Stronger security bounds for OMAC, TMAC, and XCBC

Abstract

OMAC, TMAC and XCBC are CBC-type MAC schemes which are provably secure for arbitrary message length. In this paper, we present a more tight upper bound on Advmac for each scheme, where Advmac denotes the maximum success (forgery) probability of adversaries. Our bounds are expressed in terms of the total length of all queries of an adversary to the MAC generation oracle while the previous bounds are expressed in terms of the maximum length of each query. In particular, a significant improvement occurs if the lengths of queries are heavily unbalanced. © Springer-Verlag Berlin Heidelberg 2003.