WO2003015088A1 - Method of authenticating cds - Google Patents

Method of authenticating cds Download PDF

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Publication number
WO2003015088A1
WO2003015088A1 PCT/GB2002/003710 GB0203710W WO03015088A1 WO 2003015088 A1 WO2003015088 A1 WO 2003015088A1 GB 0203710 W GB0203710 W GB 0203710W WO 03015088 A1 WO03015088 A1 WO 03015088A1
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WO
WIPO (PCT)
Prior art keywords
lengths
pits
cds
lands
standard
Prior art date
Application number
PCT/GB2002/003710
Other languages
French (fr)
Inventor
Jonathan Michael Blackledge
Johnson W.N.H.
Original Assignee
Durand Technology Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GB0119589A external-priority patent/GB0119589D0/en
Application filed by Durand Technology Limited filed Critical Durand Technology Limited
Publication of WO2003015088A1 publication Critical patent/WO2003015088A1/en

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Classifications

    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F21/00—Security arrangements for protecting computers, components thereof, programs or data against unauthorised activity
    • G06F21/70—Protecting specific internal or peripheral components, in which the protection of a component leads to protection of the entire computer
    • G06F21/78—Protecting specific internal or peripheral components, in which the protection of a component leads to protection of the entire computer to assure secure storage of data
    • G06F21/80—Protecting specific internal or peripheral components, in which the protection of a component leads to protection of the entire computer to assure secure storage of data in storage media based on magnetic or optical technology, e.g. disks with sectors
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B19/00—Driving, starting, stopping record carriers not specifically of filamentary or web form, or of supports therefor; Control thereof; Control of operating function ; Driving both disc and head
    • G11B19/02—Control of operating function, e.g. switching from recording to reproducing
    • G11B19/12—Control of operating function, e.g. switching from recording to reproducing by sensing distinguishing features of or on records, e.g. diameter end mark
    • G11B19/122—Control of operating function, e.g. switching from recording to reproducing by sensing distinguishing features of or on records, e.g. diameter end mark involving the detection of an identification or authentication mark
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/00086—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/00086—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy
    • G11B20/00094—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy involving measures which result in a restriction to authorised record carriers
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/00086—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy
    • G11B20/00094—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy involving measures which result in a restriction to authorised record carriers
    • G11B20/00115—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy involving measures which result in a restriction to authorised record carriers wherein the record carrier stores a unique medium identifier
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/00086—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy
    • G11B20/00094—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy involving measures which result in a restriction to authorised record carriers
    • G11B20/00123—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy involving measures which result in a restriction to authorised record carriers the record carrier being identified by recognising some of its unique characteristics, e.g. a unique defect pattern serving as a physical signature of the record carrier
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/00086—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy
    • G11B20/00166—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy involving measures which result in a restriction to authorised contents recorded on or reproduced from a record carrier, e.g. music or software
    • G11B20/00173—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy involving measures which result in a restriction to authorised contents recorded on or reproduced from a record carrier, e.g. music or software wherein the origin of the content is checked, e.g. determining whether the content has originally been retrieved from a legal disc copy or another trusted source
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/00086—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy
    • G11B20/00188—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy involving measures which result in a restriction to authorised devices recording or reproducing contents to/from a record carrier
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/00086—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy
    • G11B20/00188—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy involving measures which result in a restriction to authorised devices recording or reproducing contents to/from a record carrier
    • G11B20/00195—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy involving measures which result in a restriction to authorised devices recording or reproducing contents to/from a record carrier using a device identifier associated with the player or recorder, e.g. serial numbers of playback apparatuses or MAC addresses
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/00086—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy
    • G11B20/0021—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy involving encryption or decryption of contents recorded on or reproduced from a record carrier
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/00086—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy
    • G11B20/0021—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy involving encryption or decryption of contents recorded on or reproduced from a record carrier
    • G11B20/00217—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy involving encryption or decryption of contents recorded on or reproduced from a record carrier the cryptographic key used for encryption and/or decryption of contents recorded on or reproduced from the record carrier being read from a specific source
    • G11B20/00224—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy involving encryption or decryption of contents recorded on or reproduced from a record carrier the cryptographic key used for encryption and/or decryption of contents recorded on or reproduced from the record carrier being read from a specific source wherein the key is obtained from a remote server
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/00086—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy
    • G11B20/00572—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy involving measures which change the format of the recording medium
    • G11B20/00586—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy involving measures which change the format of the recording medium said format change concerning the physical format of the recording medium
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/00086—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy
    • G11B20/00572—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy involving measures which change the format of the recording medium
    • G11B20/00586—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy involving measures which change the format of the recording medium said format change concerning the physical format of the recording medium
    • G11B20/00594—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy involving measures which change the format of the recording medium said format change concerning the physical format of the recording medium wherein the shape of recording marks is altered, e.g. the depth, width, or length of pits
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/00086—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy
    • G11B20/00855—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy involving a step of exchanging information with a remote server
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/10—Digital recording or reproducing
    • G11B20/10009—Improvement or modification of read or write signals
    • G11B20/10046—Improvement or modification of read or write signals filtering or equalising, e.g. setting the tap weights of an FIR filter
    • G11B20/10212—Improvement or modification of read or write signals filtering or equalising, e.g. setting the tap weights of an FIR filter compensation for data shift, e.g. pulse-crowding effects
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/10—Digital recording or reproducing
    • G11B20/14—Digital recording or reproducing using self-clocking codes
    • G11B20/1403—Digital recording or reproducing using self-clocking codes characterised by the use of two levels
    • G11B20/1423—Code representation depending on subsequent bits, e.g. delay modulation, double density code, Miller code
    • G11B20/1426—Code representation depending on subsequent bits, e.g. delay modulation, double density code, Miller code conversion to or from block codes or representations thereof
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/10—Digital recording or reproducing
    • G11B20/14—Digital recording or reproducing using self-clocking codes
    • G11B20/1403—Digital recording or reproducing using self-clocking codes characterised by the use of two levels
    • G11B20/1423—Code representation depending on subsequent bits, e.g. delay modulation, double density code, Miller code
    • G11B20/1426—Code representation depending on subsequent bits, e.g. delay modulation, double density code, Miller code conversion to or from block codes or representations thereof
    • G11B2020/1461—8 to 14 modulation, e.g. the EFM code used on CDs or mini-discs
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/10—Digital recording or reproducing
    • G11B20/18—Error detection or correction; Testing, e.g. of drop-outs
    • G11B20/1833—Error detection or correction; Testing, e.g. of drop-outs by adding special lists or symbols to the coded information
    • G11B2020/1836—Error detection or correction; Testing, e.g. of drop-outs by adding special lists or symbols to the coded information using a Reed Solomon [RS] code
    • G11B2020/184—Error detection or correction; Testing, e.g. of drop-outs by adding special lists or symbols to the coded information using a Reed Solomon [RS] code using a cross-interleaved Reed Solomon [CIRC]

