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Paper 2017/525

Kurosawa-Desmedt Meets Tight Security

Romain Gay and Dennis Hofheinz and Lisa Kohl

Abstract

At EUROCRYPT 2016, Gay et al. presented the first pairing-free public-key encryption (PKE) scheme with a tight security reduction to a standard assumption. Their scheme is competitive in efficiency with state-of-the art PKE schemes and has very compact ciphertexts (of three group elements), but suffers from a large public key (of about 200 group elements). In this work, we present an improved pairing-free PKE scheme with a tight security reduction to the Decisional Diffie-Hellman assumption, small ciphertexts (of three group elements), and small public keys (of six group elements). Compared to the work of Gay et al., our scheme thus has a considerably smaller public key and comparable other characteristics, although our encryption and decryption algorithms are somewhat less efficient. Technically, our scheme borrows ideas both from the work of Gay et al. and from a recent work of Hofheinz (EUROCRYPT, 2017). The core technical novelty of our work is an efficient and compact designated-verifier proof system for an OR-like language. We show that adding such an OR-proof to the ciphertext of the state-of-the-art PKE scheme from Kurosawa and Desmedt enables a tight security reduction.

Metadata
Available format(s)
PDF
Publication info
A major revision of an IACR publication in CRYPTO 2017
Keywords
public key encryptiontight security
Contact author(s)
Romain Gay @ ens fr
Dennis Hofheinz @ kit edu
Lisa Kohl @ kit edu
History
2017-10-24: last of 2 revisions
2017-06-05: received
See all versions
Short URL
https://ia.cr/2017/525
License
Creative Commons Attribution
CC BY
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