Copy protection - Wikipedia, the free encyclopedia
`
`Page 1 of 18
`
`Copy protection
`
`From Wikipedia, the free encyclopedia
`
`Copy protection, also known as content protection, copy prevention and copy restriction, is any
`effort designed to prevent the reproduction of software, films, music, and other media, usually for
`copyright reasons.[1] Various methods have been devised to prevent reproduction so that companies will
`gain benefit from each person who obtains an authorized copy of their product. Unauthorized copying
`and distribution accounted for $2.4 billion in lost revenue in the United States alone in the 1990s,[2] and
`is assumed to be causing impact on revenues in the music and the game industry, leading to proposal of
`stricter copyright laws such as PIPA. Some methods of copy protection have also led to criticisms
`because it caused inconvenience for honest consumers, or it secretly installed additional or unwanted
`software to detect copying activities on the consumer's computer. Making copy protection effective
`while protecting consumer rights is still an ongoing problem with media publication.
`
`Contents
`
`◾ 1 Terminology
`◾ 2 Business rationale
`◾ 3 Technical challenges
`◾ 4 Methods
`◾ 4.1 Computer software
`◾ 4.1.1 Early ages
`◾ 4.1.2 1980s Locksmith
`◾ 4.1.3 1990s CD-R
`◾ 4.1.4 Recent practices
`◾ 4.1.5 Problems and criticisms
`◾ 4.2 Early video games
`◾ 4.3 Video game console systems
`◾ 4.4 Videotape
`◾ 4.5 Audio CDs
`◾ 4.6 Other digital media
`◾ 5 Notable payloads
`◾ 6 Anti-piracy
`◾ 7 Anti-piracy in file sharing
`◾ 8 Examples
`◾ 9 See also
`◾ 10 References
`◾ 11 External links
`
`Terminology
`
`https://en.wikipedia.org/wiki/Copy_protection
`
`6/27/2016
`
`IPR2016-01271
`UNIFIED 1053
`
`

`
`Copy protection - Wikipedia, the free encyclopedia
`
`Page 2 of 18
`
`Media corporations have always used the term copy protection, but critics argue that the term tends to
`sway the public into identifying with the publishers, who favor restriction technologies, rather than with
`the users.[3] Copy prevention and copy control may be more neutral terms. "Copy protection" is a
`misnomer for some systems, because any number of copies can be made from an original and all of
`these copies will work, but only in one computer, or only with one dongle, or only with another device
`that cannot be easily copied.
`
`The term is also often related to, and confused with, the concept of digital rights management. Digital
`rights management is a more general term because it includes all sorts of management of works,
`including copy restrictions. Copy protection may include measures that are not digital. A more
`appropriate term may be "technological protection measures" (TPMs),[4] which is often defined as the
`use of technological tools in order to restrict the use or access to a work.
`Business rationale
`
`Copy protection is most commonly found on videotapes, DVDs, computer software discs, video game
`discs and cartridges, audio CDs and some VCDs.
`
`Many media formats are easy to copy using a machine, allowing consumers to distribute copies to their
`friends, a practice known as "casual copying".
`
`Companies publish works under copy protection because they believe that the cost of implementing the
`copy protection will be less than the revenue produced by consumers who buy the product instead of
`acquiring it through casually copied media.
`
`Opponents of copy protection argue that people who obtain free copies only use what they can get for
`free, and would not purchase their own copy if they were unable to obtain a free copy. Some even argue
`that free copies increase profit; people who receive a free copy of a music CD may then go and buy
`more of that band's music, which they would not have done otherwise.
`
`Some publishers have avoided copy-protecting their products, on the theory that the resulting
`inconvenience to their users outweighs any benefit of frustrating "casual copying".
`
`From the perspective of the end user, copy protection is always a cost. DRM and license managers
`sometimes fail, are inconvenient to use, and may not afford the user all of the legal use of the product he
`has purchased.
