How Secure is the Default Password Hasher in ASP.NET Identity?

Detailed explanation of ASP.NET Identity default password hasher security mechanism

Background and implementation

The ASP.NET Identity framework's default password hasher (accessed through the UserManager class in ASP.NET MVC 5) uses a strong security algorithm to protect user passwords. The password hashing process combines a key derivation function (KDF) and a randomly generated salt.

Salt value: Prevent static salt value vulnerability

For enhanced password protection, the password hasher generates a unique salt value for each password. This salt value is not a static value but is included as part of the output hash. By including the salt in this way, each hashed password is different, effectively preventing brute force attacks that rely on precomputed hash tables.

Hash and verification process

The hashing algorithm Rfc2898DeriveBytes uses a salt value to generate a password hash. This hash is stored in a 49-byte value that contains the salt and the actual hash.

During password verification, the hashed password is again split into its salt and hash components. The provided password is then hashed using the retrieved salt value and the result is compared to the stored hash. If they match, password verification is successful.

Security Impact

The default password hasher in ASP.NET Identity provides strong password protection by using a combination of salts and KDF. The addition of salt ensures that each password has a unique hash value, and KDF prevents passwords from being efficiently cracked via brute force or rainbow table attacks.

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