At 8:10 PM -0400 4/9/07, Robert Cummings wrote:
On Mon, 2007-04-09 at 17:14 -0400, tedd wrote:
At 4:39 PM -0400 4/9/07, Robert Cummings wrote:
>On Mon, 2007-04-09 at 22:27 +0200, Tijnema ! wrote:
>
> > This is exactly what tedd did in his last arrow example. He edited the
>> header of the GIF image, and so that would result in different MD5.
>>
>> Finding this part and skipping it in the MD5 check would do the job. :)
>
>Yep, that's an obvious solution since it's the same way virus signatures
> >are matched. The entire image needs some kind of permutation. Passing a
> >couple of curved ripples across the image as a transformation, and in
>different directions should suffice to obfuscate the image signature
> >without obfuscating the image itself :) Similarly watermarking the image
> >using fractal patterns should also provide good noise.
>
>Cheers,
>Rob.
Rob:
It doesn't need to be complicated, just random placed pixels on the
image from a selection of colors would provide millions of
permutations.
No, you're wrong. Read the part about I mentioned about virus
signatures. A small portion of the whole can be used as an identifier
where that portion is unique to the overall entity. For instance, I can
throw a tub of tar over you, then a tub of feathers ;) ;) and if one of
your fingers doesn't get covered, I can still identify your chicken
ass ;)
Cheers,
Rob.
Rob:
Your use of metaphor is quite colorful, but if you if change a single
pixel in an image, then you change the MD5 signature -- that is what
I was talking about -- and that is not wrong.
Plus, if you:
[A] Passing a couple of curved ripples across the image as a
transformation, and in different directions should suffice to
obfuscate the image signature without obfuscating the image itself
or
[B] Similarly watermarking the image using fractal patterns should
also provide good noise.
You would still leave at least one pixel the same as it was before so
your chicken ass would still be exposed, right? Or does your
ripple/watermark application alter every pixel by changing its alpha
channel or something?
And if so, then why is it that you are required to change every
pixel? I am sure that there are images that have at least one pixel
in common, so I don't see the point you're trying to make -- please
explain.
Cheers,
tedd
--
-------
http://sperling.com http://ancientstones.com http://earthstones.com
--
PHP General Mailing List (http://www.php.net/)
To unsubscribe, visit: http://www.php.net/unsub.php
