From cb348b6c659e0316bc319cd3c1ca73ac322eba07 Mon Sep 17 00:00:00 2001
From: Mike Dilger <mike@mikedilger.com>
Date: Mon, 15 Sep 2025 07:18:50 +1200
Subject: [PATCH] PR #1907: Support messages longer than 65,535 bytes

---
 src/error.rs           |  2 +-
 src/lib.rs             | 23 +++++++++++++++++------
 src/nip44.vectors.json |  8 +++++++-
 src/tests.rs           |  2 +-
 4 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/src/error.rs b/src/error.rs
index af5dc63..aba1759 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -26,7 +26,7 @@ pub enum Error {
     #[error("Message is empty")]
     MessageIsEmpty,
 
-    /// Message is too long (max len 65536 - 128)
+    /// Message is too long (max len 4_294_967_296 - 128)
     #[error("Message is too long")]
     MessageIsTooLong,
 
diff --git a/src/lib.rs b/src/lib.rs
index d991471..dd41df5 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -88,12 +88,17 @@ fn pad(unpadded: &str) -> Result<Vec<u8>, Error> {
     if len < 1 {
         return Err(Error::MessageIsEmpty);
     }
-    if len > 65536 - 128 {
+    if len > 4_294_967_296 - 128 {
         return Err(Error::MessageIsTooLong);
     }
 
     let mut padded: Vec<u8> = Vec::new();
-    padded.extend_from_slice(&(len as u16).to_be_bytes());
+    if len < 65536 {
+        padded.extend_from_slice(&(len as u16).to_be_bytes());
+    } else {
+        padded.extend_from_slice(&(0 as u16).to_be_bytes());
+        padded.extend_from_slice(&(len as u32).to_be_bytes());
+    }
     padded.extend_from_slice(unpadded.as_bytes());
     padded.extend(std::iter::repeat(0).take(calc_padding(len) - len));
     Ok(padded)
@@ -162,18 +167,24 @@ pub fn decrypt(conversation_key: &[u8; 32], base64_ciphertext: &str) -> Result<S
     }
     let mut cipher = ChaCha20::new(&keys.encryption().into(), &keys.nonce().into());
     cipher.apply_keystream(&mut buffer);
-    let unpadded_len = u16::from_be_bytes(buffer[0..2].try_into().unwrap()) as usize;
-    if buffer.len() < 2 + unpadded_len {
+
+    let mut lensize = 2;
+    let mut unpadded_len = u16::from_be_bytes(buffer[0..2].try_into().unwrap()) as usize;
+    if unpadded_len == 0 {
+        lensize = 6;
+        unpadded_len = u32::from_be_bytes(buffer[2..6].try_into().unwrap()) as usize;
+    }
+    if buffer.len() < lensize + unpadded_len {
         return Err(Error::InvalidPadding);
     }
-    let unpadded = &buffer[2..2 + unpadded_len];
+    let unpadded = &buffer[lensize..lensize + unpadded_len];
     if unpadded.is_empty() {
         return Err(Error::MessageIsEmpty);
     }
     if unpadded.len() != unpadded_len {
         return Err(Error::InvalidPadding);
     }
-    if buffer.len() != 2 + calc_padding(unpadded_len) {
+    if buffer.len() != lensize + calc_padding(unpadded_len) {
         return Err(Error::InvalidPadding);
     }
     Ok(String::from_utf8(unpadded.to_vec())?)
diff --git a/src/nip44.vectors.json b/src/nip44.vectors.json
index 9ff2184..58a98d9 100644
--- a/src/nip44.vectors.json
+++ b/src/nip44.vectors.json
@@ -2,6 +2,12 @@
   "v2": {
     "valid": {
       "get_conversation_key": [
+        {
+          "sec1": "315e59ff51cb9209768cf7da80791ddcaae56ac9775eb25b6dee1234bc5d2268",
+          "pub2": "c2f9d9948dc8c7c38321e4b85c8558872eafa0641cd269db76848a6073e69133",
+          "conversation_key": "3dfef0ce2a4d80a25e7a328accf73448ef67096f65f79588e358d9a0eb9013f1",
+          "note": "issue17"
+        },
         {
           "sec1": "fffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364139",
           "pub2": "0000000000000000000000000000000000000000000000000000000000000002",
@@ -247,4 +253,4 @@
         ]
     }
   }
-}
\ No newline at end of file
+}
diff --git a/src/tests.rs b/src/tests.rs
index a6057d6..d8223dc 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -221,7 +221,7 @@ fn test_invalid_decrypt() {
         Error::InvalidMac,
         Error::InvalidMac,
         Error::InvalidPadding,
-        Error::MessageIsEmpty,
+        Error::InvalidPadding,
         Error::InvalidPadding,
         Error::InvalidPadding,
     ];