The notion of "document security" is a common desire in business and legal contexts. PDFs are a standard representation of documents, whereas JPGs are less common (TIFF might count since it's a somewhat common scanned document format, but I digress).
Subverting the most popular document format, one which even provides built-in support for digital signatures is probably much more interesting than subverting the JPG format.
Open challenge: build two signed PDFs with identical signatures and different contents - it's not necessarily hard, and it would definitely drive the point home.
I wonder if this is the 'standard' thing to do when you have a broken hash function. I took a introductory course in computer security a year ago and we had to create MD5 hash-colliding documents for homework[0].
I'm interested in taking a look at this assignment for my own learning, but it looks like there are a bunch of files you need. It would be cool if you put them in a git repo!
Subverting the most popular document format, one which even provides built-in support for digital signatures is probably much more interesting than subverting the JPG format.
Open challenge: build two signed PDFs with identical signatures and different contents - it's not necessarily hard, and it would definitely drive the point home.