DVD Content Scramble System (CSS)
- The DVD Copy Control Association manages CSS. It grants licenses to use the technology and provides the necessary technical support.
- Mark Barry at UCSD has posted an introduction to DVD CSS.
- Another introduction by DVD software vendor Digiarty.
- A detailed discussion of the crypto mechanisms by Gregory Kesden at CMU.
Three Elements of Crypto Security
- Safe zones protect important data
- Secret keys remain secret
- Crypto mechanisms resist attacks
Jon Johansen co-authored DeCSS and released it in 1999. It was quickly distributed via web sites and Internet discussion groups. Some experts questioned its legality, and a few countries passed laws against “copyright circumvention” software. The discussion was complicated in the United States by the First Amendment, arguing that computer software was a form of protected free speech.
- A “gallery” of DeCSS descramblers hosted at CMU
- Electronic Frontier Foundation on DVD technology
- Archived articles about legal actions against Jon Johansen regarding DeCSS
Keeping Secret Keys Secret
- Physically protect them
- Make them changeable
- Make them hard to guess
Attacking the CSS mechanism
In 1999, Frank Stevenson of CMU reviewed an unofficial copy of the CSS source code program he found on the Internet. He reported significant weaknesses in the stream cipher design. This led to an attack requiring only 225 trials. He could crack a DVD disk key in a matter of seconds.
Movie DVDs encrypted their contents to prevent copying. The encryption did not prevent copying.
Video notes: cys.me/vid/c06.
Video #7 examines key wrapping on DVDs and privileges vimeo.com/202238441
The previous video explains how to detect message alterations using hash functions vimeo.com/199836576
See the entire Cryptosmith series in its album vimeo.com/album/4229550