Welcome to the resource topic for 2023/1443
Title:
Security with Functional Re-Encryption from CPA
Authors: Yevgeniy Dodis, Shai Halevi, Daniel Wichs
Abstract:The notion of functional re-encryption security (funcCPA) for public-key encryption schemes was recently introduced by Akavia et al. (TCC’22), in the context of homomorphic encryption. This notion lies in between CPA security and CCA security: we give the attacker a functional re-encryption oracle instead of the decryption oracle of CCA security. This oracle takes a ciphertext c and a function f, and returns fresh encryption of the output of f applied to the decryption of c; in symbols, c'=Enc(f(Dec(c))). More generally, we even allow for a multi-input version, where the oracle takes an arbitrary number of ciphetexts c_1,\ldots,c_\ell and outputs c' = Enc(f(Dec(c_1), \ldots, Dec(c_\ell))).
In this work we observe that funcCPA security may have applications beyond homomorphic encryption, and set out to study its properties. As our main contribution, we prove that funcCPA is ``closer to CPA than to CCA’'; that is, funcCPA secure encryption can be constructed in a black-box manner from CPA-secure encryption. We stress that, prior to our work, this was not known even for basic re-encryption queries corresponding to the identity function f.
At the core of our result is a new technique, showing how to handle adaptive functional re-encryption queries using tools previously developed in the context of non-malleable encryption, which roughly corresponds to a single non-adaptive parallel decryption query.
ePrint: https://eprint.iacr.org/2023/1443
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