public static string Key
        {
            get
            {
                return key;
            }
            set
            {
                key = value;
            }
        }

        /// <summary>        
        /// DES Encrypt    
        /// </summary>
        /// <param name="encryptString">要加密的字符串</param>
        /// <returns>加密后的字符串</returns>
        public static string DesEncrypt(string encryptString)
        {
            byte[] keyBytes = System.Text.Encoding.UTF8.GetBytes(key.Substring(0, 8));
            byte[] keyIV = keyBytes;
            byte[] inputByteArray = Encoding.UTF8.GetBytes(encryptString);
            System.Security.Cryptography.DESCryptoServiceProvider provider = new System.Security.Cryptography.DESCryptoServiceProvider();
            System.IO.MemoryStream mStream = new System.IO.MemoryStream();
            System.Security.Cryptography.CryptoStream cStream = new System.Security.Cryptography.CryptoStream(mStream, provider.CreateEncryptor(keyBytes, keyIV), System.Security.Cryptography.CryptoStreamMode.Write);
            cStream.Write(inputByteArray, 0, inputByteArray.Length);
            cStream.FlushFinalBlock();
            return Convert.ToBase64String(mStream.ToArray());

        }    

         /// <summary>        
        /// Function : DES Decrypt
        /// </summary>
        /// <param name="decryptString">要解密的字符串</param>
        /// <returns>解密后的字符串</returns>
        public static string DesDecrypt(string decryptString)
        {
            byte[] keyBytes = Encoding.UTF8.GetBytes(key.Substring(0, 8));
            byte[] keyIV = keyBytes;
            byte[] inputByteArray = Convert.FromBase64String(decryptString);
            System.Security.Cryptography.DESCryptoServiceProvider provider = new System.Security.Cryptography.DESCryptoServiceProvider();
            System.IO.MemoryStream mStream = new System.IO.MemoryStream();
            System.Security.Cryptography.CryptoStream cStream = new System.Security.Cryptography.CryptoStream(mStream, provider.CreateDecryptor(keyBytes, keyIV), System.Security.Cryptography.CryptoStreamMode.Write);
            cStream.Write(inputByteArray, 0, inputByteArray.Length);
            cStream.FlushFinalBlock();
            return Encoding.UTF8.GetString(mStream.ToArray());
        }