Modeling Random Oracles under Unpredictable Queries.
IACR Cryptology ePrint Archive(2016)
摘要
In recent work, Bellare, Hoang, and Keelveedhi CRYPTO 2013 introduced a new abstraction called Universal Computational Extractors UCEs, and showed how they can replace random oracles ROs across a wide range of cryptosystems. We formulate a new framework, called Interactive Computational Extractors ICEs, that extends UCEs by viewing them as models of ROs under unpredictable aka. high-entropy queries. We overcome a number of limitations of UCEs in the new framework, and in particular prove the adaptive RKA and semi-adaptive KDM securities of a highly efficient symmetric encryption scheme using ICEs under key offsets. We show both negative and positive feasibility results for ICEs. On the negative side, we demonstrate ICE attacks on the $\\mathsf {HMAC}$ and $\\mathsf {NMAC}$ constructions. On the positive side we show that: 1 ROs are indeed ICE secure, thereby confirming the structural soundness of our definition and enabling a finer layered approach to protocol design in the RO model; and 2 a modified version of Liskov's Zipper Hash is ICE secure with respect to an underlying fixed-input-length RO, for appropriately restricted classes of adversaries. This brings the first result closer to practice by moving away from variable-input-length ROs. Our security proofs employ techniques from indifferentiability in multi-stage settings.
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关键词
Random oracle,Unpredictability,UCE,RKA security,KDM security,Zipper Hash,Indifferentiability,Multi-stage security
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