if the salt were secret, how would you ever check the user's password?
the salt exists to keep dictionary attacks from being ridiculously efficient. imagine if there were no salt in the unix crypt scheme. i could calculate the hash of every word in the dictionary ahead of time and then simply compare that one list against every /etc/passwd i come across. if i were good, i could probably even remember the hash of a few of the more common passwords and be able to get an account here and there just by glancing at the passwd file. the salt just makes it so i have to run crypt on every word in the dictionary for each password i encounter because it has a different salt. no matter what i've always got to do some work.
anders pearson