Definitions

  • THIS INVENTION relates to a method of checking the source of CDs as herein defined and/or for checking for unauthorised copies of CDs.
  • CDs Compact Discs
  • Digital Versatile Disc DVDs
  • CDs Compact Discs
  • Digital Versatile Discs DVDs
  • CDs are now a familiar medium for carrying data in digital form, whether digitally recorded sound or computer data.
  • a sophisticated version of the CD, the "Digital Versatile Disc” DVD is now also available which utilises substantially the same principles but provides a denser packing of information and thus makes it possible to store, in digital form, a larger amount of data, for example embodying full length cinema presentations, on a single disc.
  • CD is also intended to include such DVDs.
  • a light-reflective disc e.g. of plastics sheet material with a metalised reflecting layer incorporated therein
  • the digital recording or data stored comprises an extended spiral "track" of such pits, i.e. a track extended in much the same way as that on the gramophone discs which were once the accepted medium for recorded music.
  • the configuration of a CD is complex and a CD track comprises pits of various lengths selected from nine "standard" lengths.
  • These lengths are herein also referred to as "clap-lengths". These pits are derived from corresponding features in a "master”, formed in a manufacturing process in which, inter alia a counterpart to the CD track is recorded by means of a laser beam on a rotating disk in a recording machine.
  • the 'clap-lengths' can be thought of in terms of lines of different length over which the opacity or reflectivity of the material changes. These Tines' are arranged over the entire spiral of the CD to give a continuous stream of data. In terms of data representation, the lines form a run-length code ' from which a bit stream is then extracted.
  • CDs may be made using "write-once" recordable CD technology in which streaks or bars of a contrasting colour to a background colour are formed by a laser in a recording/writing device, or may be made using re-write technology, in which variations in reflectivity are induced reversibly in any of various ways by a writing laser are used to provide marks which, to a "standard” CD player or "CD ROM” data reading device, simulate the pits referred to in the mass- produced CDs.
  • the master in a conventional CD ROM production technique, like the "write- once" and “re-write” systems referred to, relies upon a writing technique in which a disc is rotated according to a standard scheme of rotary movement, (the rotational rate is not constant but is generally varied throughout recording to achieve a generally uniform velocity of the spiral track through the focus of the writing laser), and a laser beam is focused onto the surface of the master and is switched on or off to provide the features and intervening spaces in the respective master, which will correspond to the pits and intervening "lands" in the manufactured CD.
  • CD recorder there may be considerable variation from CD recorder to CD recorder in deviations from the actual positions (times, in terms of the replay signal) in the CD track at which transitions from pit to successive land or from land to successive pit occur, as compared with the notional product of an ideal, perfect, recording machine.
  • a method of authenticating CDs comprising measuring precisely the lengths of the pits corresponding to the several "standard” pits, i.e. measuring precisely the respective "clap-lengths", and/or of the lands between such pits, and/or comprising measuring precisely the positions of the ends of such pits, (i.e. of the transitions between pits and lands) relative to their notional ideal positions, performing a statistical or other mathematical analysis on the resulting measurements to establish averages, distributions and/or other statistical measures, and comparing the results of corresponding results for CDs from the totality of legitimate sources, to determine the likelihood that the CD emanates from any of the legitimate sources.
  • a method of authenticating CDs comprising measuring precisely the lengths of the pits corresponding to the several "standard” pits, i.e. measuring precisely the respective "clap-lengths", and/or of the lands between such pits, and/or comprising measuring precisely the positions of the ends of such pits, (i.e. of the transitions between pits and lands) relative to their notional ideal positions, to establish a statistical fingerprint or phase portrait based on chaotic data analysis using appropriate phase spaces and/or other standard and/or Levy statistical measures, and comparing the results with corresponding results for CDs from the totality of legitimate sources, to determine the likelihood that the CD emanates from any of the legitimate sources.
