Reducing Communication Overhead of the Subset Difference Scheme

Abstract

In Broadcast Encryption (BE) systems like Pay-TV, AACS, online content sharing and broadcasting, reducing the header length (communication overhead per session) is of practical interest. The Subset Difference (SD) scheme due to Naor-Naor-Lotspiech (NNL) is the most popularly used BE scheme. We introduce the $(a,b,\gamma)$ augmented binary tree subset difference ( $(a,b,\gamma)$ -ABTSD) scheme which is a generalization of the NNL-SD scheme. By varying the parameters $(a,b,\gamma)$ , it is possible to obtain $O(n\log n)$ different schemes. The average header length achieved by the new schemes is smaller than all known schemes having the same decryption time as that of the NNL-SD scheme and achieving non-trivial trade-offs between the user storage and the header size. The amount of key material that a user is required to store increases. For the earlier mentioned applications, reducing header size and achieving fast decryption is perhaps more of a concern than the user storage.