Re: [PATCH] Delete cryptoloop

Marc Ballarin
2004-07-27T10:09:58Z

On Tue, 27 Jul 2004 01:40:47 -0700
Junio C Hamano <junkio@cox.net> wrote:

>
> Jari's exploit uses the property that his watermarks are
> encrypted to identical ciphertext blocks, but does it mean that
> the technique can be used to prove that identical ciphertext are
> from the watermarks and not coming from mere coincidence?
>

You can't prove anything by a single found watermark, but you can encode
additional information by placing the watermarks at chosen offsets in your
file.

For example, take prime numbers starting at 2 as offsets, and place the
encodings in a chosen order at those offsets.

The chances for a random occurence of this pattern are marginal, and -
unless the watermarked file becomes strongly fragmented - this pattern is
easy to retrieve.

While this might not be evidence in the legal sense (it could well be, but
IANAL), it is at the very least a strong indication.

Regards