Key recovery attacks on the RMAC, TMAC, and IACBC

Abstract

The RMAC[6] is a variant of CBC-MAC, which resists birthday attacks and gives provably full security. The RMAC uses 2k-bit keys and the size of the RMAC is 2n, where n is the size of underlying block cipher. The TMAC[10] is the improved MAC scheme of XCBC[4] such that it requires (k +n)-bit keys while the XCBC requires (k +2n)-bit keys. In this paper, we introduce trivial key recovery attack on the RMAC with about 2n computations, which is more realistic than the attacks in [9]. Also we give a new attack on the TMAC using about 2 n/2+1 texts, which can recover an (k + n)-bit key. However this attack can not be applied to the XCBC. Furthermore we analyzed the IACBC mode[8], which gives confidentiality and message integrity. © 2003 Springer-Verlag Berlin Heidelberg.