Hi @asaldanha
I know it is too late but want to leave the solution for the next error
Unable to cast object of type 'Org.BouncyCastle.X509.X509Certificate' to type 'Org.BouncyCastle.Crypto.AsymmetricCipherKeyPair'.
The code below resolve this error
private static RSA ImportPrivateKey(string privateKeyFile)
{
var pr = new PemReader(File.OpenText(privateKeyFile));
var rsaPrivateKeyParameters = (RsaPrivateCrtKeyParameters)pr.ReadObject();
var rsaParams = DotNetUtilities.ToRSAParameters(rsaPrivateKeyParameters);
var rsa = RSA.Create();
rsa.ImportParameters(rsaParams);
return rsa;
}