How thorough are the hash breaks, anyway?

[Nicholas Bohm]

At 16:09 26/08/2004, Trei, Peter wrote:
>[snip]
>Looking over the recent work on hash collisions, one
>thing that struck me was that they all seem to be 
>attacks on known plaintext - the 'plaintexts' which
>collided were very close to each other,  varying in 
>only a few bits. 
>
>While any weakness is a concern, and I'm not
>going to use any of the compromised algorithms
>in new systems, this type of break seems to be
>of limited utility. 
>
>It allows you (if you're fortunate) to modify a signed
>message and have the signature still check out. 
>However, if you don't know the original plaintext
>it does not seem to allow you construct a second
>message with the same hash.
[snip]

 From a lawyer's perspective, it seems worrying that a message into which the word "not" has been inserted might still have the same hash as the original (assuming the hash to be a component of an electronic signature)

Regards

Nicholas Bohm

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