john-users - Re: quite fast MD5 hashing implementation

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Date: Mon, 29 Sep 2008 17:28:03 +0200
From: "Slythers Bro" <slythers@...il.com>
To: john-users@...ts.openwall.com
Subject: Re: quite fast MD5 hashing implementation

>why can we only revserse only the round 4?

because md5 is designed for be a secure hash algorithm ( they tried)
it's all based on chaos theory
http://en.wikipedia.org/wiki/Chaos_theory

there are (cyclical) functions who create chaos, too many possibilities if
we want to reverse more
example
when on 32 bit cpu a + b = c, if you know only c = 0x01
there are  0x7fffffff possibilities for a and b (0x00
+0x01,0x02+0xffffffff,0x03+0xfffffffe,etc ...) and will be more long to
compute than a traditional brute force. and here i don't speak about the
memory needed for that.