[BUG] MLDsaPublicKeyParameters FromEncoded ArgumentException("invalid encoding") (Wrong length check)

[pshoey]

Importing an ML-DSA public key from a previously generated key that has been exported with GetEncoded() method, does not import - instead throws ArgumentException "invalid encoding". The check in MLDsaPublicKeyParameters FromEncoded method on the length of the encoding parameter only checks against the public key length - it needs to include the length of the seed key. The encoded data length is 1984 bytes (1952 public key length + 32 seed length).

Create a new ML-DSA key pair, export the public key and create a new ML-DSA public key from the encoded data.

    var mlDsaKeyGenerationParameters =
        new MLDsaKeyGenerationParameters(new SecureRandom(),
        MLDsaParameters.ml_dsa_65);

    var keyPairGenerator = new MLDsaKeyPairGenerator();

    keyPairGenerator.Init(mlDsaKeyGenerationParameters);
    var key = keyPairGenerator.GenerateKeyPair();

    var privateKey = (MLDsaPrivateKeyParameters)key.Private;
    var publicKey = (MLDsaPublicKeyParameters)key.Public;

    var privateKeyEncoded = privateKey.GetEncoded();
    var publicKeyEncoded = publicKey.GetEncoded();

    var newPrivateKey = MLDsaPrivateKeyParameters.FromEncoding(
        MLDsaParameters.ml_dsa_65, privateKeyEncoded);

    var newPublicKey = MLDsaPublicKeyParameters.FromEncoding(
        MLDsaParameters.ml_dsa_65, publicKeyEncoded);

The final call to MLDsaPublicKeyParameters.FromEncoding throws ArgumentException("invalid encoding").

Using BouncyCastle.Cryptography nuget package v2.5.0

[peterdettman]

I don't get an exception running the above code, and the lengths involved are correct; encoded PK length for ML-DSA-65 is 1952 i.e. 32 (rho) + 32610 (t1). We also have test coverage based on NIST test vectors.