  • Copying a CD or DVD leads to a copy CD or DVD having the same (binary) information as the copied CD.
  • the physical nature (i.e. the laser burn) of the copy can be different from one replicator to another due to the natural 'jitter' of the copier, i.e. the natural errors that occur in the mechanics of the copier and the (laser) modulator.
  • 'jitter' introduced by a replicator has a unique statistical signature which may be determined by carrying out operation such as computing the population density of the 'clap-lengths'.
  • the 'clap-lengths' are the lengths of the laser burn on the CD - from T3 to Tl 1.
  • the procedure involved may be as follows:
  • the method requires only that the 'clap-lengths' on the CD can be measured and that a data base of the frequency distributions associated with authorised replicators is available for cross-correlation.
  • the procedure involved in a preferred embodiment of the invention may be as follows: (i) compute the phase portrait for lands and pits on the entire CD, or possibly over only part of the CD;
  • the method requires only that the 'clap-lengths' on the CD can be measured and that a data base of the phase portraits, for lands and pits, associated with authorised replicators is available for cross-correlation.
  • a consumer - oriented CD ROM drive or a computer incorporating such a CD ROM drive may be arranged to carry out or participate in the method of the present invention by being designed to, or adapted to make the measurements and collect the data forming the basis for such a statistical fingerprint or phase portrait, and possibly to carry out part or all of the necessary processing of such data.
  • a computer incorporating such a CD ROM drive may be used in a download protection scheme, so that when a CD bearing software from, or purporting to be from, a software supplier, is loaded into the CD ROM for loading into the computer, the software will only be loaded after the fingerprint or phase portrait of the CD ROM has been checked against a database of legitimate replicators, eg.
  • the "signature", "fingerprint” or “portrait” of the CD can be uploaded and checked centrally on a database and then key additional files or file changes made to enable the software to be loaded onto the user's machine.
  • the extracting of analogue data and computation of the signature can, it is believed, be carried out very quickly as the applicants believe it should only be necessary to measure the first 10,000 pits or so on the disk to get the mass of data needed.
  • phase spaces or phase portraits can form the basis for the pattern recognition approach to identify the 'fingerprint' of an authorised CD replicator.
  • fingerprints can be collated into a database of templates from which a CD can be validated.
  • the method requires only that the 'clap-lengths' on the CD can be measured and that a database of the phase space templates associated with the authorised replicators is available for cross-correlation.
  • the laser pickup When a standard player reads a CD/DVD the laser pickup receives an analogue signal corresponding to the interference of the laser light caused by the pits. The analogue signal then is converted into a digital signal and is passed to an
  • EFM eight to fourteen modulation
  • CIRC cross interleaved Reed-Solomon code
  • the subcode is added at the recording stage and extracted at the reading stage to designate the subcode channels P,Q,R,S,T,U,V and W. For example the P subcode is used to indicate silence between tracks.
  • the acquisition of the "fingerprint” or “portrait” referred to is carried out using the analogue signal referred to above, before digitisation.
  • This analogue signal comprises a series of run lengths (the electrical counterparts of the pits in the CD), measured in time (pico seconds or equivalent depending upon the speed). The variation in these run lengths may be used for the "fingerprint” analysis. It is envisaged that before spirming the disk to full speed, which can be 40x or more, the raw data will be measured for the first part of the disc at lx and the validation process started.
  • This validation could be routinely undertaken so that the fingerprint of the CD DVD is automatically taken when it is inserted into a reader. Using various methods, such as on-line registration, this fingerprint could be compared with authentic fingerprints so that counterfeits would not be loaded. In another embodiment authentic fingerprints could included on the CD/DVD but encoded in such a way that a counterfeiter could not add a fictitious fingerprint to the database. On CD music players and DVD players this would mean changes to the design of the software within the machine. Validation on a PC would be easier to accomplish because of the ease with which software can be modified and loaded onto it. For stand-alone CD/DVD players a new chip may be needed.

