Deniable Cryptosystems: Simpler Constructions and Achieving Leakage Resilience

Deniable encryption (Canetti et al. in CRYPTO ’97) is an intriguing primitive, which provides security guarantee against coercion by allowing a sender to convincingly open the ciphertext into a fake message. Despite the notable result by Sahai and Waters in STOC ’14 and other efforts in functionality extension, all the deniable public key encryption ( \(\textsf{DPKE}\) ) schemes suffer from intolerable overhead due to the heavy building blocks, e.g., translucent sets or indistinguishability obfuscation. Besides, none of them considers the possible damage from leakage in the real world, obstructing these protocols from practical use. To fill the gap, in this work we first present a simple and generic approach of sender- \(\textsf{DPKE}\) from ciphertext-simulatable encryption, which can be instantiated with nearly all the common \(\textsf{PKE}\) schemes. The core of this design is a newly-designed framework for flipping a bit-string that offers inverse polynomial distinguishability. Then we theoretically and experimentally expound on how classic side-channel attacks (timing or simple power attacks), can help the coercer break deniability, along with feasible countermeasures.