Method and apparatus for rendering unauthorized copies of digital content traceable to authorized copies

Abstract

A method for customizing a copyrighted digital work that is distributed in multiple data objects on, for example, a writable media, such as an optical disc, or across a global network, such as the Internet, so that an unauthorized second-generation copy can be traced to the licensee. Bits of the license-enforcement data are embedded in a licensed copy by choosing one of two previously prepared versions of each data object. These two versions both have the effect that the artist intended. The licensor can read the enforcement data more easily when digital fingerprints of the application data are carried along with the data objects. In order to remove the enforcement data with a degree of reliability, it would be necessary to introduce subtle changes in the application data and then recompute the fingerprints. This may constitute willful infringement rather than just careless copying. To discourage such determined piracy, the fingerprints are computed using a one-way hash function and encrypted using a public-key encryption algorithm. Public notice is given of the selected one-way hash function and public-key cryptography algorithm along with the value of the public key in use. Consequently anyone can authenticate a copy of the work, and persons who traffic in pirate copies can therefore be held accountable. Certain weaknesses of the method are overcome by concatenating the fingerprints before encryption and overwriting the fingerprints from the same bit positions after encryption.