|c| c.as_ref())),
+        );
+
+        // Responses
+        let response_opening =
+            produce_response(&witness_commitment_opening, &challenge, commitment_opening);
+        let response_private_elgamal_key = produce_response(
+            &witness_private_elgamal_key,
+            &challenge,
+            &elgamal_keypair.private_key().0,
+        );
+        let response_keys = produce_responses(&witness_keys, &challenge, ephemeral_keys);
+        let response_attributes = produce_responses(
+            &witness_attributes,
+            &challenge,
+            &private_attributes.iter().collect::<Vec<_>>(),
+        );
+
+        ProofCmCs {
+            challenge,
+            response_opening,
+            response_private_elgamal_key,
+            response_keys,
+            response_attributes,
+        }
+    }
+
+    pub(crate) fn verify(
+        &self,
+        params: &Parameters,
+        pub_key: &elgamal::PublicKey,
+        commitment: &G1Projective,
+        attributes_ciphertexts: &[elgamal::Ciphertext],
+    ) -> bool {
+        if self.response_keys.len() != attributes_ciphertexts.len() {
+            return false;
+        }
+
+        // recompute h
+        let h = hash_g1(commitment.to_bytes());
+        let g1 = params.gen1();
+
+        let hs_bytes = params
+            .gen_hs()
+            .iter()
+            .map(|h| h.to_bytes())
+            .collect::<Vec<_>>();
+
+        // recompute witnesses commitments
+        let commitment_private_key_elgamal =
+            pub_key * &self.challenge + g1 * self.response_private_elgamal_key;
+
+        // Aw[i] = (c * c1[i]) + (rk[i] * g1)
+        let commitment_keys1_bytes = attributes_ciphertexts
+            .iter()
+            .map(|ciphertext| ciphertext.c1())
+            .zip(self.response_keys.iter())
+            .map(|(c1, res_k)| c1 * self.challenge + g1 * res_k)
+            .map(|witness| witness.to_bytes())
+            .collect::<Vec<_>>();
+
+        // Bw[i] = (c * c2[i]) + (rk[i] * gamma) + (rm[i] * h)
+        let commitment_keys2_bytes = izip!(
+            attributes_ciphertexts
+                .iter()
+                .map(|ciphertext| ciphertext.c2()),
+            self.response_keys.iter(),
+            self.response_attributes.iter()
+        )
+        .map(|(c2, res_key, res_attr)| c2 * self.challenge + pub_key * res_key + h * res_attr)
+        .map(|witness| witness.to_bytes())
+        .collect::<Vec<_>>();
+
+        // Cw = (cm * c) + (rr * g1) + (rm[0] * hs[0]) + ... + (rm[n] * hs[n])
+        let commitment_attributes = commitment * self.challenge
+            + g1 * self.response_opening
+            + self
+                .response_attributes
+                .iter()
+                .zip(params.gen_hs().iter())
+                .map(|(res_attr, hs)| hs * res_attr)
+                .sum::<G1Projective>();
+
+        let ciphertexts_bytes = attributes_ciphertexts
+            .iter()
+            .map(|c| c.to_bytes())
+            .collect::<Vec<_>>();
+
+        // re-compute the challenge
+        let challenge = compute_challenge::<ChallengeDigest, _, _>(
+            std::iter::once(params.gen1().to_bytes().as_ref())
+                .chain(hs_bytes.iter().map(|hs| hs.as_ref()))
+                .chain(std::iter::once(h.to_bytes().as_ref()))
+                .chain(std::iter::once(pub_key.to_bytes().as_ref()))
+                .chain(std::iter::once(commitment.to_bytes().as_ref()))
+                .chain(std::iter::once(commitment_attributes.to_bytes().as_ref()))
+                .chain(std::iter::once(
+                    commitment_private_key_elgamal.to_bytes().as_ref(),
+                ))
+                .chain(commitment_keys1_bytes.iter().map(|aw| aw.as_ref()))
+                .chain(commitment_keys2_bytes.iter().map(|bw| bw.as_ref()))
+                .chain(ciphertexts_bytes.iter().map(|c| c.as_ref())),
+        );
+
+        challenge == self.challenge
+    }
+
+    // challenge || rr || rk.len() || rk || rm.len() || rm
+    pub(crate) fn to_bytes(&self) -> Vec<u8> {
+        let keys_len = self.response_keys.len() as u64;
+        let attributes_len = self.response_attributes.len() as u64;
+
+        let mut bytes = Vec::with_capacity(16 + (keys_len + attributes_len + 3) as usize * 32);
+
+        bytes.extend_from_slice(&self.challenge.to_bytes());
+        bytes.extend_from_slice(&self.response_opening.to_bytes());
+        bytes.extend_from_slice(&self.response_private_elgamal_key.to_bytes());
+        bytes.extend_from_slice(&keys_len.to_le_bytes());
+
+        for rk in &self.response_keys {
+            bytes.extend_from_slice(&rk.to_bytes());
+        }
+
+        bytes.extend_from_slice(&attributes_len.to_le_bytes());
+
+        for rm in &self.response_attributes {
+            bytes.extend_from_slice(&rm.to_bytes());
+        }
+
+        bytes
+    }
+
+    pub(crate) fn from_bytes(bytes: &[u8]) -> Result<Self> {
+        // at the very minimum there must be a single attribute being proven
+        if bytes.len() < 32 * 4 + 16 || (bytes.len() - 16) % 32 != 0 {
+            return Err(
+                CoconutError::Deserialization(
+                    "tried to deserialize proof of ciphertexts and commitment with bytes of invalid length".to_string())
+            );
+        }
+
+        let mut idx = 0;
+        let challenge_bytes = bytes[idx..idx + 32].try_into().unwrap();
+        idx += 32;
+        let response_opening_bytes = bytes[idx..idx + 32].try_into().unwrap();
+        idx += 32;
+        let response_private_elgamal_key_bytes = bytes[idx..idx + 32].try_into().unwrap();
+        idx += 32;
+
+        let challenge = try_deserialize_scalar(
+            &challenge_bytes,
+            CoconutError::Deserialization("Failed to deserialize challenge".to_string()),
+        )?;
+        let response_opening = try_deserialize_scalar(
+            &response_opening_bytes,
+            CoconutError::Deserialization(
+                "Failed to deserialize the response to the random".to_string(),
+            ),
+        )?;
+        let response_private_elgamal_key = try_deserialize_scalar(
+            &response_private_elgamal_key_bytes,
+            CoconutError::Deserialization(
+                "Failed to deserialize the response to the private ElGamal key".to_string(),
+            ),
+        )?;
+
+        let rk_len = u64::from_le_bytes(bytes[idx..idx + 8].try_into().unwrap());
+        idx += 8;
+        if bytes[idx..].len() < rk_len as usize * 32 + 8 {
+            return Err(
+                CoconutError::Deserialization(
+                    "tried to deserialize proof of ciphertexts and commitment with insufficient number of bytes provided".to_string()),
+            );
+        }
+
+        let rk_end = idx + rk_len as usize * 32;
+        let response_keys = try_deserialize_scalar_vec(
+            rk_len,
+            &bytes[idx..rk_end],
+            CoconutError::Deserialization("Failed to deserialize keys response".to_string()),
+        )?;
+
+        let rm_len = u64::from_le_bytes(bytes[rk_end..rk_end + 8].try_into().unwrap());
+        let response_attributes = try_deserialize_scalar_vec(
+            rm_len,
+            &bytes[rk_end + 8..],
+            CoconutError::Deserialization("Failed to deserialize attributes response".to_string()),
+        )?;
+
+        Ok(ProofCmCs {
+            challenge,
+            response_opening,
+            response_private_elgamal_key,
+            response_keys,
+            response_attributes,
+        })
+    }
+}
+
+#[derive(Debug)]
+#[cfg_attr(test, derive(PartialEq))]
+pub struct ProofKappa {
+    challenge: Scalar,
+    response_attributes: Vec<Scalar>,
+    response_blinder: Scalar,
+}
+
+impl ProofKappa {
+    pub fn construct(
+        params: &Parameters,
+        verification_key: &VerificationKey,
+        blinding_factor: &Scalar,
+        blinded_message: &G2Projective,
+        private_attributes: &[Attribute],
+        verifier_id: &[u8; 32],
+        timestamp: &[u8; 32],
+    ) -> Self {
+        // create the witnesses
+        let witness_blinder = params.random_scalar();
+        let witness_attributes = params.n_random_scalars(private_attributes.len());
+
+        let beta_bytes = verification_key
+            .beta
+            .iter()
+            .map(|beta_i| beta_i.to_bytes())
+            .collect::<Vec<_>>();
+
+        // witnesses commitments
+        // Aw = g2 * wt + alpha + beta[0] * wm[0] + ... + beta[i] * wm[i]
+        let commitment_kappa = params.gen2() * witness_blinder
+            + verification_key.alpha
+            + witness_attributes
+                .iter()
+                .zip(verification_key.beta.iter())
+                .map(|(wm_i, beta_i)| beta_i * wm_i)
+                .sum::<G2Projective>();
+
+        let challenge = compute_challenge::<ChallengeDigest, _, _>(
+            std::iter::once(params.gen2().to_bytes().as_ref())
+                .chain(std::iter::once(blinded_message.to_bytes().as_ref())) //kappa
+                .chain(std::iter::once(verification_key.alpha.to_bytes().as_ref()))
+                .chain(beta_bytes.iter().map(|b| b.as_ref()))
+                .chain(std::iter::once(commitment_kappa.to_bytes().as_ref()))
+                .chain(std::iter::once(verifier_id.as_ref()))
+                .chain(std::iter::once(timestamp.as_ref())),
+        );
+
+        // responses
+        let response_blinder = produce_response(&witness_blinder, &challenge, blinding_factor);
+        let response_attributes =
+            produce_responses(&witness_attributes, &challenge, private_attributes);
+
+        ProofKappa {
+            challenge,
+            response_attributes,
+            response_blinder,
+        }
+    }
+
+    pub fn private_attributes_len(&self) -> usize {
+        self.response_attributes.len()
+    }
+
+    pub fn verify(
+        &self,
+        params: &Parameters,
+        verification_key: &VerificationKey,
+        kappa: &G2Projective,
+        verifier_id: &[u8; 32],
+        timestamp: &[u8; 32],
+    ) -> bool {
+        let beta_bytes = verification_key
+            .beta
+            .iter()
+            .map(|beta_i| beta_i.to_bytes())
+            .collect::<Vec<_>>();
+
+        // re-compute witnesses commitments
+        // Aw = (c * kappa) + (rt * g2) + ((1 - c) * alpha) + (rm[0] * beta[0]) + ... + (rm[i] * beta[i])
+        let commitment_kappa = kappa * self.challenge
+            + params.gen2() * self.response_blinder
+            + verification_key.alpha * (Scalar::one() - self.challenge)
+            + self
+                .response_attributes
+                .iter()
+                .zip(verification_key.beta.iter())
+                .map(|(priv_attr, beta_i)| beta_i * priv_attr)
+                .sum::<G2Projective>();
+
+        // compute the challenge
+        let challenge = compute_challenge::<ChallengeDigest, _, _>(
+            std::iter::once(params.gen2().to_bytes().as_ref())
+                .chain(std::iter::once(kappa.to_bytes().as_ref()))
+                .chain(std::iter::once(verification_key.alpha.to_bytes().as_ref()))
+                .chain(beta_bytes.iter().map(|b| b.as_ref()))
+                .chain(std::iter::once(commitment_kappa.to_bytes().as_ref()))
+                .chain(std::iter::once(verifier_id.as_ref()))
+                .chain(std::iter::once(timestamp.as_ref())),
+        );
+
+        challenge == self.challenge
+    }
+
+    pub fn to_bytes(&self) -> Vec<u8> {
+        let attributes_len = self.response_attributes.len() as u64;
+        let mut bytes = Vec::with_capacity(8 + (attributes_len + 2) as usize * 32);
+
+        bytes.extend_from_slice(&self.challenge.to_bytes());
+        bytes.extend_from_slice(&self.response_blinder.to_bytes());
+
+        bytes.extend_from_slice(&attributes_len.to_le_bytes());
+
+        for rm in &self.response_attributes {
+            bytes.extend_from_slice(&rm.to_bytes());
+        }
+
+        bytes
+    }
+
+    pub fn from_bytes(bytes: &[u8]) -> Result<Self> {
+        // at the very minimum there must be a single attribute being proven
+        if bytes.len() < 32 * 2 + 8 || (bytes.len() - 8) % 32 != 0 {
+            return Err(
+                CoconutError::Deserialization(
+                    "tried to deserialize proof of ciphertexts and commitment with bytes of invalid length".to_string())
+            );
+        }
+
+        let challenge_bytes = bytes[..32].try_into().unwrap();
+        let challenge = try_deserialize_scalar(
+            &challenge_bytes,
+            CoconutError::Deserialization("Failed to deserialize challenge".to_string()),
+        )?;
+
+        let blinder_bytes = bytes[32..64].try_into().unwrap();
+        let response_blinder = try_deserialize_scalar(
+            &blinder_bytes,
+            CoconutError::Deserialization("failed to deserialize the blinder".to_string()),
+        )?;
+
+        let rm_len = u64::from_le_bytes(bytes[64..64 + 8].try_into().unwrap());
+        let response_attributes = try_deserialize_scalar_vec(
+            rm_len,
+            &bytes[64 + 8..],
+            CoconutError::Deserialization("Failed to deserialize attributes response".to_string()),
+        )?;
+
+        Ok(ProofKappa {
+            challenge,
+            response_attributes,
+            response_blinder,
+        })
+    }
+}
+
+#[derive(Debug)]
+#[cfg_attr(test, derive(PartialEq))]
+pub struct ProofKappaNu {
+    // c
+    challenge: Scalar,
+
+    // responses
+    response_serial_number: Scalar,
+    response_binding_number: Scalar,
+    response_blinder: Scalar,
+}
+
+impl ProofKappaNu {
+    pub(crate) fn construct(
+        params: &Parameters,
+        verification_key: &VerificationKey,
+        serial_number: &Attribute,
+        binding_number: &Attribute,
+        blinding_factor: &Scalar,
+        blinded_message: &G2Projective,
+        blinded_serial_number: &G2Projective,
+    ) -> Self {
+        // create the witnesses
+        let witness_blinder = params.random_scalar();
+        let witness_serial_number = params.random_scalar();
+        let witness_binding_number = params.random_scalar();
+        let witness_attributes = vec![witness_serial_number, witness_binding_number];
+
+        let beta_bytes = verification_key
+            .beta
+            .iter()
+            .map(|beta_i| beta_i.to_bytes())
+            .collect::<Vec<_>>();
+
+        // witnesses commitments
+        // Aw = g2 * wt + alpha + beta[0] * wm[0] + ... + beta[i] * wm[i]
+        let commitment_kappa = params.gen2() * witness_blinder
+            + verification_key.alpha
+            + witness_attributes
+                .iter()
+                .zip(verification_key.beta.iter())
+                .map(|(wm_i, beta_i)| beta_i * wm_i)
+                .sum::<G2Projective>();
+
+        // zeta is the public value associated with the serial number
+        let commitment_zeta = params.gen2() * witness_serial_number;
+
+        let challenge = compute_challenge::<ChallengeDigest, _, _>(
+            std::iter::once(params.gen2().to_bytes().as_ref())
+                .chain(std::iter::once(blinded_message.to_bytes().as_ref()))
+                .chain(std::iter::once(blinded_serial_number.to_bytes().as_ref())) //kappa
+                .chain(std::iter::once(verification_key.alpha.to_bytes().as_ref()))
+                .chain(beta_bytes.iter().map(|b| b.as_ref()))
+                .chain(std::iter::once(commitment_kappa.to_bytes().as_ref()))
+                .chain(std::iter::once(commitment_zeta.to_bytes().as_ref())),
+        );
+
+        // responses
+        let response_blinder = produce_response(&witness_blinder, &challenge, blinding_factor);
+        let response_serial_number =
+            produce_response(&witness_serial_number, &challenge, serial_number);
+        let response_binding_number =
+            produce_response(&witness_binding_number, &challenge, binding_number);
+
+        ProofKappaNu {
+            challenge,
+            response_serial_number,
+            response_binding_number,
+            response_blinder,
+        }
+    }
+
+    pub(crate) fn private_attributes_len(&self) -> usize {
+        2
+    }
+
+    pub(crate) fn verify(
+        &self,
+        params: &Parameters,
+        verification_key: &VerificationKey,
+        kappa: &G2Projective,
+        zeta: &G2Projective,
+    ) -> bool {
+        let beta_bytes = verification_key
+            .beta
+            .iter()
+            .map(|beta_i| beta_i.to_bytes())
+            .collect::<Vec<_>>();
+
+        let response_attributes = vec![self.response_serial_number, self.response_binding_number];
+        // re-compute witnesses commitments
+        // Aw = (c * kappa) + (rt * g2) + ((1 - c) * alpha) + (rm[0] * beta[0]) + ... + (rm[i] * beta[i])
+        let commitment_kappa = kappa * self.challenge
+            + params.gen2() * self.response_blinder
+            + verification_key.alpha * (Scalar::one() - self.challenge)
+            + response_attributes
+                .iter()
+                .zip(verification_key.beta.iter())
+                .map(|(priv_attr, beta_i)| beta_i * priv_attr)
+                .sum::<G2Projective>();
+
+        // zeta is the public value associated with the serial number
+        let commitment_zeta = zeta * self.challenge + params.gen2() * self.response_serial_number;
+
+        // compute the challenge
+        let challenge = compute_challenge::<ChallengeDigest, _, _>(
+            std::iter::once(params.gen2().to_bytes().as_ref())
+                .chain(std::iter::once(kappa.to_bytes().as_ref()))
+                .chain(std::iter::once(zeta.to_bytes().as_ref()))
+                .chain(std::iter::once(verification_key.alpha.to_bytes().as_ref()))
+                .chain(beta_bytes.iter().map(|b| b.as_ref()))
+                .chain(std::iter::once(commitment_kappa.to_bytes().as_ref()))
+                .chain(std::iter::once(commitment_zeta.to_bytes().as_ref())),
+        );
+
+        challenge == self.challenge
+    }
+
+    // challenge || rm.len() || rm || rt
+    pub(crate) fn to_bytes(&self) -> Vec<u8> {
+        //let attributes_len = self.response_attributes.len() as u64;
+        let attributes_len = 2;
+        let mut bytes = Vec::with_capacity((attributes_len + 1) as usize * 32);
+
+        bytes.extend_from_slice(&self.challenge.to_bytes());
+        bytes.extend_from_slice(&self.response_serial_number.to_bytes());
+        bytes.extend_from_slice(&self.response_binding_number.to_bytes());
+
+        bytes.extend_from_slice(&self.response_blinder.to_bytes());
+
+        bytes
+    }
+
+    pub(crate) fn from_bytes(bytes: &[u8]) -> Result<Self> {
+        // at the very minimum there must be a single attribute being proven
+        if bytes.len() < 32 * 3 || (bytes.len()) % 32 != 0 {
+            return Err(CoconutError::DeserializationInvalidLength {
+                actual: bytes.len(),
+                modulus_target: bytes.len(),
+                modulus: 32,
+                object: "kappa and zeta".to_string(),
+                target: 32 * 3 + 8,
+            });
+        }
+
+        let challenge_bytes = bytes[..32].try_into().unwrap();
+        let challenge = try_deserialize_scalar(
+            &challenge_bytes,
+            CoconutError::Deserialization("Failed to deserialize challenge".to_string()),
+        )?;
+
+        // let rm_len = u64::from_le_bytes(bytes[32..40].try_into().unwrap());
+        if bytes[32..].len() != (2 + 1) as usize * 32 {
+            return Err(
+                CoconutError::Deserialization(
+                    format!("Tried to deserialize proof of kappa and zeta with insufficient number of bytes provided, expected {} got {}.", (2 + 1) as usize * 32, bytes[32..].len())
+                )
+            );
+        }
+
+        let serial_number_bytes = &bytes[32..64].try_into().unwrap();
+        let response_serial_number = try_deserialize_scalar(
+            serial_number_bytes,
+            CoconutError::Deserialization("failed to deserialize the serial number".to_string()),
+        )?;
+
+        let binding_number_bytes = &bytes[64..96].try_into().unwrap();
+        let response_binding_number = try_deserialize_scalar(
+            binding_number_bytes,
+            CoconutError::Deserialization("failed to deserialize the binding number".to_string()),
+        )?;
+
+        let blinder_bytes = bytes[96..].try_into().unwrap();
+        let response_blinder = try_deserialize_scalar(
+            &blinder_bytes,
+            CoconutError::Deserialization("failed to deserialize the blinder".to_string()),
+        )?;
+
+        Ok(ProofKappaNu {
+            challenge,
+            response_serial_number,
+            response_binding_number,
+            response_blinder,
+        })
+    }
+}
+
+// proof builder:
+// - commitment
+// - challenge
+// - responses
+
+#[cfg(test)]
+mod tests {
+    use group::Group;
+    use rand::thread_rng;
+
+    use crate::scheme::issuance::{compute_attribute_encryption, compute_commitment_hash};
+    use crate::scheme::keygen::keygen;
+    use crate::scheme::setup::setup;
+    use crate::scheme::verification::{compute_kappa, compute_zeta};
+
+    use super::*;
+
+    #[test]
+    fn proof_cm_cs_bytes_roundtrip() {
+        let mut rng = thread_rng();
+        let mut params = setup(1).unwrap();
+
+        let elgamal_keypair = elgamal::elgamal_keygen(&params);
+        let private_attributes = params.n_random_scalars(1);
+
+        // we don't care about 'correctness' of the proof. only whether we can correctly recover it from bytes
+        let cm = G1Projective::random(&mut rng);
+        let r = params.random_scalar();
+
+        let commitment_hash = compute_commitment_hash(cm);
+        let (attributes_ciphertexts, _): (Vec<_>, Vec<_>) = compute_attribute_encryption(
+            &params,
+            private_attributes.as_ref(),
+            elgamal_keypair.public_key(),
+            commitment_hash,
+        );
+        let ephemeral_keys = params.n_random_scalars(1);
+
+        // 0 public 1 private
+        let pi_s = ProofCmCs::construct(
+            &mut params,
+            &elgamal_keypair,
+            &ephemeral_keys,
+            &cm,
+            &r,
+            &private_attributes,
+            &*attributes_ciphertexts,
+        );
+
+        let bytes = pi_s.to_bytes();
+        assert_eq!(ProofCmCs::from_bytes(&bytes).unwrap(), pi_s);
+
+        // 2 private
+        let private_attributes = params.n_random_scalars(2);
+        let ephemeral_keys = params.n_random_scalars(2);
+
+        let pi_s = ProofCmCs::construct(
+            &mut params,
+            &elgamal_keypair,
+            &ephemeral_keys,
+            &cm,
+            &r,
+            &private_attributes,
+            &*attributes_ciphertexts,
+        );
+
+        let bytes = pi_s.to_bytes();
+        assert_eq!(ProofCmCs::from_bytes(&bytes).unwrap(), pi_s);
+    }
+
+    #[test]
+    fn proof_kappa_nu_bytes_roundtrip() {
+        let mut params = setup(1).unwrap();
+
+        let keypair = keygen(&mut params);
+
+        // we don't care about 'correctness' of the proof. only whether we can correctly recover it from bytes
+        let serial_number = params.random_scalar();
+        let binding_number = params.random_scalar();
+        let private_attributes = vec![serial_number, binding_number];
+
+        let r = params.random_scalar();
+        let kappa = compute_kappa(&params, &keypair.verification_key(), &private_attributes, r);
+        let zeta = compute_zeta(&params, serial_number);
+
+        // 0 public 2 private
+        let pi_v = ProofKappaNu::construct(
+            &mut params,
+            &keypair.verification_key(),
+            &serial_number,
+            &binding_number,
+            &r,
+            &kappa,
+            &zeta,
+        );
+
+        let bytes = pi_v.to_bytes();
+        assert_eq!(ProofKappaNu::from_bytes(&bytes).unwrap(), pi_v);
+
+        // 2 public 2 private
+        let mut params = setup(4).unwrap();
+        let keypair = keygen(&mut params);
+
+        let pi_v = ProofKappaNu::construct(
+            &mut params,
+            &keypair.verification_key(),
+            &serial_number,
+            &binding_number,
+            &r,
+            &kappa,
+            &zeta,
+        );
+
+        let bytes = pi_v.to_bytes();
+        assert_eq!(ProofKappaNu::from_bytes(&bytes).unwrap(), pi_v);
+    }
+}

