Registered (Inner-Product) Functional Encryption

Danilo Francati; Daniele Friolo; Monosij Maitra; Giulio Malavolta; Ahmadreza Rahimi; Daniele Venturi

Paper 2023/395

Registered (Inner-Product) Functional Encryption

Danilo Francati

, Aarhus University

Daniele Friolo

, Sapienza University of Rome

Monosij Maitra, Ruhr-Universität Bochum, Max-Planck Institute for Security and Privacy

Giulio Malavolta, Bocconi University, Max-Planck Institute for Security and Privacy

Ahmadreza Rahimi

, Max-Planck Institute for Security and Privacy

Daniele Venturi

, Sapienza University of Rome

Abstract

Registered encryption (Garg $et\ al.$, TCC'18) is an emerging paradigm that tackles the key-escrow problem associated with identity-based encryption by replacing the private-key generator with a much weaker entity known as the key curator. The key curator holds no secret information, and is responsible to: (i) update the master public key whenever a new user registers its own public key to the system; (ii) provide helper decryption keys to the users already registered in the system, in order to still enable them to decrypt after new users join the system. For practical purposes, tasks (i) and (ii) need to be efficient, in the sense that the size of the public parameters, of the master public key, and of the helper decryption keys, as well as the running times for key generation and user registration, and the number of updates, must be small. In this paper, we generalize the notion of registered encryption to the setting of functional encryption (FE). As our main contribution, we show an efficient construction of registered FE for the special case of ($attribute\text{-}hiding$) inner-product predicates, built over asymmetric bilinear groups of prime order. Our scheme supports a $large$ attribute universe and is proven secure in the bilinear generic group model. We also implement our scheme and experimentally demonstrate the efficiency requirements of the registered settings. Our second contribution is a feasibility result where we build registered FE for $\mathsf{P}/\mathsf{poly}$ based on indistinguishability obfuscation and somewhere statistically binding hash functions.

Note: Corrections in affiliations from the prior version

Metadata

Available format(s): PDF
Category: Public-key cryptography
Publication info: A major revision of an IACR publication in ASIACRYPT 2023
Keywords: Registered encryption functional encryption inner-product predicate encryption.
Contact author(s): dfrancati @ cs au dk
friolo @ di uniroma1 it
monosij maitra @ rub de
giulio malavolta @ unibocconi it
ahmadrezar @ pm me
venturi @ di uniroma1 it
History: 2023-09-06: last of 5 revisions; 2023-03-20: received; See all versions
Short URL: https://ia.cr/2023/395
License: CC0

BibTeX

@misc{cryptoeprint:2023/395,
      author = {Danilo Francati and Daniele Friolo and Monosij Maitra and Giulio Malavolta and Ahmadreza Rahimi and Daniele Venturi},
      title = {Registered (Inner-Product) Functional Encryption},
      howpublished = {Cryptology ePrint Archive, Paper 2023/395},
      year = {2023},
      note = {\url{https://eprint.iacr.org/2023/395}},
      url = {https://eprint.iacr.org/2023/395}
}