Predicate privacy in encryption systems

Abstract

Predicate encryption is a new encryption paradigm which gives the secret key owner finegrained control over access to encrypted data. The secret key owner can generate tokens, or capabilities, corresponding to predicates. An encryption of a plaintext x can be decrypted using a token corresponding to a predicate f if the plaintext satisfies the predicate, i.e., f(x) = 1. Prior work on public key predicate encryption focuses on the notion of plaintext privacy, that is, the property that the ciphertext should not reveal information about the encrypted plaintext. In this paper, we consider a new notion called predicate privacy, that is, the property that a token should not reveal information about the query predicate encoded in it. Predicate privacy is inherently not possible in the public key setting, and has therefore received little attention in prior work. In this work, we consider security of predicate encryption in the symmetric key setting and present a symmetric key predicate encryption scheme which supports inner product queries. We prove that our scheme achieves both plaintext privacy and predicate privacy.