[Discuss] salt question

[Eric Chadbourne]

Hi,

I have a basic question about salt.

I was reading this:
http://www.openwall.com/articles/PHP-Users-Passwords

And don't quite understand this line:
"Salts are normally stored along with the hashes. They are not secret."

So if they are not secret what is the advantage if your site is 
exploited?  Such as if the salt is stored in a config file couldn't the 
attacker utilize this with his rainbow tables?  Also I see in PHP 
crypt() you don't have to supply a salt.  How does that work?  Is there 
a distinct salt per hash, and if yes, where is this stored?

I have a log in system I wrote myself with sha1 but from everything I've 
been reading this seems inadequate.

Thanks for any tips!

--
Eric Chadbourne
http://theMnemeProject.org/