Unbounded Predicate Inner Product Functional Encryption from Pairings

Predicate inner product functional encryption (P-IPFE) is essentially attribute-based IPFE (AB-IPFE) which additionally hides attributes associated to ciphertexts. In a P-IPFE, a message x x is encrypted under an attribute w w and a secret key is generated for a pair (y, v) ( y , v ) such that recovery of x, y ⟨ x , y ⟩ requires the vectors w, v w , v to satisfy a linear relation. We call a P-IPFE unbounded if it can encrypt unbounded length attributes and message vectors. • ∙ zero predicate IPFE . We construct the first unbounded zero predicate IPFE (UZP-IPFE) which recovers x, y ⟨ x , y ⟩ if w, v =0 ⟨ w , v ⟩ = 0 . This construction is inspired by the unbounded IPFE of Tomida and Takashima (ASIACRYPT 2018) and the unbounded zero inner product encryption of Okamoto and Takashima (ASIACRYPT 2012). The UZP-IPFE stands secure against general attackers capable of decrypting the challenge ciphertext. Concretely, it provides full attribute-hiding security in the indistinguishability-based semi-adaptive model under the standard symmetric external Diffie–Hellman assumption. • ∙ non-zero predicate IPFE . We present the first unbounded non-zero predicate IPFE (UNP-IPFE) that successfully recovers x, y ⟨ x , y ⟩ if w, v ≠ 0 ⟨ w , v ⟩ ≠ 0 . We generically transform an unbounded quadratic FE (UQFE) scheme to weak attribute-hiding UNP-IPFE in both public and secret key setting. Interestingly, our secret key simulation secure UNP-IPFE has succinct secret keys and is constructed from a novel succinct UQFE that we build in the random oracle model. We leave the problem of constructing a succinct public key UNP-IPFE or UQFE in the standard model as an important open problem.