Re: Saving and Encoding Passwords

[" "@deneb.cygnus.argh.org (Florian Weimer)]

kilgallen@eisner.decus.org (Larry Kilgallen) writes:

> In article <87u2m8exf8.fsf@deneb.cygnus.argh.org>, Florian Weimer <fw@s.netic.de> writes:
> 
> > It is considered close to impossible to recover the password from
> > the hash value if the cryptographic hash function is one of the most
> > commonly used and thoroughly analyzed (i.e. MD5 or SHA-1).
> 
> But that consideration is only of interest to mathematicians.

Eh, maybe. ;)

> Security folk realize that passwords freely chosen by humans
> are highly susceptible to brute force guessing attacks.  The
> common defenses are:
> 
> 	Include a secret per-user pseudo-random seed number
> 	in the hash, to prevent pre-computation of hashes for
> 	a particular username.

There's no such thing like a `secret per-user pseudo-random seed number'.
The application needs to know it in order to verify the password,
which means it can't that secret.  Of course, a password salt will
tremendously increase the size of a precomputed dictionary without much
effort on the application programmer's side.