[Resource Topic] 2023/314: Memory-Tight Multi-Challenge Security of Public-Key Encryption

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Memory-Tight Multi-Challenge Security of Public-Key Encryption

Authors: Joseph Jaeger, Akshaya Kumar


We give the first examples of public-key encryption schemes which can be proven to achieve multi-challenge, multi-user CCA security via reductions that are tight in time, advantage, and memory. Our constructions are obtained by applying the KEM-DEM paradigm to variants of Hashed ElGamal and the Fujisaki-Okamoto transformation that are augmented by adding uniformly random strings to their ciphertexts and/or keys.

The reductions carefully combine recent proof techniques introduced by Bhattacharyya’20 and Ghoshal- Ghosal-Jaeger-Tessaro’22. Our proofs for the augmented ECIES version of Hashed-ElGamal make use of a new computational Diffie-Hellman assumption wherein the adversary is given access to a pairing to a random group, which we believe may be of independent interest.

ePrint: https://eprint.iacr.org/2023/314

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