How Can I Securely Hash Passwords Using PBKDF2?

Password Secure Hashing: The Complete Guide

Securely storing passwords is critical to maintaining user privacy and security. While encryption may seem like a simple solution, it's not the ideal method for this purpose. Hashing, on the other hand, is the preferred method for securely storing passwords.

Step-by-step password hashing process

Step 1: Generate salt value

First, create a random salt (unique value) using a cryptographically secure pseudo-random number generator (PRNG):

<code class="language-c#">byte[] salt;
new RNGCryptoServiceProvider().GetBytes(salt = new byte[16]);</code>

Step 2: Hash Password

Next, initialize the PBKDF2 (Password-Based Key Derivation Function 2) algorithm:

<code class="language-c#">var pbkdf2 = new Rfc2898DeriveBytes(password, salt, 100000);
byte[] hash = pbkdf2.GetBytes(20);</code>

Step 3: Combine Salt and Hash

Combine salt and password hash bytes for later use:

<code class="language-c#">byte[] hashBytes = new byte[36];
Array.Copy(salt, 0, hashBytes, 0, 16);
Array.Copy(hash, 0, hashBytes, 16, 20);</code>

Step 4: Encode for storage

Convert the combined salt and hash value to a Base64 string for safe storage:

<code class="language-c#">string savedPasswordHash = Convert.ToBase64String(hashBytes);</code>

Step 5: Verify Password

To verify the user-entered password against the stored hash, retrieve the stored hash:

<code class="language-c#">/* 获取存储的值 */
string savedPasswordHash = DBContext.GetUser(u => u.UserName == user).Password;</code>

Extract bytes and salt:

<code class="language-c#">/* 提取字节 */
byte[] hashBytes = Convert.FromBase64String(savedPasswordHash);
/* 获取盐值 */
byte[] salt = new byte[16];
Array.Copy(hashBytes, 0, salt, 0, 16);</code>

Calculate the hash value of the password entered by the user:

<code class="language-c#">var pbkdf2 = new Rfc2898DeriveBytes(password, salt, 100000);
byte[] hash = pbkdf2.GetBytes(20);</code>

Comparison results:

<code class="language-c#">/* 比较结果 */
for (int i=0; i < 20; i++)
    if (hashBytes[i+16] != hash[i])
        throw new UnauthorizedAccessException();</code>

By following these steps, you can hash passwords for your applications efficiently and securely.

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