If I make the SALT random for each user, how do I authenticate them?

Question

I\'ve been reading up on the benefits of salting and hashing passwords, but one thing still eludes me...

When I provide a random salt for each user, how do I then know

Answer 1

The salt prevents someone from getting a copy of your encrypted password database and mounting an offline attack against all of the passwords at the same time. It doesn't prevent attacks against a single password.

You might enjoy reading the original Unix password security article. It does a very good job explaining what a salt is, and why we have them: http://portal.acm.org/citation.cfm?id=359172