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

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

Available format(s)
Public-key cryptography
Publication info
A major revision of an IACR publication in ASIACRYPT 2023
Registered encryptionfunctional encryptioninner-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
2023-09-06: last of 5 revisions
2023-03-20: received
See all versions
Short URL
No rights reserved


      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{}},
      url = {}
Note: In order to protect the privacy of readers, does not use cookies or embedded third party content.