Abstract
Between 2000 and 2005 Kasahara and Sakai proposed the multivariate public key cryptosystems RSE(2)PKC and RSSE(2)PKC whose central maps have a step-wise structure. In 2004, Wolf, Braeken, and Preneel proposed an attack, called the rank attack, against these cryptosystems, which is based just on the step-wise structure. In this paper, we perform an exact analysis of the rank attack for evaluating its validity. We reveal that some property on the calculation of the rank, which is assumed implicitly in the rank attack, does not necessarily hold. Thus we show that the rank attack is not a generic attack against these cryptosystems.