common/nymcoconut/src/scheme/aggregation.rs

@@ -0,0 +1,388 @@
+// Copyright 2021 Nym Technologies SA
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use core::iter::Sum;
+use core::ops::Mul;
+
+use bls12_381::{G2Prepared, G2Projective, Scalar};
+use group::Curve;
+use itertools::Itertools;
+
+use crate::error::{CoconutError, Result};
+use crate::scheme::verification::check_bilinear_pairing;
+use crate::scheme::{PartialSignature, Signature, SignatureShare, SignerIndex, VerificationKey};
+use crate::utils::perform_lagrangian_interpolation_at_origin;
+use crate::{Attribute, Parameters};
+
+pub(crate) trait Aggregatable: Sized {
+    fn aggregate(aggregatable: &[Self], indices: Option<&[SignerIndex]>) -> Result<Self>;
+
+    fn check_unique_indices(indices: &[SignerIndex]) -> bool {
+        // if aggregation is a threshold one, all indices should be unique
+        indices.iter().unique_by(|&index| index).count() == indices.len()
+    }
+}
+
+// includes `VerificationKey`
+impl<T> Aggregatable for T
+where
+    T: Sum,
+    for<'a> T: Sum<&'a T>,
+    for<'a> &'a T: Mul<Scalar, Output = T>,
+{
+    fn aggregate(aggregatable: &[T], indices: Option<&[u64]>) -> Result<T> {
+        if aggregatable.is_empty() {
+            return Err(CoconutError::Aggregation("Empty set of values".to_string()));
+        }
+
+        if let Some(indices) = indices {
+            if !Self::check_unique_indices(indices) {
+                return Err(CoconutError::Aggregation("Non-unique indices".to_string()));
+            }
+            perform_lagrangian_interpolation_at_origin(indices, aggregatable)
+        } else {
+            // non-threshold
+            Ok(aggregatable.iter().sum())
+        }
+    }
+}
+
+impl Aggregatable for PartialSignature {
+    fn aggregate(sigs: &[PartialSignature], indices: Option<&[u64]>) -> Result<Signature> {
+        let h = sigs
+            .get(0)
+            .ok_or_else(|| CoconutError::Aggregation("Empty set of signatures".to_string()))?
+            .sig1();
+
+        // TODO: is it possible to avoid this allocation?
+        let sigmas = sigs.iter().map(|sig| *sig.sig2()).collect::<Vec<_>>();
+        let aggr_sigma = Aggregatable::aggregate(&sigmas, indices)?;
+
+        Ok(Signature(*h, aggr_sigma))
+    }
+}
+
+/// Ensures all provided verification keys were generated to verify the same number of attributes.
+fn check_same_key_size(keys: &[VerificationKey]) -> bool {
+    keys.iter().map(|vk| vk.beta.len()).all_equal()
+}
+
+pub fn aggregate_verification_keys(
+    keys: &[VerificationKey],
+    indices: Option<&[SignerIndex]>,
+) -> Result<VerificationKey> {
+    if !check_same_key_size(keys) {
+        return Err(CoconutError::Aggregation(
+            "Verification keys are of different sizes".to_string(),
+        ));
+    }
+    Aggregatable::aggregate(keys, indices)
+}
+
+pub fn aggregate_signatures(
+    params: &Parameters,
+    verification_key: &VerificationKey,
+    attributes: &[Attribute],
+    signatures: &[PartialSignature],
+    indices: Option<&[SignerIndex]>,
+) -> Result<Signature> {
+    // aggregate the signature
+
+    let signature = match Aggregatable::aggregate(signatures, indices) {
+        Ok(res) => res,
+        Err(err) => return Err(err),
+    };
+
+    // Verify the signature
+    let alpha = verification_key.alpha;
+
+    let tmp = attributes
+        .iter()
+        .zip(verification_key.beta.iter())
+        .map(|(attr, beta_i)| beta_i * attr)
+        .sum::<G2Projective>();
+
+    if !check_bilinear_pairing(
+        &signature.0.to_affine(),
+        &G2Prepared::from((alpha + tmp).to_affine()),
+        &signature.1.to_affine(),
+        params.prepared_miller_g2(),
+    ) {
+        return Err(CoconutError::Aggregation(
+            "Verification of the aggregated signature failed".to_string(),
+        ));
+    }
+    Ok(signature)
+}
+
+pub fn aggregate_signature_shares(
+    params: &Parameters,
+    verification_key: &VerificationKey,
+    attributes: &[Attribute],
+    shares: &[SignatureShare],
+) -> Result<Signature> {
+    let (signatures, indices): (Vec<_>, Vec<_>) = shares
+        .iter()
+        .map(|share| (*share.signature(), share.index()))
+        .unzip();
+
+    aggregate_signatures(
+        params,
+        verification_key,
+        attributes,
+        &signatures,
+        Some(&indices),
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use bls12_381::G1Projective;
+    use group::Group;
+
+    use crate::scheme::issuance::sign;
+    use crate::scheme::keygen::ttp_keygen;
+    use crate::scheme::setup::Parameters;
+    use crate::scheme::verification::verify;
+
+    use super::*;
+
+    #[test]
+    fn key_aggregation_works_for_any_subset_of_keys() {
+        let mut params = Parameters::new(2).unwrap();
+        let keypairs = ttp_keygen(&mut params, 3, 5).unwrap();
+
+        let vks = keypairs
+            .into_iter()
+            .map(|keypair| keypair.verification_key())
+            .collect::<Vec<_>>();
+
+        let aggr_vk1 = aggregate_verification_keys(&vks[..3], Some(&[1, 2, 3])).unwrap();
+        let aggr_vk2 = aggregate_verification_keys(&vks[2..], Some(&[3, 4, 5])).unwrap();
+
+        assert_eq!(aggr_vk1, aggr_vk2);
+
+        // TODO: should those two actually work or not?
+        // aggregating threshold+1
+        let aggr_more = aggregate_verification_keys(&vks[1..], Some(&[2, 3, 4, 5])).unwrap();
+        assert_eq!(aggr_vk1, aggr_more);
+
+        // aggregating all
+        let aggr_all = aggregate_verification_keys(&vks, Some(&[1, 2, 3, 4, 5])).unwrap();
+        assert_eq!(aggr_all, aggr_vk1);
+
+        // not taking enough points (threshold was 3)
+        let aggr_not_enough = aggregate_verification_keys(&vks[..2], Some(&[1, 2])).unwrap();
+        assert_ne!(aggr_not_enough, aggr_vk1);
+
+        // taking wrong index
+        let aggr_bad = aggregate_verification_keys(&vks[2..], Some(&[42, 123, 100])).unwrap();
+        assert_ne!(aggr_vk1, aggr_bad);
+    }
+
+    #[test]
+    fn key_aggregation_doesnt_work_for_empty_set_of_keys() {
+        let keys: Vec<VerificationKey> = vec![];
+        assert!(aggregate_verification_keys(&keys, None).is_err());
+    }
+
+    #[test]
+    fn key_aggregation_doesnt_work_if_indices_have_invalid_length() {
+        let keys = vec![VerificationKey::identity(3)];
+
+        assert!(aggregate_verification_keys(&keys, Some(&[])).is_err());
+        assert!(aggregate_verification_keys(&keys, Some(&[1, 2])).is_err());
+    }
+
+    #[test]
+    fn key_aggregation_doesnt_work_for_non_unique_indices() {
+        let keys = vec![VerificationKey::identity(3), VerificationKey::identity(3)];
+
+        assert!(aggregate_verification_keys(&keys, Some(&[1, 1])).is_err());
+    }
+
+    #[test]
+    fn key_aggregation_doesnt_work_for_keys_of_different_size() {
+        let keys = vec![VerificationKey::identity(3), VerificationKey::identity(1)];
+
+        assert!(aggregate_verification_keys(&keys, None).is_err())
+    }
+
+    #[test]
+    fn signature_aggregation_works_for_any_subset_of_signatures() {
+        let mut params = Parameters::new(2).unwrap();
+        let attributes = params.n_random_scalars(2);
+
+        let keypairs = ttp_keygen(&mut params, 3, 5).unwrap();
+
+        let (sks, vks): (Vec<_>, Vec<_>) = keypairs
+            .into_iter()
+            .map(|keypair| (keypair.secret_key(), keypair.verification_key()))
+            .unzip();
+
+        let sigs = sks
+            .iter()
+            .map(|sk| sign(&mut params, sk, &attributes).unwrap())
+            .collect::<Vec<_>>();
+
+        // aggregating (any) threshold works
+        let aggr_vk_1 = aggregate_verification_keys(&vks[..3], Some(&[1, 2, 3])).unwrap();
+        let aggr_sig1 = aggregate_signatures(
+            &params,
+            &aggr_vk_1,
+            &attributes,
+            &sigs[..3],
+            Some(&[1, 2, 3]),
+        )
+        .unwrap();
+
+        let aggr_vk_2 = aggregate_verification_keys(&vks[2..], Some(&[3, 4, 5])).unwrap();
+        let aggr_sig2 = aggregate_signatures(
+            &params,
+            &aggr_vk_1,
+            &attributes,
+            &sigs[2..],
+            Some(&[3, 4, 5]),
+        )
+        .unwrap();
+        assert_eq!(aggr_sig1, aggr_sig2);
+
+        // verify credential for good measure
+        assert!(verify(&params, &aggr_vk_1, &attributes, &aggr_sig1));
+        assert!(verify(&params, &aggr_vk_2, &attributes, &aggr_sig2));
+
+        // aggregating threshold+1 works
+        let aggr_vk_more = aggregate_verification_keys(&vks[1..], Some(&[2, 3, 4, 5])).unwrap();
+        let aggr_more = aggregate_signatures(
+            &params,
+            &aggr_vk_more,
+            &attributes,
+            &sigs[1..],
+            Some(&[2, 3, 4, 5]),
+        )
+        .unwrap();
+        assert_eq!(aggr_sig1, aggr_more);
+
+        // aggregating all
+        let aggr_vk_all = aggregate_verification_keys(&vks, Some(&[1, 2, 3, 4, 5])).unwrap();
+        let aggr_all = aggregate_signatures(
+            &params,
+            &aggr_vk_all,
+            &attributes,
+            &sigs,
+            Some(&[1, 2, 3, 4, 5]),
+        )
+        .unwrap();
+        assert_eq!(aggr_all, aggr_sig1);
+
+        // not taking enough points (threshold was 3) should fail
+        let aggr_vk_not_enough = aggregate_verification_keys(&vks[..2], Some(&[1, 2])).unwrap();
+        let aggr_not_enough = aggregate_signatures(
+            &params,
+            &aggr_vk_not_enough,
+            &attributes,
+            &sigs[..2],
+            Some(&[1, 2]),
+        )
+        .unwrap();
+        assert_ne!(aggr_not_enough, aggr_sig1);
+
+        // taking wrong index should fail
+        let aggr_vk_bad = aggregate_verification_keys(&vks[2..], Some(&[1, 2, 3])).unwrap();
+        assert!(aggregate_signatures(
+            &params,
+            &aggr_vk_bad,
+            &attributes,
+            &sigs[2..],
+            Some(&[42, 123, 100]),
+        )
+        .is_err());
+    }
+
+    fn random_signature() -> Signature {
+        let mut rng = rand::thread_rng();
+        Signature(
+            G1Projective::random(&mut rng),
+            G1Projective::random(&mut rng),
+        )
+    }
+
+    #[test]
+    fn signature_aggregation_doesnt_work_for_empty_set_of_signatures() {
+        let signatures: Vec<Signature> = vec![];
+        let mut params = Parameters::new(2).unwrap();
+        let attributes = params.n_random_scalars(2);
+        let keypairs = ttp_keygen(&mut params, 3, 5).unwrap();
+
+        let (_, vks): (Vec<_>, Vec<_>) = keypairs
+            .into_iter()
+            .map(|keypair| (keypair.secret_key(), keypair.verification_key()))
+            .unzip();
+
+        let aggr_vk_all = aggregate_verification_keys(&vks, None).unwrap();
+        assert!(
+            aggregate_signatures(&params, &aggr_vk_all, &attributes, &signatures, None).is_err()
+        );
+    }
+
+    #[test]
+    fn signature_aggregation_doesnt_work_if_indices_have_invalid_length() {
+        let signatures = vec![random_signature()];
+        let mut params = Parameters::new(2).unwrap();
+        let attributes = params.n_random_scalars(2);
+        let keypairs = ttp_keygen(&mut params, 3, 5).unwrap();
+        let (_, vks): (Vec<_>, Vec<_>) = keypairs
+            .into_iter()
+            .map(|keypair| (keypair.secret_key(), keypair.verification_key()))
+            .unzip();
+        let aggr_vk_all = aggregate_verification_keys(&vks, None).unwrap();
+
+        assert!(
+            aggregate_signatures(&params, &aggr_vk_all, &attributes, &signatures, Some(&[]))
+                .is_err()
+        );
+        assert!(aggregate_signatures(
+            &params,
+            &aggr_vk_all,
+            &attributes,
+            &signatures,
+            Some(&[1, 2]),
+        )
+        .is_err());
+    }
+
+    #[test]
+    fn signature_aggregation_doesnt_work_for_non_unique_indices() {
+        let signatures = vec![random_signature(), random_signature()];
+        let mut params = Parameters::new(2).unwrap();
+        let attributes = params.n_random_scalars(2);
+        let keypairs = ttp_keygen(&mut params, 3, 5).unwrap();
+        let (_, vks): (Vec<_>, Vec<_>) = keypairs
+            .into_iter()
+            .map(|keypair| (keypair.secret_key(), keypair.verification_key()))
+            .unzip();
+        let aggr_vk_all = aggregate_verification_keys(&vks, None).unwrap();
+
+        assert!(aggregate_signatures(
+            &params,
+            &aggr_vk_all,
+            &attributes,
+            &signatures,
+            Some(&[1, 1]),
+        )
+        .is_err());
+    }
+
+    // TODO: test for aggregating non-threshold keys
+}

