加密和解密常用于保护敏感的数据，比如url中的查询参数，防止被人手动修改等等。。。

/// <summary>
        /// md5加密(密文128位，一般不可逆)
        /// </summary>
        /// <param name="data">要加密的字符串</param>
        /// <returns></returns>
        public string Md5CryptData(string data)
        {
            MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();

            byte[] dataByte = Encoding.UTF8.GetBytes(data);

            byte[] md5Data = md5.ComputeHash(dataByte);

            StringBuilder sb=new StringBuilder();

            foreach (var b in md5Data)
            {
                //0xA转换为0x0A
                sb.Append(b.ToString("x2"));
            }

            return sb.ToString();
        }

        /// <summary>
        /// DES加密(密文64位，密钥64位，IV向量64位)
        /// </summary>
        /// <param name="data"></param>
        /// <returns></returns>
        public string DesEnCryptData(string data)
        {
            const string key = "a1b2c3d4";
            const string iv = "a1b2c3d4";
            byte[] keyByte = Encoding.UTF8.GetBytes(key);
            byte[] ivByte = Encoding.UTF8.GetBytes(iv);

            DESCryptoServiceProvider desEncrypt = new DESCryptoServiceProvider();

            MemoryStream memoryStream=new MemoryStream();

            CryptoStream cryptoStream = new CryptoStream(memoryStream, desEncrypt.CreateEncryptor(keyByte, ivByte),
                                                         CryptoStreamMode.Write);

            byte[] dataByte = Encoding.UTF8.GetBytes(data);

            cryptoStream.Write(dataByte, 0, dataByte.Length);

            cryptoStream.FlushFinalBlock();

            byte[] tmp = memoryStream.ToArray();

            return Convert.ToBase64String(tmp);
;
        }

        /// <summary>
        /// DES解密
        /// </summary>
        /// <param name="data"></param>
        /// <returns></returns>
        public string DesDeCryptData(string data)
        {

            byte[] dataByte = Convert.FromBase64String(data);

            MemoryStream memoryStream = new MemoryStream(dataByte);

            const string key = "a1b2c3d4";
            const string iv = "a1b2c3d4";
            byte[] keyByte = Encoding.UTF8.GetBytes(key);
            byte[] ivByte = Encoding.UTF8.GetBytes(iv);

            DESCryptoServiceProvider desEncrypt = new DESCryptoServiceProvider();

            CryptoStream cryptoStream = new CryptoStream(memoryStream, desEncrypt.CreateDecryptor(keyByte, ivByte),
                                                         CryptoStreamMode.Read);
            byte[] tmp = new byte[dataByte.Length];

            cryptoStream.Read(tmp, 0, tmp.Length);

            return Encoding.UTF8.GetString(tmp);
        }

        /// <summary>
        /// Rijndael加密(密文128位，最长196位，IV向量16位,密钥16、24、32位)
        /// </summary>
        /// <param name="data"></param>
        /// <returns></returns>
        public string EncryptData(string data)
        {
            string key = "12345678123456781234567812345678";
            string iv = "1234567812345678";
            byte[] keyByte = Encoding.UTF8.GetBytes(key);
            byte[] ivByte = Encoding.UTF8.GetBytes(iv);

            Rijndael rijndael = Rijndael.Create();

            MemoryStream mStream=new MemoryStream();

            CryptoStream cryptoStream = new CryptoStream(mStream, rijndael.CreateEncryptor(keyByte, ivByte),
                                                         CryptoStreamMode.Write);
            byte[] dataByte = Encoding.UTF8.GetBytes(data);

            cryptoStream.Write(dataByte,0,dataByte.Length);

            cryptoStream.FlushFinalBlock();

            byte[] tmp = mStream.ToArray();

            return Convert.ToBase64String(tmp);
        }

        /// <summary>
        /// Rijndael解密
        /// </summary>
        /// <param name="data"></param>
        /// <returns></returns>
        public string DecryptData(string data)
        {
            byte[] dataByte = Convert.FromBase64String(data);
            string key = "12345678123456781234567812345678";
            string iv = "1234567812345678";
            byte[] keyByte = Encoding.UTF8.GetBytes(key);
            byte[] ivByte = Encoding.UTF8.GetBytes(iv);

            MemoryStream memoryStream=new MemoryStream(dataByte);

            Rijndael rijndael = Rijndael.Create();

            CryptoStream cryptoStream = new CryptoStream(memoryStream, rijndael.CreateDecryptor(keyByte, ivByte),
                                                         CryptoStreamMode.Read);
            byte[] tmp=new byte[dataByte.Length];

            cryptoStream.Read(tmp,0,tmp.Length);

            return Encoding.UTF8.GetString(tmp);

        }