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Date: Tue, 27 Mar 2012 21:09:15 +0530
From: SAYANTAN DATTA <std2048@...il.com>
To: john-dev@...ts.openwall.com
Subject: Re: JtR: GPU for slow hashes
On Tue, Mar 27, 2012 at 8:08 PM, Solar Designer <solar@...nwall.com> wrote:
> On Tue, Mar 27, 2012 at 05:21:44PM +0530, SAYANTAN DATTA wrote:
> > I have a basic question regarding MSCash2.
>
> BTW, you probably already found these, but in case not:
>
> http://openwall.info/wiki/john/MSCash2_simple_code
> http://openwall.info/wiki/john/MSCash2
>
> These are a couple of implementations/descriptions of MSCash2 written by
> contributors to JtR. These may be easier to understand than code
> currently in JtR is.
>
> > In above algorithm two inputs namely ussrname and password are used to
> > produce a certain hash.Then the generated hash is compared with the
> stored
> > value and if they are equal then the username and password entered are
> > correct.Now we hit and try different values of password to produce a hash
> > which matches the given value .So does this mean the username is some
> fixed
> > string??
>
> For one hash being cracked, yes.
>
> > i.e is the username known to us beforehand and we only have to
> > guess the password?
>
> Yes.
>
> > Right now my code assumes the username a fixed string.Is it all right??
>
> Maybe not, depending on what you mean by assuming a fixed string -
> compile time constant vs. runtime value fixed only for a given hash
> currently being processed (out of many loaded for cracking).
>
> JtR supports cracking of many hashes at once, which may correspond to
> different usernames. In MSCash2, the usernames are effectively used as
> salts - so JtR formats' interfaces for salts are used to support them.
> You also need to support running with an arbitrary set of salts
> (usernames) and hashes loaded for cracking at once (e.g., there might be
> 10000 hashes with 9900 different salts).
>
> Also note that you only need to implement the PBKDF2 step on GPU - the
> rest may stay on CPU. Lukas did the same in his CUDA code (based on my
> suggestion). This may simplify the task, and it will let us easily
> reuse the PBKDF2 with SHA-1 implementation for things such as WPA.
>
> Alexander
>
>
>
hi,
Yeah I mean runtime value fixed only for a given hash being processed.
And thank you for the suggestion.
-Sayantan
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