Copy prevention

From Academic Kids

Copy prevention, also known as copy protection, is any technical measure designed to prevent duplication of information. Copy prevention is often hotly debated, and is sometimes thought to infringe on customers' property rights: for example, the right to make a backup copy of a videotape they have purchased, or to install and use computer software on multiple computers.



From a technical standpoint, it would seem impossible to completely prevent all users from making copies of such media as CDs, DVDs, videotapes, computer software discs, or video game discs. The basic technical fact is that all these types of media require a "player"—a CD player, DVD player, videotape player, computer, or video game console, in these five examples. 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, whether to the same type of media that was read, or to some other format, such as a file on a hard disk.

Copying of information goods which are downloaded (rather than embedded in physical media) can be restricted more effectively. They can be encrypted in a fashion which is unique for each user's computer, and the decryption system can be made tamper-resistant (see also traitor tracing).

At a minimum, digital copy prevention is subject to the analog hole: regardless of the digital restrictions, if music can be played on speakers, it can also be recorded. Copying text in this way is more tedious, but if it can be printed or displayed, it can also be scanned and OCRed.

Since this basic technical fact exists, copy prevention is not intended to stop professional operations involved in the unauthorized mass duplication of media, but rather to stop casual copying in which one friend makes a copy of a disc for another friend and thus (arguably) decreases the possible market for that disc by one copy.

Note on terminology

Publishers who implement copy prevention have historically referred to the technology as copy protection as it carries the implication of preventing destruction or suffering. However, as the act of copying information does not necessarily result in destruction, suffering, or even loss of business profits, many people believe this term is misleading. Advocates of copyright reform and copyright abolishment in particular believe the term wrongly encourages people to identify with publishers who benefit from copy prevention rather than the users who are restricted by it. Copy prevention is a neutral term which simply describes the purpose of the technology without passing judgment on whether the act of copying is inherently damaging.

Copy prevention on various media

Copy prevention has been attempted in many ways, long before computers and digital media entered the picture. For example, the ancient practice of watermarking is an attempt to, if not prevent a copy, at least prove the authenticity of the original. The music industry in particular has long sought a reliable copy prevention method—early attempts included adding a high frequency spoiler signal to an analog recording so that tape recorders would generate an unpleasant whistle when the spoiler heterodyned with the bias oscillator. These attempts were largely unsuccessful since the spoiler was either audible to the listener, or else so high that it would not be reproduced reliably when played back. Videotape manufacturers had more success, with companies like Macrovision inventing clever schemes that would make copies unusable if they were created with a normal VCR, and licensing this technology to videotape manufacturers.

Some modern forms of copy prevention are invisible to the end-user, such as CD subchannel data or other mechanisms such as SafeDisc which only become apparent once an attempt to copy is made.

Copy prevention for computer software

Copy prevention for early home computer software, especially for games, started a long cat-and-mouse struggle between publishers and crackers. Programmers who as a hobby would defeat copy prevention on software often 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.

Software copy prevention schemes for early computers such as the Apple II and Commodore 64 computers depended on precise knowledge of what exactly would happen if that hardware were forced to do something unusual, such as to read a disk sector that was unformatted, or to take just a few microseconds longer than necessary when instructing the floppy disk drive arm motor to move. This sort of physical copy prevention continues today on software shipped on CD-ROM, with companies like Macrovision and Sony providing copy prevention schemes that work by writing data to places on the CD-ROM where a CD-R drive cannot normally write. Such a scheme has been used for the Sony PlayStation and cannot be circumvented easily without the use of a modchip.

For software publishers, a less expensive method of copy prevention 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 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 BTO vulnerability, so that once crackers circumvent the copy prevention on a piece of software, the resulting cracked product is more convenient than the original software, creating a disincentive to buying an original. As a result, user-interactive copy prevention of this kind has mostly disappeared.

Other software copy prevention techniques include:

  • A dongle, a piece of hardware that must be plugged into the computer to run the software. This adds extra cost for the software publisher, so dongles are uncommon for games and are found mostly in high-end software packages costing several thousand dollars.
  • Registration key, one single registration key that is "hard-coded" into the program's source that is asked for when running the program.
  • Name & Serial, a name and serial number that is usually given to the user at the purchase of the software and is almost always required to install it. The serial number is generated based upon the name given.
  • Keyfile, which requires the user to have a keyfile in the same directory as the program is installed to run it.
  • Serial, the program has an algorithm that allows multiple serial numbers to be entered in. Usually asks for the serial at installation or while running the program.
  • Nag screens, annoying messages that appear during or at the start of the program telling the user to register the program.
  • Time limit, allows user to use the software for x number of days before they have to register the program.
  • Use limit, allows user to use the software for x number of times before they have to reigster the program.
  • Crippleware, some functions may be disabled until the user registers the program.
  • A phone activation code, which requires the user to call a number and register the product to receive a computer-specific serial number.
  • Internet product activation, which requires the user to connect to the Internet and type in a serial number so the software can "call home" and notify the manufacturer who has installed the software and where, and prevent other users from installing the software if they attempt to use the same serial number.

