An Improvement of Chen Et al.´s Scheme for Mobile Pay-TV

Recently, Chen et al. proposed an anonymous authentication scheme for mobile pay-TV, they claim that their scheme can defend against reply attacks, off-line password guessing attacks, impersonation attack, forgery attack, man-in-the-middle attack, and insider attack. In this paper, we show that Chen et al.´s scheme is still vulnerable to off-line password guessing attacks and fails provide mutual authentication. Notably, problems remain in situations which the user lost a mobile device. To remedy these flaws, we propose an improved scheme on Chen et al.´s anonymous authentication scheme.