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On the Attacker's Knowledge in Shared-Key Cryptosystems

Fabrizio Biondi 1 Thomas Given-Wilson 1 Axel Legay 1
1 ESTASYS - Efficient STAtistical methods in SYstems of systems
Inria Rennes – Bretagne Atlantique , IRISA-D4 - LANGAGE ET GÉNIE LOGICIEL
Abstract : Recent work has presented max-equivocation as a measure of the resistance of a cryptosystem to attacks when the attacker is aware of the encoder function and message distribution. Here we consider the vulnerability of a cryptosystem in the one-try attack scenario when the attacker has incomplete information about the encoder function and message distribution. We show that encoder functions alone yield information to the attacker, and combined with inferable information about the ciphertexts, information about the message distribution can be discovered. We show that the whole encoder function need not be fixed or shared a priori for an effective cryptosystem, and this can be exploited to increase the equivocation over an a priori shared encoder. Finally we present two algorithms that operate in these scenarios and achieve good equivocation results, ExPad that demonstrates the key concepts, and ShortPad that has less overhead than ExPad.
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Submitted on : Saturday, December 12, 2015 - 2:39:27 PM
Last modification on : Thursday, January 20, 2022 - 5:33:18 PM
Long-term archiving on: : Sunday, March 13, 2016 - 10:18:14 AM


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Fabrizio Biondi, Thomas Given-Wilson, Axel Legay. On the Attacker's Knowledge in Shared-Key Cryptosystems. 2015. ⟨hal-01241374⟩



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