Abstract

A method of authenticating CDs comprises measuring precisely the lengths of the pits corresponding to the several 'standard' 'T lengths' or 'clap-lengths', and/or of the lands between such pits, performing a statistical analysis on the measured lengths of such pits and/or lands to establish averages, distributions and/or other statistical measures, and comparing the results of corresponding results for CDs from the totality of legitimate sources, to determine the likelihood that the CD emanates from any of the legitimate sources. The method may also, or alternatively, comprise measuring precisely the positions of ends of the pits in the CD track, (i.e. of the transitions between pits and lands) relative to their notional ideal positions, in order to obtain data for derivation of the desired 'fingerprint'. The method may be used in a copy protection scheme or software authentication scheme.

Description

Title of Invention:
"Method of Authenticating CDs"
THIS INVENTION relates to a method of checking the source of CDs as herein defined and/or for checking for unauthorised copies of CDs.
CDs (Compact Discs) are now a familiar medium for carrying data in digital form, whether digitally recorded sound or computer data. A sophisticated version of the CD, the "Digital Versatile Disc" DVD, is now also available which utilises substantially the same principles but provides a denser packing of information and thus makes it possible to store, in digital form, a larger amount of data, for example embodying full length cinema presentations, on a single disc. For the purposes of the present Application, the term "CD" is also intended to include such DVDs.
In a CD, information is recorded upon a light-reflective disc, e.g. of plastics sheet material with a metalised reflecting layer incorporated therein, by forming ditches or pits elongated substantially in the circumferential direction to a greater or lesser degree, the information recorded on the disc being recorded digitally. The digital recording or data stored comprises an extended spiral "track" of such pits, i.e. a track extended in much the same way as that on the gramophone discs which were once the accepted medium for recorded music. In practice, of course, the configuration of a CD is complex and a CD track comprises pits of various lengths selected from nine "standard" lengths. These lengths, conventionally referenced T3,T4, ..Ti l, are herein also referred to as "clap-lengths". These pits are derived from corresponding features in a "master", formed in a manufacturing process in which, inter alia a counterpart to the CD track is recorded by means of a laser beam on a rotating disk in a recording machine.
The 'clap-lengths' can be thought of in terms of lines of different length over which the opacity or reflectivity of the material changes. These Tines' are arranged over the entire spiral of the CD to give a continuous stream of data. In terms of data representation, the lines form a run-length code' from which a bit stream is then extracted.
The most common type of mass-produced CD is made, in a manner analogous to that in which gramophone records used to be made, by pressing from a master, the pressed surface being thereafter covered by a protective transparent layer. For private use, or in "trial" production runs, CDs may be made using "write-once" recordable CD technology in which streaks or bars of a contrasting colour to a background colour are formed by a laser in a recording/writing device, or may be made using re-write technology, in which variations in reflectivity are induced reversibly in any of various ways by a writing laser are used to provide marks which, to a "standard" CD player or "CD ROM" data reading device, simulate the pits referred to in the mass- produced CDs.
The master, in a conventional CD ROM production technique, like the "write- once" and "re-write" systems referred to, relies upon a writing technique in which a disc is rotated according to a standard scheme of rotary movement, (the rotational rate is not constant but is generally varied throughout recording to achieve a generally uniform velocity of the spiral track through the focus of the writing laser), and a laser beam is focused onto the surface of the master and is switched on or off to provide the features and intervening spaces in the respective master, which will correspond to the pits and intervening "lands" in the manufactured CD. Whilst there may be said to be, for example, in a conventional CD ROM, a "standard" length for a T3 pit, another "standard" length for a T4 pit, and so on, there may be considerable variation from CD recorder to CD recorder in the actual length of nominally equivalent pits, (and, indeed, to a lesser degree, such variations from one position in a single CD to another position therein). It is, of course, the great advantage of a digital system that such variations can be ignored and have no effect in corrupting the data concerned provided that they do not exceed the limit at which a pit of one type, eg. a T3 pit, can be confused with a pit of another type, eg. a T4 pit. Likewise, there may be considerable variation from CD recorder to CD recorder in deviations from the actual positions (times, in terms of the replay signal) in the CD track at which transitions from pit to successive land or from land to successive pit occur, as compared with the notional product of an ideal, perfect, recording machine.