common/nymcoconut/src/scheme/issuance.rs

@@ -0,0 +1,397 @@
+// Copyright 2021 Nym Technologies SA
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use std::convert::TryFrom;
+use std::convert::TryInto;
+
+use bls12_381::{G1Affine, G1Projective, Scalar};
+use group::{Curve, GroupEncoding};
+
+use crate::elgamal::{Ciphertext, EphemeralKey};
+use crate::error::{CoconutError, Result};
+use crate::proofs::ProofCmCs;
+use crate::scheme::setup::Parameters;
+use crate::scheme::BlindedSignature;
+use crate::scheme::SecretKey;
+/// Creates a Coconut Signature under a given secret key on a set of public attributes only.
+#[cfg(test)]
+use crate::Signature;
+use crate::{elgamal, Attribute, ElGamalKeyPair};
+// TODO: possibly completely remove those two functions.
+// They only exist to have a simpler and smaller code snippets to test
+// basic functionalities.
+use crate::traits::{Base58, Bytable};
+use crate::utils::{hash_g1, try_deserialize_g1_projective};
+
+// TODO NAMING: double check this one
+// Lambda
+#[derive(Debug)]
+#[cfg_attr(test, derive(PartialEq))]
+pub struct BlindSignRequest {
+    // cm
+    commitment: G1Projective,
+    // h
+    commitment_hash: G1Projective,
+    // c
+    private_attributes_ciphertexts: Vec<elgamal::Ciphertext>,
+    // pi_s
+    pi_s: ProofCmCs,
+}
+
+impl TryFrom<&[u8]> for BlindSignRequest {
+    type Error = CoconutError;
+
+    fn try_from(bytes: &[u8]) -> Result<BlindSignRequest> {
+        if bytes.len() < 48 + 48 + 8 + 96 {
+            return Err(CoconutError::DeserializationMinLength {
+                min: 48 + 48 + 8 + 9,
+                actual: bytes.len(),
+            });
+        }
+
+        let mut j = 0;
+        let commitment_bytes_len = 48;
+        let commitment_hash_bytes_len = 48;
+
+        let cm_bytes = bytes[..j + commitment_bytes_len].try_into().unwrap();
+        let commitment = try_deserialize_g1_projective(
+            &cm_bytes,
+            CoconutError::Deserialization(
+                "Failed to deserialize compressed commitment".to_string(),
+            ),
+        )?;
+        j += commitment_bytes_len;
+
+        let cm_hash_bytes = bytes[j..j + commitment_hash_bytes_len].try_into().unwrap();
+        let commitment_hash = try_deserialize_g1_projective(
+            &cm_hash_bytes,
+            CoconutError::Deserialization(
+                "Failed to deserialize compressed commitment hash".to_string(),
+            ),
+        )?;
+        j += commitment_hash_bytes_len;
+
+        let c_len = u64::from_le_bytes(bytes[j..j + 8].try_into().unwrap());
+        j += 8;
+        if bytes[j..].len() < c_len as usize * 96 {
+            return Err(CoconutError::DeserializationMinLength {
+                min: c_len as usize * 96,
+                actual: bytes[56..].len(),
+            });
+        }
+
+        let mut private_attributes_ciphertexts = Vec::with_capacity(c_len as usize);
+        for i in 0..c_len as usize {
+            let start = j + i * 96;
+            let end = start + 96;
+            private_attributes_ciphertexts.push(Ciphertext::try_from(&bytes[start..end])?)
+        }
+
+        let pi_s = ProofCmCs::from_bytes(&bytes[j + c_len as usize * 96..])?;
+
+        Ok(BlindSignRequest {
+            commitment,
+            commitment_hash,
+            private_attributes_ciphertexts,
+            pi_s,
+        })
+    }
+}
+
+impl Bytable for BlindSignRequest {
+    fn to_byte_vec(&self) -> Vec<u8> {
+        let cm_bytes = self.commitment.to_affine().to_compressed();
+        let cm_hash_bytes = self.commitment_hash.to_affine().to_compressed();
+        let c_len = self.private_attributes_ciphertexts.len() as u64;
+        let proof_bytes = self.pi_s.to_bytes();
+
+        let mut bytes = Vec::with_capacity(48 + 48 + 8 + c_len as usize * 96 + proof_bytes.len());
+
+        bytes.extend_from_slice(&cm_bytes);
+        bytes.extend_from_slice(&cm_hash_bytes);
+        bytes.extend_from_slice(&c_len.to_le_bytes());
+        for c in &self.private_attributes_ciphertexts {
+            bytes.extend_from_slice(&c.to_bytes());
+        }
+
+        bytes.extend_from_slice(&proof_bytes);
+
+        bytes
+    }
+
+    fn try_from_byte_slice(slice: &[u8]) -> Result<Self> {
+        BlindSignRequest::from_bytes(slice)
+    }
+}
+
+impl Base58 for BlindSignRequest {}
+
+impl BlindSignRequest {
+    fn verify_proof(&self, params: &Parameters, pub_key: &elgamal::PublicKey) -> bool {
+        self.pi_s.verify(
+            params,
+            pub_key,
+            &self.commitment,
+            &self.private_attributes_ciphertexts,
+        )
+    }
+
+    pub fn get_commitment_hash(&self) -> G1Projective {
+        self.commitment_hash
+    }
+
+    // TODO: perhaps also include pi_s.len()?
+    // to be determined once we implement serde to make sure its 1:1 compatible
+    // with bincode
+    // cm || c.len() || c || pi_s
+    pub fn to_bytes(&self) -> Vec<u8> {
+        self.to_byte_vec()
+    }
+
+    pub fn from_bytes(bytes: &[u8]) -> Result<BlindSignRequest> {
+        BlindSignRequest::try_from(bytes)
+    }
+}
+
+pub fn compute_private_attributes_commitment(
+    params: &Parameters,
+    private_attributes: &[Attribute],
+    hs: &[G1Affine],
+) -> (Scalar, G1Projective) {
+    let commitment_opening = params.random_scalar();
+
+    // Produces h0 ^ m0 * h1^m1 * .... * hn^mn
+    // where m0, m1, ...., mn are private attributes
+    let attr_cm = private_attributes
+        .iter()
+        .zip(hs)
+        .map(|(&m, h)| h * m)
+        .sum::<G1Projective>();
+
+    // Produces g1^r * h0 ^ m0 * h1^m1 * .... * hn^mn
+    let commitment = params.gen1() * commitment_opening + attr_cm;
+    (commitment_opening, commitment)
+}
+
+pub fn compute_commitment_hash(commitment: G1Projective) -> G1Projective {
+    hash_g1(commitment.to_bytes())
+}
+
+pub fn compute_attribute_encryption(
+    params: &Parameters,
+    private_attributes: &[Attribute],
+    pub_key: &elgamal::PublicKey,
+    commitment_hash: G1Projective,
+) -> (Vec<Ciphertext>, Vec<EphemeralKey>) {
+    private_attributes
+        .iter()
+        .map(|m| pub_key.encrypt(params, &commitment_hash, m))
+        .unzip()
+}
+
+/// Builds cryptographic material required for blind sign.
+pub fn prepare_blind_sign(
+    params: &Parameters,
+    elgamal_keypair: &ElGamalKeyPair,
+    private_attributes: &[Attribute],
+    public_attributes: &[Attribute],
+) -> Result<BlindSignRequest> {
+    if private_attributes.is_empty() {
+        return Err(CoconutError::Issuance(
+            "Tried to prepare blind sign request for an empty set of private attributes"
+                .to_string(),
+        ));
+    }
+
+    let hs = params.gen_hs();
+    if private_attributes.len() + public_attributes.len() > hs.len() {
+        return Err(CoconutError::IssuanceMaxAttributes {
+            max: hs.len(),
+            requested: private_attributes.len() + public_attributes.len(),
+        });
+    }
+
+    let (commitment_opening, commitment) =
+        compute_private_attributes_commitment(params, private_attributes, hs);
+
+    // Compute the challenge as the commitment hash
+    let commitment_hash = compute_commitment_hash(commitment);
+    // build ElGamal encryption
+    let (private_attributes_ciphertexts, ephemeral_keys): (Vec<_>, Vec<_>) =
+        compute_attribute_encryption(
+            params,
+            private_attributes,
+            elgamal_keypair.public_key(),
+            commitment_hash,
+        );
+
+    let pi_s = ProofCmCs::construct(
+        params,
+        elgamal_keypair,
+        &ephemeral_keys,
+        &commitment,
+        &commitment_opening,
+        private_attributes,
+        &*private_attributes_ciphertexts,
+    );
+
+    Ok(BlindSignRequest {
+        commitment,
+        commitment_hash,
+        private_attributes_ciphertexts,
+        pi_s,
+    })
+}
+
+pub fn blind_sign(
+    params: &Parameters,
+    signing_secret_key: &SecretKey,
+    prover_pub_key: &elgamal::PublicKey,
+    blind_sign_request: &BlindSignRequest,
+    public_attributes: &[Attribute],
+) -> Result<BlindedSignature> {
+    let num_private = blind_sign_request.private_attributes_ciphertexts.len();
+    let hs = params.gen_hs();
+
+    if num_private + public_attributes.len() > hs.len() {
+        return Err(CoconutError::IssuanceMaxAttributes {
+            max: hs.len(),
+            requested: num_private + public_attributes.len(),
+        });
+    }
+
+    // Verify the commitment hash
+    let h = hash_g1(blind_sign_request.commitment.to_bytes());
+    if !(h == blind_sign_request.commitment_hash) {
+        return Err(CoconutError::Issuance(
+            "Failed to verify the commitment hash".to_string(),
+        ));
+    }
+
+    // Verify the ZK proof
+    if !blind_sign_request.verify_proof(params, prover_pub_key) {
+        return Err(CoconutError::Issuance(
+            "Failed to verify the proof of knowledge".to_string(),
+        ));
+    }
+
+    // in python implementation there are n^2 G1 multiplications, let's do it with a single one instead.
+    // i.e. compute h ^ (pub_m[0] * y[m + 1] + ... + pub_m[n] * y[m + n]) directly (where m is number of PRIVATE attributes)
+    // rather than ((h ^ pub_m[0]) ^ y[m + 1] , (h ^ pub_m[1]) ^ y[m + 2] , ...).sum() separately
+    let signed_public = h * public_attributes
+        .iter()
+        .zip(signing_secret_key.ys.iter().skip(num_private))
+        .map(|(attr, yi)| attr * yi)
+        .sum::<Scalar>();
+
+    // c1[0] ^ y[0] * ... * c1[m] ^ y[m]
+    let sig_1 = blind_sign_request
+        .private_attributes_ciphertexts
+        .iter()
+        .map(|ciphertext| ciphertext.c1())
+        .zip(signing_secret_key.ys.iter())
+        .map(|(c1, yi)| c1 * yi)
+        .sum();
+
+    // h ^ x + c2[0] ^ y[0] + ... c2[m] ^ y[m] + h ^ (pub_m[0] * y[m + 1] + ... + pub_m[n] * y[m + n])
+    let sig_2 = blind_sign_request
+        .private_attributes_ciphertexts
+        .iter()
+        .map(|ciphertext| ciphertext.c2())
+        .zip(signing_secret_key.ys.iter())
+        .map(|(c2, yi)| c2 * yi)
+        .chain(std::iter::once(h * signing_secret_key.x))
+        .chain(std::iter::once(signed_public))
+        .sum();
+
+    Ok(BlindedSignature(h, elgamal::Ciphertext(sig_1, sig_2)))
+}
+
+#[cfg(test)]
+pub fn sign(
+    params: &mut Parameters,
+    secret_key: &SecretKey,
+    public_attributes: &[Attribute],
+) -> Result<Signature> {
+    if public_attributes.len() > secret_key.ys.len() {
+        return Err(CoconutError::IssuanceMaxAttributes {
+            max: secret_key.ys.len(),
+            requested: public_attributes.len(),
+        });
+    }
+
+    // TODO: why in the python implementation this hash onto the curve is present
+    // while it's not used in the paper? the paper uses random exponent instead.
+    // (the python implementation hashes string representation of all attributes onto the curve,
+    // but I think the same can be achieved by just summing the attributes thus avoiding the unnecessary
+    // transformation. If I'm wrong, please correct me.)
+    let attributes_sum = public_attributes.iter().sum::<Scalar>();
+    let h = hash_g1((params.gen1() * attributes_sum).to_bytes());
+
+    // x + m0 * y0 + m1 * y1 + ... mn * yn
+    let exponent = secret_key.x
+        + public_attributes
+            .iter()
+            .zip(secret_key.ys.iter())
+            .map(|(m_i, y_i)| m_i * y_i)
+            .sum::<Scalar>();
+
+    let sig2 = h * exponent;
+    Ok(Signature(h, sig2))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn blind_sign_request_bytes_roundtrip() {
+        let mut params = Parameters::new(1).unwrap();
+        let public_attributes = params.n_random_scalars(0);
+        let private_attributes = params.n_random_scalars(1);
+        let elgamal_keypair = elgamal::elgamal_keygen(&params);
+
+        let lambda = prepare_blind_sign(
+            &mut params,
+            &elgamal_keypair,
+            &private_attributes,
+            &public_attributes,
+        )
+        .unwrap();
+
+        let bytes = lambda.to_bytes();
+        println!("{:?}", bytes.len());
+        assert_eq!(
+            BlindSignRequest::try_from(bytes.as_slice()).unwrap(),
+            lambda
+        );
+
+        let mut params = Parameters::new(4).unwrap();
+        let public_attributes = params.n_random_scalars(2);
+        let private_attributes = params.n_random_scalars(2);
+        let lambda = prepare_blind_sign(
+            &mut params,
+            &elgamal_keypair,
+            &private_attributes,
+            &public_attributes,
+        )
+        .unwrap();
+
+        let bytes = lambda.to_bytes();
+        assert_eq!(
+            BlindSignRequest::try_from(bytes.as_slice()).unwrap(),
+            lambda
+        );
+    }
+}

