基于C#对用户密码使用MD5加密与解密

/// <summary>
/// 16位MD5加密
/// </summary>
/// <param name="password"></param>
/// <returns></returns>
public static string MD5Encrypt16(string password)
{
  var md5 = new MD5CryptoServiceProvider();
  string t2 = BitConverter.ToString(md5.ComputeHash(Encoding.Default.GetBytes(password)), 4, 8);
  t2 = t2.Replace("-", "");
  return t2;
} 

/// <summary>
/// 32位MD5加密
/// </summary>
/// <param name="password"></param>
/// <returns></returns>
public static string MD5Encrypt32(string password)
{
  string cl = password;
  string pwd = "";
  MD5 md5 = MD5.Create(); //实例化一个md5对像
  // 加密后是一个字节类型的数组，这里要注意编码UTF8/Unicode等的选择　
  byte[] s = md5.ComputeHash(Encoding.UTF8.GetBytes(cl));
  // 通过使用循环，将字节类型的数组转换为字符串，此字符串是常规字符格式化所得
  for (int i = 0; i < s.Length; i++)
  {
    // 将得到的字符串使用十六进制类型格式。格式后的字符是小写的字母，如果使用大写（X）则格式后的字符是大写字符 
    pwd = pwd + s[i].ToString("X");
  }
  return pwd;
} 

public static string MD5Encrypt64(string password)
{
  string cl = password;
  //string pwd = "";
  MD5 md5 = MD5.Create(); //实例化一个md5对像
  // 加密后是一个字节类型的数组，这里要注意编码UTF8/Unicode等的选择　
  byte[] s = md5.ComputeHash(Encoding.UTF8.GetBytes(cl));
  return Convert.ToBase64String(s);
}

/// <summary>
/// 加密用户密码
/// </summary>
/// <param name="password">密码</param>
/// <param name="codeLength">加密位数</param>
/// <returns>加密密码</returns>
public static string md5(string password, int codeLength)
{
  if (!string.IsNullOrEmpty(password))
  {
    // 16位MD5加密（取32位加密的9~25字符） 
    if (codeLength == 16)
    {
      return System.Web.Security.FormsAuthentication.HashPasswordForStoringInConfigFile(password, "MD5").ToLower().Substring(8, 16);
    }
    // 32位加密
    if (codeLength == 32)
    {
      return System.Web.Security.FormsAuthentication.HashPasswordForStoringInConfigFile(password, "MD5").ToLower();
    }
  }
  return string.Empty;
}

/// <summary>
/// 登陆
/// </summary>
public Model.UserInfo UserLogOn(string USERID, string pwd, out string statusCode)
{
  //假设已经通过用户ID获取到UserInfo的Model对象
  Model.UserInfo model = GetModel(USERID);
  if (model != null)
  {
    if (model.PASSWORD == MD5Encrypt64(pwd))
    {
      statusCode = "登陆成功";
    }
    else {
      statusCode = “密码错误”；
    }
  }
  else
  {
    statusCode = "用户不存在！";
    model = null;
  }  
  return model;
} 

/// <summary>
/// DES数据加密
/// </summary>
/// <param name="targetValue">目标值</param>
/// <param name="key">密钥</param>
/// <returns>加密值</returns>
public static string Encrypt(string targetValue, string key)
{
  if (string.IsNullOrEmpty(targetValue))
  {
    return string.Empty;
  }
  var returnValue = new StringBuilder();
  var des = new DESCryptoServiceProvider();
  byte[] inputByteArray = Encoding.Default.GetBytes(targetValue);
  // 通过两次哈希密码设置对称算法的初始化向量  
  des.Key = Encoding.ASCII.GetBytes(FormsAuthentication.HashPasswordForStoringInConfigFile
                      (FormsAuthentication.HashPasswordForStoringInConfigFile(key, "md5").
                        Substring(0, 8), "sha1").Substring(0, 8));
  // 通过两次哈希密码设置算法的机密密钥  
  des.IV = Encoding.ASCII.GetBytes(FormsAuthentication.HashPasswordForStoringInConfigFile
                      (FormsAuthentication.HashPasswordForStoringInConfigFile(key, "md5")
                        .Substring(0, 8), "md5").Substring(0, 8));
  var ms = new MemoryStream();
  var cs = new CryptoStream(ms, des.CreateEncryptor(), CryptoStreamMode.Write);
  cs.Write(inputByteArray, 0, inputByteArray.Length);
  cs.FlushFinalBlock();
  foreach (byte b in ms.ToArray())
  {
    returnValue.AppendFormat("{0:X2}", b);
  }
  return returnValue.ToString();
}

/// <summary>
/// DES数据解密
/// </summary>
/// <param name="targetValue"></param>
/// <param name="key"></param>
/// <returns></returns>
public static string Decrypt(string targetValue, string key)
{
  if (string.IsNullOrEmpty(targetValue))
  {
    return string.Empty;
  }
  // 定义DES加密对象
  var des = new DESCryptoServiceProvider();
  int len = targetValue.Length / 2;
  var inputByteArray = new byte[len];
  int x, i;
  for (x = 0; x < len; x++)
  {
    i = Convert.ToInt32(targetValue.Substring(x * 2, 2), 16);
    inputByteArray[x] = (byte)i;
  }
  // 通过两次哈希密码设置对称算法的初始化向量  
  des.Key = Encoding.ASCII.GetBytes(FormsAuthentication.HashPasswordForStoringInConfigFile
                      (FormsAuthentication.HashPasswordForStoringInConfigFile(key, "md5").
                        Substring(0, 8), "sha1").Substring(0, 8));
  // 通过两次哈希密码设置算法的机密密钥  
  des.IV = Encoding.ASCII.GetBytes(FormsAuthentication.HashPasswordForStoringInConfigFile
                      (FormsAuthentication.HashPasswordForStoringInConfigFile(key, "md5")
                        .Substring(0, 8), "md5").Substring(0, 8));
  // 定义内存流
  var ms = new MemoryStream();
  // 定义加密流
  var cs = new CryptoStream(ms, des.CreateDecryptor(), CryptoStreamMode.Write);
  cs.Write(inputByteArray, 0, inputByteArray.Length);
  cs.FlushFinalBlock();
  return Encoding.Default.GetString(ms.ToArray());
}