Re: Hash question

From: Tom St Denis <tom@xxxxxxx>
Date: Tue, 20 Jul 2010 07:52:11 -0700 (PDT)

On Jul 20, 10:08 am, Peter Fairbrother <zenadsl6...@xxxxxxxxx> wrote:

The problem:

I have two unknown strings which differ by a known amount, and two
hashes. To make it easier, suppose the strings and the hashes are the
same length, 256 bits, and the strings differ in 32 bits.

The first hash is a hash of the first string, I want to know whether the
second hash is a hash of the second string, with good probability. How
hard is it?

Now resistance against that is not quite in the usual properties of a
hash - preimage resistance and so on - but I'm not very up on hashes, so
maybe someone has done some work on that problem. If so, can someone
give me a pointer to it please?

If not, any thoughts?

You're literally asking for a differential attack on the hash.
Cryptographic hashes are designed to not emit useful differentials.

Tom
.

References:
- Hash question
  - From: Peter Fairbrother

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