Decentralized Multi-Client Functional Encryption with Strong Security
Authors
Ky Nguyen, David Pointcheval, Robert Schädlich
Ky Nguyen
DIENS, Ecole normale superieure, CNRS, Inria, PSL University, Paris, France
ky dot nguyen at ens dot fr
ky dot nguyen at ens dot fr
David Pointcheval
DIENS, Ecole normale superieure, CNRS, Inria, PSL University, Paris, France
david dot pointcheval at ens dot fr
david dot pointcheval at ens dot fr
Robert Schädlich
DIENS, Ecole normale superieure, CNRS, Inria, PSL University, Paris, France
robert dot schaedlich at ens dot fr
robert dot schaedlich at ens dot fr
Abstract
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: the adversary can adaptively query multiple challenge ciphertexts and multiple challenge keys, with unbounded repetitions of the same tags in the ciphertext-queries and a fixed polynomially-large number of repetitions of the same tags in the key-queries. Previous constructions were proven secure in the selective setting only.
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History
Submitted: 2024-01-08
Accepted: 2024-06-04
Published: 2024-07-08
Accepted: 2024-06-04
Published: 2024-07-08
How to cite
Ky Nguyen, David Pointcheval, and Robert Schädlich, "Decentralized Multi-Client Functional Encryption with Strong Security," IACR Communications in Cryptology, vol. 1, no. 2, Jul 08, 2024, doi: 10.62056/andkp2fgx.
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