[UTCTF 2022] Sunset

[UTCTF 2021] Sunset

tl;dr

Break a scheme for generating a shared secret with a cryptosystem relating to some sort of discrete fourier transform (DFT). The solution described here involves NOT reversing the values of the keys as probably intended (which can be done by some linear algebra), but instead exploits the some of group properties of a cyclic array under convolution modulo a prime.

Description

cryptography/Sunset; 15 solves, 996 points

Challenge author: oops

subset sumset what did i do Wrap the value of key with utflag{} for the flag.

Files: main.py and output.txt

The writeup

See writeup I wrote at https://ubcctf.github.io/2022/03/utctf-sunset/.