Analog hole
Encyclopedia
The analog hole is a fundamental and inevitable vulnerability
in copy protection
schemes for noninteractive works in digital
formats which can be exploited to duplicate copy-protected works that are ultimately reproduced using analog
means. Once digital information is converted to a human-perceptible (analog) form, it is a relatively simple matter to digitally recapture that analog reproduction in an unrestricted form, thereby fundamentally circumventing any and all restrictions placed on copyright
ed digitally-distributed work. Media publishers who use digital rights management
(DRM), to restrict how a work can be used, perceive the necessity to make it visible and/or audible as a "hole" in the control that DRM otherwise affords them.
films may have poor audio
, or highly washed-out video. At a minimum, copy protection
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. Naturally, the use of high quality conversion equipment reduces the amount of noise added, to the point where such noise is essentially imperceptible to the human senses.
Regardless of any digital or software
copy control mechanisms, if sound
can be heard by an ear, it can also be recorded by a microphone
. And if images (static images or video/film), including text
, can be seen by the eye
, it can also be recorded by a camera. In the case of text the image can be converted back to text using optical character recognition
.
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. These proposals are discussed in the Content Protection Status Report
, Consumer Broadband and Digital Television Promotion Act
, and Analog Reconversion Discussion Group. 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.
In theory, it is possible to bypass all these measures by constructing a player that creates a copy of every frame and sound it plays. Although this is not within the capability of most people, many bootleggers simply record the video being displayed with a video camera or use recording and playing devices that are not designed to use the protection measures. In fact, the Motion Picture Association of America
has recommended use of a camcorder as an alternative to circumventing the Content Scrambling System on DVDs.
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 by the European Parliament 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. The legislators, hearing a very general piece of computer jargon (caching)
associated with infringement, banned it, not realizing it was a basic digital storage technique found in most modern equipment. A BBC article describing the controversy itself demonstrates the difficulty of explaining to legislators and the general public the aspect that every computer and most digital devices of any kind would have to be destroyed were the law to be evenly enforced. Far from a specialized illegality, caching is a universally used computer memory technique, leading to comparisons of this law to the Indiana Pi Bill
.
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 these means is 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. One does not have to be an engineer to understand that it is simply not possible to simultaneously display and conceal a signal. In particular, an audio signal must be converted to analog before it reaches the listener.
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 dither
ing.
, especially as the cost of such equipment continues to drop and as direct digital piracy becomes more difficult.
Vulnerability (computing)
In computer security, a vulnerability is a weakness which allows an attacker to reduce a system's information assurance.Vulnerability is the intersection of three elements: a system susceptibility or flaw, attacker access to the flaw, and attacker capability to exploit the flaw...
in copy protection
Copy protection
Copy protection, also known as content protection, copy obstruction, copy prevention and copy restriction, refer to techniques used for preventing the reproduction of software, films, music, and other media, usually for copyright reasons.- Terminology :Media corporations have always used the term...
schemes for noninteractive works in digital
Digital
A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...
formats which can be exploited to duplicate copy-protected works that are ultimately reproduced using analog
Analog signal
An analog or analogue signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It differs from a digital signal in terms of small fluctuations in the signal which are...
means. Once digital information is converted to a human-perceptible (analog) form, it is a relatively simple matter to digitally recapture that analog reproduction in an unrestricted form, thereby fundamentally circumventing any and all restrictions placed on copyright
Copyright
Copyright is a legal concept, enacted by most governments, giving the creator of an original work exclusive rights to it, usually for a limited time...
ed digitally-distributed work. Media publishers who use digital rights management
Digital rights management
Digital rights management is a class of access control technologies that are used by hardware manufacturers, publishers, copyright holders and individuals with the intent to limit the use of digital content and devices after sale. DRM is any technology that inhibits uses of digital content that...
(DRM), to restrict how a work can be used, perceive the necessity to make it visible and/or audible as a "hole" in the control that DRM otherwise affords them.
Overview
Although the technology for creating digital recordings from analog sources has existed for some time, it was not necessarily viewed as a "hole" until the widespread deployment of DRM in the late 1990s. It should be pointed out that this kind of duplication is not a direct digital copy, and therefore has flaws, the magnitude of which depends on the nature of the reproduction methods used. This kind of reproduction is, in many ways, similar to the initial digitization of any analog medium or performance, with all the pitfalls and benefits of such digitization. For example, bootlegBootleg recording
A bootleg recording is an audio or video recording of a performance that was not officially released by the artist or under other legal authority. The process of making and distributing such recordings is known as bootlegging...
films may have poor audio
Sound recording and reproduction
Sound recording and reproduction is an electrical or mechanical inscription and re-creation of sound waves, such as spoken voice, singing, instrumental music, or sound effects. The two main classes of sound recording technology are analog recording and digital recording...
