cipherplane

John Hammond | February 4th, 2018

---

This is a project based off of my reaction to the "DES" challenge during SharifCTF 2018.

The DES challenge offered about a thousand known plaintext/ciphertext pairs, and asked you to determine the key to submit as the flag. The real difficulty in this challenge was just sorting through the pairs to find duplicates or similarities in the pairs. Had we found one single similarity in a plaintext or ciphertext, we would have been able to find a lead on the challenge and probably solve it.

But, we didn't have anything that would smartly detect duplicates or similarities in the data. I tossed the challenge aside and never completed it during the competition, but after reading the writeups I realized we seriously needed that capability.

So this is just some Python code to do that. It doesn't have support for command-line arguments or anything fancy... I expect dirty usage, just slapping in your own data for the script. It will still get you the information you need.

The project is nicknamed cipherplane, as a gag off of "ciphertext" and "plaintext."