Paper 2025/821

Multi-Client Attribute-Based and Predicate Encryption, Revisited

Robert Schädlich, École normale supérieure, PSL University, CNRS, Inria, Paris, France
Abstract

Multi-client Attribute-Based Encryption (ABE) is a generalization of key-policy ABE where attributes can be independently encrypted across several ciphertexts w.r.t. labels, and a joint decryption of these ciphertexts is possible if and only if (1) all ciphertexts share the same label, and (2) the combination of attributes satisfies the policy of the decryption key. All encryptors have their own secret key and security is preserved even if some of them are known to the adversary. Very recently, Pointcheval et al. (TCC 2024) presented a semi-generic construction of MC-ABE for restricted function classes, e.g., NC0 and constant-threshold policies. We identify an abstract criterion common to all their policy classes which suffices to present the construction in a fully black-box way and allows for a slight strengthening of the supported policy classes. The construction of Pointcheval et al. is based on pairings. We additionally provide a new lattice-based instantiation from (public-coin) evasive LWE. Furthermore, we revisit existing constructions for policies that can be viewed as a conjunction of local policies (one per encryptor). Existing constructions from MDDH (Agrawal et al., CRYPTO 2023) and LWE (Francati et al., EUROCRYPT 2023) do not support encryption w.r.t. different labels. We show how this feature can be included. Notably, the security model of Francati et al. additionally guarantees attribute-hiding but does not capture collusions. Our new construction is also attribute-hiding and provides resilience against any polynomially bounded number of collusions which must be fixed at the time of setup.

Metadata
Available format(s)
PDF
Category
Cryptographic protocols
Publication info
A major revision of an IACR publication in PKC 2025
DOI
10.1007/978-3-031-91832-2_2
Keywords
multi-clientattribute based encryptionpredicate encryption
Contact author(s)
robert schaedlich @ ens fr
History
2025-05-09: approved
2025-05-08: received
See all versions
Short URL
https://ia.cr/2025/821
License
Creative Commons Attribution
CC BY

BibTeX

@misc{cryptoeprint:2025/821,
      author = {Robert Schädlich},
      title = {Multi-Client Attribute-Based and Predicate Encryption, Revisited},
      howpublished = {Cryptology {ePrint} Archive, Paper 2025/821},
      year = {2025},
      doi = {10.1007/978-3-031-91832-2_2},
      url = {https://eprint.iacr.org/2025/821}
}
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