private static RsaKeyParameters GetRsaKeyParameters(string privateKey) { var decodedPublicKeyString = Convert.FromBase64String(privateKey); var inputStream = new Asn1InputStream(decodedPublicKeyString); var derObject = inputStream.ReadObject(); var asn1Sequence = Asn1Sequence.GetInstance(derObject); var keyStruct = new RsaPrivateKeyStructure(asn1Sequence); return new RsaKeyParameters(true, keyStruct.Modulus, keyStruct.PrivateExponent); }