/// <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;
}

2）32位的MD5加密

/// <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(); //實例化一個md5對像
  // 加密后是一個字節(jié)類型的數(shù)組，這里要注意編碼UTF8/Unicode等的選擇　
  byte[] s = md5.ComputeHash(Encoding.UTF8.GetBytes(cl));
  // 通過使用循環(huán)，將字節(jié)類型的數(shù)組轉(zhuǎn)換為字符串，此字符串是常規(guī)字符格式化所得
  for (int i = 0; i < s.Length; i++)
  {
    // 將得到的字符串使用十六進制類型格式。格式后的字符是小寫的字母，如果使用大寫（X）則格式后的字符是大寫字符 
    pwd = pwd + s[i].ToString("X");
  }
  return pwd;
}

3）64位的MD5加密

public static string MD5Encrypt64(string password)
{
  string cl = password;
  //string pwd = "";
  MD5 md5 = MD5.Create(); //實例化一個md5對像
  // 加密后是一個字節(jié)類型的數(shù)組，這里要注意編碼UTF8/Unicode等的選擇　
  byte[] s = md5.ComputeHash(Encoding.UTF8.GetBytes(cl));
  return Convert.ToBase64String(s);
}

4）使用MD5為用戶密碼加密

/// <summary>
/// 加密用戶密碼
/// </summary>
/// <param name="password">密碼</param>
/// <param name="codeLength">加密位數(shù)</param>
/// <returns>加密密碼</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;
}

由于MD5是不可逆的，所以加密之后就無法解密，取用戶名和密碼時候，需要再加密一邊用戶輸入的數(shù)據(jù)與數(shù)據(jù)庫中已加密的數(shù)據(jù)進行比對。如果比對結(jié)果一致，則可以判定登陸成功！代碼如下所示：

/// <summary>
/// 登陸
/// </summary>
public Model.UserInfo UserLogOn(string USERID, string pwd, out string statusCode)
{
  //假設(shè)已經(jīng)通過用戶ID獲取到UserInfo的Model對象
  Model.UserInfo model = GetModel(USERID);
  if (model != null)
  {
    if (model.PASSWORD == MD5Encrypt64(pwd))
    {
      statusCode = "登陸成功";
    }
    else {
      statusCode = “密碼錯誤”；
    }
  }
  else
  {
    statusCode = "用戶不存在！";
    model = null;
  }  
  return model;
}

5）通過DESCryptoServiceProvider對象對字符串進行加密解密

/// <summary>
/// DES數(shù)據(jù)加密
/// </summary>
/// <param name="targetValue">目標值</param>
/// <param name="key">密鑰</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);
  // 通過兩次哈希密碼設(shè)置對稱算法的初始化向量  
  des.Key = Encoding.ASCII.GetBytes(FormsAuthentication.HashPasswordForStoringInConfigFile
                      (FormsAuthentication.HashPasswordForStoringInConfigFile(key, "md5").
                        Substring(0, 8), "sha1").Substring(0, 8));
  // 通過兩次哈希密碼設(shè)置算法的機密密鑰  
  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();
}

此種算法可以通過加密密鑰進行解密，解密方法如下：

/// <summary>
/// DES數(shù)據(jù)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;
  }
  // 定義DES加密對象
  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;
  }
  // 通過兩次哈希密碼設(shè)置對稱算法的初始化向量  
  des.Key = Encoding.ASCII.GetBytes(FormsAuthentication.HashPasswordForStoringInConfigFile
                      (FormsAuthentication.HashPasswordForStoringInConfigFile(key, "md5").
                        Substring(0, 8), "sha1").Substring(0, 8));
  // 通過兩次哈希密碼設(shè)置算法的機密密鑰  
  des.IV = Encoding.ASCII.GetBytes(FormsAuthentication.HashPasswordForStoringInConfigFile
                      (FormsAuthentication.HashPasswordForStoringInConfigFile(key, "md5")
                        .Substring(0, 8), "md5").Substring(0, 8));
  // 定義內(nèi)存流
  var ms = new MemoryStream();
  // 定義加密流
  var cs = new CryptoStream(ms, des.CreateDecryptor(), CryptoStreamMode.Write);
  cs.Write(inputByteArray, 0, inputByteArray.Length);
  cs.FlushFinalBlock();
  return Encoding.Default.GetString(ms.ToArray());
}

以上內(nèi)容是基于C#對用戶密碼使用MD5加密與解密的全部敘述，希望大家喜歡。

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