Issue when encrypt using RSA_OAEP_256 and A256GCM

[frankl1m]

public static string EncodeJWE(string body)
{
string spki = "-----BEGIN PUBLIC KEY-----\nENCODED PUBLIC KEY\n-----END PUBLIC KEY-----".Replace("\n-----END PUBLIC KEY-----", "").Replace("-----BEGIN PUBLIC KEY-----\n", "");
JweRecipient r3 = new JweRecipient(JweAlgorithm.RSA_OAEP_256,Convert.FromBase64String(spki));
return JWE.Encrypt(body, new[] { r3 }, JweEncryption.A256GCM);
}

When i try to encrypt always i have only public Key, but always i get System.ArgumentException: 'RsaKeyManagement algorithm expects key to be of CngKey, RSACryptoServiceProvider, RSA types or Jwk type with kty='rsa'.' I am using Netfx 4.7.2

[dvsekhvalnov]

Hi @frankl1m ,

your spki var is a string and this is not something library accepts as a key.

Checkout docs: https://github.com/dvsekhvalnov/jose-jwt#rsa--key-management-family-of-algorithms

Your easiest option is to use openssl to convert you PEM encoded key into .p12 or see https://stackoverflow.com/questions/11506891/how-to-load-the-rsa-public-key-from-file-in-c-sharp

[frankl1m]

private static RSA rsa = null;

    public static void GenRSAIfNull()
    {
        if (rsa == null)
        {
            rsa = RSA.Create();
            rsa.FromXmlString(certificatestringxml);
            string text = EncodeJWE("prueba");

            string dec = DecodeJWE(text);

        }
    }

    public static string EncodeJWE(string body)
    {
        return JWT.Encode(body, rsa,JweAlgorithm.RSA_OAEP_256, JweEncryption.A256GCM);
    }

    public static string DecodeJWE(string encbody)
    {
        return JWT.Decode(encbody, rsa, JweAlgorithm.RSA_OAEP_256, JweEncryption.A256GCM);
    }

i have this code, all on encryption is OK, when i try decode the same string encoded before, always get same Exception System.Security.Cryptography.CryptographicException: 'Invalid key to use in the specified state.

[dvsekhvalnov]

Hey @frankl1m , did you export private key? To decode encrypted payload you need private part of keypair.

Typically when exporting RSA key you want RSA.ToXmlString(true) to preserve private part in xml

[frankl1m]

The certificate used only have Public Key, so if RSA.ToXmlString(true) get exception

[dvsekhvalnov]

@frankl1m you can't decrypt with public key only. You need private key to do it.