Efficient adaptively secure public-key trace and revoke from subset cover using Déjá Q framework

Abstract

We provide an efficient and secure construction for the trace and revoke from subset cover (TRSC) systems in the public-key setting, having ciphertext size proportional to the number of revoked users and public parameter of constant size. The system is obtained by tweaking the identity based encryption scheme of Wee (TCC 2016) under the subset cover framework. Existing TRSC constructions are inefficient with respect to the size of the parameters and derive their security from the q-type assumptions in the random oracle model. Our construction is the first adaptively secure TRSC system to achieve such parameters without using any random oracles. In addition, we are able to eliminate the q-type assumptions by integrating the Déjá Q framework of Chase and Meiklejohn (EUROCRYPT 2014) and its extension by Wee (TCC 2016) in our construction and analyze its security under the hardness of static subgroup decision problems over bilinear group setting. Moreover, this is the first proposal to feature optimally short private keys, even in the standard security model without any security breach.