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Message-ID: <20110821143717.GA9435@openwall.com>
Date: Sun, 21 Aug 2011 18:37:17 +0400
From: Solar Designer <solar@...nwall.com>
To: john-users@...ts.openwall.com
Subject: Re: Some problems to build chr
On Sun, Aug 21, 2011 at 03:41:37PM +0200, madfran wrote:
> If I understood well, to avoid a overflow:
> ((SIZE ** LENGTH) * SCALE) must fit in 64 bits.
> That means ((SIZE ** LENGTH) * SCALE) < 2**64
> So, if I want to cover the complete range of characters (FF) the max.
>
> size must be 8 and the scale 1.
> 256**8*1 = 2**64
That's almost correct.
You can't really have 256 characters, because NUL terminates a string
in C (and thus not only in JtR, but also in many/most systems that the
passwords being cracked could be used on). So the maximum is 255
different ASCII codes, 1 through 0xFF inclusive.
Also, the actual requirement is slightly more relaxed than what the
comment says, so some higher values of SCALE will also work with 255
characters and length 8 - e.g., I've just tested that SCALE of 10 also
works, resulting in slightly greater precision and thus maybe more
optimal order in which candidate passwords are tried. You may give
this a try if you like, or you may strictly meet the requirement stated
in the comment, which means that SCALE must be 1 when SIZE is 255 and
LENGTH is 8.
Anyway, all of this complexity should be gone soon. Stay tuned.
Alexander
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