`
`The term copy protection refers to the technology used to attempt to frustrate copying, and not to the
`legal remedies available to publishers or authors whose copyrights are violated. Software usage models
`range from node locking to floating licenses (where a fixed number licenses can be concurrently used
`across an enterprise), grid computing (where multiple computers function as one unit and so use a
`common license) and electronic licensing (where features can be purchased and activated online). The
`term license management refers to broad platforms which enable the specification, enforcement and
`tracking of software licenses. To safeguard copy protection and license management technologies
`themselves against tampering and hacking, software anti-tamper methods are used.
`
`https://en.wikipedia.org/wiki/Copy_protection
`
`6/27/2016
`
`

`
`Copy protection - Wikipedia, the free encyclopedia
`
`Page 3 of 18
`
`Floating licenses are also being referred to as Indirect Licenses, and are licenses that at the time they are
`issued, there is no actually user who will use them. That has some technical influence over some of their
`characteristics. Direct Licenses are issued after a certain user requires it. As an example, an activated
`Microsoft product, contains a Direct License which is locked to the PC where the product is installed.
`
`From business standpoint, on the other hand, some services now try to monetize on additional services
`other than the media content so users can have better experience than simply obtaining the copied
`product.[5]
`Technical challenges
`
`From a technical standpoint, it would seem theoretically impossible to completely prevent users from
`making copies of the media they purchase, as long as a "writer" is available that can write to blank
`media. The basic technical fact is that all types of media require a "player" — a CD player, DVD player,
`videotape player, computer or video game console. The player has to be able to read the media in order
`to display it to a human. In turn, then, logically, a player could be built that first reads the media, and
`then writes out an exact copy of what was read, to the same type of media.
`
`At a minimum, digital copy protection of non-interactive works is subject to the analog hole: regardless
`of any digital restrictions, if music can be heard by the human ear, it can also be recorded (at the very
`least, with a microphone and tape recorder); if a film can be viewed by the human eye, it can also be
`recorded (at the very least, with a video camera and recorder). In practice, almost-perfect copies can
`typically be made by tapping into the analog output of a player (e.g. the speaker output or headphone
`jacks) and, once redigitized into an unprotected form, duplicated indefinitely. Copying text-based
`content in this way is more tedious, but the same principle applies: if it can be printed or displayed, it
`can also be scanned and OCRed. With basic software and some patience, these techniques can be
`applied by a typical computer-literate user.
`
`Since these basic technical facts exist, it follows that a determined individual will definitely succeed in
`copying any media, given enough time and resources. Media publishers understand this; copy protection
`is not intended to stop professional operations involved in the unauthorized mass duplication of media,
`but rather to stop "casual copying".
`
`Copying of information goods which are downloaded (rather than being mass-duplicated as with
`physical media) can be inexpensively customized for each download, and thus restricted more
`effectively, in a process known as "traitor tracing". They can be encrypted in a fashion which is unique
`for each user's computer, and the decryption system can be made tamper-resistant.
`Methods
`
`For information on individual protection schemes and technologies, see List of copy protection schemes
`or relevant category page.
`
`Computer software
`
`https://en.wikipedia.org/wiki/Copy_protection
`
`6/27/2016
`
`

`
`Copy protection - Wikipedia, the free encyclopedia
`
`Page 4 of 18
`
`Copy protection for computer software, especially for games, has been a long cat-and-mouse struggle
`between publishers and crackers. These were (and are) programmers who would defeat copy protection
`on software as a hobby, add their alias to the title screen, and then distribute the "cracked" product to the
`network of warez BBSes or Internet sites that specialized in distributing unauthorized copies of
`software.
`
`Early ages
`
`When computer software was still distributed in audio cassettes, audio copying was unreliable, while
`digital copying was time consuming. Software prices were comparable with audio cassette price.[2][6] To
`make digital copying more difficult, many programs used non-standard loading methods (loaders
`incompatible with standard BASIC loaders, or loaders that used different transfer speed.