The two latter methods imply tying the software installation to a specific machine by noting some particular unique feature of the machine. Some machines have a serial number in ROM, while others do not, and so some other metric, such as the date and time (to the second) of initialisation of the hard disk can be used. On machines with Ethernet cards, the MAC address, which is unique and factory-assigned, is a popular surrogate for a machine serial number (however, this address is programmable on modern cards). The problem with these sorts of schemes are that they can cause problems for a validly licensed user who upgrades to a new machine or reinstalls the software having reinitialised the disk, though some Internet product activation products can allow replacement copies to be issued to registered users or multiple copies to the same licensee. Like other software, copy-prevention software not infrequently contains bugs, whose effect may be to deny access to validly licensed users. As with all similar schemes, they are often easy to crack, and the resulting cracked software is perceived as being more valuable than the uncracked version.

There is also the tool of software blacklisting that is used to enhance certain copy prevention schemes.

Copy prevention for old games

During the 80's and 90's, pre-CD computer games were usually protected with a user-interactive method that demanded the user to have the original package or an item of it, like the manual. Copy protection was activated not at the installation, but every time the game was executed.

Sometimes, the code was needed not at the execution, but in a later point (or points) of the game. This helped the gamer to experience the game (eg. in demonstrations) before buying it, and also made sure that the gamer didn't borrow the manual.

Usually 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 Ath word on the Bth line of page C?") was often used at the beginning of each game session, but for abovementioned reasons it was abandoned.
  • Manual 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), maze guides etc.
  • Some sort of code with symbols, not existing on the keyboard or the ASCII code. This code was arranged in a grid, and was needed to be entered via a vitual keyboard at the request "What is the code at line X row Y?". These tables were printed in dark paper (Maniac Mansion), or were visible only through a red transparent layer (Indiana Jones and the Last Crusade), so that it was impossible to photocopy.
  • 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.
  • Superior Soccer had no outward signs of copy protection, but if it decided it was illegally copied, it would make the soccer ball in the game invisible, thus making it impossible to play the game.
  • Not exactly a protection, but the game companies used to offer goodies with the package, like funny manuals, posters, or fictional documentation concerning the game (eg. the Grail Diary for Indiana Jones or a police cadet notebook with Police Quest) in order to convince the gamers to buy the package.

Copy prevention for audio CDs

Starting in 2000, record publishers started to sell CDs with various copy prevention schemes. Most of these are playback restrictions that aim to make the CD unusable in devices that can also be conveniently used for duplicating (e.g., CD-ROM drives in computers), leaving only dedicated audio CD players for playback. This does not, however, prevent such a CD from being copied via analogue connections, which has led critics to question the usefulness of such schemes.

This 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 knowledge. CD-ROM drives additionally need to support mixed mode CDs (combined audio and data tracks) and multisession 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 don't support (for example, an audio player will not even look for a second session containing the copy prevention 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 intelligence required for audio playback. Especially car radios with CD playback, portable CD players, CD players with additional support for data CDs containing MP3 files and DVD players are likely to be problematic.

The deviation from the Red Book standard that defines audio CDs required the publishers of CDs produced in such a manner 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.

Examples of copy prevention schemes are Cactus Data Shield and Copy control.

Copy prevention in recent digital media

More recently, publishers of music and movies in digital form have turned to encryption to make copying more difficult. CSS, which is used on DVDs, is a particularly famous example of this. It is a form of copy prevention that uses 40-bit encryption. Copies will not be playable since they will be missing the key, which is not writable on DVD-R or DVD-RW discs. With this technique, the work is encrypted using a key known only to authorized players, which allow only "legitimate" uses of the work (usually restricted forms of playback, but no conversion or modification). The Digital Millennium Copyright Act provides a legal protection for this in the US, making it illegal to distribute unauthorized players—which was supposed to eliminate the possibility of building a DVD copier. However, CSS and other such software-based solutions have been reverse engineered (DeCSS), providing access to the encryption keys and methods. The cat-and-mouse struggle continues.

In the future, software cracking may become more difficult to perform with the release of the Fritz-chip in combination with certain software, like Nexus in the next major operating system from Microsoft, code-named Longhorn.

See also

Shareware solutions

  • PELock (

External links

de:Kopierschutz ja:コピーガード


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