Paper 2024/764

Decentralized Multi-Client Functional Encryption with Strong Security

Ky Nguyen, DIENS, Ecole normale superieure, CNRS, Inria, PSL University, Paris, France
David Pointcheval, DIENS, Ecole normale superieure, CNRS, Inria, PSL University, Paris, France
Robert Schädlich, DIENS, Ecole normale superieure, CNRS, Inria, PSL University, Paris, France

Decentralized Multi-Client Functional Encryption (DMCFE) extends the basic functional encryption to multiple clients that do not trust each other. They can independently encrypt the multiple plaintext-inputs to be given for evaluation to the function embedded in the functional decryption key, defined by multiple parameter-inputs. And they keep control on these functions as they all have to contribute to the generation of the functional decryption keys. Tags can be used in the ciphertexts and the keys to specify which inputs can be combined together. As any encryption scheme, DMCFE provides privacy of the plaintexts. But the functions associated to the functional decryption keys might be sensitive too (e.g. a model in machine learning). The function-hiding property has thus been introduced to additionally protect the function evaluated during the decryption process. In this paper, we provide new proof techniques to analyze a new concrete construction of function-hiding DMCFE for inner products, with strong security guarantees in the random oracle model: the adversary can adaptively query multiple challenge ciphertexts and multiple challenge keys, with unbounded repetitions of the same message tags in the ciphertext-queries and a fixed polynomially-large number of repetitions of the same key tags in the key-queries, allowing static corruption of the secret encryption keys. Previous constructions were proven secure in the selective setting only.

Available format(s)
Public-key cryptography
Publication info
Functional EncryptionInner ProductFunction-Hiding
Contact author(s)
ky nguyen @ ens fr
david pointcheval @ ens fr
robert schaedlich @ ens fr
2024-05-20: approved
2024-05-19: received
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Creative Commons Attribution


      author = {Ky Nguyen and David Pointcheval and Robert Schädlich},
      title = {Decentralized Multi-Client Functional Encryption with Strong Security},
      howpublished = {Cryptology ePrint Archive, Paper 2024/764},
      year = {2024},
      note = {\url{}},
      url = {}
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