With widespread use of the Internet and improvements in streaming media and
compression technology, digital music, images, DVDs, books and games can be distributed
instantaneously across the Internet to end-users. Many digital service providers sell their
digital content not only through DVDs but also over computer networks. However, without
protection and management of digital rights, digital content can be easily copied, changed,
and distributed to a large number of recipients, which could cause revenue loss to media
companies. To protect commercial digital intellectual property and avoid digital piracy, we
need a system that prevents unauthorized access to digital content and manages content
usage rights. (Liu and Safavi-Naini and Sheppard 2003) Estimating revenue losses due to
illegal downloads is challenging because it is difficult to determine what fraction of illegal
downloads result in lost revenue for the industry and whether illegal downloads, through
the free publicity they generate, have any positive impacts on box office revenues.
However, it is likely that redistribution of unauthorized copies through the Internet will
increasingly affect DVD movie sales and paid Internet distribution of movies. As the ease
of downloading unauthorized copies of movies grows with the availability of low-cost,
high-bandwidth Internet connections and peer-to-peer file sharing networks, the movie
industry concerns about illegal downloads is intensifying. These concerns are heightened
by unauthorized copies of movies becoming available on the Internet prior to their U.S.
theater release (Seiler and Snider 2003)
Piracy is the unauthorized use or reproduction of music, movies, books, and other types of
content that are granted protection under copyright law. This kind of protection typically
gives the owner of the content the exclusive right to perform certain actions on the content
or to authorize others to do so. We recognize that determining whether an action is
authorized or unauthorized may require protracted and subtle debate and that reasonable
people may differ in their assessment of a given situation. There are many kinds of content
that do not qualify for copyright protection because they do not contain any original
authorship and are common public property. Even content that does qualify receives
protection only for a limited time, after which that work becomes public property. We refer
to these types of content, which are not granted copyright protection, as public content.
(Biddle, England, Peinado, and Willman 2004)
There are generally two ways in which piracy can occur: Unauthorized acquisition is the
form of piracy with which most people are familiar occurs when a consumer obtains
