Multi-Client Functional Encryption for Separable Functions

Michele Ciampi, Luisa Siniscalchi, Hendrik Waldner

Research output: Chapter in Book/Report/Conference proceedingConference contribution


In this work, we provide a compiler that transforms a single-input functional encryption scheme for the class of polynomially bounded circuits into a multi-client functional encryption (MCFE) scheme for the class of separable functions. An n-input function f is called separable if it can be described as a list of polynomially bounded circuits f1,..., fs.t.  f(x1,..., xn)= f1(x1)+ ... + fn(xn) for all x1,..., xn. Our compiler extends the works of Brakerski et al. [Eurocrypt 2016] and of Komargodski et al. [Eurocrypt 2017] in which a generic compiler is proposed to obtain multi-input functional encryption (MIFE) from single-input functional encryption. Our construction achieves the stronger notion of MCFE but for the less generic class of separable functions. Prior to our work, a long line of results has been proposed in the setting of MCFE for the inner-product functionality, which is a special case of a separable function. We also propose a modified version of the notion of decentralized MCFE introduced by Chotard et al. [Asiacrypt 2018] that we call outsourceable mulit-client functional encryption (OMCFE). Intuitively, the notion of OMCFE makes it possible to distribute the load of the decryption procedure among at most n different entities, which will return decryption shares that can be combined (e.g., additively) thus obtaining the output of the computation. This notion is especially useful in the case of a very resource consuming decryption procedure, while the combine algorithm is non-time consuming. We also show how to extend the presented MCFE protocol to obtain an OMCFE scheme for the same functionality class.
Original languageEnglish
Title of host publicationPublic-Key Cryptography -- PKC 2021
EditorsJuan A. Garay
Place of PublicationCham
PublisherSpringer International Publishing
Number of pages30
ISBN (Electronic)978-3-030-75245-3
ISBN (Print)978-3-030-75244-6
Publication statusPublished - 1 May 2021
Event24th IACR International Conference on Practice and Theory of Public Key Cryptography - Online
Duration: 10 May 202113 May 2021

Publication series

NameLecture Notes in Computer Science
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349


Conference24th IACR International Conference on Practice and Theory of Public Key Cryptography
Abbreviated titlePKC 2021
Internet address


  • multi client
  • functional encryption
  • separable functions
  • compiler


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