common/nymcoconut/src/scheme/keygen.rs

@@ -0,0 +1,550 @@
+// Copyright 2021 Nym Technologies SA
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use core::borrow::Borrow;
+use core::iter::Sum;
+use core::ops::{Add, Mul};
+use std::convert::TryFrom;
+use std::convert::TryInto;
+
+use bls12_381::{G2Projective, Scalar};
+use group::Curve;
+use serde_derive::{Deserialize, Serialize};
+
+use crate::error::{CoconutError, Result};
+use crate::scheme::aggregation::aggregate_verification_keys;
+use crate::scheme::setup::Parameters;
+use crate::scheme::SignerIndex;
+use crate::traits::Bytable;
+use crate::utils::{
+    try_deserialize_g2_projective, try_deserialize_scalar, try_deserialize_scalar_vec, Polynomial,
+};
+use crate::Base58;
+
+#[derive(Debug, Clone)]
+#[cfg_attr(test, derive(PartialEq))]
+pub struct SecretKey {
+    pub(crate) x: Scalar,
+    pub(crate) ys: Vec<Scalar>,
+}
+
+impl TryFrom<&[u8]> for SecretKey {
+    type Error = CoconutError;
+
+    fn try_from(bytes: &[u8]) -> Result<SecretKey> {
+        if bytes.len() < 32 * 2 + 8 || (bytes.len() - 8) % 32 != 0 {
+            return Err(CoconutError::DeserializationInvalidLength {
+                actual: bytes.len(),
+                modulus_target: bytes.len() - 8,
+                target: 32 * 2 + 8,
+                modulus: 32,
+                object: "secret key".to_string(),
+            });
+        }
+
+        // this conversion will not fail as we are taking the same length of data
+        let x_bytes: [u8; 32] = bytes[..32].try_into().unwrap();
+        let ys_len = u64::from_le_bytes(bytes[32..40].try_into().unwrap());
+        let actual_ys_len = (bytes.len() - 40) / 32;
+
+        if ys_len as usize != actual_ys_len {
+            return Err(CoconutError::Deserialization(format!(
+                "Tried to deserialize secret key with inconsistent ys len (expected {}, got {})",
+                ys_len, actual_ys_len
+            )));
+        }
+
+        let x = try_deserialize_scalar(
+            &x_bytes,
+            CoconutError::Deserialization("Failed to deserialize secret key scalar".to_string()),
+        )?;
+        let ys = try_deserialize_scalar_vec(
+            ys_len,
+            &bytes[40..],
+            CoconutError::Deserialization("Failed to deserialize secret key scalars".to_string()),
+        )?;
+
+        Ok(SecretKey { x, ys })
+    }
+}
+
+impl SecretKey {
+    /// Derive verification key using this secret key.
+    pub fn verification_key(&self, params: &Parameters) -> VerificationKey {
+        let g2 = params.gen2();
+        VerificationKey {
+            alpha: g2 * self.x,
+            beta: self.ys.iter().map(|y| g2 * y).collect(),
+        }
+    }
+
+    // x || ys.len() || ys
+    pub fn to_bytes(&self) -> Vec<u8> {
+        let ys_len = self.ys.len() as u64;
+        let mut bytes = Vec::with_capacity(8 + (ys_len + 1) as usize * 32);
+
+        bytes.extend_from_slice(&self.x.to_bytes());
+        bytes.extend_from_slice(&ys_len.to_le_bytes());
+        for y in self.ys.iter() {
+            bytes.extend_from_slice(&y.to_bytes())
+        }
+        bytes
+    }
+
+    pub fn from_bytes(bytes: &[u8]) -> Result<SecretKey> {
+        SecretKey::try_from(bytes)
+    }
+}
+
+impl Bytable for SecretKey {
+    fn to_byte_vec(&self) -> Vec<u8> {
+        self.to_bytes()
+    }
+
+    fn try_from_byte_slice(slice: &[u8]) -> Result<Self> {
+        SecretKey::try_from(slice)
+    }
+}
+
+impl Base58 for SecretKey {}
+
+// TODO: perhaps change points to affine representation
+// to make verification slightly more efficient?
+#[derive(Debug, PartialEq, Clone)]
+pub struct VerificationKey {
+    // TODO add gen2 as per the paper or imply it from the fact library is using bls381?
+    pub alpha: G2Projective,
+    pub beta: Vec<G2Projective>,
+}
+
+impl TryFrom<&[u8]> for VerificationKey {
+    type Error = CoconutError;
+
+    fn try_from(bytes: &[u8]) -> Result<VerificationKey> {
+        if bytes.len() < 96 * 2 + 8 || (bytes.len() - 8) % 96 != 0 {
+            return Err(CoconutError::DeserializationInvalidLength {
+                actual: bytes.len(),
+                modulus_target: bytes.len() - 8,
+                target: 96 * 2 + 8,
+                modulus: 96,
+                object: "secret key".to_string(),
+            });
+        }
+
+        // this conversion will not fail as we are taking the same length of data
+        let alpha_bytes: [u8; 96] = bytes[..96].try_into().unwrap();
+        let beta_len = u64::from_le_bytes(bytes[96..104].try_into().unwrap());
+        let actual_beta_len = (bytes.len() - 104) / 96;
+
+        if beta_len as usize != actual_beta_len {
+            return Err(
+                CoconutError::Deserialization(
+                    format!("Tried to deserialize verification key with inconsistent beta len (expected {}, got {})",
+                            beta_len, actual_beta_len
+                    )));
+        }
+
+        let alpha = try_deserialize_g2_projective(
+            &alpha_bytes,
+            CoconutError::Deserialization(
+                "Failed to deserialize verification key G2 point (alpha)".to_string(),
+            ),
+        )?;
+
+        let mut beta = Vec::with_capacity(actual_beta_len);
+        for i in 0..actual_beta_len {
+            let start = 104 + i * 96;
+            let end = start + 96;
+            let beta_i_bytes = bytes[start..end].try_into().unwrap();
+            let beta_i = try_deserialize_g2_projective(
+                &beta_i_bytes,
+                CoconutError::Deserialization(
+                    "Failed to deserialize verification key G2 point (beta)".to_string(),
+                ),
+            )?;
+
+            beta.push(beta_i)
+        }
+
+        Ok(VerificationKey { alpha, beta })
+    }
+}
+
+impl<'b> Add<&'b VerificationKey> for VerificationKey {
+    type Output = VerificationKey;
+
+    #[inline]
+    fn add(self, rhs: &'b VerificationKey) -> VerificationKey {
+        // If you're trying to add two keys together that were created
+        // for different number of attributes, just panic as it's a
+        // nonsense operation.
+        assert_eq!(
+            self.beta.len(),
+            rhs.beta.len(),
+            "trying to add verification keys generated for different number of attributes"
+        );
+
+        VerificationKey {
+            alpha: self.alpha + rhs.alpha,
+            beta: self
+                .beta
+                .iter()
+                .zip(rhs.beta.iter())
+                .map(|(self_beta, rhs_beta)| self_beta + rhs_beta)
+                .collect(),
+        }
+    }
+}
+
+impl<'a> Mul<Scalar> for &'a VerificationKey {
+    type Output = VerificationKey;
+
+    #[inline]
+    fn mul(self, rhs: Scalar) -> Self::Output {
+        VerificationKey {
+            alpha: self.alpha * rhs,
+            beta: self.beta.iter().map(|b_i| b_i * rhs).collect(),
+        }
+    }
+}
+
+impl<T> Sum<T> for VerificationKey
+where
+    T: Borrow<VerificationKey>,
+{
+    #[inline]
+    fn sum<I>(iter: I) -> Self
+    where
+        I: Iterator<Item = T>,
+    {
+        let mut peekable = iter.peekable();
+        let head_attributes = match peekable.peek() {
+            Some(head) => head.borrow().beta.len(),
+            None => {
+                // TODO: this is a really weird edge case. You're trying to sum an EMPTY iterator
+                // of VerificationKey. So should it panic here or just return some nonsense value?
+                return VerificationKey::identity(0);
+            }
+        };
+
+        peekable.fold(VerificationKey::identity(head_attributes), |acc, item| {
+            acc + item.borrow()
+        })
+    }
+}
+
+impl VerificationKey {
+    /// Create a (kinda) identity verification key using specified
+    /// number of 'beta' elements
+    pub(crate) fn identity(beta_size: usize) -> Self {
+        VerificationKey {
+            alpha: G2Projective::identity(),
+            beta: vec![G2Projective::identity(); beta_size],
+        }
+    }
+
+    pub fn aggregate(sigs: &[Self], indices: Option<&[SignerIndex]>) -> Result<Self> {
+        aggregate_verification_keys(sigs, indices)
+    }
+
+    pub fn alpha(&self) -> &G2Projective {
+        &self.alpha
+    }
+
+    pub fn beta(&self) -> &Vec<G2Projective> {
+        &self.beta
+    }
+
+    pub fn to_bytes(&self) -> Vec<u8> {
+        let beta_len = self.beta.len() as u64;
+        let mut bytes = Vec::with_capacity(8 + (beta_len + 1) as usize * 96);
+
+        bytes.extend_from_slice(&self.alpha.to_affine().to_compressed());
+        bytes.extend_from_slice(&beta_len.to_le_bytes());
+        for beta in self.beta.iter() {
+            bytes.extend_from_slice(&beta.to_affine().to_compressed())
+        }
+        bytes
+    }
+
+    pub fn from_bytes(bytes: &[u8]) -> Result<VerificationKey> {
+        VerificationKey::try_from(bytes)
+    }
+}
+
+impl Bytable for VerificationKey {
+    fn to_byte_vec(&self) -> Vec<u8> {
+        self.to_bytes()
+    }
+
+    fn try_from_byte_slice(slice: &[u8]) -> Result<Self> {
+        VerificationKey::try_from(slice)
+    }
+}
+
+impl Base58 for VerificationKey {}
+
+#[derive(Debug, Serialize, Deserialize)]
+#[cfg_attr(test, derive(PartialEq))]
+pub struct KeyPair {
+    secret_key: SecretKey,
+    verification_key: VerificationKey,
+
+    /// Optional index value specifying polynomial point used during threshold key generation.
+    pub index: Option<SignerIndex>,
+}
+
+impl KeyPair {
+    const MARKER_BYTES: &'static [u8] = b"coconutkeypair";
+
+    pub fn secret_key(&self) -> SecretKey {
+        self.secret_key.clone()
+    }
+
+    pub fn verification_key(&self) -> VerificationKey {
+        self.verification_key.clone()
+    }
+
+    pub fn to_bytes(&self) -> Vec<u8> {
+        // Schema is coconutkeypair[14]|secret_key_len[8]|secret_key[secret_key_len]|verification_key_len[8]|verification_key[verification_key_len]|signer_index[8] - optional
+        self.to_byte_vec()
+    }
+
+    pub fn from_bytes(bytes: &[u8]) -> Result<Self> {
+        KeyPair::try_from_byte_slice(bytes)
+    }
+}
+
+impl Bytable for KeyPair {
+    fn to_byte_vec(&self) -> Vec<u8> {
+        // Schema is coconutkeypair[14]|secret_key_len[8]|secret_key[secret_key_len]|verification_key_len[8]|verification_key[verification_key_len]|signer_index[8] - optional
+        let mut byts = vec![];
+        let secret_key_bytes = self.secret_key.to_bytes();
+        let secret_key_len = (secret_key_bytes.len() as u64).to_le_bytes();
+        let verification_key_bytes = self.verification_key.to_bytes();
+        let verification_key_len = (verification_key_bytes.len() as u64).to_le_bytes();
+        byts.extend_from_slice(Self::MARKER_BYTES);
+        byts.extend_from_slice(&secret_key_len);
+        byts.extend_from_slice(&secret_key_bytes);
+        byts.extend_from_slice(&verification_key_len);
+        byts.extend_from_slice(&verification_key_bytes);
+        if let Some(index) = self.index {
+            byts.extend_from_slice(&index.to_le_bytes())
+        }
+        byts
+    }
+
+    fn try_from_byte_slice(slice: &[u8]) -> Result<Self> {
+        KeyPair::try_from(slice)
+    }
+}
+
+impl Base58 for KeyPair {}
+
+impl TryFrom<&[u8]> for KeyPair {
+    type Error = CoconutError;
+
+    fn try_from(bytes: &[u8]) -> Result<KeyPair> {
+        let header_len = Self::MARKER_BYTES.len();
+
+        // we must be able to at the very least read the length of secret key which is past the header
+        // and is 8 bytes long
+        if bytes.len() < header_len + 8 {
+            return Err(CoconutError::DeserializationMinLength {
+                min: header_len + 8,
+                actual: bytes.len(),
+            });
+        }
+
+        let secret_key_len =
+            u64::from_le_bytes(bytes[header_len..header_len + 8].try_into().unwrap()) as usize;
+        let secret_key_start = header_len + 8;
+
+        let secret_key =
+            SecretKey::try_from(&bytes[secret_key_start..secret_key_start + secret_key_len])?;
+
+        // we must be able to read the length of verification key
+        if bytes.len() < secret_key_start + secret_key_len + 8 {
+            return Err(CoconutError::DeserializationMinLength {
+                min: secret_key_start + secret_key_len + 8,
+                actual: bytes.len(),
+            });
+        }
+
+        let verification_key_len = u64::from_le_bytes(
+            bytes[secret_key_start + secret_key_len..secret_key_start + secret_key_len + 8]
+                .try_into()
+                .unwrap(),
+        ) as usize;
+        let verification_key_start = secret_key_start + secret_key_len + 8;
+
+        let verification_key = VerificationKey::try_from(
+            &bytes[verification_key_start..verification_key_start + verification_key_len],
+        )?;
+        let consumed_bytes = verification_key_start + verification_key_len;
+        let index = if consumed_bytes < bytes.len() && [consumed_bytes..].len() == 8 {
+            Some(u64::from_le_bytes(
+                bytes[consumed_bytes..consumed_bytes + 8]
+                    .try_into()
+                    .unwrap(),
+            ))
+        } else {
+            None
+        };
+        Ok(KeyPair {
+            secret_key,
+            verification_key,
+            index,
+        })
+    }
+}
+
+/// Generate a single Coconut keypair ((x, y0, y1...), (g2^x, g2^y0, ...)).
+/// It is not suitable for threshold credentials as all subsequent calls to `keygen` generate keys
+/// that are independent of each other.
+#[cfg(test)]
+pub fn keygen(params: &Parameters) -> KeyPair {
+    let attributes = params.gen_hs().len();
+
+    let x = params.random_scalar();
+    let ys = params.n_random_scalars(attributes);
+
+    let secret_key = SecretKey { x, ys };
+    let verification_key = secret_key.verification_key(params);
+
+    KeyPair {
+        secret_key,
+        verification_key,
+        index: None,
+    }
+}
+
+/// Generate a set of n Coconut keypairs [((x, y0, y1...), (g2^x, g2^y0, ...)), ...],
+/// such that they support threshold aggregation by `threshold` number of parties.
+/// It is expected that this procedure is executed by a Trusted Third Party.
+pub fn ttp_keygen(
+    params: &Parameters,
+    threshold: u64,
+    num_authorities: u64,
+) -> Result<Vec<KeyPair>> {
+    if threshold == 0 {
+        return Err(CoconutError::Setup(
+            "Tried to generate threshold keys with a 0 threshold value".to_string(),
+        ));
+    }
+
+    if threshold > num_authorities {
+        return Err(
+            CoconutError::Setup(
+                "Tried to generate threshold keys for threshold value being higher than number of the signing authorities".to_string(),
+            ));
+    }
+
+    let attributes = params.gen_hs().len();
+
+    // generate polynomials
+    let v = Polynomial::new_random(params, threshold - 1);
+    let ws = (0..attributes)
+        .map(|_| Polynomial::new_random(params, threshold - 1))
+        .collect::<Vec<_>>();
+
+    // TODO: potentially if we had some known authority identifier we could use that instead
+    // of the increasing (1,2,3,...) sequence
+    let polynomial_indices = (1..=num_authorities).collect::<Vec<_>>();
+
+    // generate polynomial shares
+    let x = polynomial_indices
+        .iter()
+        .map(|&id| v.evaluate(&Scalar::from(id)));
+    let ys = polynomial_indices.iter().map(|&id| {
+        ws.iter()
+            .map(|w| w.evaluate(&Scalar::from(id)))
+            .collect::<Vec<_>>()
+    });
+
+    // finally set the keys
+    let secret_keys = x.zip(ys).map(|(x, ys)| SecretKey { x, ys });
+
+    let keypairs = secret_keys
+        .zip(polynomial_indices.iter())
+        .map(|(secret_key, index)| {
+            let verification_key = secret_key.verification_key(params);
+            KeyPair {
+                secret_key,
+                verification_key,
+                index: Some(*index),
+            }
+        })
+        .collect();
+
+    Ok(keypairs)
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::scheme::setup::setup;
+
+    use super::*;
+
+    #[test]
+    fn keypair_bytes_roundtrip() {
+        let mut params1 = setup(1).unwrap();
+        let mut params5 = setup(5).unwrap();
+
+        let keypair1 = keygen(&mut params1);
+        let keypair5 = keygen(&mut params5);
+
+        let bytes1 = keypair1.to_bytes();
+        let bytes5 = keypair5.to_bytes();
+
+        assert_eq!(KeyPair::from_bytes(&bytes1).unwrap(), keypair1);
+        assert_eq!(KeyPair::from_bytes(&bytes5).unwrap(), keypair5);
+    }
+
+    #[test]
+    fn secret_key_bytes_roundtrip() {
+        let mut params1 = setup(1).unwrap();
+        let mut params5 = setup(5).unwrap();
+
+        let keypair1 = keygen(&mut params1);
+        let keypair5 = keygen(&mut params5);
+
+        let bytes1 = keypair1.secret_key.to_bytes();
+        let bytes5 = keypair5.secret_key.to_bytes();
+
+        assert_eq!(SecretKey::from_bytes(&bytes1).unwrap(), keypair1.secret_key);
+        assert_eq!(SecretKey::from_bytes(&bytes5).unwrap(), keypair5.secret_key);
+    }
+
+    #[test]
+    fn verification_key_bytes_roundtrip() {
+        let mut params1 = setup(1).unwrap();
+        let mut params5 = setup(5).unwrap();
+
+        let keypair1 = &keygen(&mut params1);
+        let keypair5 = &keygen(&mut params5);
+
+        let bytes1: Vec<u8> = keypair1.verification_key.to_bytes();
+        let bytes5: Vec<u8> = keypair5.verification_key.to_bytes();
+
+        assert_eq!(
+            VerificationKey::try_from(bytes1.as_slice()).unwrap(),
+            keypair1.verification_key
+        );
+        assert_eq!(
+            VerificationKey::try_from(bytes5.as_slice()).unwrap(),
+            keypair5.verification_key
+        );
+    }
+}

