Re: Report of collision-generation with MD5

From: Fernando Gleiser (fgleiser_at_cactus.fi.uba.ar)
Date: 08/19/04

  • Next message: Borja Marcos: "Re: Report of collision-generation with MD5" 
    Date: Wed, 18 Aug 2004 21:23:07 -0300 (ART)
To: Chris Doherty <chris-freebsd@randomcamel.net>

    On Wed, 18 Aug 2004, Chris Doherty wrote:

    >
    > well, technically you're not "reversing the hash": you can't re-create a
    > message from its hash, because the information is simply gone--digesting
    > algorithms are massively lossy by definition. that is, you can't take a
    > 128-bit MD5 hash and recover the original 2-megabyte message, which makes
    > sense.
    >
    > what you can do, if you have a proper attack formula, is find *a* message
    > that produces *that one hash*. that is, if I have message M which produces
    > hash H, I can use the attack to find *a* message M' which will also
    > produce hash H.

    There are (potentially) infinite inputs and just 2^128 outputs, so you
    can always (given enough time and/or horsepower) greate a colision.

    The problem is you need to create a message M' such that it is similar
    enough to the original one so the recipient gets fooled he got
    the original one. I think the odds of backdooring a source code file
    and modifying it so it hashes to the same value are very small.

                            Fer
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  • Next message: Borja Marcos: "Re: Report of collision-generation with MD5"

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