4 ms·
You can reuse the PDF from Google because it's not particularly reliant on the contents of the images. You can replace the images that Google used with your ow
by dsp1234 10y ago
You can reuse the PDF from Google because it's not particularly reliant on the contents of the images. You can replace the images that Google used with your own (indeed that's what the service does) and it will output two files that themselves have the same hash (but that hash will be different than the original provided PDFs)
- simcop2387 10y agoInteresting. I need to read more into this because I didn't think that kind of thing was possible. I thought you'd have to recalculate it from scratch because of the two images being different but apparently I didn't understand how this worked.
- dsp1234 10y ago(very)psuedocode: goto showImage1; showImage1: renderImage1(); exit showImage2: renderImage2(); exit If an attacker can hash a block that means "goto showImage1" and "goto showImage2" with the same hash, then you can see that the contents of those images doesn't matter, as long as the data for those images occurs after the logic for choosing them. (and no that's not what this attack does in reality, but just a logical framework for understanding why the images don't matter)
- modeless 10y agoBoth images are in both files. The only difference is the part of the file (where Google put the collision) which switches the image shown.