Wallet operation to burn some coins (#172)

* Burn transaction for testing
* Burn bug fixes, embed burn key in keychain
* Better error logging in API, wallet fee calc fix

keychain/src/extkey.rs

@@ -135,6 +135,12 @@ impl Identifier {
 		Identifier(identifier)
 	}
 
+	pub fn from_pubkey(secp: &Secp256k1, pubkey: &PublicKey) -> Identifier {
+		let bytes = pubkey.serialize_vec(secp, true);
+		let identifier = blake2b(20, &[], &bytes[..]);
+		Identifier::from_bytes(&identifier.as_bytes())
+	}
+
 	fn from_hex(hex: &str) -> Result<Identifier, Error> {
 		// TODO - error handling, don't unwrap here
 		let bytes = util::from_hex(hex.to_string()).unwrap();
@@ -245,9 +251,7 @@ impl ExtendedKey {
 	// corresponding to the underlying SecretKey
 	pub fn identifier(&self, secp: &Secp256k1) -> Result<Identifier, Error> {
 		let pubkey = PublicKey::from_secret_key(secp, &self.key)?;
-		let bytes = pubkey.serialize_vec(secp, true);
-		let identifier = blake2b(20, &[], &bytes[..]);
-		Ok(Identifier::from_bytes(&identifier.as_bytes()))
+		Ok(Identifier::from_pubkey(secp, &pubkey))
 	}
 
 	/// Derive an extended key from an extended key

keychain/src/keychain.rs

@@ -48,6 +48,10 @@ impl From<extkey::Error> for Error {
 pub struct Keychain {
 	secp: Secp256k1,
 	extkey: extkey::ExtendedKey,
+
+	/// for tests and burn only, associate the zero fingerprint to a known
+	/// dummy private key
+	pub enable_burn_key: bool,
 }
 
 impl Keychain {
@@ -61,6 +65,7 @@ impl Keychain {
 		let keychain = Keychain {
 			secp: secp,
 			extkey: extkey,
+			enable_burn_key: false,
 		};
 		Ok(keychain)
 	}
@@ -82,6 +87,13 @@ impl Keychain {
 	// TODO - smarter lookups - can we cache key_id/fingerprint -> derivation
 	// number somehow?
 	fn derived_key(&self, pubkey: &Identifier) -> Result<SecretKey, Error> {
+		if self.enable_burn_key {
+			// for tests and burn only, associate the zero fingerprint to a known
+			// dummy private key
+			if pubkey.fingerprint().to_string() == "00000000" {
+				return Ok(SecretKey::from_slice(&self.secp, &[1; 32])?);
+			}
+		}
 		for i in 1..10000 {
 			let extkey = self.extkey.derive(&self.secp, i)?;
 			if extkey.identifier(&self.secp)? == *pubkey {