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Re: MD5 To Be Considered Harmful Someday
From: Gandalf The White <gandalf () digital net>
Date: Tue, 07 Dec 2004 16:54:34 -0600

Greetings and Salutations:

On 12/6/04 5:29 PM, "Dan Kaminsky" <dan () doxpara com> wrote:
Some highlights from the paper:
* The attack itself is pretty limited -- essentially, we can create
"doppelganger" blocks (my term) anywhere inside a file that may be
swapped out, one for another, without altering the final MD5 hash.  This
lets us create any number of binary-inequal files with the same md5sum.

From my reading it appears that you need the original source to create the
doppelganger blocks.  It also appears that given a MD5 hash you could not
create a input that would give that MD5 back.  Passwords encoded with MD5
would not fall prey to your discovery.  Is this correct?

Unfortunately when "The Press" publicized the MD5 hash discovery by Joux and
Wang it almost sounded like "The Press" was surprised to find collisions in
the MD5 domain (intuitive to me, a limited number of outputs and a infinite
number of inputs = Collisions).  I assume that a "good" hash would have a
even distribution of collisions across the domain and that the larger number
of bits for the output the better the hash (assuming no cryptographic
algorithm errors).


Do not meddle in the affairs of wizards for they are subtle and
quick to anger.
Ken Hollis - Gandalf The White - gandalf () digital net - O- TINLC
WWW Page - http://digital.net/~gandalf/
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