Simple Countermeasure to Non-Linear Collusion Attacks Targeted for Spread-Spectrum Fingerprinting Scheme

Abstract

SUMMARYBased 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 [1], [2] 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.

Obfuscation in digital fingerprinting

“…To our knowledge, there is only one technique which claims to thwart both the MMX and uniform attacks, namely the obfuscation described in [Kur16,KS15]. Previous works have applied obfuscation as one of several advanced features in a complex system, and evaluated the complete system only.…”

Image fingerprinting system based on collusion secure code and watermarking method

“…In order to prevent colluders from accessing the host signal, a spreading operation was introduced at the embedding procedure in [8]. According to a secret key, a PN-sequence ρ t ∈ {±1} is generated.…”

“…Under the Kerckhoffs' principle [6], it is not difficult for colluders to access to the raw channel [7]. In order to prevent colluders from analyzing the components selected for embedding, an obfuscation technique presented in [8] can be utilized at the feature selection. It makes difficult for colluders to derive the components for embedding without a secret key even if they collect many copies.…”

“…By introducing some secret keys into the modules in the system, we consider attacks on some possible channels of digital color images. The embedding module, protected by a secret key, is simplified into an equivalent operation considering the obfuscation technique in [8]. The actual performance of the proposed method and the alternative method is evaluated by experiments.…”