An asymmetric fingerprinting code for collusion-resistant buyer-seller watermarking

A buyer seller watermarking protocol is intended to ensure copyright protection, privacy and security for both the buyer and seller simultaneously in an e-commerce application. A traitor should not be able to deny his responsibility of a copyright violation caused by him in such protocols. This feature is identified as non-repudiation in the literature. An efficient approach taken is through secure embedding of watermarks in an encrypted domain by using dither modulation and homomorphic encryption. To support non-repudiation along with collusion resistance, one needs an asymmetric collusion resistant fingerprinting code that is compatible with the watermarking technique. The design of such codes has not yet studied thoroughly with an exception of a recent work by Charpentier et. al. in [4]. In this paper, we propose an asymmetric binary fingerprinting code based on Boneh-Shaw code. When applied to the secure embedding of watermarks, we show that our code outperforms the code introduced by [4]: (i) we achieve constant communication round, (ii) we do not require any oblivious transfer protocol and (iii) we do not require any public Write Once Read Many (WORM) directory.