Re: MD5 & bot Question

On Tue, 2007-04-10 at 13:13 -0400, Robert Cummings wrote: > On Tue, 2007-04-10 at 08:47 -0400, tedd wrote: > > > > 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. > > Yes but you completely missed the point of my metaphor :) The point is, > I can take an md5 signature of subset of the image's pixels and still > identify it if the subset is representative (this is the point about > still ID'ing someone with their finger print despite the rest of them > being tarred and feathered :) This is how many virus detection systems > work. They find a single portion of virus' binary program that is > representative and can use it as a search within other binaries to > detect the presence of the virus. So if you only change a few pixels, > there is a high likelyhood of a subset set md5 signature still being > recognized. > > > > > 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? > > These would alter every pixel, without generally affecting a human's > perception of the object... this is the point since now subset of the That should have read: "... since no subset of..." > images pixels would be representative. > > > 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. > > Explanation above :) > > Cheers, > Rob. -- .------------------------------------------------------------. | InterJinn Application Framework - http://www.interjinn.com | :------------------------------------------------------------: | An application and templating framework for PHP. Boasting | | a powerful, scalable system for accessing system services | | such as forms, properties, sessions, and caches. InterJinn | | also provides an extremely flexible architecture for | | creating re-usable components quickly and easily. | `------------------------------------------------------------'