请教加密类代码
using System;
using System.Collections.Generic;
using System.Text;
using System.IO;
using System.Security.Cryptography;

namespace Coding

{
  /**//// <summary>
  /// DES 加密/解密
  /// </summary>
  public class DES
  {
  private static readonly string _StringKey = "79a1e098"; //加密所需8位密匙

  /**//// <summary>
  /// 加密字符串
  /// </summary>
  /// <param name="QueryString">需要加密的字符串</param>
  /// <returns>加密后的字符串</returns>
  public static string EncryptString(string QueryString)
  {
  return Encrypt(QueryString, _StringKey);
  }

  /**//// <summary>
  /// 解密字符串
  /// </summary>
  /// <param name="QueryString">需要解密的字符串</param>
  /// <returns>解密后的字符串</returns>
  public static string DecryptString(string QueryString)
  {
  return Decrypt(QueryString, _StringKey);
  }

  /**//// <summary>
  /// 加密字符串，自定义8位密匙
  /// 加密密匙必须与解密密匙相同
  /// </summary>
  /// <param name="pToEncrypt">需要加密的字符串</param>
  /// <param name="sKey">8位字符密匙</param>
  /// <returns>加密后的字符串</returns>
  protected static string Encrypt(string pToEncrypt, string sKey)
  {
  DESCryptoServiceProvider des = new DESCryptoServiceProvider();　//把字符串放到byte数组中

  byte[] inputByteArray = Encoding.Default.GetBytes(pToEncrypt);
  //byte[]　inputByteArray=Encoding.Unicode.GetBytes(pToEncrypt);

  des.Key = ASCIIEncoding.ASCII.GetBytes(sKey);　//建立加密对象的密钥和偏移量
  des.IV = ASCIIEncoding.ASCII.GetBytes(sKey);　 //原文使用ASCIIEncoding.ASCII方法的GetBytes方法
  MemoryStream ms = new MemoryStream();　　 //使得输入密码必须输入英文文本
  CryptoStream cs = new CryptoStream(ms, des.CreateEncryptor(), CryptoStreamMode.Write);

  cs.Write(inputByteArray, 0, inputByteArray.Length);
  cs.FlushFinalBlock();

  StringBuilder ret = new StringBuilder();
  foreach (byte b in ms.ToArray())
  {
  ret.AppendFormat("{0:X2}", b);
  }
  ret.ToString();
  return ret.ToString();
  }

  /**//// <summary>
  /// 解密字符串，自定义8位密匙
  /// 加密密匙必须与解密密匙相同
  /// </summary>
  /// <param name="pToDecrypt">需要解密的字符串</param>
  /// <param name="sKey">8位字符密匙</param>
  /// <returns>解密后的字符串</returns>
  protected static string Decrypt(string pToDecrypt, string sKey)
  {
  DESCryptoServiceProvider des = new DESCryptoServiceProvider();

  byte[] inputByteArray = new byte[pToDecrypt.Length / 2];
  for (int x = 0; x < pToDecrypt.Length / 2; x++)
  {
  int i = (Convert.ToInt32(pToDecrypt.Substring(x * 2, 2), 16));
  inputByteArray[x] = (byte)i;
  }

  des.Key = ASCIIEncoding.ASCII.GetBytes(sKey);　//建立加密对象的密