, or highly washed-out video. At a minimum, copy protection
Copy protection
Copy protection, also known as content protection, copy obstruction, copy prevention and copy restriction, refer to techniques used for preventing the reproduction of software, films, music, and other media, usually for copyright reasons.- Terminology :Media corporations have always used the term...
can be circumvented for types of material whose value is aesthetic
Aesthetics
Aesthetics is a branch of philosophy dealing with the nature of beauty, art, and taste, and with the creation and appreciation of beauty. It is more scientifically defined as the study of sensory or sensori-emotional values, sometimes called judgments of sentiment and taste...
, 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
Information theory
Information theory is a branch of applied mathematics and electrical engineering involving the quantification of information. Information theory was developed by Claude E. Shannon to find fundamental limits on signal processing operations such as compressing data and on reliably storing and...
sense relative to the original digital signal. This noise can be measured and quantified. Naturally, the use of high quality conversion equipment reduces the amount of noise added, to the point where such noise is essentially imperceptible to the human senses.
Regardless of any digital or software
Computer software
Computer software, or just software, is a collection of computer programs and related data that provide the instructions for telling a computer what to do and how to do it....
copy control mechanisms, if sound
Sound
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
can be heard by an ear, it can also be recorded by a microphone
Microphone
A microphone is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1877, Emile Berliner invented the first microphone used as a telephone voice transmitter...
. And if images (static images or video/film), including text
Character (computing)
In computer and machine-based telecommunications terminology, a character is a unit of information that roughly corresponds to a grapheme, grapheme-like unit, or symbol, such as in an alphabet or syllabary in the written form of a natural language....
, can be seen by the eye
Human eye
The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
, it can also be recorded by a camera. In the case of text the image can be converted back to text using optical character recognition
Optical character recognition
Optical character recognition, usually abbreviated to OCR, is the mechanical or electronic translation of scanned images of handwritten, typewritten or printed text into machine-encoded text. It is widely used to convert books and documents into electronic files, to computerize a record-keeping...
.
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. These proposals are discussed in the Content Protection Status Report
Content Protection Status Report
The Content Protection Status Report is the title of a series of three documents submitted to the United States Senate Committee on the Judiciary during 2002 by the Motion Picture Association of America. The Content Protection Status Report is the title of a series of three documents submitted to...
, Consumer Broadband and Digital Television Promotion Act
Consumer Broadband and Digital Television Promotion Act
The Consumer Broadband and Digital Television Promotion Act was a United States bill proposed in 2002 that would have prohibited any kind of technology that could be used to read digital content without digital rights management —which prohibits copying and reading any content under copyright...
, and Analog Reconversion Discussion Group. 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
Patent
A patent is a form of intellectual property. It consists of a set of exclusive rights granted by a sovereign state to an inventor or their assignee for a limited period of time in exchange for the public disclosure of an invention....
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, MacrovisionMacrovisionRovi Corporation is a globally operating, US-based company that provides guidance technology, entertainment data, copy protection, industry standard networking and media management technology for digital entertainment devices and services...
attempts to defeat recording by VCRs by outputting a deliberately distorted signal, crippling the automatic gain controlAutomatic gain controlAutomatic gain control is an adaptive system found in many electronic devices. The average output signal level is fed back to adjust the gain to an appropriate level for a range of input signal levels...
for videoVideoVideo is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...
, causing the brightnessBrightnessBrightness is an attribute of visual perception in which a source appears to be radiating or reflecting light. In other words, brightness is the perception elicited by the luminance of a visual target...
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 computerPersonal computerA personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
s. Devices exist, however, to counteract this measure. - Manufacturers of recording devices can be required to screen analog inputs for watermarks (or MacrovisionMacrovisionRovi Corporation is a globally operating, US-based company that provides guidance technology, entertainment data, copy protection, industry standard networking and media management technology for digital entertainment devices and services...
or DCS Copy ProtectionDCS Copy ProtectionDCS Copy Protection Ltd is a UK company that licenses proprietary content protection technology. It is a direct competitor to Rovi in the field of analogue copy protection....
or CGMS-ACGMS-ACopy Generation Management System - Analog is a copy protection mechanism for analog television signals. It consists of a waveform inserted into the non-picture Vertical Blanking Interval of an analogue video signal...
