Can I use ECDSA key for creating sshPrivateKey?

Question

I am using bouncy castle for generating ECKey pair but i am not able to create sshprivatekey from it. How can i accomplish this task?

Answer 1

To create an SshPrivateKey from a BouncyCastle EC key pair, you have to encode the key pair into a DER-encoded PKCS #8 format - this results i na byte array (or a file) that can be loaded into SshPrivateKey.

With the C# version of BouncyCastle, this can be achieved by the following code:

public static byte[] BouncyPrivateKeyParametersToPkcs8(Org.BouncyCastle.Crypto.Parameters.ECPrivateKeyParameters parameters)
{
    if (parameters == null)
    {
        throw new ArgumentNullException("parameters");
    }

    if (parameters.AlgorithmName != "ECDSA")
    {
        throw new CryptographicException("Not an ECDSA key.");
    }

    if (parameters.PublicKeyParamSet == null)
    {
        throw new CryptographicException("Not a named curve keypair.");
    }

    var bcPrivateKeyInfo = Org.BouncyCastle.Pkcs.PrivateKeyInfoFactory.CreatePrivateKeyInfo(parameters);
    return bcPrivateKeyInfo.GetDerEncoded();
}

Then, just load the resulting byte array into SshPrivateKey:

byte[] pkcs8 = BouncyPrivateKeyParametersToPkcs8(bcPrivateKey);
var sshPrivateKey = new SshPrivateKey(pkcs8);

Comments

I am getting "{"Object reference not set to an instance of an object."}" execption.

I am using below code to generate byte array in der format

        public static byte[] BouncyPrivateKeyParametersToPkcs8()
        {
            SecureRandom secureRandom = new SecureRandom();
            var keygenParam = new KeyGenerationParameters(secureRandom, 521);
            var keyGenerator = new ECKeyPairGenerator();
            keyGenerator.Init(keygenParam);
            AsymmetricKeyParameter key = keyGenerator.GenerateKeyPair().Private;

            var bcPrivateKeyInfo = Org.BouncyCastle.Pkcs.PrivateKeyInfoFactory.CreatePrivateKeyInfo(key);
            byte[] stream = bcPrivateKeyInfo.GetDerEncoded();
            return stream;
        }

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Which versions of Rebex and BouncyCastle do you use? With current versions of both, your code seems to work fine. Please download my test project from https://www.rebex.net/getfile/81541e8057b5480c96506fc5e529ee5a/BouncyToRebex.zip and give it a try. Does this work or does it fail as well?

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I have executed the exact code you have shared but it is still giving me same exception. I am using trial version of Rebex and  BouncyCastle version 1.0.0.0

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My test project above references specific versions of Rebex and BouncyCastle from NuGet.org: Rebex.Common/Rebex.Networking 5.0.7027.0 and BouncyCastle 1.8.5. Could you please try using these versions instead of BouncyCastle 1.0.0.0?

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This worked. Thanks.

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Thanks for letting us know!