Thomas Jefferson, Needles and Haystacks

It is difficult to balance arguments for open access with commercial reward. However, technology has made the debate real. Denying the tremendous amount of turmoil which exists in the music business as a result of CD ripping, real time exchange of audio files with networking protocols, and anonymous theft, is no longer an option.

Enabling the individualization of copies of a song with provably secure digital watermarks and a supporting infrastructure for third party authentication of music are likely to be the best way for artists and rights holders to continue to profit from their work.

We originally defined a digital watermark to mean "an ability to establish responsibility for a digital copy." Thus, we first describe the technology of digital watermarking invented by my company, Blue Spike, and then evaluate other competing technologies.

Perhaps best described as a means for binding a "digital signature" to a music signal, in a manner which ensures that attempts at erasure cause audible damage to the song, secure Blue Spike watermarks can be used to tamperproof individual instances of a digital copy of any media content.

Any suspect copy can be checked with the appropriately generated "key," or keys, in the case of multiple rights that were used to embed the signature at the time of purchase. If the information cannot be securely embedded, it is likely that any sacrifice of the signal's quality should be avoided.

Essentially, watermarking is strictly a security technology; the embedded digital watermark information has intrinsic value independent of the audio signal itself. Where the consumer is not bothered by the inaudible tag, the rights holder is able to differentiate between authentic and pirated instances of the song.

A watermarking key is basically a string of cryptographically generated binary digits, or "bits." The key is also a map of how the watermark has been embedded into the target signal. This simple improvement over traditional cryptography is the dramatic difference between digital watermarks and strict digital signature or related encryption technologies. If the key is needed for third party authentication, even by consumers, we use commonly used mathematical tricks to split the key into a key pair. These tricks were discovered in the 1970s and form the basis of public key cryptography.

For watermarking, encoding and encryption is handled by the key, not just encryption.

The private key is used to encode the digital watermark into the music. The public key is used to decode the digital watermark from the music without revealing the private key. The consumer can even authenticate a copy of a song themselves with their public key, just like a purchase receipt.

I originally conceived the technology because of experiences with theft. A ruler with a permanent red marker signature was stolen way back in the eighth grade. Luckily, a friend recovered the stolen item. Though only one of many of the varied experiences of junior high school, I subsequently used a pen knife to etch my initials into CD jewel cases and CDs in a manner not obvious to any casual observer in the early 1980s. The reason: at the time, CDs were scarce and confrontation over the theft of a CD in college is not a preferred means for maintaining control over the property in question!

Extending this means for intentional acts of hiding or "obfuscation" to tagging a media signal is really very straightforward. The parallels with physical good distribution are also uncanny and relevant.

The same way physical media companies seek to monitor materials and distribution of goods by marking those goods with serial numbers (Cartier, for instance) or limiting "authenticity" with "holographic patches" (Levis, for instance), digital watermarks enable artists and rights holders to better track and differentiate between two seemingly "identical" digital recordings. As is commonly the case with highly sought-after goods, such as US$100 bills, Channel bags, and Nike clothing, piracy will exist; but tracking will allow the rights owners to continue to exercise a measure of control over their works.

Moreover, clinical approaches to rights management which ignore the serendipitous nature of recognition, and its big brother, fame, miss the point that works need to be freely accessible with their rights intact to provide beneficial marketing data to musical acts.

Originally, the ability to watermark was defined by me as akin to hiding needles in a haystack. But informationally, the haystack, or song, is not difficult to search quickly. The increases in computational processing speed and access to bandwidth makes the notion of information hiding and other forms of obfuscation more problematic. Simply, it is computationally easy to search vast amounts of information quickly, no matter how cleverly the information is hidden.

There are existing means for enabling permanent changes to be maintained and subsequently detected: we call these "digital signatures."

Since copyrights are intended to last for long periods of time, more secure means for embedding authenticity information, a digital signature for example, into copyrighted media signals, has become invaluable. We can only embed in a finite number of locations in any given song, since the song has a limited amount of data that comprises it.

However, the additional uniqueness required to differentiate between two similar songs can be saved in a watermarking key. This prevents successful attempts at collusion: the comparison of watermarked songs to reveal watermark locations to make erasure easy. The arguments I make here are not unlike arguments being made for any form of security and I will focus on why advanced data security, called cryptography, needs to be bridged with the ability "to hide things in plain view," or steganography.

Digital watermarking is a secure form of steganography.

Steganography has a history at least as old, or older, than cryptography, the art of secret codes. That the application of digital watermarking first happens with music is instructive to present interpretations of security, trust and value. Security needs to be bridged with human perception to enable the many wonderful network technologies and artistic expression possible to be profitable.