Cryptology ePrint Archive: Report 2015/089

On the security margin of MAC striping

Thomas Eisenbarth and Aaron Meyerowitz and Rainer Steinwandt

Abstract: MAC striping has been suggested as a technique to authenticate encrypted payloads using short tags. For an idealized MAC scheme, the probability of a selective forgery has been estimated as $\binom{\ell+m}{m}^{-1}\cdot 2^{-m}$, when utilizing MAC striping with $\ell$-bit payloads and $m$-bit tags. We show that this estimate is too optimistic. For $m\le\ell$ and any payload, we achieve a selective forgery with probability $\ge \binom{\ell+m}{m}^{-1}$, and usually many orders of magnitude more than that.

Category / Keywords: secret-key cryptography / cryptanalysis; MAC; MAC striping; selective forgery

Date: received 5 Feb 2015

Contact author: teisenbarth at wpi edu, meyerowi@fau edu, rsteinwa@fau edu

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Version: 20150216:045423 (All versions of this report)

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