International Association
for Cryptologic Research

The Q-problem has been introduced as a new post-quantum hard problem. We present two man-in-the-middle and three key recovery attacks against the key exchange protocol based on the Q-problem. The man-in-the-middle attacks take negligible time and allow the attacker to recover the exchanged key. The most effective key recovery attack has a computational complexity of $2^{40}$. We also propose countermeasures against all attacks.