Blind pattern matching attack on watermarking systems

Billions of dollars allegedly lost to piracy of multimedia content have triggered the industry to rethink the way music and films are distributed on the Internet. As encryption is vulnerable to digital or analog re-recording, currently almost all copyright protection mechanisms rely to a certain extent on watermarking. A watermark is an imperceptive secret hidden into a host signal. We analyze the security of multimedia copyright protection systems that use watermarks by proposing a new breed of attacks on generic watermarking systems. A typical blind pattern matching attack relies on the observation that multimedia content is often highly repetitive. Thus, the attack procedure identifies subsets of signal blocks that are similar and permutes these blocks. Assuming the permuted blocks are marked with distinct secrets, it can be shown that any watermark detector is facing a task of exponential complexity to reverse the permutations as a preprocessing step for watermark detection. We describe the logistics of the attack and an implementation against a spread-spectrum and a quantization index modulation data hiding technology for audio signals.