Digital watermarks embed information into a host artifact in such a way that the functionalities of the artifact remain unchanged. Allowing for the timely retrieval of authorship/ownership information, and ideally hard to be removed, watermarks discourage piracy and have thus been regarded as important tools to protect the intellectual property. A watermark aimed at uniquely identifying an artifact is referred to as a fingerprint. After presenting a formal definition of digital watermarks, we introduce an unbiased fingerprinting protocol -- based on oblivious transfer -- that lends no advantage to the prosecuting party in a dispute around intellectual property breach.