以下是关于对称加密算法的C#实现代码，大家可以根据需要更改不同的算法，文中以Rijndael算法为例：

using System;

using System.IO;

using System.Security.Cryptography;

using System.Text;

namespace DataCrypto
{
 /// <summary>
 /// 对称加密算法类
 /// </summary>
 public class SymmetricMethod
 {
  
  private SymmetricAlgorithm mobjCryptoService;
  private string Key;
  /// <summary>
  /// 对称加密类的构造函数
  /// </summary>
  public SymmetricMethod()
  {
   mobjCryptoService = new RijndaelManaged();
   Key = “Guz(%&hj7x89H$yuBI0456FtmaT5&fvHUFCy76*h%(HilJ$lhj!y6&(*jkP87jH7”;
  }
  /// <summary>
  /// 获得密钥
  /// </summary>
  /// <returns>密钥</returns>
  private byte[] GetLegalKey()
  {
   string sTemp = Key;
   mobjCryptoService.GenerateKey();
   byte[] bytTemp = mobjCryptoService.Key;
   int KeyLength = bytTemp.Length;
   if (sTemp.Length > KeyLength)
    sTemp = sTemp.Substring(0, KeyLength);
   else if (sTemp.Length < KeyLength)
    sTemp = sTemp.PadRight(KeyLength, ‘ ‘);
   return ASCIIEncoding.ASCII.GetBytes(sTemp);
  }
  /// <summary>
  /// 获得初始向量IV
  /// </summary>
  /// <returns>初试向量IV</returns>
  private byte[] GetLegalIV()
  {
   string sTemp = “E4ghj*Ghg7!rNIfb&95GUY86GfghUb#er57HBh(u%g6HJ($jhWk7&!hg4ui%$hjk”;
   mobjCryptoService.GenerateIV();
   byte[] bytTemp = mobjCryptoService.IV;
   int IVLength = bytTemp.Length;
   if (sTemp.Length > IVLength)
    sTemp = sTemp.Substring(0, IVLength);
   else if (sTemp.Length < IVLength)
    sTemp = sTemp.PadRight(IVLength, ‘ ‘);
   return ASCIIEncoding.ASCII.GetBytes(sTemp);
  }
  /// <summary>
  /// 加密方法
  /// </summary>
  /// <param name=”Source”>待加密的串</param>
  /// <returns>经过加密的串</returns>
  public string Encrypto(string Source)
  {
   byte[] bytIn = UTF8Encoding.UTF8.GetBytes(Source);
   MemoryStream ms = new MemoryStream();
   mobjCryptoService.Key = GetLegalKey();
   mobjCryptoService.IV = GetLegalIV();
   ICryptoTransform encrypto = mobjCryptoService.CreateEncryptor();
   CryptoStream cs = new CryptoStream(ms, encrypto, CryptoStreamMode.Write);
   cs.Write(bytIn, 0, bytIn.Length);
   cs.FlushFinalBlock();
   ms.Close();
   byte[] bytOut = ms.ToArray();
   return Convert.ToBase64String(bytOut);
  }
  /// <summary>
  /// 解密方法
  /// </summary>
  /// <param name=”Source”>待解密的串</param>
  /// <returns>经过解密的串</returns>
  public string Decrypto(string Source)
  {
   byte[] bytIn = Convert.FromBase64String(Source);
   MemoryStream ms = new MemoryStream(bytIn, 0, bytIn.Length);
   mobjCryptoService.Key = GetLegalKey();
   mobjCryptoService.IV = GetLegalIV();
   ICryptoTransform encrypto = mobjCryptoService.CreateDecryptor();
   CryptoStream cs = new CryptoStream(ms, encrypto, CryptoStreamMode.Read);
   StreamReader sr = new StreamReader(cs);
   return sr.ReadToEnd();
  }
 }
}