Paper 2023/268

Verifiable Decentralized Multi-Client Functional Encryption for Inner Product

Dinh Duy Nguyen, LTCI, Telecom Paris, Institut Polytechnique de Paris, France
Duong Hieu Phan, LTCI, Telecom Paris, Institut Polytechnique de Paris, France
David Pointcheval, DIENS, École normale supérieure, CNRS, Inria, PSL University, Paris, France
Abstract

Joint computation on encrypted data is becoming increasingly crucial with the rise of cloud computing. In recent years, the development of multi-client functional encryption (MCFE) has made it possible to perform joint computation on private inputs, without any interaction. Well-settled solutions for linear functions have become efficient and secure, but there is still a shortcoming: if one user inputs incorrect data, the output of the function might become meaningless for all other users (while still useful for the malicious user). To address this issue, the concept of verifiable functional encryption was introduced by Badrinarayanan et al. at Asiacrypt ’16 (BGJS). However, their solution was impractical because of strong statistical requirements. More recently, Bell et al. introduced a related concept for secure aggregation, with their ACORN solution, but it requires multiple rounds of interactions between users. In this paper, – we first propose a computational definition of verifiability for MCFE. Our notion covers the computational version of BGJS and extends it to handle any valid inputs defined by predicates. The BGJS notion corresponds to the particular case of a fixed predicate, in our setting; – we then introduce a new technique called Combine-then-Descend, which relies on the class group. It allows us to construct One-time Decentralized Sum (ODSUM) on verifiable private inputs. ODSUM is the building block for our final protocol of a verifiable decentralized MCFE for inner-product, where the inputs are within a range. Our approach notably enables the efficient identification of malicious users, thereby addressing an unsolved problem in ACORN.

Metadata
Available format(s)
PDF
Category
Public-key cryptography
Publication info
A minor revision of an IACR publication in ASIACRYPT 2023
Keywords
VerifiabilityDecentralizedFunctional EncryptionInner Product
Contact author(s)
dinh nguyen @ telecom-paris fr
hieu phan @ telecom-paris fr
david pointcheval @ ens fr
History
2023-09-12: last of 3 revisions
2023-02-23: received
See all versions
Short URL
https://ia.cr/2023/268
License
Creative Commons Attribution
CC BY

BibTeX

@misc{cryptoeprint:2023/268,
      author = {Dinh Duy Nguyen and Duong Hieu Phan and David Pointcheval},
      title = {Verifiable Decentralized Multi-Client Functional Encryption for Inner Product},
      howpublished = {Cryptology ePrint Archive, Paper 2023/268},
      year = {2023},
      note = {\url{https://eprint.iacr.org/2023/268}},
      url = {https://eprint.iacr.org/2023/268}
}
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