Tags: crypto re 

Rating:

Decompile with uncompyle6, treat everything as polynomial points, bruteforce last character and check the last point on the polynomial each time.
Read more here: https://thegoonies.github.io/2021/01/31/justctf-2020-thats-not-crypto

Original writeup (https://thegoonies.github.io/2021/01/31/justctf-2020-thats-not-crypto).