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Simple Countermeasure to Non-Linear Collusion Attacks Targeted for Spread-Spectrum Fingerprinting Scheme
IEICE TRANSACTIONS on Information and Systems
Publication Date: 2016/01/01
Online ISSN: 1745-1361
Type of Manuscript: Special Section PAPER (Special Section on Enriched Multimedia---Creation of a New Society through Value-added Multimedia Content---)
fingerprinting, spread spectrum, Kerckhoffs' principle, host signal,
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Based upon the Kerckhoffs' principle, illegal users can get to know the embedding and detection algorithms except for a secret key. Then, it is possible to access to a host signal which may be selected from frequency components of a digital content for embedding watermark signal. Especially for a fingerprinting scheme which embeds user's information as a watermark, the selected components can be easily found by the observation of differently watermarked copies of a same content. In this scenario, it is reported that some non-linear collusion attacks will be able to remove/modify the embedded signal. In this paper, we study the security analysis of our previously proposed spread-spectrum (SS) fingerprinting scheme,  under the Kerckhoffs' principle, and reveal its drawback when an SS sequence is embedded in a color image. If non-linear collusion attacks are performed only to the components selected for embedding, the traceability is greatly degraded while the pirated copy keeps high quality after the attacks. We also propose a simple countermeasure to enhance the robustness against non-linear collusion attacks as well as possible signal processing attacks for the underlying watermarking method.