提供一个基于C 的加密/解密算法

SymmCrypto de = new SymmCrypto(SymmCrypto.SymmProvEnum.DES);
Response.Write(x.Decrypting(de.Encrypting("ok","yyy"),"yyy"));

using System;
using System.Security.Cryptography;
using System.IO;
using System.Text;

namespace eMeng
{
  /// <summary>
  /// SymmCrypto 的摘要说明。
  /// SymmCrypto类实现.NET框架下的加密和解密服务。
  /// 原作者： Frank Fang : fangfrank@hotmail.com
  /// </summary>
  public class SymmCrypto
  {
      public enum SymmProvEnum : int
      {
        DES, RC2, Rijndael
      }

    private SymmetricAlgorithm mobjCryptoService;

    /// <remarks>
    /// 使用.Net SymmetricAlgorithm 类的构造器.
    /// </remarks>
    public SymmCrypto(SymmProvEnum NetSelected)
    {
      switch (NetSelected)
      {
        case SymmProvEnum.DES:
          mobjCryptoService = new DESCryptoServiceProvider();
          break;
        case SymmProvEnum.RC2:
          mobjCryptoService = new RC2CryptoServiceProvider();
          break;
        case SymmProvEnum.Rijndael:
          mobjCryptoService = new RijndaelManaged();
          break;
      }
    }

    /// <remarks>
    /// 使用自定义SymmetricAlgorithm类的构造器.
    /// </remarks>
    public SymmCrypto(SymmetricAlgorithm ServiceProvider)
    {
      mobjCryptoService = ServiceProvider;
    }

    /// <remarks>
    /// Depending on the legal key size limitations of 
    /// a specific CryptoService provider and length of 
    /// the private key provided, padding the secret key 
    /// with space character to meet the legal size of the algorithm.
    /// </remarks>
    private byte[] GetLegalKey(string Key)
    {
      string sTemp;
      if (mobjCryptoService.LegalKeySizes.Length > 0)
      {
        int lessSize = 0, moreSize = mobjCryptoService.LegalKeySizes[0].MinSize;
        // key sizes are in bits
        while (Key.Length * 8 > moreSize)
        {
          lessSize = moreSize;
          moreSize  = mobjCryptoService.LegalKeySizes[0].SkipSize;
        }
        sTemp = Key.PadRight(moreSize / 8, ' ');
      }
      else
        sTemp = Key;

      // convert the secret key to byte array
      return ASCIIEncoding.ASCII.GetBytes(sTemp);
    }

    public string Encrypting(string Source, string Key)
    {
      byte[] bytIn = System.Text.ASCIIEncoding.ASCII.GetBytes(Source);
      // create a MemoryStream so that the process can be done without I/O files
      System.IO.MemoryStream ms = new System.IO.MemoryStream();

      byte[] bytKey = GetLegalKey(Key);

      // set the private key
      mobjCryptoService.Key = bytKey;
      mobjCryptoService.IV = bytKey;

      // create an Encryptor from the Provider Service instance
      ICryptoTransform encrypto = mobjCryptoService.CreateEncryptor();

      // create Crypto Stream that transforms a stream using the encryption
      CryptoStream cs = new CryptoStream(ms, encrypto, CryptoStreamMode.Write);

      // write out encrypted content into MemoryStream
      cs.Write(bytIn, 0, bytIn.Length);
      cs.FlushFinalBlock();
            
      // get the output and trim the '\0' bytes
      byte[] bytOut = ms.GetBuffer();
      int i = 0;
      for (i = 0; i < bytOut.Length; i  )
        if (bytOut[i] == 0)
          break;
                    
      // convert into Base64 so that the result can be used in <a href="http://dev.21tx.com/dotnet/XML/" target="_blank">XML</a>
      return System.Convert.ToBase64String(bytOut, 0, i);
    }

    public string Decrypting(string Source, string Key)
    {
      // convert from Base64 to binary
      byte[] bytIn = System.Convert.FromBase64String(Source);
      // create a MemoryStream with the input
      System.IO.MemoryStream ms = new System.IO.MemoryStream(bytIn, 0, bytIn.Length);

      byte[] bytKey = GetLegalKey(Key);

      // set the private key
      mobjCryptoService.Key = bytKey;
      mobjCryptoService.IV = bytKey;

      // create a Decryptor from the Provider Service instance
      ICryptoTransform encrypto = mobjCryptoService.CreateDecryptor();
 
      // create Crypto Stream that transforms a stream using the decryption
      CryptoStream cs = new CryptoStream(ms, encrypto, CryptoStreamMode.Read);

      // read out the result from the Crypto Stream
      System.IO.StreamReader sr = new System.IO.StreamReader( cs );
      return sr.ReadToEnd();
    }
  }
}