Are salts useless for security if the attacker knows them?

Question

Let\'s say I have a table of users set up like this:

CREATE TABLE `users` (
    `id` INTEGER PRIMARY KEY,
    `name` TEXT,
    `hashed_password` TEXT,
    `salt`         


        

Answer 1

No, they're not useless.

So long as you use a unique salt for each row, then the salt will prevent slow down an attack. The attacker will need to mount a brute force attack, rather than using rainbow tables against the password hashes.

As mentioned in the comments, you should ensure that the salt is a sensible size.