Fast and Secure CBC-Type MAC Algorithms

The CBC-MAC or cipher block chaining message authentication code, is a well-known method to generate message authentication codes. Unfortunately, it is not forgery-secure over an arbitrary domain. There are several secure variants of CBC-MAC, among which OMAC is a widely-used candidate. To authenticate an s-block message, OMAC costs (s+1) block cipher encryptions (one of these is a zero block encryption), and only one block cipher key is used. In this paper, we propose two secure and efficient variants of CBC-MAC: namely, GCBC1 and GCBC2. Our constructions cost only s block cipher encryptions to authenticate an s-block message, for all s ≥ 2. Moreover, GCBC2 needs only one block cipher encryption for almost all single block messages, and for all other single block messages, it costs two block cipher encryptions. We have also defined a class of generalized CBC-MAC constructions, and proved a sufficient condition for prf-security. In particular, we have provided an unified prf-security analysis of CBC-type constructions, e.g., XCBC, TMAC and our proposals GCBC1 and GCBC2.