common/nymcoconut/src/scheme/mod.rs

@@ -0,0 +1,600 @@
+// Copyright 2021 Nym Technologies SA
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// TODO: implement https://crates.io/crates/signature traits?
+
+use std::convert::TryFrom;
+use std::convert::TryInto;
+
+use bls12_381::{G1Projective, G2Prepared, G2Projective, Scalar};
+use group::Curve;
+
+pub use keygen::{SecretKey, VerificationKey};
+
+use crate::elgamal::Ciphertext;
+use crate::error::{CoconutError, Result};
+use crate::scheme::setup::Parameters;
+use crate::scheme::verification::check_bilinear_pairing;
+use crate::traits::{Base58, Bytable};
+use crate::utils::try_deserialize_g1_projective;
+use crate::{elgamal, Attribute};
+
+pub mod aggregation;
+pub mod issuance;
+pub mod keygen;
+pub mod setup;
+pub mod verification;
+
+pub type SignerIndex = u64;
+
+// (h, s)
+#[derive(Debug, Clone, Copy)]
+#[cfg_attr(test, derive(PartialEq))]
+pub struct Signature(pub G1Projective, pub G1Projective);
+
+pub type PartialSignature = Signature;
+
+impl TryFrom<&[u8]> for Signature {
+    type Error = CoconutError;
+
+    fn try_from(bytes: &[u8]) -> Result<Signature> {
+        if bytes.len() != 96 {
+            return Err(CoconutError::Deserialization(format!(
+                "Signature must be exactly 96 bytes, got {}",
+                bytes.len()
+            )));
+        }
+
+        let sig1_bytes: &[u8; 48] = &bytes[..48].try_into().expect("Slice size != 48");
+        let sig2_bytes: &[u8; 48] = &bytes[48..].try_into().expect("Slice size != 48");
+
+        let sig1 = try_deserialize_g1_projective(
+            sig1_bytes,
+            CoconutError::Deserialization("Failed to deserialize compressed sig1".to_string()),
+        )?;
+
+        let sig2 = try_deserialize_g1_projective(
+            sig2_bytes,
+            CoconutError::Deserialization("Failed to deserialize compressed sig2".to_string()),
+        )?;
+
+        Ok(Signature(sig1, sig2))
+    }
+}
+
+impl Signature {
+    pub(crate) fn sig1(&self) -> &G1Projective {
+        &self.0
+    }
+
+    pub(crate) fn sig2(&self) -> &G1Projective {
+        &self.1
+    }
+
+    pub fn randomise(&self, params: &Parameters) -> (Signature, Scalar) {
+        let r = params.random_scalar();
+        let r_prime = params.random_scalar();
+        let h_prime = self.0 * r_prime;
+        let s_prime = (self.1 * r_prime) + (h_prime * r);
+        (Signature(h_prime, s_prime), r)
+    }
+
+    pub fn to_bytes(self) -> [u8; 96] {
+        let mut bytes = [0u8; 96];
+        bytes[..48].copy_from_slice(&self.0.to_affine().to_compressed());
+        bytes[48..].copy_from_slice(&self.1.to_affine().to_compressed());
+        bytes
+    }
+
+    pub fn from_bytes(bytes: &[u8]) -> Result<Signature> {
+        Signature::try_from(bytes)
+    }
+}
+
+impl Bytable for Signature {
+    fn to_byte_vec(&self) -> Vec<u8> {
+        self.to_bytes().to_vec()
+    }
+
+    fn try_from_byte_slice(slice: &[u8]) -> Result<Self> {
+        Signature::from_bytes(slice)
+    }
+}
+
+impl Base58 for Signature {}
+
+#[derive(Debug)]
+#[cfg_attr(test, derive(PartialEq))]
+pub struct BlindedSignature(G1Projective, elgamal::Ciphertext);
+
+impl Bytable for BlindedSignature {
+    fn to_byte_vec(&self) -> Vec<u8> {
+        self.to_bytes().to_vec()
+    }
+
+    fn try_from_byte_slice(slice: &[u8]) -> Result<Self> {
+        Self::from_bytes(slice)
+    }
+}
+
+impl Base58 for BlindedSignature {}
+
+impl TryFrom<&[u8]> for BlindedSignature {
+    type Error = CoconutError;
+
+    fn try_from(bytes: &[u8]) -> Result<BlindedSignature> {
+        if bytes.len() != 144 {
+            return Err(CoconutError::Deserialization(format!(
+                "BlindedSignature must be exactly 144 bytes, got {}",
+                bytes.len()
+            )));
+        }
+
+        let h_bytes: &[u8; 48] = &bytes[..48].try_into().expect("Slice size != 48");
+
+        let h = try_deserialize_g1_projective(
+            h_bytes,
+            CoconutError::Deserialization("Failed to deserialize compressed h".to_string()),
+        )?;
+        let c_tilde = Ciphertext::try_from(&bytes[48..])?;
+
+        Ok(BlindedSignature(h, c_tilde))
+    }
+}
+
+impl BlindedSignature {
+    pub fn unblind(
+        &self,
+        params: &Parameters,
+        private_key: &elgamal::PrivateKey,
+        partial_verification_key: &VerificationKey,
+        private_attributes: &[Attribute],
+        public_attributes: &[Attribute],
+        commitment_hash: &G1Projective,
+    ) -> Result<Signature> {
+        // parse the signature
+        let h = &self.0;
+        let c = &self.1;
+        let sig2 = private_key.decrypt(c);
+
+        // Verify the commitment hash
+        if !(commitment_hash == h) {
+            return Err(CoconutError::Unblind(
+                "Verification of commitment hash from signature failed".to_string(),
+            ));
+        }
+
+        let alpha = partial_verification_key.alpha;
+
+        let tmp = private_attributes
+            .iter()
+            .chain(public_attributes.iter())
+            .zip(partial_verification_key.beta.iter())
+            .map(|(attr, beta_i)| beta_i * attr)
+            .sum::<G2Projective>();
+
+        // Verify the signature share
+        if !check_bilinear_pairing(
+            &h.to_affine(),
+            &G2Prepared::from((alpha + tmp).to_affine()),
+            &sig2.to_affine(),
+            params.prepared_miller_g2(),
+        ) {
+            return Err(CoconutError::Unblind(
+                "Verification of signature share failed".to_string(),
+            ));
+        }
+
+        Ok(Signature(self.0, sig2))
+    }
+
+    pub fn to_bytes(&self) -> [u8; 144] {
+        let mut bytes = [0u8; 144];
+        bytes[..48].copy_from_slice(&self.0.to_affine().to_compressed());
+        bytes[48..].copy_from_slice(&self.1.to_bytes());
+        bytes
+    }
+
+    pub fn from_bytes(bytes: &[u8]) -> Result<BlindedSignature> {
+        BlindedSignature::try_from(bytes)
+    }
+}
+
+// perhaps this should take signature by reference? we'll see how it goes
+pub struct SignatureShare {
+    signature: Signature,
+    index: SignerIndex,
+}
+
+impl SignatureShare {
+    pub fn new(signature: Signature, index: SignerIndex) -> Self {
+        SignatureShare { signature, index }
+    }
+
+    pub fn signature(&self) -> &Signature {
+        &self.signature
+    }
+
+    pub fn index(&self) -> SignerIndex {
+        self.index
+    }
+
+    // pub fn aggregate(shares: &[Self]) -> Result<Signature> {
+    //     aggregate_signature_shares(shares)
+    // }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::scheme::aggregation::{aggregate_signatures, aggregate_verification_keys};
+    use crate::scheme::issuance::{blind_sign, prepare_blind_sign, sign};
+    use crate::scheme::keygen::{keygen, ttp_keygen};
+    use crate::scheme::verification::{prove_bandwidth_credential, verify, verify_credential};
+
+    use super::*;
+
+    #[test]
+    fn verification_on_two_private_attributes() {
+        let mut params = Parameters::new(2).unwrap();
+        let serial_number = params.random_scalar();
+        let binding_number = params.random_scalar();
+        let private_attributes = vec![serial_number, binding_number];
+        let elgamal_keypair = elgamal::elgamal_keygen(&mut params);
+
+        let keypair1 = keygen(&mut params);
+        let keypair2 = keygen(&mut params);
+
+        let lambda =
+            prepare_blind_sign(&mut params, &elgamal_keypair, &private_attributes, &[]).unwrap();
+
+        let sig1 = blind_sign(
+            &mut params,
+            &keypair1.secret_key(),
+            elgamal_keypair.public_key(),
+            &lambda,
+            &[],
+        )
+        .unwrap()
+        .unblind(
+            &params,
+            elgamal_keypair.private_key(),
+            &keypair1.verification_key(),
+            &private_attributes,
+            &[],
+            &lambda.get_commitment_hash(),
+        )
+        .unwrap();
+
+        let sig2 = blind_sign(
+            &mut params,
+            &keypair2.secret_key(),
+            elgamal_keypair.public_key(),
+            &lambda,
+            &[],
+        )
+        .unwrap()
+        .unblind(
+            &params,
+            elgamal_keypair.private_key(),
+            &keypair2.verification_key(),
+            &private_attributes,
+            &[],
+            &lambda.get_commitment_hash(),
+        )
+        .unwrap();
+
+        let theta1 = prove_bandwidth_credential(
+            &mut params,
+            &keypair1.verification_key(),
+            &sig1,
+            serial_number,
+            binding_number,
+        )
+        .unwrap();
+
+        let theta2 = prove_bandwidth_credential(
+            &mut params,
+            &keypair2.verification_key(),
+            &sig2,
+            serial_number,
+            binding_number,
+        )
+        .unwrap();
+
+        assert!(verify_credential(
+            &params,
+            &keypair1.verification_key(),
+            &theta1,
+            &[],
+        ));
+
+        assert!(verify_credential(
+            &params,
+            &keypair2.verification_key(),
+            &theta2,
+            &[],
+        ));
+
+        assert!(!verify_credential(
+            &params,
+            &keypair1.verification_key(),
+            &theta2,
+            &[],
+        ));
+    }
+
+    #[test]
+    fn verification_on_two_public_attributes() {
+        let mut params = Parameters::new(2).unwrap();
+        let attributes = params.n_random_scalars(2);
+
+        let keypair1 = keygen(&mut params);
+        let keypair2 = keygen(&mut params);
+        let sig1 = sign(&mut params, &keypair1.secret_key(), &attributes).unwrap();
+        let sig2 = sign(&mut params, &keypair2.secret_key(), &attributes).unwrap();
+
+        assert!(verify(
+            &params,
+            &keypair1.verification_key(),
+            &attributes,
+            &sig1,
+        ));
+
+        assert!(!verify(
+            &params,
+            &keypair2.verification_key(),
+            &attributes,
+            &sig1,
+        ));
+
+        assert!(!verify(
+            &params,
+            &keypair1.verification_key(),
+            &attributes,
+            &sig2,
+        ));
+    }
+
+    #[test]
+    fn verification_on_two_public_and_two_private_attributes() {
+        let mut params = Parameters::new(4).unwrap();
+        let public_attributes = params.n_random_scalars(2);
+        let serial_number = params.random_scalar();
+        let binding_number = params.random_scalar();
+        let private_attributes = vec![serial_number, binding_number];
+        let elgamal_keypair = elgamal::elgamal_keygen(&mut params);
+
+        let keypair1 = keygen(&mut params);
+        let keypair2 = keygen(&mut params);
+
+        let lambda = prepare_blind_sign(
+            &mut params,
+            &elgamal_keypair,
+            &private_attributes,
+            &public_attributes,
+        )
+        .unwrap();
+
+        let sig1 = blind_sign(
+            &mut params,
+            &keypair1.secret_key(),
+            elgamal_keypair.public_key(),
+            &lambda,
+            &public_attributes,
+        )
+        .unwrap()
+        .unblind(
+            &params,
+            elgamal_keypair.private_key(),
+            &keypair1.verification_key(),
+            &private_attributes,
+            &public_attributes,
+            &lambda.get_commitment_hash(),
+        )
+        .unwrap();
+
+        let sig2 = blind_sign(
+            &mut params,
+            &keypair2.secret_key(),
+            elgamal_keypair.public_key(),
+            &lambda,
+            &public_attributes,
+        )
+        .unwrap()
+        .unblind(
+            &params,
+            elgamal_keypair.private_key(),
+            &keypair2.verification_key(),
+            &private_attributes,
+            &public_attributes,
+            &lambda.get_commitment_hash(),
+        )
+        .unwrap();
+
+        let theta1 = prove_bandwidth_credential(
+            &mut params,
+            &keypair1.verification_key(),
+            &sig1,
+            serial_number,
+            binding_number,
+        )
+        .unwrap();
+
+        let theta2 = prove_bandwidth_credential(
+            &mut params,
+            &keypair2.verification_key(),
+            &sig2,
+            serial_number,
+            binding_number,
+        )
+        .unwrap();
+
+        assert!(verify_credential(
+            &params,
+            &keypair1.verification_key(),
+            &theta1,
+            &public_attributes,
+        ));
+
+        assert!(verify_credential(
+            &params,
+            &keypair2.verification_key(),
+            &theta2,
+            &public_attributes,
+        ));
+
+        assert!(!verify_credential(
+            &params,
+            &keypair1.verification_key(),
+            &theta2,
+            &public_attributes,
+        ));
+    }
+
+    #[test]
+    fn verification_on_two_public_and_two_private_attributes_from_two_signers() {
+        let mut params = Parameters::new(4).unwrap();
+        let public_attributes = params.n_random_scalars(2);
+        let serial_number = params.random_scalar();
+        let binding_number = params.random_scalar();
+        let private_attributes = vec![serial_number, binding_number];
+        let elgamal_keypair = elgamal::elgamal_keygen(&params);
+
+        let keypairs = ttp_keygen(&mut params, 2, 3).unwrap();
+
+        let lambda = prepare_blind_sign(
+            &mut params,
+            &elgamal_keypair,
+            &private_attributes,
+            &public_attributes,
+        )
+        .unwrap();
+
+        let sigs = keypairs
+            .iter()
+            .map(|keypair| {
+                blind_sign(
+                    &mut params,
+                    &keypair.secret_key(),
+                    elgamal_keypair.public_key(),
+                    &lambda,
+                    &public_attributes,
+                )
+                .unwrap()
+                .unblind(
+                    &params,
+                    elgamal_keypair.private_key(),
+                    &keypair.verification_key(),
+                    &private_attributes,
+                    &public_attributes,
+                    &lambda.get_commitment_hash(),
+                )
+                .unwrap()
+            })
+            .collect::<Vec<_>>();
+
+        let vks = keypairs
+            .into_iter()
+            .map(|keypair| keypair.verification_key())
+            .collect::<Vec<_>>();
+
+        let mut attributes = Vec::with_capacity(private_attributes.len() + public_attributes.len());
+        attributes.extend_from_slice(&private_attributes);
+        attributes.extend_from_slice(&public_attributes);
+
+        let aggr_vk = aggregate_verification_keys(&vks[..2], Some(&[1, 2])).unwrap();
+        let aggr_sig =
+            aggregate_signatures(&params, &aggr_vk, &attributes, &sigs[..2], Some(&[1, 2]))
+                .unwrap();
+
+        let theta = prove_bandwidth_credential(
+            &mut params,
+            &aggr_vk,
+            &aggr_sig,
+            serial_number,
+            binding_number,
+        )
+        .unwrap();
+
+        assert!(verify_credential(
+            &params,
+            &aggr_vk,
+            &theta,
+            &public_attributes,
+        ));
+
+        // taking different subset of keys and credentials
+        let aggr_vk = aggregate_verification_keys(&vks[1..], Some(&[2, 3])).unwrap();
+        let aggr_sig =
+            aggregate_signatures(&params, &aggr_vk, &attributes, &sigs[1..], Some(&[2, 3]))
+                .unwrap();
+
+        let theta = prove_bandwidth_credential(
+            &mut params,
+            &aggr_vk,
+            &aggr_sig,
+            serial_number,
+            binding_number,
+        )
+        .unwrap();
+
+        assert!(verify_credential(
+            &params,
+            &aggr_vk,
+            &theta,
+            &public_attributes,
+        ));
+    }
+
+    #[test]
+    fn signature_bytes_roundtrip() {
+        let params = Parameters::default();
+        let r = params.random_scalar();
+        let s = params.random_scalar();
+        let signature = Signature(params.gen1() * r, params.gen1() * s);
+        let bytes = signature.to_bytes();
+
+        // also make sure it is equivalent to the internal g1 compressed bytes concatenated
+        let expected_bytes = [
+            signature.0.to_affine().to_compressed(),
+            signature.1.to_affine().to_compressed(),
+        ]
+        .concat();
+        assert_eq!(expected_bytes, bytes);
+        assert_eq!(signature, Signature::try_from(&bytes[..]).unwrap())
+    }
+
+    #[test]
+    fn blinded_signature_bytes_roundtrip() {
+        let params = Parameters::default();
+        let r = params.random_scalar();
+        let s = params.random_scalar();
+        let t = params.random_scalar();
+        let blinded_sig = BlindedSignature(
+            params.gen1() * t,
+            Ciphertext(params.gen1() * r, params.gen1() * s),
+        );
+        let bytes = blinded_sig.to_bytes();
+
+        // also make sure it is equivalent to the internal g1 compressed bytes concatenated
+        let expected_bytes = [
+            blinded_sig.0.to_affine().to_compressed(),
+            blinded_sig.1 .0.to_affine().to_compressed(),
+            blinded_sig.1 .1.to_affine().to_compressed(),
+        ]
+        .concat();
+        assert_eq!(expected_bytes, bytes);
+        assert_eq!(blinded_sig, BlindedSignature::try_from(&bytes[..]).unwrap())
+    }
+}

