Paper 2024/1956 Original: eprint.iacr.org/2024/1956 ↗

MultiReg-FE: Registered FE for Unbounded Inner-Product and Attribute-Weighted Sums

Abstract

Francati et al. (Asiacrypt 2023) provided the first registered functional encryption (Reg-FE) beyond predicates. Reg-FE addresses the key escrow problem in functional encryption by allowing users to generate their own key pairs, effectively replacing the traditional private-key generator with a key curator. The key curator holds no secret information and runs deterministic algorithms to generate master public key for encryption and helper keys for decryption. However, existing Reg-FE schemes under standard assumptions require fixed data sizes, which limits their practicality in real-world applications. In this work, we introduce Multi-Function Registered Functional Encryption for Inner-Product (MultiReg-FE for IP), a novel extension of Reg-FE. It enables users to register multiple functions under a single public key. With MultiReg-FE, we achieve both Reg-FE for Unbounded Inner-Product (Unbounded IP), which removes the need to predetermine vector lengths, and Reg-FE for Attribute-Weighted Sums (with Inner-Product) (AWSw/IP), allowing computations over arbitrary numbers of attribute-value pairs. Specifically, we present: · MultiReg-FE for Inner-Product, which supports unbounded number of function vectors from each user and achieves adaptive-IND-security; · Reg-FE for Unbounded Inner-Product, removing the need for preset vector lengths and achieves adaptive-IND-security; · The Reg-FE for AWSw/IP in public-key settings with very selective IND-security.