WO1990009663A1 - Signal security system - Google Patents
Signal security system Download PDFInfo
- Publication number
- WO1990009663A1 WO1990009663A1 PCT/GB1990/000268 GB9000268W WO9009663A1 WO 1990009663 A1 WO1990009663 A1 WO 1990009663A1 GB 9000268 W GB9000268 W GB 9000268W WO 9009663 A1 WO9009663 A1 WO 9009663A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- data words
- identifying
- certain
- identified
- digits
- Prior art date
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Classifications
-
- 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
- G11B20/00884—Circuits for prevention of unauthorised reproduction or copying, e.g. piracy involving a watermark, i.e. a barely perceptible transformation of the original data which can nevertheless be recognised by an algorithm
-
- 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
- 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
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F2211/00—Indexing scheme relating to details of data-processing equipment not covered by groups G06F3/00 - G06F13/00
- G06F2211/007—Encryption, En-/decode, En-/decipher, En-/decypher, Scramble, (De-)compress
Landscapes
- Engineering & Computer Science (AREA)
- Computer Security & Cryptography (AREA)
- Signal Processing (AREA)
- Signal Processing For Digital Recording And Reproducing (AREA)
Abstract
A system of identifying a digitally encoded signal comprising a series of data words identifies certain data words (4) according to a predetermined criteria relating to the value of the data words, such as those data words whose value is above a predetermined threshold level. Once certain data words have been identified, a subset of the identified data words is created, preferably in accordance with the output from a random or pseudo-random number generator. A certain digit, typically the most significant digit, of each selected data word is stored together with the intervals between the successively selected data words, to form a unique identifying pattern.
Description
SIGNAL SECURITY SYSTEM
This invention relates to a system for identifying a signal, or a digitally encoded version of such a signal which comprises a series of data words. It should be understood that the signal can be either analogue sampled values, or a digitally encoded version of such samples, and the term "digitally encoded signal' will be used herein to encompass both of these possibilities.
A need exists for a system which facilitates the identification of the source of recorded material with a high degree of certainty. This is increasingly required as facilities for high quality unauthorised copying -of recorded material such as from compact discs and video tapes become more readily available on the market.
In O89/08915 we describe an invasive security coding technique in which certain insignificant digits of the recorded material are replaced with ja, code digit from an independently generated sequence. It is an object of the present invention to provide a non-invasive system as a supplement or alternative to the system of WO89/08915.
Accordingly, there is provided a method of identifying a digitally encoded signal comprising a series of data words, the method being characterised by the steps of identifying certain data words according to a predetermined criteria relating to the value of the data words; selecting a subset of the identified data words; and storing a certain digit of each selected data word and the intervals between the successively selected data words as a unique identifying pattern.
Conceivably, the words to form the subset ate selected at equal sampling intervals, or in accordance
with a predetermined repeating sequence of sampling intervals, but more preferably the subset of words is selected in accordance with the output from a random or pseudo-random number generator. Preferably the certain digit which is stored is the most significant digit.
The predetermined criteria on which certain data words are identified preferably comprises identifying those data words whose value is above a predetermined threshold level. For example, this may involve the examination of the data words representing the sampled values of the source material in order to determine those words which correspond to sampled values having a positive value in excess of some predetermined threshold value. Alternatively, the selection of large valued negative samples, or a combination of large valued positive and large valued negative samples could be used. Conceivably, those samples having a value lying within some predetermined value range could be selected. Whichever criteria is employed, a certain digit, typically the most significant digit, which will generally be a one in the case of large valued positive samples, is stored together with the intervals between the successively selected data words. This information constitutes the identifying pattern.
The invention further resides in a method of identifying a digitally encoded signal comprising a series of data words, the method being characterised by the steps of taking a master version of the digitally encoded signal; identifying certain data words according to a predetermined criteria relating to the value of the data words; selecting a subset of the identified data words; storing a certain digit of each selected data word and the intervals between the successively selected data words as a unique identifying pattern; taking a copy of the digitally encoded signal; identifying the certain
- 3 - i ' digit of each data word in accordance with the unique identifying pattern; comparing the identified certain digits and those of the identifying pattern; and # indicating whether the degree of correlation between the identified certain digits and those of the identifying" pattern exceeds a predetermined threshold value. "
Thus the verification of the copy is carried"pΛit by comparing certain digits of the copy with those of the identifying pattern, and assessing the degree of correlation thereof.
