詳細(xì)說明對密碼執(zhí)行散列與 salt 運算方法

Credentials.cs

using System;
using System.IO;
using System.Text;
using System.Security.Cryptography;
 
namespace BookStore.Common
{
       /// <summary>
       /// Credentials 的摘要說明。
       /// 原理：
       /// 對密碼執(zhí)行散列運算
       /// 若要避免以明文形式存儲密碼，一種常見的安全做法是對密碼執(zhí)行散列運算。如以下代碼所示，使用 System.Security.Cryptography 命名空間（它實現(xiàn) 160 位 SHA-1 標(biāo)準(zhǔn)）對密碼進(jìn)行散列運算。有關(guān)更多信息，請參見 SHA1 成員。
       /// 對散列執(zhí)行 Salt 運算
       /// 雖然對密碼執(zhí)行散列運算的一個好的開端，但若要增加免受潛在攻擊的安全性，則可以對密碼散列執(zhí)行 Salt 運算。Salt 就是在已執(zhí)行散列運算的密碼中插入的一個隨機(jī)數(shù)字。這一策略有助于阻止?jié)撛诘墓�擊者利用預(yù)先計算的字典攻擊。字典攻擊是攻擊者使用密鑰的所有可能組合來破解密碼的攻擊。當(dāng)您使用 Salt 值使散列運算進(jìn)一步隨機(jī)化后，攻擊者將需要為每個 Salt 值創(chuàng)建一個字典，這將使攻擊變得非常復(fù)雜且成本極高。
       /// Salt 值隨散列存儲在一起，并且未經(jīng)過加密。所存儲的 Salt 值可以在隨后用于密碼驗證。
       /// </summary>
       public class Credentials
       {
              private static string key = "!48%0d-F=cj>,s&2";  //密鑰（增加密碼復(fù)雜度，好像比較多余）
              private const int saltLength = 4;                         //定義salt值的長度
 
              /// <summary>
              /// 對密碼進(jìn)行Hash 和 Salt
              /// </summary>
              /// <param name="Password">用戶輸入的密碼</param>
              /// <returns></returns>
              public static byte[] HashAndSalt(string Password)
              {
                     return CreateDbPassword(HashPassword(Password));
              }
 
              /// <summary>
              /// 對用戶輸入的密碼加上密鑰key后進(jìn)行SHA1散列
              /// </summary>
              /// <param name="Password">用戶輸入的密碼</param>
              /// <returns>返回 160 位 SHA-1 散列后的的byte[]（160位對應(yīng)20個字節(jié)）</returns>
              private static byte[] HashPassword( string Password )
              {
                     //創(chuàng)建SHA1的對象實例sha1
                     SHA1 sha1 = SHA1.Create();
                     //計算輸入數(shù)據(jù)的哈希值
                     return sha1.ComputeHash( Encoding.Unicode.GetBytes( Password + key ) );
              }
             
              /// <summary>
              /// 比較數(shù)據(jù)庫中的密碼和所輸入的密碼是否相同
              /// </summary>
              /// <param name="storedPassword">數(shù)據(jù)庫中的密碼</param>
              /// <param name="Password">用戶輸入的密碼</param>
              /// <returns>true：相等/false：不等</returns>
              public static bool ComparePasswords(byte[] storedPassword, string Password)
              {
                     //首先將用戶輸入的密碼進(jìn)行Hash散列
                     byte[] hashedPassword = HashPassword(Password);
 
                     if (storedPassword == null hashedPassword == null hashedPassword.Length != storedPassword.Length - saltLength)
                     {
                            return false;
                     }
 
                     //獲取數(shù)據(jù)庫中的密碼的salt 值，數(shù)據(jù)庫中的密碼的后4個字節(jié)為salt 值
                     byte[] saltValue = new byte[saltLength];
                     int saltOffset = storedPassword.Length - saltLength;
                     for (int i = 0; i < saltLength; i++){
                            saltValue[i] = storedPassword[saltOffset + i];
                     }
                    
                     //用戶輸入的密碼用戶輸入的密碼加上salt 值，進(jìn)行salt
                     byte[] saltedPassword = CreateSaltedPassword(saltValue, hashedPassword);
             
                     //比較數(shù)據(jù)庫中的密碼和經(jīng)過salt的用戶輸入密碼是否相等
                     return CompareByteArray(storedPassword, saltedPassword);
              }
 
              /// <summary>
              /// 比較兩個ByteArray，看是否相等
              /// </summary>
              /// <param name="array1"></param>
              /// <param name="array2"></param>
              /// <returns>true：相等/false：不等</returns>
              private static bool CompareByteArray(byte[] array1, byte[] array2)
              {
                     if (array1.Length != array2.Length)
                     {
                            return false;
                     }
                     for (int i = 0; i < array1.Length; i++)
                     {
                            if (array1[i] != array2[i])
                            {
                                   return false;
                            }
                     }
                     return true;
              }
 
              /// <summary>
              /// 對要存儲的密碼進(jìn)行salt運算
              /// </summary>
              /// <param name="unsaltedPassword">沒有進(jìn)行過salt運算的hash散列密碼</param>
              /// <returns>經(jīng)過salt的密碼（經(jīng)過salt的密碼長度為：20+4=24，存儲密碼的字段為Binary(24)）</returns>
              private static byte[] CreateDbPassword(byte[] unsaltedPassword)
              {
                     //獲得 salt 值
                     byte[] saltValue = new byte[saltLength];
                     RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider();
                     rng.GetBytes(saltValue);
                    
                     return CreateSaltedPassword(saltValue, unsaltedPassword);
              }
             
              /// <summary>
              /// 創(chuàng)建一個經(jīng)過salt的密碼
              /// </summary>
              /// <param name="saltValue">salt 值</param>
              /// <param name="unsaltedPassword">沒有進(jìn)行過salt運算的hash散列密碼</param>
              /// <returns>經(jīng)過salt的密碼</returns>
              private static byte[] CreateSaltedPassword(byte[] saltValue, byte[] unsaltedPassword)
              {
                     //將salt值數(shù)組添加到hash散列數(shù)組后拼接成rawSalted數(shù)組中
                     byte[] rawSalted  = new byte[unsaltedPassword.Length + saltValue.Length];
                     unsaltedPassword.CopyTo(rawSalted,0);
                     saltValue.CopyTo(rawSalted,unsaltedPassword.Length);
                    
                     //將合并后的rawSalted數(shù)組再進(jìn)行SHA1散列的到saltedPassword數(shù)組（長度為20字節(jié)）
                     SHA1 sha1 = SHA1.Create();
                     byte[] saltedPassword = sha1.ComputeHash(rawSalted);
 
                     //將salt值數(shù)組在添加到saltedPassword數(shù)組后拼接成dbPassword數(shù)組（長度為24字節(jié)）
                     byte[] dbPassword  = new byte[saltedPassword.Length + saltValue.Length];
                     saltedPassword.CopyTo(dbPassword,0);
                     saltValue.CopyTo(dbPassword,saltedPassword.Length);
 
                     return dbPassword;
              }
 
       }
}