The inventor has discovered that such variations, (also referred to herein as "jitter"), and in particular how these variations are distributed statistically, are measurably characteristic to particular recording machines and that such a statistical distribution provides, in effect, a "fingerprint" or unique identity for a particular recording machine.
It is an object of the present invention to provide a method of authenticating CDs or of detecting unauthorised copies of the same, utilising these variations.
According to one aspect of the invention, there is provided a method of authenticating CDs comprising measuring precisely the lengths of the pits corresponding to the several "standard" pits, i.e. measuring precisely the respective "clap-lengths", and/or of the lands between such pits, and/or comprising measuring precisely the positions of the ends of such pits, (i.e. of the transitions between pits and lands) relative to their notional ideal positions, performing a statistical or other mathematical analysis on the resulting measurements to establish averages, distributions and/or other statistical measures, and comparing the results of corresponding results for CDs from the totality of legitimate sources, to determine the likelihood that the CD emanates from any of the legitimate sources.
According to another aspect of the invention, there is provided a method of authenticating CDs comprising measuring precisely the lengths of the pits corresponding to the several "standard" pits, i.e. measuring precisely the respective "clap-lengths", and/or of the lands between such pits, and/or comprising measuring precisely the positions of the ends of such pits, (i.e. of the transitions between pits and lands) relative to their notional ideal positions, to establish a statistical fingerprint or phase portrait based on chaotic data analysis using appropriate phase spaces and/or other standard and/or Levy statistical measures, and comparing the results with corresponding results for CDs from the totality of legitimate sources, to determine the likelihood that the CD emanates from any of the legitimate sources.
The following discussion sets out in other terms the principle by which a CD can be analysed, in accordance with the invention, to test whether or not it is a copy made by an unauthorised (CD or DVD) replicator.
Copying a CD or DVD leads to a copy CD or DVD having the same (binary) information as the copied CD. However, as indicated above, the physical nature (i.e. the laser burn) of the copy can be different from one replicator to another due to the natural 'jitter' of the copier, i.e. the natural errors that occur in the mechanics of the copier and the (laser) modulator. For the reasons discussed above, 'jitter' introduced by a replicator has a unique statistical signature which may be determined by carrying out operation such as computing the population density of the 'clap-lengths'. The 'clap-lengths' are the lengths of the laser burn on the CD - from T3 to Tl 1.
In one embodiment of the invention, the procedure involved may be as follows:
(i) compute the number of 'clap-lengths' from T3 to Tl 1 on the entire CD;
(ii) compute the population density (i.e. the frequency distribution) of these 'clap-lengths'
(iii) compare this population density with that associated with a CD generated by an authorised replicator using statistical analysis algorithms;
(iv) if this statistical test provides a correlation with one of a number of authorised replicators, then pass the CD as being genuine, otherwise conclude that the CD is an unauthorised copy.
The method requires only that the 'clap-lengths' on the CD can be measured and that a data base of the frequency distributions associated with authorised replicators is available for cross-correlation.
The procedure involved in a preferred embodiment of the invention may be as follows: (i) compute the phase portrait for lands and pits on the entire CD, or possibly over only part of the CD;
(ii) compare statistically this portrait with that associated with a CD generated by an authorised replicator using statistical analysis algorithms;
(iii) if this statistical test provides a correlation with one of a number of authorised replicators, then pass the CD as being genuine, otherwise conclude that the CD is an unauthorised copy.
The method requires only that the 'clap-lengths' on the CD can be measured and that a data base of the phase portraits, for lands and pits, associated with authorised replicators is available for cross-correlation.
It is envisaged that a consumer - oriented CD ROM drive or a computer incorporating such a CD ROM drive may be arranged to carry out or participate in the method of the present invention by being designed to, or adapted to make the measurements and collect the data forming the basis for such a statistical fingerprint or phase portrait, and possibly to carry out part or all of the necessary processing of such data. It is envisaged, for example, that a computer incorporating such a CD ROM drive may be used in a download protection scheme, so that when a CD bearing software from, or purporting to be from, a software supplier, is loaded into the CD ROM for loading into the computer, the software will only be loaded after the fingerprint or phase portrait of the CD ROM has been checked against a database of legitimate replicators, eg. after the data retrieved (and possibly at least part-processed) by the consumer computer/drive, has been transmitted, via the internet for example, to the software supplier for checking against such database, after which the software supplier may transmit to the consumer computer an appropriate decryption key or the like element necessary to the loading or ninning of the software concerned on the consumer computer. A similar scheme might, of course be used in relation to audio CDs, audio/video DVDs, etc.