`
`Unauthorized software copying began to be a problem when floppy disks became the common storage
`media.[6] The ease of copying depended on the system; Jerry Pournelle wrote in BYTE in 1983 that
`"CP/M doesn't lend itself to copy protection" so its users "haven't been too worried" about it, while
`"Apple users, though, have always had the problem. So have those who used TRS-DOS, and I
`understand that MS-DOS has copy protection features".[7] Apple and Commodore 64 computers were
`extremely varied and creative because most of the floppy disk reading and writing was controlled by
`software (or firmware), not by hardware. The first copy protection was for cassette tapes and consisted
`of a loader at the beginning of the tape, which read a specially formatted section which followed.
`
`The first protection of floppy disks consisted of changing the address marks, bit slip marks, data marks,
`or end of data marks for each sector. For example, Apple’s standard sector markings were:
`
`◾ D5 AA 96 for the address mark. That was followed by track, sector, and checksum.
`◾ DE AA EB concluded the address header with what are known as bit slip marks.
`◾ D5 AA AD was used for the data mark and the end of data mark was another DE AA EB.
`
`Changing any of these marks required fairly minimal changes to the software routines in Apple DOS
`which read and wrote the floppy disk, but produced a disk that could not be copied by any of the
`standard copiers, such as Apple's COPYA program. Some protection schemes used more complicated
`systems that changed the marks by track or even within a track.
`
`1980s Locksmith
`
`Pournelle disliked copy protection and, except for games, refused to review software that used it. He did
`not believe that it was useful, writing in 1983 that "For every copy protection scheme there's a hacker
`ready to defeat it. Most involve so-called nibble/nybble copiers, which try to analyze the original disk
`and then make a copy".[7] IBM's Don Estridge agreed: "I guarantee that whatever scheme you come up
`with will take less time to break than to think of it." While calling piracy "a threat to software
`development. It's going to dry up the software", he said "It's wrong to copy-protect programs ... There
`ought to be some way to stop [piracy] without creating products that are unusable."[8]
`
`https://en.wikipedia.org/wiki/Copy_protection
`
`6/27/2016
`
`

`
`Copy protection - Wikipedia, the free encyclopedia
`
`Page 5 of 18
`
`By 1980, the first 'nibble' copier, Locksmith, was introduced. These copiers reproduced copy protected
`floppy disks an entire track at a time, ignoring how the sectors were marked. This was harder to do than
`it sounds for two reasons: firstly, Apple disks did not use the index hole to mark the start of a track; their
`drives could not even detect the index hole. Tracks could thus start anywhere, but the copied track had to
`have this "write splice", which always caused some bits to be lost or duplicated due to speed variations,
`roughly in the same (unused for payload data) place as the original, or it would not work. Secondly,
`Apple used special "self-sync" bytes to achieve agreement between drive controller and computer about
`where any byte ended and the next one started on the disk. These bytes were written as normal data
`bytes followed by a slightly longer than normal pause, which was notoriously unreliable to detect on
`read-back; still, you had to get the self-sync bytes roughly right as without them being present in the
`right places, the copy would not work, and with them present in too many places, the track would not fit
`on the destination disk. Locksmith copied Apple II disks by taking advantage of the fact that these sync
`fields between sectors almost always consisted of a long string of FF (hex) bytes. It found the longest
`string of FFs, which usually occurred between the last and first sectors on each track, and began writing
`the track in the middle of that; also it assumed that any long string of FF bytes was a sync sequence and
`introduced the necessary short pauses after writing each of them to the copy. Ironically, Locksmith
`would not copy itself. The first Locksmith measured the distance between sector 1 of each track. Copy
`protection engineers quickly figured out what Locksmith was doing and began to use the same technique
`to defeat it. Locksmith countered by introducing the ability to reproduce track alignment and prevented
`itself from being copied by embedding a special sequence of nibbles, that if found, would stop the copy
`process. Henry Roberts (CTO of Nalpeiron (http://www.nalpeiron.com)), a graduate student in computer
`science at the University of South Carolina, reverse engineered Locksmith, found the sequence and
`distributed the information to some of the 7 or 8 people producing copy protection at the time.
`
`For some time, Locksmith continued to defeat virtually all of the copy protection systems in existence.
