微信小程序获取用户信息签名解密C#

在做小程序时，官方没有C#的解密，自己给写一个封装，希望可以帮到大家

     #region 解密

        #region 私有方法

        private static byte[] AES_Decrypt(String Input, byte[] Iv, byte[] Key)
        {
            RijndaelManaged aes = new RijndaelManaged();
            aes.KeySize = 128;//原始：256
            aes.BlockSize = 128;
            aes.Mode = CipherMode.CBC;
            aes.Padding = PaddingMode.PKCS7;
            aes.Key = Key;
            aes.IV = Iv;
            var decrypt = aes.CreateDecryptor(aes.Key, aes.IV);
            byte[] xBuff = null;
            using (var ms = new MemoryStream())
            {
                using (var cs = new CryptoStream(ms, decrypt, CryptoStreamMode.Write))
                {
                    //        cs.Read(decryptBytes, 0, decryptBytes.Length);
                    //        cs.Close();
                    //        ms.Close();

                    byte[] xXml = Convert.FromBase64String(Input);
                    byte[] msg = new byte[xXml.Length + 32 - xXml.Length % 32];
                    Array.Copy(xXml, msg, xXml.Length);
                    cs.Write(xXml, 0, xXml.Length);
                }
                xBuff = decode2(ms.ToArray());
            }
            return xBuff;
        }

        private static byte[] decode2(byte[] decrypted)
        {
            int pad = (int)decrypted[decrypted.Length - 1];
            if (pad < 1 || pad > 32)
            {
                pad = 0;
            }
            byte[] res = new byte[decrypted.Length - pad];
            Array.Copy(decrypted, 0, res, 0, decrypted.Length - pad);
            return res;
        }

        #endregion

        /// <summary>
        /// 解密所有消息的基础方法
        /// </summary>
        /// <param name="sessionKey">储存在 SessionBag 中的当前用户 会话 SessionKey</param>
        /// <param name="encryptedData">接口返回数据中的 encryptedData 参数</param>
        /// <param name="iv">接口返回数据中的 iv 参数，对称解密算法初始向量</param>
        /// <returns></returns>
        public static string DecodeEncryptedData(string sessionKey, string encryptedData, string iv)
        {
            var aesCipher = Convert.FromBase64String(encryptedData);
            var aesKey = Convert.FromBase64String(sessionKey);
            var aesIV = Convert.FromBase64String(iv);

            var result = AES_Decrypt(encryptedData, aesIV, aesKey);
            var resultStr = Encoding.UTF8.GetString(result);
            return resultStr;
        }
        #endregion