) and limit recording as a condition of private contractContractA contract is an agreement entered into by two parties or more with the intention of creating a legal obligation, which may have elements in writing. Contracts can be made orally. The remedy for breach of contract can be "damages" or compensation of money. In equity, the remedy can be specific...
s. For example, a manufacturer who licenses patents or trade secretTrade secretA trade secret is a formula, practice, process, design, instrument, pattern, or compilation of information which is not generally known or reasonably ascertainable, by which a business can obtain an economic advantage over competitors or customers...
s 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 boxSet-top boxA set-top box or set-top unit is an information appliance device that generally contains a tuner and connects to a television set and an external source of signal, turning the signal into content which is then displayed on the television screen or other display device.-History:Before the...
es 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 controlSelectable output controlSelectable Output Control is a content protection Digital Rights Management technology that is incorporated into approved devices that enables the Multichannel Video Programming Distributor to disable non-secure audio-video output by encoding the video with a specific signal...
. 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.
In theory, it is possible to bypass all these measures by constructing a player that creates a copy of every frame and sound it plays. Although this is not within the capability of most people, many bootleggers simply record the video being displayed with a video camera or use recording and playing devices that are not designed to use the protection measures. In fact, the Motion Picture Association of America
Motion Picture Association of America
The Motion Picture Association of America, Inc. , originally the Motion Picture Producers and Distributors of America , was founded in 1922 and is designed to advance the business interests of its members...
has recommended use of a camcorder as an alternative to circumventing the Content Scrambling System on DVDs.
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 by the European Parliament 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. The legislators, hearing a very general piece of computer jargon (caching)
Cache
In computer engineering, a cache is a component that transparently stores data so that future requests for that data can be served faster. The data that is stored within a cache might be values that have been computed earlier or duplicates of original values that are stored elsewhere...
associated with infringement, banned it, not realizing it was a basic digital storage technique found in most modern equipment. A BBC article describing the controversy itself demonstrates the difficulty of explaining to legislators and the general public the aspect that every computer and most digital devices of any kind would have to be destroyed were the law to be evenly enforced. Far from a specialized illegality, caching is a universally used computer memory technique, leading to comparisons of this law to the Indiana Pi Bill
Indiana Pi Bill
The Indiana Pi Bill is the popular name for bill #246 of the 1897 sitting of the Indiana General Assembly, one of the most famous attempts to establish scientific truth by legislative fiat...
.
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 these means is 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. One does not have to be an engineer to understand that it is simply not possible to simultaneously display and conceal a signal. In particular, an audio signal must be converted to analog before it reaches the listener.
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 dither
Dither
Dither is an intentionally applied form of noise used to randomize quantization error, preventing large-scale patterns such as color banding in images...
ing.
Copyright law vs. particular techniques
Copyright law has been defined in terms of general definitions of infringement in any concrete medium. This classically focused 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-restricted medium, there are two grades of equipment: consumer, which may include copy restriction, and professional, which by necessity, allows access in a way that is above copy restriction. In most countries, the sale of professional equipment is not regulated, although price alone prevents most users from getting access to it. The price may not discourage piracy organizations that understand such a purchase as an investment with a good returnRate of return
In finance, rate of return , also known as return on investment , rate of profit or sometimes just return, is the ratio of money gained or lost on an investment relative to the amount of money invested. The amount of money gained or lost may be referred to as interest, profit/loss, gain/loss, or...
, especially as the cost of such equipment continues to drop and as direct digital piracy becomes more difficult.
See also
- Digital rights managementDigital rights managementDigital rights management is a class of access control technologies that are used by hardware manufacturers, publishers, copyright holders and individuals with the intent to limit the use of digital content and devices after sale. DRM is any technology that inhibits uses of digital content that...
- Copy protection in Japan
- Secure cryptoprocessorSecure cryptoprocessorA secure cryptoprocessor is a dedicated computer on a chip or microprocessor for carrying out cryptographic operations, embedded in a packaging with multiple physical security measures, which give it a degree of tamper resistance....
- Trusted Platform ModuleTrusted Platform ModuleIn computing, Trusted Platform Module is both the name of a published specification detailing a secure cryptoprocessor that can store cryptographic keys that protect information, as well as the general name of implementations of that specification, often called the "TPM chip" or "TPM Security...
- Trusted ComputingTrusted ComputingTrusted Computing is a technology developed and promoted by the Trusted Computing Group. The term is taken from the field of trusted systems and has a specialized meaning. With Trusted Computing, the computer will consistently behave in expected ways, and those behaviors will be enforced by...
- Digital Transition Content Security ActDigital Transition Content Security ActThe United States The Digital Transition Content Security Act was a bill introduced by House Judiciary Committee Chairman James Sensenbrenner Jr., a Wisconsin Republican, on December 16, 2005. The bill was backed by Democratic Rep. John Conyers.Its goal is "To require certain analog conversion...
- Fair useFair useFair use is a limitation and exception to the exclusive right granted by copyright law to the author of a creative work. In United States copyright law, fair use is a doctrine that permits limited use of copyrighted material without acquiring permission from the rights holders...