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Date: Thu, 9 Mar 2006 13:42:29 +0100 (CET)
From: rembrandt@...erlin.de
To: john-users@...ts.openwall.com
Subject: Re: checking only first 5 characters of a md5 hash


> Maybe I didn't explained in a good way (sorry for my english) :
> the first 5 chars are not of the password, but they are the first 5 of the
> md5 HASH.

Yes but that wont change anything I guess.
but solar is able to answer this more precise I guess.

> with "abc123" ? Is this way faster then crack the entire HASH right?
> (abc123

Yes it is but...

> can correspond to first part of many different hashes -> many possible
> passwords -> the first I find is good) .

You mean collision
One hash -> many plaintext results

> Is correct the idea? Becouse I don't know how the md5 algorithm works
> exactly....

As far as I know MD5 used by login uses Salts too to prevent such htings.
But the problem si the same: if you know the first letters of the hash or
the password:

You would need to know the entry MD5-Table because john can`t (as far as I
know) reduce the keyspace (and this is a reducing) by known
plaintext/cyphertext.

For that you may need a precalculated MD5-Table to take a look where the
keyspace ends or begins. Maybe this can be done also without such a Table
but john would have to pre-calculate the limited keyspace first to know
how many Passwords should be tried. THis would be possible if the
algorithm would be used vice versa.

I`m not that expert so I hope solar will answer too.

Kind regards,
Rembrandt

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