7 , 2017-12-28 , Department of Mathematical Sciences, Faculty of Science, University of the Ryukyus , 琉球大学理学部数理科学教室
The unbalanced oil and vinegar signature scheme (UOV) is a signature scheme whose public key is a set of multivariate quadratic forms over a finitefield. This -signature scheme has been considered to be secure and efficient enough under suitable parameter selections. However, the key size of UOV isrelatively large and then reducing the key size of UOV is an important issue. Recently in Inscrypt 2015, a new variant of UOV called Cubic UOV was proposed,and in ICISC 2016, two variants of Cubic UOV called CSSv and SVSv were proposed. It has been claimed that these variants were more efficient thanthe original UOV and were secure enough. However, the security analyses of these schemes were not enough and they can be broken easily. In the presentpaper, we describe the weaknesses of these schemes.