The Digital Millennium Copyright Act (DMCA) is an extension to United States copyright law passed unanimously on May 14, 1998, which criminalizes the production and dissemination of technology that allows users to circumvent technical copy-restriction methods. Under the Act, circumvention of a technological measure that effectively controls access to a work is illegal if done with the primary intent of violating the rights of copyright holders.
Although the Act contains an exception for research, the DMCA has had an impact on the worldwide cryptography research community, because many fear that their cryptanalytic research violates, or might be construed to violate the law. The arrest of Russian programmer Dmitry Sklyarov in 2001, for alleged infringement of the DMCA, was a highly publicized example of the law's use to prevent or penalize development of anti-digital rights management measures. Sklyarov was arrested in the United States after a presentation at DEF CON, and subsequently spent several months in jail. The DMCA has also been cited as chilling to non-criminal inclined users, such as students of cryptanalysis (including, in a well-known instance, Professor Felten and students at Princeton), and security consultants such as the Netherlands based Niels Ferguson, who has declined to publish information about vulnerabilities he discovered in an Intel secure-computing scheme because of his concern about being arrested under the DMCA when he travels to the United States.
Free speech lawsuits have resulted surrounding the publication of DeCSS and the AACS encryption key, both dealing with the "cracking" of copy-protected movies (on DVD and Blu-ray Disc/HD DVD, respectively).