RSA-OAEP-256 not in SupportedAlgorithms.IsSupportedRsaAlgorithm()

I’m trying to decrypt a JWE + JWS token and here is the first part of the token :

eyJ6aXAiOiJERUYiLCJlbmMiOiJBMjU2Q0JDLUhTNTEyIiwiYWxnIjoiUlNBLU9BRVAtMjU2In0

which after a base64ToString is giving :

{"zip":"DEF","enc":"A256CBC-HS512","alg":"RSA-OAEP-256"}

The problem is that when I’m trying to decrypt the token it goes down to the method SupportedAlgorithms.IsSupportedRsaAlgorithm() but RSA-OAEP-256 isn’t listed and I can’t decrypt my token. Do you plan to support it any time soon or I’m missing something ?

Thanks !

[jlodom]

+1 This was one of two issues I ran into in the question below (I will be updating the entry in the next 24 hours to reflect solution/workaround hopefully). https://stackoverflow.com/questions/68106472/decrypting-jsonwebtoken-using-jsonwebkey-or-jsonwebkeyset-in-c-sharp Since the alg does have cross-platform support in dotnet generally, it would be good to have: https://docs.microsoft.com/en-us/dotnet/standard/security/cross-platform-cryptography

[lapo-luchini]

(I will be updating the entry in the next 24 hours to reflect solution/workaround hopefully

I tried the work-around and it works for OAEP-256.

(AES-GCM decryption works fine without any change, so in the end I decided it wasn’t worth it to add support for AES-GCM encryption to the provider.)

using System.Security.Cryptography;
using Microsoft.IdentityModel.Tokens;

// inspired to: https://stackoverflow.com/a/68272468/166524
public class OAEP256CryptoProvider : ICryptoProvider
{
    public const string OAEP_256 = "RSA-OAEP-256";

    public bool IsSupportedAlgorithm(string algorithm, params object[] args)
    {
        return (algorithm == OAEP_256);
    }

    public object Create(string algorithm, params object[] args)
    {
        return new RsaOaepKeyWrapProvider(args[0] as SecurityKey, algorithm);
    }

    public void Release(object cryptoInstance)
    {
    }

    private class RsaOaepKeyWrapProvider : KeyWrapProvider
    {
        public RsaOaepKeyWrapProvider(SecurityKey key, string algorithm)
        {
            Key = (RsaSecurityKey) key;
            Algorithm = algorithm;
        }

        protected override void Dispose(bool disposing)
        {
        }

        public override byte[] UnwrapKey(byte[] keyBytes)
        {
            return Key.Rsa.Decrypt(keyBytes, RSAEncryptionPadding.OaepSHA256);
        }

        public override byte[] WrapKey(byte[] keyBytes)
        {
            return Key.Rsa.Encrypt(keyBytes, RSAEncryptionPadding.OaepSHA256);
        }

        public override string Algorithm { get; }
        public override string Context { get; set; }
        public override RsaSecurityKey Key { get; }
    }

}