`The next advance came from Henry Roberts' thesis on software copy protection, which devised a way of
`replacing Apple’s sync field of FFs with random appearing patterns of bytes. Because the graduate
`student had frequent copy protection discussions with Apple’s copy protection engineer, Apple
`developed a copy protection system which made use of this technique. Henry Roberts then wrote a
`competitive program to Locksmith, Back It UP. He devised several methods for defeating that, and
`ultimately a method was devised for reading self sync fields directly, regardless of what nibbles they
`contained. The back and forth struggle between copy protection engineers and nibble copiers continued
`until the Apple II became obsolete and was replaced by the IBM PC and its clones.
`
`In 1989 Gilman Louie, head of Spectrum Holobyte, stated that copy protection added about $0.50 per
`copy to the cost of production of a game.[9]
`
`1990s CD-R
`
`Floppy disks were later displaced by CDs as the preferred method of distribution, with companies like
`Macrovision and Sony providing copy protection schemes that worked by writing data to places on the
`CD-ROM where a CD-R drive cannot normally write. Such a scheme had been used for the PlayStation
`and could not be circumvented easily without the use of a modchip.
`
`For software publishers, a less expensive method of copy protection is to write the software so that it
`requires some evidence from the user that they have actually purchased the software, usually by asking a
`question that only a user with a software manual could answer (for example, "What is the 4th word on
`
`https://en.wikipedia.org/wiki/Copy_protection
`
`6/27/2016
`
`

`
`Copy protection - Wikipedia, the free encyclopedia
`
`Page 6 of 18
`
`the 6th line of page 37?"). This approach can be defeated by users who have the patience to copy the
`manual with a photocopier, and it also suffers from cracked product becoming more convenient than
`original.
`
`Recent practices
`
`It has become very common for software to require activation by entering some proof of legal purchase
`such as:
`
`◾ Name & Serial, a name and serial number that is given to the user at the time the software is
`purchased
`◾ A phone activation code, which requires the user to call a number and register the product to
`receive a computer-specific serial number.
`◾ Device ID, specifically tying a copy of software to a computer or mobile device based on a unique
`identifier only known to that device (like the IMEI of a smartphone).
`
`To limit reusing activation keys to install the software on multiple machines, it has been attempted to tie
`the installed software to a specific machine by involving some unique feature of the machine. Serial
`number in ROM could not be used because some machines do not have them. Some popular surrogate
`for a machine serial number were date and time (to the second) of initialization of the hard disk or MAC
`address of Ethernet cards (although this is programmable on modern cards). With the rise of
`virtualization, however, the practice of locking has to add to these simple hardware parameters to still
`prevent copying.[10] Another approach to associating user and/or machine with serial number is product
`activation over the Internet, where users are required to have access to the Internet so the information on
`which serial number is installed on which machine gets sent to a server to be authenticated.
`Unauthorized users are not allowed to install or use the software. Microsoft's Windows Genuine
`Advantage system is a far-reaching example of this. With rise of Cloud computing, requiring Internet
`access is becoming more popular for software verification. Beyond online authentication, a standalone
`software may be integrated with the cloud so that key data or code is stored online. This could greatly
`strengthen the protection; for example, the software could store a property file or execute a process
`needed by the application in the cloud instead on the user's computer.
`
`Problems and criticisms
`
`The copy protection schemes described above have all been criticized for causing problems for validly
`licensed users who upgrade to a new machine, or have to reinstall the software after reinitializing their
`hard disk. Some Internet product activation products allow replacement copies to be issued to registered
`users or multiple copies to the same license. Like all software, copy-protection software sometimes
`contains bugs, whose effect may be to deny access to validly licensed users. Most copy protection
`schemes are easy to crack, and once crackers circumvent the copy protection, the resulting cracked
`software is then more convenient and hence more valuable than the non-cracked version, because users
`can make additional copies of the software. Due to this problem, user-interactive copy protection by
`asking questions from manuals has mostly disappeared.
`
`In his 1976 Open Letter to Hobbyists, Bill Gates complained that "most of you steal your software."
