class DesHelper
    {

        /// <summary>
        /// DES加密方法
        /// </summary>
        /// <param name="prestr">待加密的字符串</param>
        /// <param name="key">加密的密码（只能为8位长）</param>
        /// <param name="encoding">编码方式(默认为UTF-8)</param>
        /// <returns>加密结果</returns>
        public static string Encrypt(string prestr, string key, Encoding encoding = null)
        {
            encoding = encoding ?? Encoding.GetEncoding("UTF-8");
            //注意iv的长度，必须和key中的密码长度相同
            var iv = Encoding.ASCII.GetBytes(key);
            var keyArray = Encoding.ASCII.GetBytes(key);
            var datas = encoding.GetBytes(prestr);
            var desCryptoServiceProvider = new DESCryptoServiceProvider();
            using (var memoryStream = new MemoryStream())
            {
                using (var cryptoStream = new CryptoStream(memoryStream, desCryptoServiceProvider.CreateEncryptor(iv, keyArray), CryptoStreamMode.Write))
                {
                    cryptoStream.Write(datas, 0, datas.Length);
                    cryptoStream.FlushFinalBlock();

                    StringBuilder ret = new StringBuilder();
                    foreach (byte b in memoryStream.ToArray())
                    {
                        ret.AppendFormat("{0:X2}", b);//十六进制编码
                    }
                    return ret.ToString();
                }
            }
        }

        /// <summary>
        /// DES 解密方法
        /// </summary>
        /// <param name="prestr">待加密的字符串</param>
        /// <param name="key">加密的密码（只能为8位长）</param>
        /// <param name="encoding">编码方式(默认为UTF-8)</param>
        /// <returns>加密之结果</returns>
        public static string Decrypt(string prestr, string key, Encoding encoding = null)
        {
            encoding = encoding ?? Encoding.GetEncoding("UTF-8");
            var iv = Encoding.ASCII.GetBytes(key);
            var keyArray = Encoding.ASCII.GetBytes(key);
            //把字符串放到byte数组中
            byte[] datas = new byte[prestr.Length / 2];
            for (int x = 0; x < prestr.Length / 2; x++)
            {
                int i = (Convert.ToInt32(prestr.Substring(x * 2, 2), 16));
                datas[x] = (byte)i;
            }
            var desCryptoServiceProvider = new DESCryptoServiceProvider();
            using (var memoryStream = new MemoryStream())
            {
                using (var cryptoStream = new CryptoStream(memoryStream, desCryptoServiceProvider.CreateDecryptor(iv, keyArray), CryptoStreamMode.Write))
                {
                    cryptoStream.Write(datas, 0, datas.Length);
                    cryptoStream.FlushFinalBlock();
                    return encoding.GetString(memoryStream.ToArray());
                }
            }
        }
    }