Analog hole
From Wikipedia, the free encyclopedia
The analog hole (sometimes analog reconversion problem or analog reconversion issue) is a fundamental, and inevitable vulnerability in copy prevention schemes for noninteractive digital content which is intended to be played back using analog means. When the information is converted to a perceptible analog form, there are no restrictions on the resulting analog signal, and the content can be captured back into digital form with no restrictions.
Because this process produces an unrestricted digital representation of a work, given an initially restricted version, publishers who use digital rights management (DRM) to impose restrictions on how a work can be used may view this possibility as a "hole" in the protection or control that DRM affords them. Although the technical possibility of making digital recordings from analog outputs has existed for some time, it was not necessarily viewed as a "hole" before widespread deployments of DRM in the late 1990s. The term "analog hole" was first popularized by the Motion Picture Association of America and some of its members during speeches and legislative advocacy in 2002; this term later fell into disrepute within the industry, being replaced by "analog reconversion problem" and similar terms.
However, this kind of reproduction is not a direct digital copy, and therefore will have flaws; the magnitude of the flaws depends on the reproduction methods used. For example, bootleg films may have poor audio, or highly washed-out video. At a minimum, the copy prevention can be circumvented for types of material whose value is aesthetic, and does not depend on its exact digital duplication. In general, performing a digital-to-analog conversion followed by an analog-to-digital conversion results in the addition of noise in an information-theoretic sense relative to the original digital signal. This noise can be measured and quantified; using better recording equipment reduces the amount of noise added.
Regardless of any digital or software copy control mechanisms, if music can be played on speakers, it can also be recorded. And just as text can be printed or displayed, it can also be scanned and recognized. However, because of its interactivity, software cannot be copied in this manner.
In 2002 and 2003, the U.S. motion picture industry publicly discussed the possibility of legislation to "close the analog hole" -- most likely through regulation of digital recording devices, limiting their ability to record analog video signals that appear to be commercial audiovisual works. See Content Protection Status Report, Consumer Broadband and Digital Television Promotion Act, and Analog Reconversion Discussion Group for more on these proposals. Inventors of digital watermark technologies were particularly interested in this possibility because of the prospect that recording devices could be required to screen inputs for the presence of a particular watermark (and hence, presumably, their manufacturers would need to pay a patent royalty to the watermark's inventor).
The motion picture industry has also pursued several private-sector approaches to eliminating the analog hole; these might be implemented without additional legislation.
- Analog signals can be degraded in ways that interfere with or confuse some recording devices. For example, Macrovision attempts to defeat recording by VCRs by outputting a deliberately-distorted signal, crippling the automatic gain control for video, causing the brightness to fluctuate wildly. While this is only supposed to happen to copies, it may, as an inadvertent side-effect, happen when viewing the original video as well. Some vendors claim to have developed equivalent techniques for preventing recording by video capture cards in personal computers.
- Manufacturers of recording devices can be required to screen analog inputs for watermarks (or Macrovision or CGMS-A) and limit recording as a condition of private contracts. For example, a manufacturer who licenses patents or trade secrets associated with a particular DRM scheme might also be obliged as a purely contractual matter to add recording limitations to digital recording products.
- Manufacturers of certain playback devices such as set-top boxes can be required, as a condition of private contracts, to allow publishers or broadcasters to disable analog outputs entirely, or to degrade the analog output quality, when particular programming is displayed. This capability is one example of Selectable Output Control. A broadcaster could then prevent all recording of a broadcast program by indicating that compliant receiving devices should refuse to output it through analog outputs at all.
Contents |
Engineering vs. business and political views
The notion of "plugging the analog hole" may be based on fundamental misconceptions of the meaning of analog and digital. There is a history of business and political desires combined with core misunderstandings of technology leading to legislation and industry practices that are counterproductive or fundamentally flawed on an engineering theory level. One example was an early law passed in Europe to support DRM in response to widespread buzz about unauthorized digital music downloads being held in computer memory caches. Apparently reasoning by analogy to "caches of arms", the use of computer memory caches was outlawed. Unfortunately, far from a specialized illegality, caching is a universally used computer memory technique, leading to comparisons of this law to the classic story of a legislature that passed a law defining pi exactly equal to three.
A body of opinion in the engineering community puts the buzz about the "analog hole" in the same category: an impossible strategy based on fundamental misunderstandings by people who are not engineers that will not solve the stated problem but cause expense and confusion. Both "analog to digital" and "digital to analog" conversion are such basic technologies, with so many possible implementations, that the idea of being able to block conversion by this means is considered unrealistic. Engineers are aware of mathematical and physical principles that often begin with "It is not possible to..." which sometimes come in direct conflict with business and political goals. Non-engineers can understand that it is simply not possible to simultaneously display and conceal a signal.
In addition to this general principle, theory says that digital watermarking and other restrictions on the "analog hole" can be simply defeated by a variety of well-known techniques, such as dithering. The response " Well, we will outlaw that too" (an impossibility) differentiates the realism of engineers from the unrealizable desires of attorneys.
Copyright law vs. particular techniques
Copyright law has been defined in terms of general definitions of infringement in any concrete medium. This classically focussed such law on whether there is infringement, rather than focus on particular engineering techniques. Detecting infringement within the social and legal system avoids a legacy of outlawing generic, universal, popular, widespread, useful, and possibly uncontrollable engineering techniques in response to specific misuses.
Consumer vs. professional equipment
In every copy protected medium, there are two grades of equipment, consumer, which may include copy protection, and professional, which by necessity, allows access in a way that is above copy protection. The issue of who professional equipment is sold to and the patent and license terms involved stands in contrast to the notion of outlawing physical properties of electricity.
See also
- Digital rights management
- Copy protection in Japan
- Secure cryptoprocessor
- Fritz-chip
- Trusted Computing
- Digital Transition Content Security Act