`However, Gates initially rejected copy protection and said "It just gets in the way."
`
`https://en.wikipedia.org/wiki/Copy_protection
`
`6/27/2016
`
`

`
`Copy protection - Wikipedia, the free encyclopedia
`
`Page 7 of 18
`
`There is also the tool of software blacklisting that is used to enhance certain copy protection schemes.
`
`Early video games
`
`During the 1980s and 1990s, video games sold on audio cassette and floppy disks were sometimes
`protected with an external user-interactive method that demanded the user to have the original package
`or a part of it, usually the manual. Copy protection was activated not at installation but every time the
`game was executed.[11]
`
`Sometimes the copy protection code was needed not at launch, but at a later point in the game. This
`helped the gamer to experience the game (e.g. as a demonstration) and perhaps could convince them to
`buy it by the time the copy protection point was reached.
`
`Several imaginative and creative methods have been employed, in order to be both fun and hard to copy.
`These include:
`
`◾ The most common method ("What is the 13th word on the 7th line of page 22?") was often used at
`the beginning of each game session, but as it proved to be troublesome and tiring for the players, it
`declined in popularity (for example, X-COM: UFO Defense used it too, but was later removed by
`the official v1.4 patch). A variant of this technique involved matching a picture provided by the
`game to one in the manual and providing an answer pertaining to the picture (Ski or Die, 4D
`Boxing and James Bond 007; the Stealth Affair used this technique). Buzz Aldrin's Race Into
`Space (in the floppy version but not the CD version) incorporated a copy protection scheme that
`required the user to input an astronaut's total duration in space (available in the manual) before the
`launch of certain missions. If the answer was incorrect, the mission would suffer a catastrophic
`failure.
`◾ Manuals containing information and hints vital to the completion of the game, like answers to
`riddles (Conquests of Camelot, King's Quest 6), recipes of spells (King's Quest 3), keys to
`deciphering non-Latin writing systems (Ultima series, see also Ultima writing systems), maze
`guides (Manhunter), dialogue spoken by other characters in the game (Wasteland, Dragon Wars),
`excerpts of the storyline (most Advanced Dungeons and Dragons games and Wing Commander I),
`or a radio frequency to use to communicate with a character to further a game (Metal Gear Solid).
`◾ Some sort of code with symbols, not existing on the keyboard or the ASCII code. This code was
`arranged in a grid, and had to be entered via a virtual keyboard at the request "What is the code at
`line 3 row 2?". These tables were printed on dark paper (Maniac Mansion, Uplink), or were
`visible only through a red transparent layer (Indiana Jones and the Last Crusade), making the
`paper very difficult to photocopy. Another variant of this method—most famously used on the ZX
`Spectrum version of Jet Set Willy—was a card with color sequences at each grid reference that
`had to be entered before starting the game. This also prevented monochrome photocopying. The
`codes in tables are based on a mathematic formula and can be calculated by using the row, line
`and page number if the formula is known, since the data would have required too much disk
`space.
`◾ The Secret of Monkey Island offered one of the most imaginative protection keys: a rotating wheel
`with halves of pirate's faces. The game showed a face composed of two different parts and asked
`when this pirate was hanged on a certain island. The player then had to match the faces on the
`wheel, and enter the year number that appeared on the island-respective hole. Its sequel had the
`same concept, but with magic potion ingredients. Other games that employed the code wheel
`system include games from Accolade like Star Control.
`
`https://en.wikipedia.org/wiki/Copy_protection
`
`6/27/2016
`
`

`
`Copy protection - Wikipedia, the free encyclopedia
`
`Page 8 of 18
`
`◾ Zork games such as Beyond Zork and Zork Zero came with "feelies" which contained information
`vital to the completion of the game. For example, the parchment found from Zork Zero contained
`clues vital to solving the final puzzle. However, whenever the player attempts to read the
`parchment, they are referred to the game package. The in-game help function alluded to this form
`of control with the response "Good luck, Blackbeard" to queries that were unsolvable without the
`original game materials.
