In-reply-to: Richard Begg's message of 8 Mar 1996 03:17:31 GMT
Newsgroups: comp.security.unix
Subject: Re: parallel crack
Date: 11 Mar 1996 12:56:11 +0000
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In article <4ho8sb$dae@oznet07.ozemail.com.au> Richard Begg <rbegg@ozemail.com.au> writes:

 >The multi-host bit of crack did this backwards by splitting up the password
 >file between nodes, if you split the dictionary between nodes, it works much
 >better.

Yeah, but the original version was written in the days when crypt()
was still relatively expensive (as indeed it still is, but on a
smaller scale) and so it was imperative to (a) reduce to an absolute
minimum the number of calls to crypt(), and (b) not use many resources
by keeping 1000s of slightly-different dictionaries online.

Remember, this was in the days when 1Gb disks were considered *huge*,
and were shared between 200+ people.  8-)

Since the number of words is severalfold greater than the number of
users, and since the dictionaries were generated on the fly, the
obvious solution to this problem was to distribute the *users* around
the nodes.

Distributing *dictionaries* around the nodes would have required
greater resources, involving a central daemon creating dictionaries on
the fly and dumping them to the remote processes (yielding either time
synch problems or vast quantities of disk) and a broadcast/multicast
IPC mechanism between all the co-operating nodes, so that once one
process had cracked the password for user "fred", all the other
processes could be notified and wouldn't waste time trying to break
it, greatly impacting speed in those days.

This was important, because every additional user that you were
(wasting your time) trying to crack could add hours, days even, to the
total elapsed time.

I suppose that your dictionary-distributed mechanism addresses
addresses this little matter of communication, or does it suffer this
bug (ie: here's an opportunity for you to speed it up further).

You see, for the time it was written, the distribute-the-users
approach wasn't really backwards at all.  It was quite sane.  8-)

 >I had it running on a 64 node machine with 32MB per node, and it could
 >run the default crack rule set on the standard dictionary against a 700 entry
 >password file in about 15 minutes.  The limiting factor is memory, as long as
 >there is enough memory on each node to hold its bit of the dictionary (and the
 >password file), then it flies - if you exceed the node's memory, then it gets
 >very ugly.

Sums it up nicely.  

If you have the kit, go for it. If not, stick with the old way.  8-)

	- alec
-- 
#!/usr/local/bin/perl -- -pwcracker-in-3-lines-of-perl-plus-disclaimer
$u{$p[1]}=$p[0] while(@p=getpwent);while(<>){chop;foreach $c (keys %u)
{printf "u=%s p=%s\n",$u{$c},$_ if(crypt($_,$c) eq $c);}} # Use: pwc dict ...