Paper 2020/1266

Multi-Party Functional Encryption

Shweta Agrawal and Rishab Goyal and Fabrice Mouhartem

Abstract

We initiate the study of multi-party functional encryption (MPFE) which unifies and abstracts out various notions of functional encryption which support distributed ciphertexts or secret keys, such as multi-input FE, multi-client FE, decentralized multi-client FE, multi-authority ABE, multi-authority FE and such others. We provide a unifying framework to capture existing multi-party FE primitives, define new, natural primitives that emerge from the framework, provide a feasibility result assuming general multi-input functional encryption (MIFE), and also provide constructions for restricted function families from standard assumptions. In more detail, we provide the following new constructions: 1. Two Input Quadratic Functional Encryption: We provide the first two input functional encryption scheme for quadratic functions from the SXDH assumption on bilinear groups. To the best of our knowledge, this is the first construction of MIFE from standard assumptions that goes beyond the inner product functionality. 2. Decentralized Inner Product Functional Encryption: We provide the first decentralized version of an inner product functional encryption scheme, generalizing the recent work of Michalevsky and Joye (ESORICS'18). Our construction supports access policies C that are representable as inner product predicates, and is secure based on the k-linear assumption, in the random oracle model. 3. Distributed Ciphertext-Policy Attribute Based Encryption. We provide a decentralized variant of the recent ciphertext-policy attribute based encryption scheme, constructed by Agrawal and Yamada (Eurocrypt'20). Our construction supports NC1 access policies, and is secure based on Learning With Errors and relies on the generic bilinear group model as well as the random oracle model. Our new abstraction predicts meaningful new primitives for multi-party functional encryption which we describe but do not instantiate — these may be constructed in future work.