Combined fingerprinting attacks against digital audio watermarking: methods, results and solutions

While a reliable protection against illegal copies does not exists today, tracking of illegal copies and prove of ownership are important detection functions, which can be realized by using passive security mechanisms of digital watermarking. Recent research has identified many watermarking algorithms for all common media types ranging from printed matter to multimedia files. The main topics of interest concentrates on transparency and robustness: The watermark must not reduce media quality and should be detectable after most common media operations and attacks. Algorithm security is discussed with regards only to key space most of the times, while especially for customer identification known as active fingerprinting specialized attacks like coalition attacks are known. Digital fingerprinting raises the additional problem that we produce different copies for each customer. Attackers can compare several fingerprinted copies to find and destroy the embedded identification string by altering the data in those places where a difference was detected. Few approaches have been introduced for image and video watermarking schemes, but there are no observations for audio fingerprinting techniques. In our paper we discuss methods for secure customer identification by digital fingerprinting for audio data. We describe first two algorithms by Boneh et al. [BoSh95] and Schwenk et al. [DBS+99] and then combine these schemes with an audio watermarking algorithm for practical evaluation of their coalition resistance to detect illegal copies. We provide test results and evaluate the security against different types of coalition attacks.