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Simulation-Sound Arguments for LWE and Applications to KDM-CCA2 Security

Abstract : The Naor-Yung paradigm is a well-known technique that constructs IND-CCA2-secure encryption schemes by means of non-interactive zero-knowledge proofs satisfying a notion of simulation-soundness. Until recently, it was an open problem to instantiate it under the sole Learning-With-Errors (LWE) assumption without relying on random oracles. While the recent results of Canetti et al. (STOC'19) and Peikert-Shiehian (Crypto'19) provide a solution to this problem by applying the Fiat-Shamir transform in the standard model, the resulting constructions are extremely inefficient as they proceed via a reduction to an NP-complete problem. In this paper, we give a direct, non-generic method for instantiating Naor-Yung under the LWE assumption outside the random oracle model. Specifically, we give a direct construction of an unbounded simulation-sound NIZK argument system which, for carefully chosen parameters, makes it possible to express the equality of plaintexts encrypted under different keys in Regev's cryptosystem. We also give a variant of our argument that provides tight security. As an application, we obtain an LWE-based public-key encryption scheme for which we can prove (tight) key-dependent message security under chosen-ciphertext attacks in the standard model.
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https://hal.inria.fr/hal-02993617
Contributor : Benoit Libert <>
Submitted on : Friday, November 6, 2020 - 8:35:12 PM
Last modification on : Thursday, December 3, 2020 - 3:53:15 PM

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Benoît Libert, Khoa Nguyen, Alain Passelègue, Radu Titiu. Simulation-Sound Arguments for LWE and Applications to KDM-CCA2 Security. Asiacrypt 2020 - 26th Annual International Conference on the Theory and Application of Cryptology and Information Security, Dec 2020, Virtual, South Korea. pp.1-67. ⟨hal-02993617⟩

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