Salting passwords

[quark76]

I'm getting really confused reading about this. I understand this makes brute force attacks harder, but as a coder how do I use salt to protect my passwords.

Do I salt the password while I'm running it through sha1, say:

sha1($salt.password)

Then store both the salt & password in the DB, so when the user logs in I have to get the salt from the DB to match it? If I do that though, how is that helping?

Thanks

[dagon]

the salt protects the stored password hash from dictionary\rainbow tables, there are plenty of articles out there that would do a better job of explaining it than me.

[NogDog]

I would probably not store the salt in the DB, since then anyone who steals the DB has the salts. Instead, I might use the login_name, perhaps messing it around a bit first with strrev() or base64_encode(), or whatever suits my fancy, so that some of the seed comes from the DB but then is transmuted by the code.

[laserlight]

Storing the salt in the database is standard practice. NogDog's idea is good when it is unlikely that the database server and the web server will be compromised together. On the other hand, this is a form of (additional) security through obscurity, so you should be careful about "whatever suits my fancy", otherwise an attacker who can guess the algorithm would be able to deduce the salt anyway. As such, I suggest storing the salt in the database; you can still have it "transmuted by the code", and it will more easily enable you to allow your users to change their login names.