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Message-ID: <20060405004613.GA7679@openwall.com>
Date: Wed, 5 Apr 2006 04:46:13 +0400
From: Solar Designer <solar@...nwall.com>
To: john-users@...ts.openwall.com
Subject: Re: about salts
On Tue, Apr 04, 2006 at 06:54:09PM -0500, Dennis Olvany wrote:
> Salts are added to passwords before hashing. Does a system normally use
> the same salt for the entire password file or is a different salt
> generally used for each different password?
The latter. Salts are typically picked at random.
> How does a system know which salt to use to rehash passwords in the
> future for authentication? I suppose the system stores a mapping
> somewhere of salts to usernames.
Salts are encoded along with hashes. With the traditional crypt(3), the
first 2 characters of the 13-character encoding are the salt (12 bits,
for 4096 possibilities).
> Here's some output from john.
>
> Loaded 3 password hashes with 3 different salts (Traditional DES [24/32 4K])
>
> So, john can tell from the hashes that different salts are used
> throughout the file?
Yes.
This output also tells me one other thing - you're probably using a
non-MMX build of John on an x86 processor. If so, you can get some
substantial speedup by switching to the MMX build, unless your CPU is
truly ancient.
--
Alexander Peslyak <solar at openwall.com>
GPG key ID: B35D3598 fp: 6429 0D7E F130 C13E C929 6447 73C3 A290 B35D 3598
http://www.openwall.com - bringing security into open computing environments
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