Thus, for example when a software CDROM or DVD is inserted into what the applicants envisage as a standard reader with only a small modification to extract the analogue data, the "signature", "fingerprint" or "portrait" of the CD can be uploaded and checked centrally on a database and then key additional files or file changes made to enable the software to be loaded onto the user's machine. The extracting of analogue data and computation of the signature can, it is believed, be carried out very quickly as the applicants believe it should only be necessary to measure the first 10,000 pits or so on the disk to get the mass of data needed.
The following discussion sets out in other terms the principle by which a CD can be analysed, in accordance with the invention, using, phase spaces or phase portraits, to test whether or not it is a copy which has been made by an unauthorised (CD or DVD) replicator. These phase spaces can form the basis for the pattern recognition approach to identify the 'fingerprint' of an authorised CD replicator. These fingerprints can be collated into a database of templates from which a CD can be validated.
The method requires only that the 'clap-lengths' on the CD can be measured and that a database of the phase space templates associated with the authorised replicators is available for cross-correlation.
As noted above, a very small modification to the design of the conventional CD player or DVD player should serve to allow the "fingerprint" or "portrait" referred to to be taken. That is to say, the method of fingerprinting envisaged should not require prohibitively expensive or bulky specialist equipment.
When a standard player reads a CD/DVD the laser pickup receives an analogue signal corresponding to the interference of the laser light caused by the pits. The analogue signal then is converted into a digital signal and is passed to an
» eight to fourteen modulation (EFM) decoder at which stage a so-called subcode is taken off before the data is passed to a cross interleaved Reed-Solomon code (CIRC) encoder to extract the data to reproduce the sound and/or video stream. The subcode is added at the recording stage and extracted at the reading stage to designate the subcode channels P,Q,R,S,T,U,V and W. For example the P subcode is used to indicate silence between tracks.
In one embodiment of the invention as applied to a consumer CD player or CD- ROM drive, the acquisition of the "fingerprint" or "portrait" referred to is carried out using the analogue signal referred to above, before digitisation. This analogue signal comprises a series of run lengths (the electrical counterparts of the pits in the CD), measured in time (pico seconds or equivalent depending upon the speed). The variation in these run lengths may be used for the "fingerprint" analysis. It is envisaged that before spirming the disk to full speed, which can be 40x or more, the raw data will be measured for the first part of the disc at lx and the validation process started.
This validation could be routinely undertaken so that the fingerprint of the CD DVD is automatically taken when it is inserted into a reader. Using various methods, such as on-line registration, this fingerprint could be compared with authentic fingerprints so that counterfeits would not be loaded. In another embodiment authentic fingerprints could included on the CD/DVD but encoded in such a way that a counterfeiter could not add a fictitious fingerprint to the database. On CD music players and DVD players this would mean changes to the design of the software within the machine. Validation on a PC would be easier to accomplish because of the ease with which software can be modified and loaded onto it. For stand-alone CD/DVD players a new chip may be needed.
For enhanced analysis of CDs, CD-ROMs, DVDs and the like to establish "fingerprints" from which the sources of such CDs, etc., can be deteirnined, it is possible, and may be preferred in some cases, in carrying out the invention, to use the methods of fractal mathematics and analysis, or the methods of the mathematics of chaos, (chaotic analysis), for example as disclosed in and referred to in W099/17268 or WOO 1/43067, the disclosure of which is incorporated herein by reference.
It should be understood that the mathematical analysis of the data used in carrying out the present invention need not comprise, or need not solely comprise, traditional statistical analysis. Assuming the data is chaotic, phase space analysis may usefully be applied.
In the present specification "comprise" means "includes or consists of and "comprising" means "including or consisting of.
The features disclosed in the foregoing description, or the following claims, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof

