Chapter

Theory of Cryptography

Volume 5444 of the series Lecture Notes in Computer Science pp 457-473

Predicate Privacy in Encryption Systems

  • Emily ShenAffiliated withMIT
  • , Elaine ShiAffiliated withCMU/PARC
  • , Brent WatersAffiliated withUT Austin

Abstract

Predicate encryption is a new encryption paradigm which gives a master secret key owner fine-grained control over access to encrypted data. The master secret key owner can generate secret key tokens corresponding to predicates. An encryption of data x can be evaluated using a secret token corresponding to a predicate f; the user learns whether the data satisfies the predicate, i.e., whether f(x) = 1.

Prior work on public-key predicate encryption has focused on the notion of data or plaintext privacy, the property that ciphertexts reveal no information about the encrypted data to an attacker other than what is inherently revealed by the tokens the attacker possesses. In this paper, we consider a new notion called predicate privacy, the property that tokens reveal no information about the encoded query predicate. Predicate privacy is inherently impossible to achieve in the public-key setting and has therefore received little attention in prior work. In this work, we consider 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.