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A tight bound for exhaustive key search attacks against MessageAuthentication Codes

Published online by Cambridge University Press:  06 November 2012

Vinícius G.P. de SÁ
Affiliation:
Depto. de Ciência da Computação, Univ. Federal do Rio de Janeiro, Brazil. vigusmao@dcc.ufrj.br
Davidson R. Boccardo
Affiliation:
Inmetro, National Institute of Metrology, Quality and Technology, Brazil; drboccardo@inmetro.gov.br; lfrust@inmetro.gov.br; rcmachado@inmetro.gov.br
Luiz Fernando Rust
Affiliation:
Inmetro, National Institute of Metrology, Quality and Technology, Brazil; drboccardo@inmetro.gov.br; lfrust@inmetro.gov.br; rcmachado@inmetro.gov.br
Raphael C.S. Machado
Affiliation:
Depto. de Ciência da Computação, Univ. Federal do Rio de Janeiro, Brazil. vigusmao@dcc.ufrj.brInmetro, National Institute of Metrology, Quality and Technology, Brazil; drboccardo@inmetro.gov.br; lfrust@inmetro.gov.br; rcmachado@inmetro.gov.br

Abstract

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A Message Authentication Code (MAC) is a function that takes a message and a key asparameters and outputs an authentication of the message. MAC are used to guarantee thelegitimacy of messages exchanged through a network, since generating a correctauthentication requires the knowledge of the key defined secretly by trusted parties.However, an attacker with access to a sufficiently large number of message/authenticationpairs may use a brute force algorithm to infer the secret key: from a set containinginitially all possible key candidates, subsequently remove those that yield an incorrectauthentication, proceeding this way for each intercepted message/authentication pair untila single key remains. In this paper, we determine an exact formula for the expected numberof message/authentication pairs that must be used before such form of attack issuccessful, along with an asymptotical bound that is both simple and tight. We conclude byillustrating a modern application where this bound comes in handy, namely the estimationof security levels in reflection-based verification of software integrity.

Information

Type
Research Article
Copyright
© EDP Sciences 2012