Claims

CLAIMS:
1. A method of authenticating CDs comprising measuring precisely the lengths of the pits corresponding to the several "standard" line lengths or "clap- lengths", and/or of the lands between such pits, perforating a statistical analysis on the measured lengths of such pits and/or lands to establish averages, distributions and/or other statistical measures, and comparing the results of corresponding results for CDs from the totality of legitimate sources, to determined the likelihood that the CD emanates from any of the legitimate sources.
2. A method of authenticating CDs comprising measuring precisely the lengths of the pits and/or lands corresponding to the several "standard" line lengths or "clap lengths", performing a statistical analysis of the measured lengths of such pits or lands to establish a statistical fingerprint or phase portrait based on chaotic data analysis using appropriate phase spaces and/or other standard and/or Levy statistical measures, and comparing the results with corresponding results for CDs from the totality of legitimate sources, to determine the likelihood that the CD emanates from any of the legitimate sources.
3. A method according to claim 1 or claim 2 wherein said statistical analysis utilises fractal or chaotic mathematics.
4. A copy protection or software verifying scheme for CDs, CD-ROMs, DVDs and the like, wherein apparatus for playing such CDs, CD-ROMs, DVDs or the like or for utilising software or data provided on such CDs, CD-ROMs, DVDs or the like, incorporates means for measuring the lengths of the pits corresponding to several the several "standard" line lengths, "T lengths" or "clap-lengths", on the CDs, CD-ROMs, DVDs or the like, and for carrying out the authentication method of claim 1 or claim2 and wherein the apparatus is arranged to block playing of such a CD, CD-ROM, DVD or the like, or to block access to data or software on the CD, CD-ROM, DVD or the like, if the authentication method concludes that the CD, CD-ROM, DVD or the like is not from an approved source.
5. Apparatus for carrying out the method of claim 1, 2 or 3, or incorporating or utilising the system of claim 4.
PCT/GB2002/003710 2001-08-10 2002-08-12 Method of authenticating cds WO2003015088A1 (en)

Applications Claiming Priority (4)

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GB0119589.0 2001-08-10
GB0119589A GB0119589D0 (en) 2001-08-10 2001-08-10 Method of authenticating cds
GB0210744.9 2002-05-10
GB0210744A GB0210744D0 (en) 2001-08-10 2002-05-10 Method of authenticating CDs

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