Tags: factoring rsa 

Rating: 5.0

tl;dr:

1. public keys share a prime
2. factor both keys
3. generate private key
4. decrypt ciphertext with first key

Full writeup here: https://github.com/p4-team/ctf/tree/master/2017-12-09-seccon-quals/crypto_ps_and_qs

Original writeup (https://github.com/p4-team/ctf/tree/master/2017-12-09-seccon-quals/crypto_ps_and_qs).