Multi-Bit Embedding in Asymmetric Digital Watermarking without Exposing Secret Information

Abstract

A new method of multi-bit embedding based on a protocol of secure asymmetric digital watermarking detection is proposed. Secure watermark detection has been achieved by means of allowing watermark verifier to detect a message without any secret information exposed in extraction process. Our methodology is based on an asymmetric property of a watermark algorithm which hybridizes a statistical watermark algorithm and a public-key algorithm. In 2004, Furukawa proposed a secure watermark detection scheme using patchwork watermarking and Paillier encryption, but the feasibility had not tested in his work. We have examined it and have shown that it has a drawback in heavy overhead in processing time. We overcome the issue by replacing the cryptosystem with the modified El Gamal encryption and improve performance in processing time. We have developed software implementation for both methods and have measured effective performance. The obtained result shows that the performance of our method is better than Frukawa's method under most of practical conditions. In our method, multiple bits can be embedded by assigning distinct generators in each bit, while the embedding algorithm of Frukawa's method assumes a single-bit message. This strongly enhances capability of multi-bit information embedding, and also improves communication and computation cost.