Analysis of a key distribution scheme in secure multicasting

This article presents an analysis of the secure key broadcasting scheme proposed by Wu, Ruan, Lai and Tseng [11]. The study of the parameters of the system is based on a connection with a special type of symmetric equations over finite fields. We present two different attacks against the system, whose efficiency depends on the choice of the parameters. In particular, a time-memory tradeoff attack is described, effective when a parameter of the scheme is chosen without care. In such a situation, more than one third of the cases can be broken with a time and space complexity in the range of the square root of the complexity of the best attack suggested by Wu et al. against their system. This leads to a feasible attack in a realistic scenario.