How Does ASP.NET Identity's Default Password Hasher Secure User Credentials?

Deep dive into ASP.NET Identity default password hasher: security and features

ASP.NET Identity’s default password hasher plays a vital role in protecting user credentials. This hashing mechanism ensures that stored passwords are protected from leakage and unauthorized access.

Understanding the IPasswordHasher interface

The IPasswordHasher interface defines the contract for password hashing and verification. It provides two methods:

• HashPassword(password): Hash the provided password.
• VerifyHashedPassword(hashedPassword, providedPassword): Verify that the provided password matches the hashed password.

Behind-the-scenes operations implemented by default

The default implementation of the IPasswordHasher interface uses a key derivation function (KDF) with a random salt to generate hash values. This salt is included in the output of KDF. Therefore, each password hashing operation produces a unique hash value.

Hash process:

<code><br>public static string HashPassword(string password)<br>{// 生成随机盐
byte[] salt;
// 使用带有盐的KDF计算哈希值
byte[] hash;
...

// 将盐和哈希值组合到最终输出中
byte[] output = new byte[salt.Length + hash.Length];
...

return Convert.ToBase64String(output);<p>}<br></p></code>

Verification process:

<code><br>public static bool VerifyHashedPassword(string hashedPassword, string password)<br>{// 从hashedPassword中提取盐
byte[] salt;
// 使用带有盐的KDF计算哈希值
byte[] calculatedHash;
...

// 从hashedPassword中提取哈希值
byte[] storedHash;
...

return ByteArraysEqual(calculatedHash, storedHash);<p>}<br></p></code>

Coping with concerns about static salt

Although the salt is included in the hashed password, it is not static. Each password hash operation generates a new random salt. This prevents attackers from using precomputed hashes or performing rainbow table attacks.

Security Impact

The default password hasher in ASP.NET Identity provides a safe and reliable way to store and verify user passwords. By using KDF with random salts, it protects against brute force attacks and reduces the risk of password leaks.

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