ASP.NET C# URL加密解密

using System.Security.Cryptography;
using System.IO;
using System.text;

/// <summary>
        /// 加密
        /// </summary>
        /// <param name="str"></param>
        /// <param name="key"></param>
        /// <returns></returns>
        public static string Encode(string str, string key)
         {
             DESCryptoServiceProvider provider = new DESCryptoServiceProvider();
             provider.Key = Encoding.ASCII.GetBytes(key.Substring(0, 8));
             provider.IV = Encoding.ASCII.GetBytes(key.Substring(0, 8));
            byte[] bytes = Encoding.GetEncoding("GB2312").GetBytes(str);
             MemoryStream stream = new MemoryStream();
             CryptoStream stream2 = new CryptoStream(stream, provider.CreateEncryptor(), CryptoStreamMode.Write);
             stream2.Write(bytes, 0, bytes.Length);
             stream2.FlushFinalBlock();
             StringBuilder builder = new StringBuilder();
            foreach (byte num in stream.ToArray())
             {
                 builder.AppendFormat("{0:X2}", num);
             }
             stream.Close();
            return builder.ToString();
         }

        /// <summary>
        /// Des 解密 GB2312
        /// </summary>
        /// <param name="str">Desc string</param>
        /// <param name="key">Key ,必须为8位 </param>
        /// <returns></returns>
        public static string Decode(string str, string key)
         {
             DESCryptoServiceProvider provider = new DESCryptoServiceProvider();
             provider.Key = Encoding.ASCII.GetBytes(key.Substring(0, 8));
             provider.IV = Encoding.ASCII.GetBytes(key.Substring(0, 8));
            byte[] buffer = new byte[str.Length / 2];
            for (int i = 0; i < (str.Length / 2); i++)
             {
                int num2 = Convert.ToInt32(str.Substring(i * 2, 2), 0x10);
                 buffer[i] = (byte)num2;
             }
             MemoryStream stream = new MemoryStream();
             CryptoStream stream2 = new CryptoStream(stream, provider.CreateDecryptor(), CryptoStreamMode.Write);
             stream2.Write(buffer, 0, buffer.Length);
             stream2.FlushFinalBlock();
             stream.Close();
            return Encoding.GetEncoding("GB2312").GetString(stream.ToArray());
         }

调用方法
/// <summary>
        /// If don't input key , Use default key
        /// Des 加密 GB2312 :
        /// </summary>
        /// <param name="str"></param>
        /// <returns></returns>
        public static string Encode(string str)
        {
            return VerifyTool.Encode(str, "Rainight");
        }
        /// <summary>
        /// 解密
        /// </summary>
        /// <param name="str"></param>
        /// <returns></returns>
        public static string Decode(string str)
        {
            return VerifyTool.Decode(str, "Rainight");
        }