Forgery and Key Recovery Attacks on PMAC and Mitchell’s TMAC Variant

In this paper we discuss the security of PMAC, a provably secue and parallelizable MAC scheme proposed by Black and Rogaway, and Michell's TMAC variant, proposed to improve the security of TMAC. We show how to devise forgery attacks on PMAC and compare the success rate of our forgery attacks with their security bound. We also present forgery attacks on TMAC variant and show the security of TMAC variant is not improved in the sense of the forgery attack. Furthermore, key recovery attacks on PMAC and TMAC variant are presented in various parameters. Our results imply they have no significant advantage in comparison with other well-established MAC schemes.