`◾ The Lenslok system used a plastic prismatic device, shipped with the game, which was used to
`descramble a code displayed on screen.
`
`While not strictly a software protection, some game companies offered "value-added" goodies with the
`package, like funny manuals, posters, comics, storybooks or fictional documentation concerning the
`game (e.g. the Grail Diary for Indiana Jones or a police cadet notebook with Police Quest or the Hero's
`manual of Quest for Glory or a copy of the National Inquisitor newspaper in Zak McKracken) in order
`to entice gamers to buy the package. This trend is re-emerging in modern gaming as an incentive to both
`buy games and discourage their resale; some games like Forza Motorsport 3 and Dragon Age: Origins
`provide bonus in-game material that will only be given if one buys the game new.
`
`Video game console systems
`
`When Sega's Dreamcast was released in 1998, it came with a newer disc format, called the GD-ROM.
`Using a modified CD player, one could access the game functionality. Using a special swap method
`could allow reading a GD-ROM game through a CD-ROM just using common MIL-CD (standard CD
`Boot loading, commonly found on Windows Installation Discs, Linux Live CDs, and others).
`Dreamcasts sold after October 2000 contain a newer firmware update, not allowing MIL-CD boot.
`
`The Xbox has a specific function: Non-booting or non-reading from CDs and DVD-Rs as a method of
`game copy protection. Also, the Xbox is said to use a different DVD file system (instead of UDF). It has
`been theorized that the discs have a second partition that is read from the outside in (opposite current
`standards thus making the second partition unreadable in PC DVD drives) which give the tracks the
`appearance that the disc was spun backwards during manufacture. The Xbox 360 copy protection
`functions by requesting the DVD drive compute the angular distance between specific data sectors on
`the disc. A duplicated DVD will return different values than a pressed original would.
`
`The PlayStation 2 has a map file that contains all of the exact positions and file size info of the CD in it,
`which is stored at a position that is beyond the file limit. The game directly calls the position at where
`the map file is supposed to be. This means that if the file is moved inside the limit, it is useless since the
`game is looking outside the limit for it, and the file will not work outside of the limit, making any copied
`disc unusable without a mod chip or the use of FMCB (free memory card boot). FMCB uses the
`memory card to trick the built-in DVD video software into booting copied games. Before a copied game
`can be played, it must have been patched with a free application.
`
`Nintendo's Wii and Nintendo GameCube have their own specialty format for copy protection. It is based
`on DVD/miniDVD (Game Cube) technology; each disc contains some deliberately placed defects. The
`exact positions of these defects, which differ for each produced disc, is encoded encrypted in the BCA
`of each disc. The BCA is readable on most standard DVD-ROM Drives, but consumer burners can
`reproduce neither the BCA nor the defects. As an additional obfuscation mechanism, the on-disc sector
`format is a little bit different from normal DVDs. Nevertheless, it can be read using some consumer
`
`https://en.wikipedia.org/wiki/Copy_protection
`
`6/27/2016
`
`

`
`Copy protection - Wikipedia, the free encyclopedia
`
`Page 9 of 18
`
`DVD-ROM drives with a firmware modification or "debug mode". It is also possible to hack the Wii to
`install unlicensed software, some of which can use the Wii's own drive to create disc images and then
`play these copies.
`
`The PSP, except the PSP Go, uses the Universal Media Disc, a media format similar to a MiniDisc. It
`holds about 1.2 GB. Although it cannot be copied, one can make an ISO image (a file version of the
`UMD) on a memory card and play it on custom firmware, which can be installed on the PSP.
`
`The PlayStation 3, Xbox One, and PlayStation 4 use Blu-ray BD-ROM discs. In addition to any
`protection provided by the consoles themselves, the BD-ROM format's specification allows for a ROM-
`Mark which cannot be duplicated by consumer-level recorders. The BD-ROM format, in addition,
`provides considerable capacity: up to 100 gigabytes per disc with potential revision to provide more
`(many BD-ROM games use 40-50 gigabytes), making it unwieldy for online file-sharing, a major
`method of video game copying. To prevent the consoles themselves being hacked and used as a means
`to defeat these protections (as happened with the Wii and partially with the PlayStation 3), contemporary
`consoles employ trusted hardware paths that authenticate the internal hardware and software prior to
`operation.
