The Effective Key Length of Watermarking Schemes
This work addresses security measurement for digital watermarking, which is crucial for protecting intellectual property and data integrity, but it is incremental as it builds on existing theoretical approaches.
The paper tackles the problem of measuring security in digital watermarking schemes by introducing a new metric called effective key length, which assesses the difficulty for an adversary to access the watermarking channel, and applies it to additive spread spectrum schemes, showing they are insecure under Known Message Attacks.
Whereas the embedding distortion, the payload and the robustness of digital watermarking schemes are well understood, the notion of security is still not completely well defined. The approach proposed in the last five years is too theoretical and solely considers the embedding process, which is half of the watermarking scheme. This paper proposes a new measurement of watermarking security, called the effective key length, which captures the difficulty for the adversary to get access to the watermarking channel. This new methodology is applied to additive spread spectrum schemes where theoretical and practical computations of the effective key length are proposed. It shows that these schemes are not secure as soon as the adversary gets observations in the Known Message Attack context.