Password salting

Use a separate salt for each password hash

Password salting gives every newly created password hash a separate, securely generated random additional value. The salt is an input to the password hash function. It does not need to be secret and is stored with the verification value. A correctly used password hashing library can handle generation and management.

In a fictional application, account-A and account-B choose the same password. The library generates independent random salts for them. The labels salt-A and salt-B stand only for those values here; they are not usable salt settings. Different salts prevent an attacker from simply reusing a precomputed hash across all accounts.

Use the stored value when verifying

At a later sign-in, the library uses the stored salt and parameters to check the entered password. It does not generate a new salt every time it verifies an existing password hash. Creating a new password hash, however, uses a fresh salt.

A salt is not a pepper: a pepper is an additional secret that can protect multiple password records and is kept separately from the password database. A salt also does not replace a sufficiently costly password hash function. Someone holding a database copy can still try candidate passwords with the respective salt; weak passwords therefore remain at risk.

Sources

• OWASP — Password Storage