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Date: Sun, 13 Nov 2005 18:32:43 +0300
From: Solar Designer <solar@...nwall.com>
To: john-users@...ts.openwall.com
Subject: Re: output tested hashes

On Sun, Nov 13, 2005 at 09:47:14AM +0100, thomas springer wrote:
> jup, precomputation, rainbowtables for the poor, if you like.
> i'd like to have a few million "standard"-hashes with fixed salts, eg.
> lm-hashes ready for lookup.
[...]
> i'm short on processor-time...

It takes around 1 second to compute a few million LM hashes.  It would
take about the same amount of time to read them off a hard drive.  OK,
if your CPU is slow and your disks are fast, maybe you can get a 10x
speedup, -- especially if you would be storing partial hashes only (like
QCrack did).  But why bother given that it's only a few seconds anyway?
Even if you fill an entire hard drive with LM hashes and you're smart to
only store partial hashes, you would save a few hours of CPU time at
best.  You can't save days of CPU time per hard drive in this way (on a
reasonable system).

You really should be using rainbow tables or not do any precomputation
at all, -- unless your target hash type would be both slow and saltless
(or allow for only a small number of different salts).

-- 
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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