common/nymcoconut/src/scheme/setup.rs

@@ -0,0 +1,99 @@
+// Copyright 2021 Nym Technologies SA
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use crate::error::{CoconutError, Result};
+use crate::utils::hash_g1;
+use bls12_381::{G1Affine, G2Affine, G2Prepared, Scalar};
+use ff::Field;
+use group::Curve;
+use rand::thread_rng;
+/// System-wide parameters used for the protocol
+pub struct Parameters {
+    /// Generator of the G1 group
+    g1: G1Affine,
+
+    /// Additional generators of the G1 group
+    hs: Vec<G1Affine>,
+
+    /// Generator of the G2 group
+    g2: G2Affine,
+
+    /// Precomputed G2 generator used for the miller loop
+    _g2_prepared_miller: G2Prepared,
+}
+
+impl Parameters {
+    pub fn new(num_attributes: u32) -> Result<Parameters> {
+        if num_attributes == 0 {
+            return Err(CoconutError::Setup(
+                "Tried to setup the scheme for 0 attributes".to_string(),
+            ));
+        }
+
+        let hs = (1..=num_attributes)
+            .map(|i| hash_g1(format!("h{}", i)).to_affine())
+            .collect();
+
+        Ok(Parameters {
+            g1: G1Affine::generator(),
+            hs,
+            g2: G2Affine::generator(),
+            _g2_prepared_miller: G2Prepared::from(G2Affine::generator()),
+        })
+    }
+
+    pub(crate) fn gen1(&self) -> &G1Affine {
+        &self.g1
+    }
+
+    pub fn gen2(&self) -> &G2Affine {
+        &self.g2
+    }
+
+    pub fn prepared_miller_g2(&self) -> &G2Prepared {
+        &self._g2_prepared_miller
+    }
+
+    pub fn gen_hs(&self) -> &[G1Affine] {
+        &self.hs
+    }
+
+    pub fn random_scalar(&self) -> Scalar {
+        // lazily-initialized thread-local random number generator, seeded by the system
+        let mut rng = thread_rng();
+        Scalar::random(&mut rng)
+    }
+
+    pub fn n_random_scalars(&self, n: usize) -> Vec<Scalar> {
+        (0..n).map(|_| self.random_scalar()).collect()
+    }
+}
+
+pub fn setup(num_attributes: u32) -> Result<Parameters> {
+    Parameters::new(num_attributes)
+}
+
+// for ease of use in tests requiring params
+// TODO: not sure if this will have to go away when tests require some specific number of generators
+#[cfg(test)]
+impl Default for Parameters {
+    fn default() -> Self {
+        Parameters {
+            g1: G1Affine::generator(),
+            hs: Vec::new(),
+            g2: G2Affine::generator(),
+            _g2_prepared_miller: G2Prepared::from(G2Affine::generator()),
+        }
+    }
+}

common/nymcoconut/src/scheme/verification.rs

@@ -0,0 +1,474 @@
+// Copyright 2021 Nym Technologies SA
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use core::ops::Neg;
+use std::convert::TryFrom;
+use std::convert::TryInto;
+
+use bls12_381::{multi_miller_loop, G1Affine, G2Prepared, G2Projective, Scalar};
+use group::{Curve, Group};
+
+use crate::error::{CoconutError, Result};
+use crate::proofs::{ProofKappa, ProofKappaNu};
+use crate::scheme::setup::Parameters;
+use crate::scheme::Signature;
+use crate::scheme::VerificationKey;
+use crate::traits::{Base58, Bytable};
+use crate::utils::try_deserialize_g2_projective;
+use crate::Attribute;
+
+// TODO NAMING: this whole thing
+// Theta
+
+#[derive(Debug)]
+#[cfg_attr(test, derive(PartialEq))]
+pub struct ThetaCovid {
+    // blinded_message (kappa)
+    pub blinded_message: G2Projective,
+    // sigma
+    pub credential: Signature,
+    // pi_v
+    pub pi_v: ProofKappa,
+}
+
+impl ThetaCovid {
+    pub fn verify_proof(
+        &self,
+        params: &Parameters,
+        verification_key: &VerificationKey,
+        verifier_id: &[u8; 32],
+        timestamp: &[u8; 32],
+    ) -> bool {
+        self.pi_v.verify(
+            params,
+            verification_key,
+            &self.blinded_message,
+            verifier_id,
+            timestamp,
+        )
+    }
+
+    // kappa || credential || proof
+    pub fn to_bytes(&self) -> Vec<u8> {
+        let blinded_message_bytes = self.blinded_message.to_affine().to_compressed();
+        let credential_bytes = self.credential.to_bytes();
+        let proof_bytes = self.pi_v.to_bytes();
+
+        let mut bytes = Vec::with_capacity(192 + proof_bytes.len());
+        bytes.extend_from_slice(&blinded_message_bytes);
+        bytes.extend_from_slice(&credential_bytes);
+        bytes.extend_from_slice(&proof_bytes);
+
+        bytes
+    }
+
+    pub fn to_bytes_tuple(&self) -> ([u8; 96], [u8; 96], Vec<u8>) {
+        let blinded_message_bytes = self.blinded_message.to_affine().to_compressed();
+        let credential_bytes = self.credential.to_bytes();
+        let proof_bytes = self.pi_v.to_bytes();
+
+        (blinded_message_bytes, credential_bytes, proof_bytes)
+    }
+
+    pub fn from_bytes(bytes: &[u8]) -> Result<ThetaCovid> {
+        if bytes.len() < 192 {
+            return Err(
+                CoconutError::Deserialization(
+                    format!("Tried to deserialize theta with insufficient number of bytes, expected >= 192, got {}", bytes.len()),
+                ));
+        }
+
+        let blinded_message_bytes = bytes[..96].try_into().unwrap();
+        let blinded_message = try_deserialize_g2_projective(
+            &blinded_message_bytes,
+            CoconutError::Deserialization("failed to deserialize kappa".to_string()),
+        )?;
+
+        let credential = Signature::try_from(&bytes[96..192])?;
+
+        let pi_v = ProofKappa::from_bytes(&bytes[192..])?;
+
+        Ok(ThetaCovid {
+            blinded_message,
+            credential,
+            pi_v,
+        })
+    }
+}
+
+#[derive(Debug)]
+#[cfg_attr(test, derive(PartialEq))]
+pub struct Theta {
+    // blinded_message (kappa)
+    pub blinded_message: G2Projective,
+    // blinded serial number (zeta)
+    pub blinded_serial_number: G2Projective,
+    // sigma
+    pub credential: Signature,
+    // pi_v
+    pub pi_v: ProofKappaNu,
+}
+
+impl TryFrom<&[u8]> for Theta {
+    type Error = CoconutError;
+
+    fn try_from(bytes: &[u8]) -> Result<Theta> {
+        if bytes.len() < 288 {
+            return Err(
+                CoconutError::Deserialization(
+                    format!("Tried to deserialize theta with insufficient number of bytes, expected >= 288, got {}", bytes.len()),
+                ));
+        }
+
+        let blinded_message_bytes = bytes[..96].try_into().unwrap();
+        let blinded_message = try_deserialize_g2_projective(
+            &blinded_message_bytes,
+            CoconutError::Deserialization("failed to deserialize kappa".to_string()),
+        )?;
+
+        let blinded_serial_number_bytes = bytes[96..192].try_into().unwrap();
+        let blinded_serial_number = try_deserialize_g2_projective(
+            &blinded_serial_number_bytes,
+            CoconutError::Deserialization("failed to deserialize zeta".to_string()),
+        )?;
+        let credential = Signature::try_from(&bytes[192..288])?;
+
+        let pi_v = ProofKappaNu::from_bytes(&bytes[288..])?;
+
+        Ok(Theta {
+            blinded_message,
+            blinded_serial_number,
+            credential,
+            pi_v,
+        })
+    }
+}
+
+impl Theta {
+    fn verify_proof(&self, params: &Parameters, verification_key: &VerificationKey) -> bool {
+        self.pi_v.verify(
+            params,
+            verification_key,
+            &self.blinded_message,
+            &self.blinded_serial_number,
+        )
+    }
+
+    // TODO: perhaps also include pi_v.len()?
+    // to be determined once we implement serde to make sure its 1:1 compatible
+    // with bincode
+    // kappa || nu || credential || pi_v
+    pub fn to_bytes(&self) -> Vec<u8> {
+        let blinded_message_bytes = self.blinded_message.to_affine().to_compressed();
+        let blinded_serial_number_bytes = self.blinded_serial_number.to_affine().to_compressed();
+        let credential_bytes = self.credential.to_bytes();
+        let proof_bytes = self.pi_v.to_bytes();
+
+        let mut bytes = Vec::with_capacity(288 + proof_bytes.len());
+        bytes.extend_from_slice(&blinded_message_bytes);
+        bytes.extend_from_slice(&blinded_serial_number_bytes);
+        bytes.extend_from_slice(&credential_bytes);
+        bytes.extend_from_slice(&proof_bytes);
+
+        bytes
+    }
+
+    pub fn from_bytes(bytes: &[u8]) -> Result<Theta> {
+        Theta::try_from(bytes)
+    }
+}
+
+impl Bytable for Theta {
+    fn to_byte_vec(&self) -> Vec<u8> {
+        self.to_bytes()
+    }
+
+    fn try_from_byte_slice(slice: &[u8]) -> Result<Self> {
+        Theta::try_from(slice)
+    }
+}
+
+impl Base58 for Theta {}
+
+pub fn compute_kappa(
+    params: &Parameters,
+    verification_key: &VerificationKey,
+    private_attributes: &[Attribute],
+    blinding_factor: Scalar,
+) -> G2Projective {
+    params.gen2() * blinding_factor
+        + verification_key.alpha
+        + private_attributes
+            .iter()
+            .zip(verification_key.beta.iter())
+            .map(|(priv_attr, beta_i)| beta_i * priv_attr)
+            .sum::<G2Projective>()
+}
+
+pub fn compute_zeta(params: &Parameters, serial_number: Attribute) -> G2Projective {
+    params.gen2() * serial_number
+}
+
+pub fn prove_covid_credential(
+    params: &Parameters,
+    verification_key: &VerificationKey,
+    signature: &Signature,
+    private_attributes: &[Attribute],
+    verifier_id: &[u8; 32],
+    timestamp: &[u8; 32],
+) -> Result<ThetaCovid> {
+    if verification_key.beta.len() < params.gen_hs().len() {
+        return Err(
+            CoconutError::Verification(
+                format!("Tried to prove a credential for higher than supported by the provided verification key number of attributes (max: {}, requested: 2)",
+                        verification_key.beta.len()
+                )));
+    }
+
+    // Randomize the signature
+    let (signature_prime, sign_blinding_factor) = signature.randomise(params);
+
+    // blinded_message : kappa in the paper.
+    // Value kappa is needed since we want to show a signature sigma'.
+    // In order to verify sigma' we need both the verification key vk and the message m.
+    // However, we do not want to reveal m to whomever we are showing the signature.
+    // Thus, we need kappa which allows us to verify sigma'. In particular,
+    // kappa is computed on m as input, but thanks to the use or random value r,
+    // it does not reveal any information about m.
+    let blinded_message = compute_kappa(
+        params,
+        verification_key,
+        &private_attributes,
+        sign_blinding_factor,
+    );
+
+    let pi_v = ProofKappa::construct(
+        params,
+        verification_key,
+        &sign_blinding_factor,
+        &blinded_message,
+        &private_attributes,
+        verifier_id,
+        timestamp,
+    );
+
+    Ok(ThetaCovid {
+        blinded_message,
+        credential: signature_prime,
+        pi_v,
+    })
+}
+
+pub fn prove_bandwidth_credential(
+    params: &Parameters,
+    verification_key: &VerificationKey,
+    signature: &Signature,
+    serial_number: Attribute,
+    binding_number: Attribute,
+) -> Result<Theta> {
+    if verification_key.beta.len() < 2 {
+        return Err(
+            CoconutError::Verification(
+                format!("Tried to prove a credential for higher than supported by the provided verification key number of attributes (max: {}, requested: 2)",
+                        verification_key.beta.len()
+                )));
+    }
+
+    // Randomize the signature
+    let (signature_prime, sign_blinding_factor) = signature.randomise(params);
+
+    // blinded_message : kappa in the paper.
+    // Value kappa is needed since we want to show a signature sigma'.
+    // In order to verify sigma' we need both the verification key vk and the message m.
+    // However, we do not want to reveal m to whomever we are showing the signature.
+    // Thus, we need kappa which allows us to verify sigma'. In particular,
+    // kappa is computed on m as input, but thanks to the use or random value r,
+    // it does not reveal any information about m.
+    let private_attributes = vec![serial_number, binding_number];
+    let blinded_message = compute_kappa(
+        params,
+        verification_key,
+        &private_attributes,
+        sign_blinding_factor,
+    );
+
+    // zeta is a commitment to the serial number (i.e., a public value associated with the serial number)
+    let blinded_serial_number = compute_zeta(params, serial_number);
+
+    let pi_v = ProofKappaNu::construct(
+        params,
+        verification_key,
+        &serial_number,
+        &binding_number,
+        &sign_blinding_factor,
+        &blinded_message,
+        &blinded_serial_number,
+    );
+
+    Ok(Theta {
+        blinded_message,
+        blinded_serial_number,
+        credential: signature_prime,
+        pi_v,
+    })
+}
+
+/// Checks whether e(P, Q) * e(-R, S) == id
+pub fn check_bilinear_pairing(p: &G1Affine, q: &G2Prepared, r: &G1Affine, s: &G2Prepared) -> bool {
+    // checking e(P, Q) * e(-R, S) == id
+    // is equivalent to checking e(P, Q) == e(R, S)
+    // but requires only a single final exponentiation rather than two of them
+    // and therefore, as seen via benchmarks.rs, is almost 50% faster
+    // (1.47ms vs 2.45ms, tested on R9 5900X)
+
+    let multi_miller = multi_miller_loop(&[(p, q), (&r.neg(), s)]);
+    multi_miller.final_exponentiation().is_identity().into()
+}
+
+pub fn verify_covid_credential(
+    params: &Parameters,
+    verification_key: &VerificationKey,
+    theta: &ThetaCovid,
+    public_attributes: &[Attribute],
+    verifier_id: &[u8; 32],
+    timestamp: &[u8; 32],
+) -> bool {
+    if public_attributes.len() + theta.pi_v.private_attributes_len() > verification_key.beta.len() {
+        return false;
+    }
+
+    if !theta.verify_proof(params, verification_key, verifier_id, timestamp) {
+        return false;
+    }
+
+    let kappa = if public_attributes.is_empty() {
+        theta.blinded_message
+    } else {
+        let signed_public_attributes = public_attributes
+            .iter()
+            .zip(
+                verification_key
+                    .beta
+                    .iter()
+                    .skip(theta.pi_v.private_attributes_len()),
+            )
+            .map(|(pub_attr, beta_i)| beta_i * pub_attr)
+            .sum::<G2Projective>();
+
+        theta.blinded_message + signed_public_attributes
+    };
+
+    check_bilinear_pairing(
+        &theta.credential.0.to_affine(),
+        &G2Prepared::from(kappa.to_affine()),
+        &(theta.credential.1).to_affine(),
+        params.prepared_miller_g2(),
+    ) && !bool::from(theta.credential.0.is_identity())
+}
+
+pub fn verify_credential(
+    params: &Parameters,
+    verification_key: &VerificationKey,
+    theta: &Theta,
+    public_attributes: &[Attribute],
+) -> bool {
+    if public_attributes.len() + theta.pi_v.private_attributes_len() > verification_key.beta.len() {
+        return false;
+    }
+
+    if !theta.verify_proof(params, verification_key) {
+        return false;
+    }
+
+    let kappa = if public_attributes.is_empty() {
+        theta.blinded_message
+    } else {
+        let signed_public_attributes = public_attributes
+            .iter()
+            .zip(
+                verification_key
+                    .beta
+                    .iter()
+                    .skip(theta.pi_v.private_attributes_len()),
+            )
+            .map(|(pub_attr, beta_i)| beta_i * pub_attr)
+            .sum::<G2Projective>();
+
+        theta.blinded_message + signed_public_attributes
+    };
+
+    check_bilinear_pairing(
+        &theta.credential.0.to_affine(),
+        &G2Prepared::from(kappa.to_affine()),
+        &(theta.credential.1).to_affine(),
+        params.prepared_miller_g2(),
+    ) && !bool::from(theta.credential.0.is_identity())
+}
+
+// Used in tests only
+#[cfg(test)]
+pub fn verify(
+    params: &Parameters,
+    verification_key: &VerificationKey,
+    public_attributes: &[Attribute],
+    sig: &Signature,
+) -> bool {
+    let kappa = (verification_key.alpha
+        + public_attributes
+            .iter()
+            .zip(verification_key.beta.iter())
+            .map(|(m_i, b_i)| b_i * m_i)
+            .sum::<G2Projective>())
+    .to_affine();
+
+    check_bilinear_pairing(
+        &sig.0.to_affine(),
+        &G2Prepared::from(kappa),
+        &sig.1.to_affine(),
+        params.prepared_miller_g2(),
+    ) && !bool::from(sig.0.is_identity())
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::scheme::keygen::keygen;
+    use crate::scheme::setup::setup;
+
+    use super::*;
+
+    #[test]
+    fn theta_bytes_roundtrip() {
+        let mut params = setup(2).unwrap();
+
+        let keypair = keygen(&mut params);
+        let r = params.random_scalar();
+        let s = params.random_scalar();
+
+        let signature = Signature(params.gen1() * r, params.gen1() * s);
+        let serial_number = params.random_scalar();
+        let binding_number = params.random_scalar();
+
+        let theta = prove_bandwidth_credential(
+            &mut params,
+            &keypair.verification_key(),
+            &signature,
+            serial_number,
+            binding_number,
+        )
+        .unwrap();
+
+        let bytes = theta.to_bytes();
+        assert_eq!(Theta::try_from(bytes.as_slice()).unwrap(), theta);
+    }
+}

