Message authentication codes from unpredictable block ciphers

Yevgeniy Dodis, John Steinberger

Research output: Chapter in Book/Report/Conference proceedingConference contribution


We design an efficient mode of operation on block ciphers, SS-NMAC. Our mode has the following properties, when instantiated with a block cipher f to yield a variable-length, keyed hash function H: (1) MAC Preservation. H is a secure message authentication code (MAC) with birthday security, as long as f is unpredictable. (2) PRF Preservation. H is a secure pseudorandom function (PRF) with birthday security, as long as f is pseudorandom. (3) Security against Side-Channels. As long as the block cipher f does not leak side-channel information about its internals to the attacker, properties (1) and (2) hold even if the remaining implementation of H is completely leaky. In particular, if the attacker can learn the transcript of all block cipher calls and other auxiliary information needed to implement our mode of operation. Our mode is the first to satisfy the MAC preservation property (1) with birthday security, solving the main open problem of Dodis et al. [7] from Eurocrypt 2008. Combined with the PRF preservation (2), our mode provides a hedge against the case when the block cipher f is more secure as a MAC than as a PRF: if it is false, as we hope, we get a secure variable-length PRF; however, even if true, we still "salvage" a secure MAC, which might be enough for a given application. We also remark that no prior mode of operation offered birthday security against side channel attacks, even if the block cipher was assumed pseudorandom. Although very efficient, our mode is three times slower than many of the prior modes, such as CBC, which do not enjoy properties (1) and (3). Thus, our work motivates further research to understand the gap between unpredictability and pseudorandomness of the existing block ciphers, such as AES.

Original languageEnglish (US)
Title of host publicationAdvances in Cryptology - CRYPTO 2009 - 29th Annual International Cryptology Conference, Proceedings
Number of pages19
StatePublished - 2009
Event29th Annual International Cryptology Conference, CRYPTO 2009 - Santa Barbara, CA, United States
Duration: Aug 16 2009Aug 20 2009

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Volume5677 LNCS
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349


Other29th Annual International Cryptology Conference, CRYPTO 2009
Country/TerritoryUnited States
CitySanta Barbara, CA

ASJC Scopus subject areas

  • Theoretical Computer Science
  • General Computer Science


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