On Wednesday 10 September 2003 05:26 pm, [EMAIL PROTECTED] wrote:
> On Wed, 10 Sep 2003 13:53:49 -0700
> =?iso-8859-1?Q?J=E9r=F4me_ou_Sally_Bonnet?=
>
> <[EMAIL PROTECTED]> wrote:
> >Is it possible to design a program that creates a file that matches
> >a specific CHK, so that it would be possible to prevent users from
> >accessing a specific file by injecting the colliding file in the
> >network before the target file becomes too popular?
>
> Yes, it is possible. But it is computationally very hard. For any given
> CHK there are an infinite number of files that yield that CHK after
> insertion. The problem is finding one of them.
To quibble, for files of a size of N bits, the number of files matching a
given SHA1 hash is going to be around (2^N)/(2^160). A pretty large number,
but a very tiny fraction of N.
All right, I just had to show off my m47h skillz...
--
"I love deadlines. I love the whooshing sound they make as they go by."
- Douglas Adams
Nick Tarleton - [EMAIL PROTECTED] - PGP key available
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