简单的使用.NET对称加密的例子

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

/// <summary>
/// 使用对称加密的例子
/// </summary>
class Class1
{

 static void Main(string[] args)
 {
  Class1 c=new Class1();
  c.StartDemo();
 }

 public void StartDemo()
 {
  //establish symmetric algorithm
  SymmetricAlgorithm sa = Rijndael.Create();

  //key and iv
  sa.GenerateKey();    //产生随机的 (32*8) 位的密钥
  //sa.GenerateIV();    //初始向量，在ECB模式里面可以不用IV
  sa.Mode = CipherMode.ECB;  //块处理模式
  sa.Padding = PaddingMode.Zeros; //末尾数据块的填充模式

   
  Console.WriteLine("密钥是：");   ///////////
  for (int i=0; i<sa.Key.Length; i++)  ///////////
  {          ///////////
   Console.Write("{0:X2} ",sa.Key[i]); ///////////
  }          ///////////
  Console.WriteLine("\n");    ///////////


  //establish crypto stream
  MemoryStream ms = new MemoryStream();
  CryptoStream cs = new CryptoStream(ms,sa.CreateEncryptor(),CryptoStreamMode.Write);

  //
  string plaintext; //原始文本
  byte[] cipherbytes; //加密后的数据
  byte[] finalbytes;  //解密后的数据

  plaintext="How are you? 这是一行文字。";
  byte[] plainbytes = Encoding.UTF8.GetBytes(plaintext);


  Console.WriteLine("原始文本是：\n{0}\n",plaintext);
  //display plaint text byte array in hex format
  Console.WriteLine("原始数据是：");   ///////////
  for (int i=0; i<plainbytes.Length; i++)  ///////////
  {           ///////////
   Console.Write("{0:X2} ",plainbytes[i]); ///////////
  }           ///////////
  Console.WriteLine("\n");     ///////////

  //加密过程
  cs.Write(plainbytes, 0, plainbytes.Length);
  cs.Close();
  cipherbytes = ms.ToArray();
  ms.Close();

  //display ciphertext byte array in hex format
  Console.WriteLine("加密后的数据是：");  ///////////
  for (int i=0; i<cipherbytes.Length; i++) ///////////
  {           ///////////
   Console.Write("{0:X2} ",cipherbytes[i]);///////////
  }           ///////////
  Console.WriteLine("\n");     ///////////


  //下面的为加密过程
  ms=new MemoryStream(cipherbytes);
  cs=new CryptoStream(ms,sa.CreateDecryptor(),CryptoStreamMode.Read);
  finalbytes=new byte[plainbytes.Length];
  cs.Read(finalbytes,0,plainbytes.Length);

  Console.WriteLine("解密后的数据是：");  ///////////
  for (int i=0; i<finalbytes.Length; i++)     ///////////
  {           ///////////
   Console.Write("{0:X2} ",finalbytes[i]); ///////////
  }           ///////////
  Console.WriteLine("\n");     ///////////

  string finaltext=Encoding.UTF8.GetString(finalbytes);

  Console.WriteLine("解密后的文本是：\n{0}\n\n",finaltext );
  Console.WriteLine("按任意键继续......");
  Console.ReadLine();

 }
}

http://blog.csdn.net/kwanhong/archive/2005/09/22/486783.aspx