Re: Report of collision-generation with MD5

From: Chris Doherty (chris-freebsd_at_randomcamel.net)
Date: 08/18/04

  • Next message: Brett Glass: "Re: Report of collision-generation with MD5" 
    Date: Wed, 18 Aug 2004 13:54:41 -0700
To: freebsd-security@freebsd.org

    On Wed, Aug 18, 2004 at 02:29:57PM -0400, Peter C. Lai said:
    > On Wed, Aug 18, 2004 at 09:08:12PM +0300, Claudiu wrote:
    > > hello,
    > >
    > > please explain what do you mean by "reverse the hash". Is this the
    > > recreation of the originial message from its hash ?
    >
    > The short answer is yes. The slightly longer answer is that such is only one
    > specific case. The general case is that the digest should not reveal any
    > information about the original message.

    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.

    I suppose the possibility exists that M' will equal the original M, but
    I'd speculate that the odds are remarkably small.

    chris

    -------------------------------
    Chris Doherty
    chris [at] randomcamel.net

    "I think," said Christopher Robin, "that we ought to eat
    all our provisions now, so we won't have so much to carry."
                   -- A. A. Milne
    -------------------------------
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  • Next message: Brett Glass: "Re: Report of collision-generation with MD5"

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