Posted on by and filed under CSAW Quals 2016.

We start out with just a link and a bit of text, the link points to http://crypto.chal.csaw.io:8001 – though this probably won’t live forever. Once you go to the page, you would probably notice a few things
  • Looks like it’s from the early xp era
  • Seems to be centered around some movie that it’s named after
  • There’s an input box with base64 in it
  • Only one of the buttons works
So turns out when you click on the “Take the Red Pill” box the text is sent I don’t really know which movie it is, but after seeing Oracle in the title, it was pretty obvious it was an Oracle attack. Gladly jlundstrom – who had perl working – got PadBuster, which can help with automating padding oracle attacks. Opening burpsuite we can see the exact post request that is being sent as follows(with an example input) So if you run You’ll eventually get the 16 bytes back! The result comes out to be: Co dalo nam flage w odszyfrowanych blokach: flag{what_if_i_told_you_you_solved_the_challenge} Again thanks to jlundstrom for his invaluable help on this chall!