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Date: Fri, 30 Jun 2006 01:21:01 +0400
From: Solar Designer <solar@...nwall.com>
To: john-users@...ts.openwall.com
Subject: Re:  Re: rules - Q vs M and their effects on speed?

On Thu, Jun 29, 2006 at 06:50:51PM +0000, Phantom wrote:
> So, regarding the first example,

It would help if you learn to quote relevant bits of context. ;-)

> it does make a difference in which order rules are entered in the
> conf/ini file

Yes - because you want rules that happen to produce a higher success
rate tried first - but this has nothing to do with the M and Q commands.

> when the rules have a possibility "creating" duplicate candidate words.

That is irrelevant to the ordering of rules - but it is a reason to use
the M and Q commands as appropriate.

> That way the Q can "cover" more than one rule/line?

All rule commands, including Q, are a part of the rule they're specified
in only.  However, when writing a rule, it is wise to take into
consideration other rules that you have in the same ruleset.

> I was under the impression that the Q and M switches were only applied to the
> rule/line in which they appeared...

That's correct.

> So how does one decide in which rules to include a Q in order to avoid 
> as many duplicates as possible

You have to think and be smart.  I'm afraid that I can't provide a better
answer.  Even if I would come up with step-by-step instructions, those
would resemble an implementation of AI on top of your brain. ;-)

> and how does Q's affect the spreed of which JTR generated the new
> candidate passwords?

They have a certain processing cost, like almost all other rule
commands do.  They also cause JtR to reject some candidate passwords
that it has already spent time on - but if those candidate passwords
would be duplicates, it is good to reject them before they're processed
further anyway.

You appear to think that the only reason to not use Qs is to avoid the
processing costs associated with them.  This is not the case.  The
primary reason why John does not imply a Q after each rule is that doing
so would reject candidate passwords that are _not_ duplicates of any
others.  Thus, Q should be used with care.

-- 
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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