【发布时间】：2013-01-07 00:29:59
【问题描述】：
我最近阅读了一篇关于使用“salt”安全地散列用户密码的有趣文章。 （这是original article，不幸的是，在本文发布时它似乎已关闭，因此here's 是缓存版本。）
我完全同意这个概念，但我似乎无法找到一种将用户登录信息安全地存储在本地 cookie（或会话）中的方法，因为 salt + PBKDF2 哈希组合每次都是随机完成的。为了更好地理解我的意思，让我从the article复制C#代码：
using System;
using System.Text;
using System.Security.Cryptography;
namespace PasswordHash
{
/// <summary>
/// Salted password hashing with PBKDF2-SHA1.
/// Author: havoc AT defuse.ca
/// www: http://crackstation.net/hashing-security.htm
/// Compatibility: .NET 3.0 and later.
/// </summary>
class PasswordHash
{
// The following constants may be changed without breaking existing hashes.
public const int SALT_BYTES = 24;
public const int HASH_BYTES = 24;
public const int PBKDF2_ITERATIONS = 1000;
public const int ITERATION_INDEX = 0;
public const int SALT_INDEX = 1;
public const int PBKDF2_INDEX = 2;
/// <summary>
/// Creates a salted PBKDF2 hash of the password.
/// </summary>
/// <param name="password">The password to hash.</param>
/// <returns>The hash of the password.</returns>
public static string CreateHash(string password)
{
// Generate a random salt
RNGCryptoServiceProvider csprng = new RNGCryptoServiceProvider();
byte[] salt = new byte[SALT_BYTES];
csprng.GetBytes(salt);
// Hash the password and encode the parameters
byte[] hash = PBKDF2(password, salt, PBKDF2_ITERATIONS, HASH_BYTES);
return PBKDF2_ITERATIONS + ":" +
Convert.ToBase64String(salt) + ":" +
Convert.ToBase64String(hash);
}
/// <summary>
/// Validates a password given a hash of the correct one.
/// </summary>
/// <param name="password">The password to check.</param>
/// <param name="goodHash">A hash of the correct password.</param>
/// <returns>True if the password is correct. False otherwise.</returns>
public static bool ValidatePassword(string password, string goodHash)
{
// Extract the parameters from the hash
char[] delimiter = { ':' };
string[] split = goodHash.Split(delimiter);
int iterations = Int32.Parse(split[ITERATION_INDEX]);
byte[] salt = Convert.FromBase64String(split[SALT_INDEX]);
byte[] hash = Convert.FromBase64String(split[PBKDF2_INDEX]);
byte[] testHash = PBKDF2(password, salt, iterations, hash.Length);
return SlowEquals(hash, testHash);
}
/// <summary>
/// Compares two byte arrays in length-constant time. This comparison
/// method is used so that password hashes cannot be extracted from
/// on-line systems using a timing attack and then attacked off-line.
/// </summary>
/// <param name="a">The first byte array.</param>
/// <param name="b">The second byte array.</param>
/// <returns>True if both byte arrays are equal. False otherwise.</returns>
private static bool SlowEquals(byte[] a, byte[] b)
{
uint diff = (uint)a.Length ^ (uint)b.Length;
for (int i = 0; i < a.Length && i < b.Length; i++)
diff |= (uint)(a[i] ^ b[i]);
return diff == 0;
}
/// <summary>
/// Computes the PBKDF2-SHA1 hash of a password.
/// </summary>
/// <param name="password">The password to hash.</param>
/// <param name="salt">The salt.</param>
/// <param name="iterations">The PBKDF2 iteration count.</param>
/// <param name="outputBytes">The length of the hash to generate, in bytes.</param>
/// <returns>A hash of the password.</returns>
private static byte[] PBKDF2(string password, byte[] salt, int iterations, int outputBytes)
{
Rfc2898DeriveBytes pbkdf2 = new Rfc2898DeriveBytes(password, salt);
pbkdf2.IterationCount = iterations;
return pbkdf2.GetBytes(outputBytes);
}
}
}
如您所见，验证密码的唯一方法是使用纯文本密码调用ValidatePassword。在我之前的普通 SHA1 实现中，为了在本地浏览器中存储用户登录信息，我将该 SHA1 值放入 cookie 中，并将其与存储在服务器上每个页面的数据库中的值进行比较。但是，您如何使用这种“安全”的方法来做同样的事情呢？
有什么想法吗？
【问题讨论】：
-
您绝对不想将哈希值存储在 cookie 中。
-
（我刚刚意识到这听起来像是一个毒品玩笑，但我是认真的......）
-
那么您将如何做到让用户不必在每个页面上都登录？
-
您应该确保 cookie 已加密。我同意@OliCharlesworth 的观点，但您不应该将哈希值存储在 cookie 中。您不能只使用 cookie 本身的存在作为登录用户的标记吗？您可以将登录用户的用户 ID 存储在 cookie 中，以便在每次请求时您都可以知道谁在浏览。
-
上面的代码与存储 cookie 以标记正在登录的用户的解决方案并不真正相关，因为不需要散列。当您登录用户时，您需要在 http 响应中添加一个 cookie。如果您使用的是 ASP.NET，网上有大量示例。只需搜索“表单身份验证”，您就会找到一堆。
标签： c# asp.net passwords cryptography