Registered Functional Encryptions from Pairings

This work initiates the study of concrete registered functional encryption (Reg-FE) beyond “all-or-nothing” functionalities: Besides focusing on the compactness of the master public key and helper keys, we also aim for compact ciphertexts in Reg-FE. Let L be the number of slots and n be the input size. Our first Reg-IPFE has weakly compact ciphertexts of size \(O(n\cdot \log L)\) while our second Reg-QFE has compact ciphertexts of size \(O(n+\log L)\) . Technically, for our first Reg-IPFE, we employ nested dual-system method within the context of Reg-IPFE; for our second Reg-QFE, we follow Wee’s “IPFE-to-QFE” transformation [TCC’ 20] but devise a set of new techniques that make our pairing-based Reg-IPFE compatible. Along the way, we introduce a new notion named Pre-Constrained Registered IPFE which generalizes slotted Reg-IPFE by constraining the form of functions that can be registered.