A Generic Approach to Invariant Subspace Attacks: Cryptanalysis of Robin, iSCREAM and Zorro.
ADVANCES IN CRYPTOLOGY - EUROCRYPT 2015, PT I(2015)
摘要
Invariant subspace attacks were introduced at CRYPTO 2011 to cryptanalyze PRINTcipher. The invariant subspaces for PRINTcipher were discovered in an ad hoc fashion, leaving a generic technique to discover invariant subspaces in other ciphers as an open problem. Here, based on a rather simple observation, we introduce a generic algorithm to detect invariant subspaces. We apply this algorithm to the CAESAR candidate iSCREAM, the closely related LS-design Robin, as well as the lightweight cipher Zorro. For all three candidates invariant subspaces were detected, and result in practical breaks of the ciphers. A closer analysis of independent interest reveals that these invariant subspaces are underpinned by a new type of self-similarity property. For all ciphers, our strongest attack shows the existence of a weak key set of density 2(-32). These weak keys lead to a simple property on the plaintexts going through the whole encryption process with probability one. All our attacks have been practically verified on reference implementations of the ciphers.
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关键词
Cryptanalysis,Lightweight cryptography,Invariant subspace,Self-similarity,iSCREAM,LS-designs,Zorro,CAESAR
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