Re: [aur-dev] [PATCH] Support for salted passwords

On Thu, Apr 15, 2010 at 3:10 PM, Dan McGee wrote:

On Thu, Apr 15, 2010 at 2:00 PM, Loui Chang wrote:

...

Hi Denis. I thought the idea behind salt is that if someone gets the database, they can't crack the passwords because the salt is secret.

That's not fully correct. Salt is not meant to be secret; it is meant to prevent the use of rainbow tables or precomputed hashes.

The idea behind salt in this case is for each user's password to be hashed with a different salt. This means if someone is to crack one person's password, it doesn't help them at all with the remaining passwords in that same database that they got their hands on because the salt is unique for every user.

Dan is right - salted passwords are used to reduce the efficiency of rainbow table attacks on the database. I'm no security expert, but it is my understanding that assigning a random salt to each user is considered pretty secure. Some implementations are even simpler - there is a single salt for all passwords in the database, the idea being that an attacker wouldn't be able to use a readily available set of rainbow tables and would have to compute his own set for the salt used. Such implementation is used by CakePHP web framework, for example. Denis.