Audio Watermarking Forensics: Detecting malicious re-embedding

Digital watermarking has become a widely used security technology in the domain of Digital Rights Management and copyright protection as well as in other applications. In this work, we investigate a particular attack strategy: Embedding a new message in media content that already carries a watermark. The possibility for such an attack strategy results from the absence of truly asymmetric watermarking schemes, especially if the watermark is to be detected in public. In public detection scenarios, every detector needs the same key the embedder used to watermark the cover. With knowledge of the embedding algorithm, everybody who is able to detect the message can also maliciously embed a new message with the same key over the old one. This scenario is relevant in the case that an attacker intends to counterfeit a copyright notice, transaction ID or to change an embedded authentication code. This work presents experimental results on mechanisms for identifying such multiple embeddings in a spread-spectrum patchwork audio watermarking approach. We demonstrate that under certain circumstances multiple embedding can be detected.