common/nymcoconut/src/tests/e2e.rs

@@ -0,0 +1,106 @@
+use crate::{
+    aggregate_signature_shares, aggregate_verification_keys, blind_sign, elgamal_keygen,
+    hash_to_scalar, prepare_blind_sign, prove_bandwidth_credential, setup, ttp_keygen,
+    verify_credential, CoconutError, Signature, SignatureShare, VerificationKey,
+};
+
+#[test]
+fn main() -> Result<(), CoconutError> {
+    let params = setup(5)?;
+
+    let public_attributes = params.n_random_scalars(2);
+    let serial_number = params.random_scalar();
+    let binding_number = params.random_scalar();
+    let private_attributes = vec![serial_number, binding_number];
+
+    let elgamal_keypair = elgamal_keygen(&params);
+
+    // generate commitment and encryption
+    let blind_sign_request = prepare_blind_sign(
+        &params,
+        &elgamal_keypair,
+        &private_attributes,
+        &public_attributes,
+    )?;
+
+    // generate_keys
+    let coconut_keypairs = ttp_keygen(&params, 2, 3)?;
+
+    let verification_keys: Vec<VerificationKey> = coconut_keypairs
+        .iter()
+        .map(|keypair| keypair.verification_key())
+        .collect();
+
+    // aggregate verification keys
+    let verification_key = aggregate_verification_keys(&verification_keys, Some(&[1, 2, 3]))?;
+
+    // generate blinded signatures
+    let mut blinded_signatures = Vec::new();
+
+    for keypair in coconut_keypairs {
+        let blinded_signature = blind_sign(
+            &params,
+            &keypair.secret_key(),
+            &elgamal_keypair.public_key(),
+            &blind_sign_request,
+            &public_attributes,
+        )?;
+        blinded_signatures.push(blinded_signature)
+    }
+
+    // Unblind
+
+    let unblinded_signatures: Vec<Signature> = blinded_signatures
+        .into_iter()
+        .zip(verification_keys.iter())
+        .map(|(signature, verification_key)| {
+            signature
+                .unblind(
+                    &params,
+                    &elgamal_keypair.private_key(),
+                    &verification_key,
+                    &private_attributes,
+                    &public_attributes,
+                    &blind_sign_request.get_commitment_hash(),
+                )
+                .unwrap()
+        })
+        .collect();
+
+    // Aggregate signatures
+
+    let signature_shares: Vec<SignatureShare> = unblinded_signatures
+        .iter()
+        .enumerate()
+        .map(|(idx, signature)| SignatureShare::new(*signature, (idx + 1) as u64))
+        .collect();
+
+    let mut attributes = Vec::with_capacity(private_attributes.len() + public_attributes.len());
+    attributes.extend_from_slice(&private_attributes);
+    attributes.extend_from_slice(&public_attributes);
+
+    // Randomize credentials and generate any cryptographic material to verify them
+    let signature =
+        aggregate_signature_shares(&params, &verification_key, &attributes, &signature_shares)?;
+
+    // Generate cryptographic material to verify them
+
+    let theta = prove_bandwidth_credential(
+        &params,
+        &verification_key,
+        &signature,
+        serial_number,
+        binding_number,
+    )?;
+
+    // Verify credentials
+
+    assert!(verify_credential(
+        &params,
+        &verification_key,
+        &theta,
+        &public_attributes,
+    ));
+
+    Ok(())
+}

common/nymcoconut/src/tests/e2e_covid.rs

@@ -0,0 +1,153 @@
+use crate::scheme::verification::{prove_covid_credential, verify_covid_credential, ThetaCovid};
+use crate::{
+    aggregate_signature_shares, aggregate_verification_keys, blind_sign, elgamal_keygen,
+    hash_to_scalar, prepare_blind_sign, setup, ttp_keygen, CoconutError, Signature, SignatureShare,
+    VerificationKey,
+};
+
+#[test]
+fn main() -> Result<(), CoconutError> {
+    let params = setup(15)?;
+
+    // validators keys
+    let coconut_keypairs = ttp_keygen(&params, 2, 3)?;
+    let verification_keys: Vec<VerificationKey> = coconut_keypairs
+        .iter()
+        .map(|keypair| keypair.verification_key())
+        .collect();
+    let verification_key = aggregate_verification_keys(&verification_keys, Some(&[1, 2, 3]))?;
+
+    // user's ElGamal keypair
+    let elgamal_keypair = elgamal_keygen(&params);
+
+    // attributes to consider
+    let patient_id = hash_to_scalar(String::from("NHS678777").as_bytes());
+    let full_name = hash_to_scalar(String::from("JaneDoe").as_bytes());
+    let vaccine_medication_product_id = hash_to_scalar(String::from("EU/1/20/1528").as_bytes());
+    let country_of_vaccination = hash_to_scalar(String::from("UK").as_bytes());
+    let issuer = hash_to_scalar(String::from("NHS").as_bytes());
+    let dob = hash_to_scalar(String::from("2021-11-05").as_bytes());
+
+    let public_attributes = vec![
+        patient_id,
+        full_name,
+        vaccine_medication_product_id,
+        country_of_vaccination,
+        issuer,
+        dob,
+    ];
+    let user_secret = params.random_scalar();
+    let private_attributes = vec![user_secret];
+
+    // ISSUANCE PROTOCOL
+    let blind_sign_request = prepare_blind_sign(
+        &params,
+        &elgamal_keypair,
+        &private_attributes,
+        &public_attributes,
+    )?;
+
+    // generate blinded signatures
+    let mut blinded_signatures = Vec::new();
+
+    let is_vaccinated = hash_to_scalar(String::from("TRUE").as_bytes());
+    let is_over_18 = hash_to_scalar(String::from("TRUE").as_bytes());
+    let is_over_21 = hash_to_scalar(String::from("TRUE").as_bytes());
+
+    // These are the attributes on which the validator issues a signature
+    let public_attributes = [
+        patient_id,
+        full_name,
+        vaccine_medication_product_id,
+        country_of_vaccination,
+        issuer,
+        dob,
+        is_vaccinated,
+        is_over_18,
+        is_over_21,
+    ];
+
+    for keypair in coconut_keypairs {
+        let blinded_signature = blind_sign(
+            &params,
+            &keypair.secret_key(),
+            &elgamal_keypair.public_key(),
+            &blind_sign_request,
+            &public_attributes,
+        )?;
+        blinded_signatures.push(blinded_signature)
+    }
+
+    let unblinded_signatures: Vec<Signature> = blinded_signatures
+        .into_iter()
+        .zip(verification_keys.iter())
+        .map(|(signature, verification_key)| {
+            signature
+                .unblind(
+                    &params,
+                    &elgamal_keypair.private_key(),
+                    &verification_key,
+                    &private_attributes,
+                    &public_attributes,
+                    &blind_sign_request.get_commitment_hash(),
+                )
+                .unwrap()
+        })
+        .collect();
+
+    let signature_shares: Vec<SignatureShare> = unblinded_signatures
+        .iter()
+        .enumerate()
+        .map(|(idx, signature)| SignatureShare::new(*signature, (idx + 1) as u64))
+        .collect();
+
+    let mut attributes = Vec::with_capacity(1 + 9);
+    attributes.extend_from_slice(&private_attributes);
+    attributes.extend_from_slice(&public_attributes);
+
+    // Randomize credentials and generate any cryptographic material to verify them
+    let signature =
+        aggregate_signature_shares(&params, &verification_key, &attributes, &signature_shares)?;
+
+    // SHOW PROTOCOL
+    let verifier_id = [11u8; 32];
+    let timestamp = [12u8; 32];
+
+    let show_private_attributes = vec![
+        user_secret,
+        patient_id,
+        full_name,
+        vaccine_medication_product_id,
+        country_of_vaccination,
+        issuer,
+        dob,
+    ];
+
+    // Prove covid credential
+    let theta_covid = prove_covid_credential(
+        &params,
+        &verification_key,
+        &signature,
+        &show_private_attributes,
+        &verifier_id,
+        &timestamp,
+    )?;
+
+    let theta_covid_bytes = theta_covid.to_bytes();
+    println!("Length of theta in bytes: {:?}", theta_covid_bytes.len());
+
+    let theta_covid_from_bytes = ThetaCovid::from_bytes(&*theta_covid_bytes).unwrap();
+
+    // Verify covid credentials
+    let disclosed_attributes = vec![is_vaccinated, is_over_18, is_over_21];
+    assert!(verify_covid_credential(
+        &params,
+        &verification_key,
+        &theta_covid_from_bytes,
+        disclosed_attributes.as_ref(),
+        &verifier_id,
+        &timestamp,
+    ));
+
+    Ok(())
+}

common/nymcoconut/src/tests/mod.rs

@@ -0,0 +1,2 @@
+mod e2e;
+mod e2e_covid;

common/nymcoconut/src/traits.rs

@@ -0,0 +1,22 @@
+use crate::CoconutError;
+
+pub trait Bytable
+where
+    Self: Sized,
+{
+    fn to_byte_vec(&self) -> Vec<u8>;
+
+    fn try_from_byte_slice(slice: &[u8]) -> Result<Self, CoconutError>;
+}
+
+pub trait Base58
+where
+    Self: Bytable,
+{
+    fn try_from_bs58<S: AsRef<str>>(x: S) -> Result<Self, CoconutError> {
+        Self::try_from_byte_slice(&bs58::decode(x.as_ref()).into_vec().unwrap())
+    }
+    fn to_bs58(&self) -> String {
+        bs58::encode(self.to_byte_vec()).into_string()
+    }
+}

