Key Recovery Attacks on the RMAC, TMAC, and IACBC

摘要

The RMAC 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 is the improved MAC scheme of XCBC 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 2~n computations, which is more realistic than the attacks in. 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, which gives confidentiality and message integrity.