International Association
for Cryptologic Research

In 2017, Ward Beullens et al. submitted Lifted Unbalanced Oil and Vinegar (LUOV), a signature scheme based on the famous multivariate public-key cryptosystem (MPKC) called Unbalanced Oil and Vinegar (UOV), to NIST for the competition for post-quantum public-key scheme standardization. The defining feature of LUOV is that, though the public key P works in the extension field of degree r of F2, the coefficients of P come from F2. This is done to significantly reduce the size of P. The LUOV scheme is now in the second round of the NIST PQC standardization process. In this paper, we introduce a new attack on LUOV. It exploits the "lifted" structure of LUOV to reduce direct attacks on it to those over a subfield. We show that this reduces the complexity below the targeted security for the NIST postquantum standardization competition.