Cryptology ePrint Archive: Report 2021/524

Decentralized Multi-Client Functional Encryption for Set Intersection with Improved Efficiency

Kwangsu Lee

Abstract: Functional encryption (FE) is a new paradigm of public key encryption that can control the exposed information of plaintexts by supporting computation on encrypted data. In this paper, we propose efficient multi-client FE (MCFE) schemes that compute the set intersection of ciphertexts generated by two clients. First, we propose an MCFE scheme that calculates the set intersection cardinality (MCFE-SIC) and prove its static security under dynamic assumptions. Next, we extend our MCFE-SIC scheme to an MCFE scheme for set intersection (MCFE-SI) and prove its static security under dynamic assumptions. The decryption algorithm of our MCFE-SI scheme is more efficient than the existing MCFE-SI scheme because it requires fewer pairing operations to calculate the intersection of two clients. Finally, we propose a decentralized MCFE scheme for set intersection (DMCFE-SI) that decentralizes the generation of function keys. Our MCFE schemes can be effectively applied to a privacy-preserving contact tracing system to prevent the spread of recent infectious diseases.

Category / Keywords: public-key cryptography / Functional encryption, Multi-client setting, Private set intersection, Contact tracing, Bilinear maps.

Date: received 20 Apr 2021, last revised 20 Apr 2021

Contact author: kwangsu at sejong ac kr

Available format(s): PDF | BibTeX Citation

Version: 20210423:122439 (All versions of this report)

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