The multivariate public key cryptosystem (MPKC), which is based on the problem of solving a set of multivariate systems of quadratic equations over a finite field, is expected to be secure against quantum attacks. Although there are several existing schemes in MPKC that survived known attacks and are much faster than RSA and ECC, there have been few discussions on security against physical attacks, aside from the work of Okeya
(2005) on side-channel attacks against Sflash. In this study, we describe general fault attacks on MPKCs including Big Field type (
Matsumoto-Imai, HFE and Sflash) and Stepwise Triangular System (STS) type (
UOV, Rainbow and TTM/TTS). For both types, recovering (parts of) the secret keys
with our fault attacks becomes more efficient than doing without them. Especially, on the Big Field type, only
fault is sufficient to recover the secret keys.