`
`Some game developers, such as Markus Persson,[12] have encouraged consumers and other developers to
`embrace the reality of unlicensed copying and utilize it positively to generate increased sales and
`marketing interest.
`
`Videotape
`
`Companies such as Macrovision and Dwight Cavendish provided schemes to videotape publishers
`making copies unusable if they were created with a normal VCR. All major videotape duplicators
`licensed Macrovision or similar technologies to copy protect video cassettes for their clients or
`themselves.
`
`Starting in 1985 with the video release of "The Cotton Club", Macrovision has licensed to publishers a
`technology that exploits the automatic gain control feature of VCRs by adding pulses to the vertical
`blanking sync signal.[13] These pulses do not affect the image a consumer sees on his TV, but do confuse
`the recording-level circuitry of consumer VCRs. This technology, which is aided by U.S. legislation
`mandating the presence of automatic gain-control circuitry in VCRs, is said to "plug the analog hole"
`and make VCR-to-VCR copies impossible, although an inexpensive circuit is widely available that will
`defeat the protection by removing the pulses. Macrovision has patented methods of defeating copy
`prevention,[14] giving it a more straightforward basis to shut down manufacture of any device that
`descrambles it than often exists in the DRM world.
`
`Audio CDs
`
`By 2000, Napster had seen mainstream adoption, and several music publishers responded by starting to
`sell some CDs with various copy protection schemes. Most of these were playback restrictions that
`aimed to make the CD unusable in computers with CD-ROM drives, leaving only dedicated audio CD
`players for playback. This did not, however, prevent such a CD from being copied via an analogue
`
`https://en.wikipedia.org/wiki/Copy_protection
`
`6/27/2016
`
`

`
`Copy protection - Wikipedia, the free encyclopedia
`
`Page 10 of 18
`
`connection or by ripping the CD under operating systems such as Linux, which was effective since
`copy-protection software was generally written for Microsoft Windows. These weaknesses led critics to
`question the usefulness of such protection.
`
`CD copy protection is achieved by assuming certain feature levels in the drives. The CD Digital Audio
`is the oldest CD standard and forms the basic feature set beyond which dedicated audio players need no
`instructions. CD-ROM drives additionally need to support mixed mode CDs (combined audio and data
`tracks) and multi-session CDs (multiple data recordings each superseding and incorporating data of the
`previous session).
`
`The play preventions in use intentionally deviate from the standards and intentionally include
`malformed multisession data or similar with the purpose of confusing the CD-ROM drives to prevent
`correct function. Simple dedicated audio CD players would not be affected by the malformed data since
`these are for features they do not support—for example, an audio player will not even look for a second
`session containing the copy protection data.
`
`In practice, results vary wildly. CD-ROM drives may be able to correct the malformed data and still play
`them to an extent that depends on the make and version of the drive. On the other hand, some audio
`players may be built around drives with more than the basic features required for audio playback. Some
`car radios with CD playback, portable CD players, CD players with additional support for data CDs
`containing MP3 files, and DVD players have had problems with these CDs.
`
`The deviation from the Red Book standard that defines audio CDs required the publishers of these copy-
`protected CDs to refrain from using the official CDDA logo on the discs or the cases. The logo is a
`trademark owned by Philips and Sony and licensed to identify compliant audio discs only. To prevent
`dissatisfied customers from returning CDs which were misrepresented as compliant audio CDs, such
`CDs also started to carry prominent notices on their covers.
`
`In general the audio can always be extracted by applying the principle of the analog hole. Additionally,
`such programs as IsoBuster may be capable of producing hidden audio files.
`
`Examples of CD copy protection schemes are Cactus Data Shield, Copy Control, and Data Position
`Measurement.
`
`Other digital media
`
`More recently, publishers of music and films in digital form have turned to encryption to make copying
`more difficult. CSS, which is used on DVDs