Cryptology ePrint Archive: Report 2003/082

Stronger Security Bounds for OMAC, TMAC and XCBC

Tetsu Iwata and Kaoru Kurosawa

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 ${\tt Adv}^{\sf mac}$ for each scheme, where ${\tt Adv}^{\sf mac}$ denotes the maximum success (forgery) probability of adversaries. Our bounds are expressed in terms of the \textit{total length} of all queries of an adversary to the MAC generation oracle while the previous bounds are expressed in terms of the \textit{maximum length} of each query. In particular, a significant improvement occurs if the lengths of queries are heavily unbalanced.

Category / Keywords: secret-key cryptography / modes of operation, message authentication codes, block cipher, provable security.

Date: received 30 Apr 2003

Contact author: iwata at cis ibaraki ac jp

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Version: 20030430:134431 (All versions of this report)

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