common/nymcoconut/src/utils.rs

@@ -0,0 +1,397 @@
+// Copyright 2021 Nym Technologies SA
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use core::iter::Sum;
+use core::ops::Mul;
+use std::convert::TryInto;
+
+use bls12_381::hash_to_curve::{ExpandMsgXmd, HashToCurve, HashToField};
+use bls12_381::{G1Affine, G1Projective, G2Affine, G2Projective, Scalar};
+use ff::Field;
+
+use crate::error::{CoconutError, Result};
+use crate::scheme::setup::Parameters;
+use crate::scheme::SignerIndex;
+
+pub struct Polynomial {
+    coefficients: Vec<Scalar>,
+}
+
+impl Polynomial {
+    // for polynomial of degree n, we generate n+1 values
+    // (for example for degree 1, like y = x + 2, we need [2,1])
+    pub fn new_random(params: &Parameters, degree: u64) -> Self {
+        Polynomial {
+            coefficients: params.n_random_scalars((degree + 1) as usize),
+        }
+    }
+
+    /// Evaluates the polynomial at point x.
+    pub fn evaluate(&self, x: &Scalar) -> Scalar {
+        if self.coefficients.is_empty() {
+            Scalar::zero()
+            // if x is zero then we can ignore most of the expensive computation and
+            // just return the last term of the polynomial
+        } else if x.is_zero() {
+            // we checked that coefficients are not empty so unwrap here is fine
+            *self.coefficients.first().unwrap()
+        } else {
+            self.coefficients
+                .iter()
+                .enumerate()
+                // coefficient[n] * x ^ n
+                .map(|(i, coefficient)| coefficient * x.pow(&[i as u64, 0, 0, 0]))
+                .sum()
+        }
+    }
+}
+
+#[inline]
+fn generate_lagrangian_coefficients_at_origin(points: &[u64]) -> Vec<Scalar> {
+    let x = Scalar::zero();
+
+    points
+        .iter()
+        .enumerate()
+        .map(|(i, point_i)| {
+            let mut numerator = Scalar::one();
+            let mut denominator = Scalar::one();
+            let xi = Scalar::from(*point_i);
+
+            for (j, point_j) in points.iter().enumerate() {
+                if j != i {
+                    let xj = Scalar::from(*point_j);
+
+                    // numerator = (x - xs[0]) * ... * (x - xs[j]), j != i
+                    numerator *= x - xj;
+
+                    // denominator = (xs[i] - x[0]) * ... * (xs[i] - x[j]), j != i
+                    denominator *= xi - xj;
+                }
+            }
+            // numerator / denominator
+            numerator * denominator.invert().unwrap()
+        })
+        .collect()
+}
+
+/// Performs a Lagrange interpolation at the origin for a polynomial defined by `points` and `values`.
+/// It can be used for Scalars, G1 and G2 points.
+pub(crate) fn perform_lagrangian_interpolation_at_origin<T>(
+    points: &[SignerIndex],
+    values: &[T],
+) -> Result<T>
+where
+    T: Sum,
+    for<'a> &'a T: Mul<Scalar, Output = T>,
+{
+    if points.is_empty() || values.is_empty() {
+        return Err(CoconutError::Interpolation(
+            "Tried to perform lagrangian interpolation for an empty set of coordinates".to_string(),
+        ));
+    }
+
+    if points.len() != values.len() {
+        return Err(CoconutError::Interpolation(
+            "Tried to perform lagrangian interpolation for an incomplete set of coordinates"
+                .to_string(),
+        ));
+    }
+
+    let coefficients = generate_lagrangian_coefficients_at_origin(points);
+
+    Ok(coefficients
+        .into_iter()
+        .zip(values.iter())
+        .map(|(coeff, val)| val * coeff)
+        .sum())
+}
+
+// A temporary way of hashing particular message into G1.
+// Implementation idea was taken from `threshold_crypto`:
+// https://github.com/poanetwork/threshold_crypto/blob/7709462f2df487ada3bb3243060504b5881f2628/src/lib.rs#L691
+// Eventually it should get replaced by, most likely, the osswu map
+// method once ideally it's implemented inside the pairing crate.
+
+// note: I have absolutely no idea what are the correct domains for those. I just used whatever
+// was given in the test vectors of `Hashing to Elliptic Curves draft-irtf-cfrg-hash-to-curve-11`
+
+// https://datatracker.ietf.org/doc/html/draft-irtf-cfrg-hash-to-curve-11#appendix-J.9.1
+const G1_HASH_DOMAIN: &[u8] = b"QUUX-V01-CS02-with-BLS12381G1_XMD:SHA-256_SSWU_RO_";
+
+// https://datatracker.ietf.org/doc/html/draft-irtf-cfrg-hash-to-curve-11#appendix-K.1
+const SCALAR_HASH_DOMAIN: &[u8] = b"QUUX-V01-CS02-with-expander";
+
+pub(crate) fn hash_g1<M: AsRef<[u8]>>(msg: M) -> G1Projective {
+    <G1Projective as HashToCurve<ExpandMsgXmd<sha2::Sha256>>>::hash_to_curve(msg, G1_HASH_DOMAIN)
+}
+
+pub fn hash_to_scalar<M: AsRef<[u8]>>(msg: M) -> Scalar {
+    let mut output = vec![Scalar::zero()];
+
+    Scalar::hash_to_field::<ExpandMsgXmd<sha2::Sha256>>(
+        msg.as_ref(),
+        SCALAR_HASH_DOMAIN,
+        &mut output,
+    );
+    output[0]
+}
+
+pub(crate) fn try_deserialize_scalar_vec(
+    expected_len: u64,
+    bytes: &[u8],
+    err: CoconutError,
+) -> Result<Vec<Scalar>> {
+    if bytes.len() != expected_len as usize * 32 {
+        return Err(err);
+    }
+
+    let mut out = Vec::with_capacity(expected_len as usize);
+    for i in 0..expected_len as usize {
+        let s_bytes = bytes[i * 32..(i + 1) * 32].try_into().unwrap();
+        let s = match Into::<Option<Scalar>>::into(Scalar::from_bytes(&s_bytes)) {
+            None => return Err(err),
+            Some(scalar) => scalar,
+        };
+        out.push(s)
+    }
+
+    Ok(out)
+}
+
+pub(crate) fn try_deserialize_scalar(bytes: &[u8; 32], err: CoconutError) -> Result<Scalar> {
+    Into::<Option<Scalar>>::into(Scalar::from_bytes(bytes)).ok_or(err)
+}
+
+pub(crate) fn try_deserialize_g1_projective(
+    bytes: &[u8; 48],
+    err: CoconutError,
+) -> Result<G1Projective> {
+    Into::<Option<G1Affine>>::into(G1Affine::from_compressed(bytes))
+        .ok_or(err)
+        .map(G1Projective::from)
+}
+
+pub(crate) fn try_deserialize_g2_projective(
+    bytes: &[u8; 96],
+    err: CoconutError,
+) -> Result<G2Projective> {
+    Into::<Option<G2Affine>>::into(G2Affine::from_compressed(bytes))
+        .ok_or(err)
+        .map(G2Projective::from)
+}
+
+// use core::fmt;
+// #[cfg(feature = "serde")]
+// use serde::de::Visitor;
+// #[cfg(feature = "serde")]
+// use serde::{self, Deserialize, Deserializer, Serialize, Serializer};
+//
+// // #[cfg(feature = "serde")]
+// #[serde(remote = "Scalar")]
+// pub(crate) struct ScalarDef(pub Scalar);
+//
+// // #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+//
+// impl Serialize for ScalarDef {
+//     fn serialize<S>(&self, serializer: S) -> core::result::Result<S::Ok, S::Error>
+//     where
+//         S: Serializer,
+//     {
+//         use serde::ser::SerializeTuple;
+//         let mut tup = serializer.serialize_tuple(32)?;
+//         for byte in self.0.to_bytes().iter() {
+//             tup.serialize_element(byte)?;
+//         }
+//         tup.end()
+//     }
+// }
+//
+// impl<'de> Deserialize<'de> for ScalarDef {
+//     fn deserialize<D>(deserializer: D) -> core::result::Result<Self, D::Error>
+//     where
+//         D: Deserializer<'de>,
+//     {
+//         struct ScalarVisitor;
+//
+//         impl<'de> Visitor<'de> for ScalarVisitor {
+//             type Value = ScalarDef;
+//
+//             fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+//                 formatter.write_str("a 32-byte canonical bls12_381 scalar")
+//             }
+//
+//             fn visit_seq<A>(self, mut seq: A) -> core::result::Result<ScalarDef, A::Error>
+//             where
+//                 A: serde::de::SeqAccess<'de>,
+//             {
+//                 let mut bytes = [0u8; 32];
+//                 for i in 0..32 {
+//                     bytes[i] = seq
+//                         .next_element()?
+//                         .ok_or_else(|| serde::de::Error::invalid_length(i, &"expected 32 bytes"))?;
+//                 }
+//
+//                 let res = Scalar::from_bytes(&bytes);
+//                 if res.is_some().into() {
+//                     Ok(ScalarDef(res.unwrap()))
+//                 } else {
+//                     Err(serde::de::Error::custom(
+//                         &"scalar was not canonically encoded",
+//                     ))
+//                 }
+//             }
+//         }
+//
+//         deserializer.deserialize_tuple(32, ScalarVisitor)
+//     }
+// }
+//
+// #[cfg(feature = "serde")]
+// pub(crate) struct G1ProjectiveSerdeHelper(Scalar);
+//
+// #[cfg(feature = "serde")]
+// pub(crate) struct G2ProjectiveSerdeHelper(Scalar);
+
+#[cfg(test)]
+mod tests {
+    use rand::RngCore;
+
+    use super::*;
+
+    #[test]
+    fn polynomial_evaluation() {
+        // y = 42 (it should be 42 regardless of x)
+        let poly = Polynomial {
+            coefficients: vec![Scalar::from(42)],
+        };
+
+        assert_eq!(Scalar::from(42), poly.evaluate(&Scalar::from(1)));
+        assert_eq!(Scalar::from(42), poly.evaluate(&Scalar::from(0)));
+        assert_eq!(Scalar::from(42), poly.evaluate(&Scalar::from(10)));
+
+        // y = x + 10, at x = 2 (exp: 12)
+        let poly = Polynomial {
+            coefficients: vec![Scalar::from(10), Scalar::from(1)],
+        };
+
+        assert_eq!(Scalar::from(12), poly.evaluate(&Scalar::from(2)));
+
+        // y = x^4 - 5x^2 + 2x - 3, at x = 3 (exp: 39)
+        let poly = Polynomial {
+            coefficients: vec![
+                (-Scalar::from(3)),
+                Scalar::from(2),
+                (-Scalar::from(5)),
+                Scalar::zero(),
+                Scalar::from(1),
+            ],
+        };
+
+        assert_eq!(Scalar::from(39), poly.evaluate(&Scalar::from(3)));
+
+        // empty polynomial
+        let poly = Polynomial {
+            coefficients: vec![],
+        };
+
+        // should always be 0
+        assert_eq!(Scalar::from(0), poly.evaluate(&Scalar::from(1)));
+        assert_eq!(Scalar::from(0), poly.evaluate(&Scalar::from(0)));
+        assert_eq!(Scalar::from(0), poly.evaluate(&Scalar::from(10)));
+    }
+
+    #[test]
+    fn performing_lagrangian_scalar_interpolation_at_origin() {
+        // x^2 + 3
+        // x, f(x):
+        // 1, 4,
+        // 2, 7,
+        // 3, 12,
+        let points = vec![1, 2, 3];
+        let values = vec![Scalar::from(4), Scalar::from(7), Scalar::from(12)];
+
+        assert_eq!(
+            Scalar::from(3),
+            perform_lagrangian_interpolation_at_origin(&points, &values).unwrap()
+        );
+
+        // x^3 + 3x^2 - 5x + 11
+        // x, f(x):
+        // 1, 10
+        // 2, 21
+        // 3, 50
+        // 4, 103
+        let points = vec![1, 2, 3, 4];
+        let values = vec![
+            Scalar::from(10),
+            Scalar::from(21),
+            Scalar::from(50),
+            Scalar::from(103),
+        ];
+
+        assert_eq!(
+            Scalar::from(11),
+            perform_lagrangian_interpolation_at_origin(&points, &values).unwrap()
+        );
+
+        // more points than it is required
+        // x^2 + x + 10
+        // x, f(x)
+        // 1, 12
+        // 2, 16
+        // 3, 22
+        // 4, 30
+        // 5, 40
+        let points = vec![1, 2, 3, 4, 5];
+        let values = vec![
+            Scalar::from(12),
+            Scalar::from(16),
+            Scalar::from(22),
+            Scalar::from(30),
+            Scalar::from(40),
+        ];
+
+        assert_eq!(
+            Scalar::from(10),
+            perform_lagrangian_interpolation_at_origin(&points, &values).unwrap()
+        );
+    }
+
+    #[test]
+    fn hash_g1_sanity_check() {
+        let mut rng = rand::thread_rng();
+        let mut msg1 = [0u8; 1024];
+        rng.fill_bytes(&mut msg1);
+        let mut msg2 = [0u8; 1024];
+        rng.fill_bytes(&mut msg2);
+
+        assert_eq!(hash_g1(msg1), hash_g1(msg1));
+        assert_eq!(hash_g1(msg2), hash_g1(msg2));
+        assert_ne!(hash_g1(msg1), hash_g1(msg2));
+    }
+
+    #[test]
+    fn hash_scalar_sanity_check() {
+        let mut rng = rand::thread_rng();
+        let mut msg1 = [0u8; 1024];
+        rng.fill_bytes(&mut msg1);
+        let mut msg2 = [0u8; 1024];
+        rng.fill_bytes(&mut msg2);
+
+        assert_eq!(hash_to_scalar(msg1), hash_to_scalar(msg1));
+        assert_eq!(hash_to_scalar(msg2), hash_to_scalar(msg2));
+        assert_ne!(hash_to_scalar(msg1), hash_to_scalar(msg2));
+    }
+}

tauri-wallet/Cargo.lock

@@ -446,30 +446,11 @@ dependencies = [
 name = "coconut-interface"
 version = "0.1.0"
 dependencies = [
- "coconut-rs",
  "getset",
+ "nymcoconut",
  "serde",
 ]
 
-[[package]]
-name = "coconut-rs"
-version = "0.5.0"
-source = "git+https://github.com/nymtech/coconut.git?branch=0.5.0#a1b72d51aa2a67b73b9f58d707030ae6dc70af7f"
-dependencies = [
- "bls12_381",
- "bs58",
- "digest 0.9.0",
- "ff",
- "getrandom 0.2.3",
- "group",
- "itertools",
- "rand 0.8.4",
- "serde",
- "serde_derive",
- "sha2",
- "thiserror",
-]
-
 [[package]]
 name = "com"
 version = "0.2.0"
@@ -2540,6 +2521,24 @@ dependencies = [
  "validator-client",
 ]
 
+[[package]]
+name = "nymcoconut"
+version = "0.5.0"
+dependencies = [
+ "bls12_381",
+ "bs58",
+ "digest 0.9.0",
+ "ff",
+ "getrandom 0.2.3",
+ "group",
+ "itertools",
+ "rand 0.8.4",
+ "serde",
+ "serde_derive",
+ "sha2",
+ "thiserror",
+]
+
 [[package]]
 name = "objc"
 version = "0.2.7"

validator-api/src/network_monitor/mod.rs

@@ -1,6 +1,23 @@
 // Copyright 2021 - Nym Technologies SA <contact@nymtech.net>
 // SPDX-License-Identifier: Apache-2.0
 
+use std::sync::Arc;
+
+use futures::channel::mpsc;
+use log::info;
+
+#[cfg(feature = "coconut")]
+use coconut_interface::{hash_to_scalar, Credential, Parameters};
+#[cfg(feature = "coconut")]
+use credentials::bandwidth::{
+    prepare_for_spending, BandwidthVoucherAttributes, BANDWIDTH_VALUE, TOTAL_ATTRIBUTES,
+};
+#[cfg(feature = "coconut")]
+use credentials::obtain_aggregate_verification_key;
+use crypto::asymmetric::{encryption, identity};
+use nymsphinx::addressing::clients::Recipient;
+use topology::NymTopology;
+
 use crate::cache::ValidatorCache;
 use crate::config::Config;
 use crate::network_monitor::monitor::preparer::PacketPreparer;
@@ -15,17 +32,6 @@ use crate::network_monitor::monitor::summary_producer::SummaryProducer;
 use crate::network_monitor::monitor::Monitor;
 use crate::network_monitor::tested_network::TestedNetwork;
 use crate::storage::ValidatorApiStorage;
-use crypto::asymmetric::{encryption, identity};
-use futures::channel::mpsc;
-use log::info;
-use nymsphinx::addressing::clients::Recipient;
-use std::sync::Arc;
-use topology::NymTopology;
-
-#[cfg(feature = "coconut")]
-use coconut_interface::Credential;
-#[cfg(feature = "coconut")]
-use credentials::{bandwidth::prepare_for_spending, obtain_aggregate_verification_key};
 
 pub(crate) mod chunker;
 pub(crate) mod gateways_reader;
@@ -180,14 +186,26 @@ async fn TEMPORARY_obtain_bandwidth_credential(
         .await
         .expect("could not obtain aggregate verification key of ALL validators");
 
-    let bandwidth_credential =
-        credentials::bandwidth::obtain_signature(&identity.to_bytes(), &validators)
-            .await
-            .expect("failed to obtain bandwidth credential!");
+    let params = Parameters::new(TOTAL_ATTRIBUTES).unwrap();
+    let bandwidth_credential_attributes = BandwidthVoucherAttributes {
+        serial_number: params.random_scalar(),
+        binding_number: params.random_scalar(),
+        voucher_value: hash_to_scalar(BANDWIDTH_VALUE.to_be_bytes()),
+        voucher_info: hash_to_scalar(String::from("BandwidthVoucher").as_bytes()),
+    };
+
+    let bandwidth_credential = credentials::bandwidth::obtain_signature(
+        &params,
+        &bandwidth_credential_attributes,
+        &validators,
+    )
+    .await
+    .expect("failed to obtain bandwidth credential!");
 
     prepare_for_spending(
         &identity.to_bytes(),
         &bandwidth_credential,
+        &bandwidth_credential_attributes,
         &verification_key,
     )
     .expect("failed to prepare bandwidth credential for spending!")