public static void EncryptXmlElement(XmlElement elementToEncrypt, X509Certificate2 certificateToEncrypt, X509Certificate2 certificateToDecrypt = null)
        {
            if (elementToEncrypt == null)
            {
                throw new ArgumentNullException("elementToEncrypt");
            }

            if (certificateToEncrypt == null)
            {
                throw new ArgumentNullException("certificateToDecrypt");
            }

            var encryptedData = new EncryptedData
            {
                Type = EncryptedXml.XmlEncElementContentUrl,
                EncryptionMethod = new EncryptionMethod(EncryptionMethod_XmlEncGost28147Url),
                KeyInfo = new KeyInfo()
            };

            using (var key = new Gost28147CryptoServiceProvider())
            {
                var encryptedXml = new EncryptedXml();
                var data = encryptedXml.EncryptData(elementToEncrypt, key, false);
                byte[] encryptedKey = null;
                if (certificateToEncrypt.PublicKey.Key is Gost3410)
                {
                    encryptedKey = CPEncryptedXml.EncryptKey(key, (Gost3410)certificateToEncrypt.PublicKey.Key);
                }
                else if (certificateToEncrypt.PublicKey.Key is Gost3410_2012_256)
                {
                    encryptedKey = CPEncryptedXml.EncryptKey(key, (Gost3410_2012_256)certificateToEncrypt.PublicKey.Key);
                }
                else if (certificateToEncrypt.PublicKey.Key is Gost3410_2012_512)
                {
                    encryptedKey = CPEncryptedXml.EncryptKey(key, (Gost3410_2012_512)certificateToEncrypt.PublicKey.Key);
                }
                else
                {
                    throw new InvalidOperationException("Unsupported key algorithm.");
                }

                var ek = new EncryptedKey
                    {
                        CipherData = new CipherData(encryptedKey),
                        EncryptionMethod = new EncryptionMethod(certificateToEncrypt.PublicKey.Key.KeyExchangeAlgorithm)
                    };

                if (certificateToDecrypt != null)
                {
                    ek.KeyInfo.AddClause(new KeyInfoX509Data(certificateToDecrypt));
                }

                encryptedData.KeyInfo.AddClause(new KeyInfoEncryptedKey(ek));
                encryptedData.CipherData.CipherValue = data;
            }

            EncryptedXml.ReplaceElement(elementToEncrypt, encryptedData, false);
        }

   public const string XmlKeyExchange2001 = "urn:ietf:params:xml:ns:cpxmlsec:algorithms:transport-gost2001";
   public const string XmlKeyExchange2012_256_PRO = "urn:ietf:params:xml:ns:cpxmlsec:algorithms:transport-gost2012-256-01";
   public const string XmlKeyExchange2012_256_P12 = "urn:ietf:params:xml:ns:cpxmlsec:algorithms:transport-gost2012-256-12";
   public const string XmlKeyExchange2012_512_PRO = "urn:ietf:params:xml:ns:cpxmlsec:algorithms:transport-gost2012-512-01";
   public const string XmlKeyExchange2012_512_P12 = "urn:ietf:params:xml:ns:cpxmlsec:algorithms:transport-gost2012-512-12";