Tags: factoring rsa

Rating: 5.0

This was a beginner RSA challenge. Unfortunately someone uploaded the primes onto factordb some time during the competition which ruined it for people and boosted the number of solves. We decided to leave the challenge as is.

tldr;
- we are given s = pow(557p-127q, n-p-q, n)
- notice that 557p - 127q = s^(-1) (mod n)
- construct a qudratic with known coefficients to recover the primes

Original writeup (https://www.josephsurin.me/posts/2020-09-20-downunderctf-2020-writeups#rot-i).