picoCTF 2018 - Dog or Frog

Posted on October 14, 2018* in ctf-writeups

Problem

Dressing up dogs are kinda the new thing, see if you can get this lovely girl ready for her costume party. Dog Or Frog

Solution

When we visit the page, we are greeted with a submission form. The instructions tell us that this is a machine learning problem and to not approach it as a web-exploitation problem. The goal is to submit an image that is similar (on a byte-by-byte basis) that is similar to the dog, but is recognized as a tree frog.

This type of problem is known as adversarial machine learning. After stumbling around some papers, I found this one, which provided a library suitable for adversarial learning: Cleverhans.

Full Script

Jupyter Binder

Final Image

The final image (left) looks visually similar to the original (right), but has added noise. When submitted to the challenge site, we receive the flag: picoCTF{n0w_th4t3_4_g00d_girl_647b3719}.