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## Abstract

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 f

^{1},..., f^{n }s.t. f(x_{1},..., x_{n})= f^{1}(x_{1})+ ... + f^{n}(x_{n}) for all x_{1},..., x_{n}. 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 language | English |
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Title of host publication | Public-Key Cryptography -- PKC 2021 |

Editors | Juan A. Garay |

Place of Publication | Cham |

Publisher | Springer International Publishing |

Pages | 724-753 |

Number of pages | 30 |

ISBN (Electronic) | 978-3-030-75245-3 |

ISBN (Print) | 978-3-030-75244-6 |

DOIs | |

Publication status | Published - 1 May 2021 |

Event | 24th IACR International Conference on Practice and Theory of Public Key Cryptography - Online Duration: 10 May 2021 → 13 May 2021 https://pkc.iacr.org/2021/ |

### Publication series

Name | Lecture Notes in Computer Science |
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Publisher | Springer |

Volume | 12710 |

ISSN (Print) | 0302-9743 |

ISSN (Electronic) | 1611-3349 |

### Conference

Conference | 24th IACR International Conference on Practice and Theory of Public Key Cryptography |
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Abbreviated title | PKC 2021 |

Period | 10/05/21 → 13/05/21 |

Internet address |

## Keywords

- multi client
- functional encryption
- separable functions
- compiler

## Fingerprint

Dive into the research topics of 'Multi-Client Functional Encryption for Separable Functions'. Together they form a unique fingerprint.## Projects

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