Paper 2023/435

Optimal Security Notion for Decentralized Multi-Client Functional Encryption

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

Research on (Decentralized) Multi-Client Functional Encryption (or (D)MCFE) is very active, with interesting constructions, especially for the class of inner products. However, the security notions have been evolving over the time. While the target of the adversary in distinguishing ciphertexts is clear, legitimate scenarios that do not consist of trivial attacks on the functionality are less obvious. In this paper, we wonder whether only trivial attacks are excluded from previous security games. And, unfortunately, this was not the case. We then propose a stronger security notion, with a large definition of admissible attacks, and prove it is optimal: any extension of the set of admissible attacks is actually a trivial attack on the functionality, and not against the specific scheme. In addition, we show that all the previous constructions are insecure w.r.t. this new security notion. Eventually, we propose new DMCFE schemes for the class of inner products that provide the new features and achieve this stronger security notion.

Metadata
Available format(s)
PDF
Category
Cryptographic protocols
Publication info
Published elsewhere. ACNS 2023
Keywords
Functional EncryptionCorruptionsSecurity Notions
Contact author(s)
ky nguyen @ ens fr
hieu phan @ telecom-paris fr
david pointcheval @ ens fr
History
2023-03-27: approved
2023-03-24: received
See all versions
Short URL
https://ia.cr/2023/435
License
Creative Commons Attribution
CC BY

BibTeX

@misc{cryptoeprint:2023/435,
      author = {Ky Nguyen and Duong Hieu Phan and David Pointcheval},
      title = {Optimal Security Notion for Decentralized Multi-Client Functional Encryption},
      howpublished = {Cryptology ePrint Archive, Paper 2023/435},
      year = {2023},
      note = {\url{https://eprint.iacr.org/2023/435}},
      url = {https://eprint.iacr.org/2023/435}
}
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