Ternary subset difference revocation in public key framework supporting outsider anonymity

Abstract

Broadcast encryption (BE) is a cryptographic primitive which sends encrypted message to the users securely. The BE scheme proposed by Naor, Naor, and Lotspiech (NNL) in 2001 is a popular BE scheme which uses a binary tree. The advanced access content system standard suggested to use it for digital right management in Blue-ray and DVD-discs. This paper puts forward an efficient broadcast encryption in public key setting employing ternary tree subset difference method for revocation. Our approach utilizes composite order bilinear group setting to achieve the tree based construction in public key setting. Our second construction is an extension of our first construction and provides outsider-anonymity by disabling the revoked users from getting any information of message and concealing the set of subscribed users from the revoked users. The construction of Fazio and Perera is the closest one to that of our second scheme (as both of these construction are in public key setting and provides outsider-anonymity). We have reduced the ciphertext size from $$r\\log N/r$$\n to min\n $$\\{N/3,N-r,2r-1\\}.$$\n Thus reduces the communication bandwidth. We have also reduced the public key size. Our constructions enjoy the revocation property. Both of our constructions achieve selective semantic security in the standard model under reasonable assumptions and new users can join without updating the pre-existing setup.