Google CTF 2018: DM Collision (176 pts, 63 solves)

Server: dm-col.ctfcompetition.com:31337
Challenge files:
- challenge.py
- not-des.py

Writeup

TL;DR: do horrible things to a one-way compression function by leveraging weak keys in the DES block cipher.

Read my writeup here.

Files

challenge.py - the service
not-des.py - python implementation of DES, with permuted S-boxes
des.c - C implementation of DES, with permuted S-boxes, that searches for a fixed point
verify_fixed_point.py - verifies found fixed point
submit.py - pwntools script to submit exploit