Abstract: This paper analyzes the security of multimedia copyright protection systems that use watermarks by proposing a new method of attacks on some watermarking systems. Such idea comes from the observation of the repetitiveness of the multimedia content. The attack procedure replaces each signal block with another computed one. If the computed replacement block is at some minimal distance from the original marked block, large portion of the embedded watermark is irreversibly removed. The logistics of the attack and an exemplary implementation against a spread-spectrum data hiding technology for audio signals are also described.

Key words: Digital watermark, Replacement attack, Similarity, High-fidelity, Substitution

摘要： 分析了多媒体版权保护系统在一种新型攻击方式下的安全性。替代攻击的思路来源于对多媒体内容高重复性的观察，因此攻击过程采用的是用一个计算出的数据块替代原有数据块。论述了这种替代所要求的条件，即这两个数据块必须保持一定的相关性，不能过于相似也不能失真过大，一旦条件得到满足，大部分嵌入信息将被移去。描述了攻击原理以及针对音频信息中的扩展频谱水印发动攻击的实现。

关键词: 数字水印, 替代攻击, 相关性, 高保真, 代换