sign method

SchnorrkelSignature sign(MerlinTranscript signingContextScript, { GenerateRandom? nonceGenerator, })

Signs a message using the Schnorrkel secret key and a specified signing context script.

This method generates a Schnorrkel signature for a given message by appending context-specific information to the signing context script and combining it with a nonce.

Parameters:

• signingContextScript: A transcript containing context-specific information for the signature.
• nonceGenerator (optional): A function that generates a nonce. Default is a function that generates a random 64-byte nonce.

Returns: A SchnorrkelSignature representing the generated signature.

Example Usage:

MerlinTranscript signingContextScript = ...;
SchnorrkelSecretKey secretKey = ...;
GenerateRandom? customNonceGenerator = (length) => ...;
SchnorrkelSignature signature = secretKey.sign(signingContextScript, customNonceGenerator);

The sign method generates a Schnorrkel signature for a message by incorporating context-specific information from the signing context script, a nonce, and the secret key. It returns a SchnorrkelSignature instance.

Implementation

SchnorrkelSignature sign(MerlinTranscript signingContextScript,
    {GenerateRandom? nonceGenerator}) {
  const int nonceLength = SchnorrkelKeyCost.nonceLength * 2;
  signingContextScript.additionalData(
      "proto-name".codeUnits, "Schnorr-sig".codeUnits);
  signingContextScript.additionalData(
      "sign:pk".codeUnits, publicKey().toBytes());
  final nonceRand = nonceGenerator?.call(nonceLength) ??
      QuickCrypto.generateRandom(nonceLength);
  if (nonceRand.length != nonceLength) {
    throw const CryptoException("invalid nonce bytes length.");
  }
  final scNonce = Ed25519Utils.scalarReduceConst(nonceRand);
  final mult = Ed25519Utils.scalarMultBase(scNonce);
  final r = RistrettoPoint.fromEdwardBytes(mult);
  signingContextScript.additionalData("sign:R".codeUnits, r.toBytes());
  final k =
      signingContextScript.toBytesWithReduceScalar("sign:c".codeUnits, 64);
  final sigS = Ed25519Utils.mulAdd(key(), k, scNonce);
  final sig = SchnorrkelSignature._(sigS, r.toBytes());
  return sig;
}