II. <strong>What</strong> Does <strong>DRM</strong> Look Like?Since the beginnings of the personalcomputer revolution, more than a quarterof a century ago, a number ofapproaches and technologies have beendeveloped to prevent unauthorizedcopying of, or to otherwise control digitalcontent. There are three broadclasses of approaches that are currentlyused, or that have been proposed in variousstandards-setting or legislative proceedings.Sometimes these approachesare used by themselves, and sometimesin combination with one another.A. Encrypting orScrambling ContentA common approach to copy protectionis encryption — the use of a mathematical/computationalprocess to scrambleinformation so that only those who havethe right key or keys can obtain accessto it. This, for example, is how yourDVD movies work — their content isscrambled so that only DVD playersthat have the right keys can decrypt thecontent so that you can watch the DVDmovie. Similarly, if you receive cable orsatellite television, your TV serviceprovider normally scrambles content inways that prevent most unauthorizedpeople (that is, nonsubscribers) fromgetting access to it.The basic approach for encryption isto encrypt the digital content so thatonly a player with both the decryptiondevice or software and the proper keycan play the content. The contentowner can broadcast the content toeveryone but unless the recipient hasvalid decryption keys he cannot play thecontent. Scrambling is a similar copyprotectionapproach, but without a userappliedkey; instead, the key thatincludes the unscrambling algorithmresides in the player device (which maybe hardware, or software, or both).There are several varieties to encryption-basedcopy protection. In the simplesttype, all content is encrypted undera single master key. This is considered avery fragile scheme because, once thesingle key is compromised, the entire7
II. <strong>What</strong> Does <strong>DRM</strong> Look Like?system is considered compromised or “broken.” 8Cryptographers generally disfavor such “BreakOnce Break <strong>Every</strong>where” (a.k.a. “BOBE”) encryptionschemes.More robust approaches avoid the pitfalls ofBOBE by using many different keys. Some encryption-basedsystems encrypt each piece of contentwith its own individual key. As a result, the loss of asingle key only means the compromising of a singlepiece of content, and not the entire system. Inthe most complex variants of encryption-based systems,the encryption keys are unique not only forthe content but for theplayer as well. Thus,In spite of the breach someone who receivedboth the encrypted contentand the encryptionof DVD copy protection,key associated withthe DVD market another person could notplay the copied content oncontinues to witness his own player.An example of this moreremarkable growth. secure encryption-basedapproach can be found inEurope, where encryptionbasedcopy protection is commonly used by paytelevisionsatellite-TV providers. Subscribers havea hardware set-top box that unscrambles the satellitetransmissions into video signals that are thendisplayed on a standard television. Users have a socalled“smart card”: a personalized device thatplugs into the set-top box and controls which televisionprograms can be decrypted and displayed.The satellite television providers transmit theirprogramming in scrambled form, and set-top boxeswith authorized smart-cards are able to unscrambleprograms for viewing. The broadcasters can alsosend instructions to individual smart cards, authorizingthem to unscramble certain television showsor prohibiting them from unscrambling others.A similar scheme, called Content Scrambling System(also known as “Content Scramble System” or“CSS”), has been used by the DVD industry. CommercialDVDs are encrypted with a series of keys.These keys are embedded in different video players,whose manufacturers are licensed to build them intotheir products. As a general result, only “authorizedviewers” (those with legitimate, authorized DVDplayers that use authorized keys) can watch theDVDs. The Content Scramble System was designedso that the administrators of the system are able to“turn off” certain keys if they are compromised —so that some DVD players with now-deauthorizedkeys could be shut out of playing new DVDs withoutcausing the entire system to fail.As it happens, however, CSS in its existing formhas already been compromised by a Norwegiancitizen named Jon Johansen, who came up with ageneralizable workaround for the DVD scramblingsystem. That workaround computer program,called “DeCSS” makes it possible forsufficiently sophisticated users to sidestep DVDscrambling and render DVD movie contentunscrambled (a.k.a., “in the clear”), so that it canbe viewed on any player and, more important inthe context of copyright policy, can be copied onthe Internet and elsewhere.In spite of this breach of the CSS system,however, movie companies continue to produceDVD movies using the existing scrambling system.As a practical matter this breach has not hurtthe DVD market, which has continued to seeremarkable growth in the period since Johansenpublished DeCSS. 9While it is not yet evident that Johansen’s“crack” of the CSS system will cause long-termharm to the DVD market, the failure of CSS tosurvive a deliberate attempt to circumvent it hasspurred both the content companies and the computerand consumer-electronics companies thatproduce players for DVDs to explore alternativesin the delivery of content that may be more secure.Trusted Computing and Tethered ContentOne idea that has gained some currency — notleast because versions of it have been promoted byIntel (the leading manufacturer of personal-computermicroprocessors) and by Microsoft (the leadingmanufacturer of personal-computer operatingsystems) — has been to deliver content inencrypted form, and allow it to be decrypted onlywithin a tamper-resistant environment within acomputer or other device. This approach relies ona new design feature for Intel-based personal com-8
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