public class Encrypt
    {
        static Encoding encoding = Encoding.UTF8;

        public static string EncryptDES(string encryptString, string key)
        {
            var input = encoding.GetBytes(encryptString);
            var ouptputData = ProcessDES(input, key, true);
            var outputStr = Convert.ToBase64String(ouptputData);

            //base64編碼中有不能作為文件名的'/'符號，這里把它替換一下，增強適用范圍
            return outputStr.Replace('/', '@');
        }

        public static string DecryptDES(string decryptString, string key)
        {
            decryptString = decryptString.Replace('@', '/');

            var input = Convert.FromBase64String(decryptString);
            var data = ProcessDES(input, key, false);
            return encoding.GetString(data);
        }


        private static byte[] ProcessDES(byte[] data, string key, bool isEncrypt)
        {
            using (var dCSP = new DESCryptoServiceProvider())
            {
                var keyData = Md5(key);
                var rgbKey = new ArraySegment<byte>(keyData, 0, 8).ToArray();
                var rgbIV = new ArraySegment<byte>(keyData, 8, 8).ToArray();
                var dCSPKey = isEncrypt ? dCSP.CreateEncryptor(rgbKey, rgbIV) : dCSP.CreateDecryptor(rgbKey, rgbIV);

                using (var memory = new MemoryStream())
                using (var cStream = new CryptoStream(memory, dCSPKey, CryptoStreamMode.Write))
                {
                    cStream.Write(data, 0, data.Length);
                    cStream.FlushFinalBlock();
                    return memory.ToArray();
                }
            }
        }

        public static byte[] Md5(string str)
        {
            using (var md5 = MD5.Create())
            {
                return md5.ComputeHash(Encoding.UTF8.GetBytes(str));
            }
        }
    }