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Message-ID: <8332b06221cb51a311e3902fb1ecf13d@smtp.hushmail.com>
Date: Thu, 4 May 2017 23:56:38 +0200
From: magnum <john.magnum@...hmail.com>
To: john-users@...ts.openwall.com
Subject: Re: Max characters for password candidates (NTLM) and
others
On 2017-05-04 23:44, Frank Dittrich wrote:
> Am 04.05.2017 um 23:27 schrieb magnum:
>> The NT formats have a max length of 27 *characters* (for performance
>> reasons).
>
> The 27 character limit isn't really a hash format limitation, but a
> limitation of John's NT format implementation, ist that correct?
Correct. Off the top of my head, the actual maximum in Windows is 255
characters.
> So, it would be possible to drop that limit (or change the limit from
> currently 27 characters to, say, 54 characters).
Sure. We could support any length but it'd be slower. Actually, for a
non-SIMD build (eg. non-Intel using OpenSSL) I think our limit is 125
bytes (which is the hard deck no-matter-what, set by legacy core code)
and that'd be just 41 characters worst case (that is, every one of them
take three bytes to represent in UTF-8).
> But trying password candidates that are longer than 27 characters would
> reduce the cracking speed to about half the speed of the current
> implementation.
Actually we could implement some kind of branching and support
27/54/81/108/125 bytes, no problem. And we could re-write John's core
and support more than 125 bytes. But with fast hashes like NT the
branching would be a significant regression. It would hurt real-world
cracking: No-one has a password of 27 characters, let alone longer.
> Does hashcat also have a 27 character limit for NT format?
Sure. In our world of Merkel-Damgård geeks, it's a perfectly even
number. In non-unicode formats like raw-md4/md5, it's 55. Actually in NT
it's 27.5 but that obviously doesn't make sense.
magnum
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