Re: Values to use for a salt?

From: Brian Hatch (bri_at_ifokr.org)
Date: 12/19/03

  • Next message: Casper ***: "Re: Values to use for a salt?" 
    Date: Fri, 19 Dec 2003 11:39:29 -0800
To: Scott Cleven-Mulcahy <scottcm3@hotmail.com>

    > Most systems that I'm aware of use the same key, I presume for speed
    > reasons.

    Or because they're written by people who don't know what
    they're doing.

    > Since the key is added to the password before hashing it seems to
    > me that it only serves to make the password more random. So "MyPassword"
    > becomes "1234MyPassword". This has only made the password more random and
    > generates the same hash code for every password that is "MyPassword".

    If you're going to salt, then you need to put the salt at the *END*
    of the password. Otherwise the cracker can precompute the salt in
    the hashing routine, and there's no speed difference between a salted
    password and an unsalted password.

            SALTpassword <== precompute hash of SALT, then do all
                                possible passwords.
            
            passwordSALT <== compute each password followed by
                                salt - no precomputation possible.

    Always put the 'known' bit last. (Here assuming the salt is
    either known (stored in the resulting hash) or knowable (it's
    stored somewhere inside the application or application logic
    and thus is essentially knowable anyway.)

    > Couldn't agree more and one benefit of using salt is that it creates more
    > random passwords.

    I still have no idea what you really mean here.

    password+salt is not a password, it's a password+salt.
    It's the 'thing to be hashed' but it's not the password
    any more. 

    --
Brian Hatch                  Turning off setuid bits
   Systems and                of important unix tools
   Security Engineer          is like poking out an
http://www.ifokr.org/bri/     eye to prevent misuse.
                              -- Nick Esborn.
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