bugtraq - Re: MD5 To Be Considered Harmful Someday

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Date: Wed, 8 Dec 2004 22:05:50 +0100 (MET)
From: Paul Wouters <paul@...net.nl>
To: Dan Kaminsky <dan@...para.com>
Cc: Gandalf The White <gandalf@...ital.net>, davids@...master.com,
	BugTraq <bugtraq@...urityfocus.com>
Subject: Re: MD5 To Be Considered Harmful Someday

On Wed, 8 Dec 2004, Dan Kaminsky wrote:

>> Can't we just truncate the password to 8 characters like in the old days
>> before doing the MD5 hash? It will greatly reduce the chance of a 
>> collision.
>> In fact, I am not even sure my systems don't do this already.
>> 
> Actually, this greatly increases the chance of a collision.  123456789 will 
> collide with 123456780.

I was talking about limiting the input, not the output. I assumed it would
be more difficult to find a collision when there are less degrees of freedom
in the input.

What I realised after my mail though, is that it is probably pretty easy to
prebuild a dictionary of all 8 character combinations and their MD5 sums.

Paul