The invention further resides in a method of identifying a digitally encoded signal comprising a series of data words, the method being characterised by the steps of taking a master version of the digitally ' encoded signals; identifying certain data words according to a predetermined criteria relating to the value of the data words; selecting a subset of the identified *data words; storing a certain digit of each selected data- word and the intervals between the successively Selected da*fca words as a unique identifying pattern; taking a cop- of the digitally encoded signal; producing an oversampled version of the digitally encoded signal; identifying the certain digit of each data word of the oversampled** digital version; comparing groups of the identifi'-SdV' certain digits with the stored identifying pattern; and indicating whether the degree of correlation betwpeQ apy > * * groups of identified digits and the stored identifying
**•* pattern exceeds a predetermined threshold value. r '
Producing an oversampled digital version oi-the- digitally encoded signal is only necessary where there is a possibility that the digitally encoded version
be the result of a digital-to-analogue and analogue-to- digital conversion process, or even a succession-of-such processes. Preferably the sampling rate of the ' '
oversampled digital version is an integer multiple of the sampling rate of the master digital version.
The invention further extends to apparatus for carrying out the method described herein. In particular, there is provided apparatus for identifying a digitally encoded signal comprising a series of data words, characterised in that the apparatus comprises means for identifying certain data words according to the predetermined criteria relating to the value of the data words; means for selecting a subset of the identified data words; and a memory means adapted to store a certain digit of each selected data word and data representing the intervals between the successively selected data words as a unique identifying pattern.
There is preferably further provided a random or pseudo-random number generator, output from which is employed by the subset selecting means in order to select a subset of the identified data words in a random or pseudo-random manner. The means for identifying certain data words preferably comprises means for determining whether the value of a particular data word is above a predetermined threshold value. Conveniently the memory means is adapted to store the most significant digit of each selected data word.
The invention further resides in apparatus for identifying a digitally encoded signal comprising a series of data words, characterised in that the apparatus comprises means for receiving and storing a unique identifying pattern comprising a series of digits and data representing the intervals between the data words containing the data digits; means for identifying a certain digit of each data word in accordance with the stored identifying pattern; means for comparing the identified certain digits and those stored as part of the
identifying pattern; and means for indicating whether the degree of correlation between the identified certain digits and those of the identifying pattern exceeds a predetermined threshold value.
The invention further resides in apparatus for identifying a digitally encoded signal comprising a series of data words, characterised in that the apparatus comprises means for receiving and storing a unique identifying pattern comprising a series of digits and data representing the intervals between the data words containing those digits; oversampling means adapted to produce an oversampled digital version of the digitally encoded signal; means for identifying a certain digit of each data word of the oversampled digital version; means for comparing groups of the identified certain digits with the stored identifying pattern; and means for indicating whether the degree of correlation between any groups of identified digits and the stored identifying pattern exceeds a predetermined threshold value. As before, the oversampling means is necessary where there is a possibility that the digitally encoded version of the source material may be the result of a digital-to- analogue and analogue-to-digital conversion process, or a succession of such processes.
The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which:
Figure 1 is a schematic representation of an original analogue signal waveform;
Figure 2 is a schematic representation of the digital version of the waveform of 'Figure 1;
Figure 3 is a schematic representation of the digital data words selected in accordance with a first aspect of the present invention;
Figure 4 is a schematic representation of a subset of the digital data words of Figure 3 selected in accordance with a further aspect of the present invention;
Figure 5 is a schematic representation of the oversampling of the digital version of Figure 2, in accordance with a further aspect of the present invention; and
Figure 6 is a schematic representation of the correlation of the oversampled version of Figure 5, in accordance with a further aspect of the present invention.
Refering to Figures 1 and 2, an original analogue source signal 1, is sampled as shown at 2, in order to produce a digital version comprising a series of data words 3. Before the original digital version is made available, it is examined in order that an identification sequence can be obtained for future use in the process of identification. The original digital version is searched and a set of digital data words 4 , corresponding to large valued positive samples having a magnitude greater than a predetermined threshold 12 is recorded. This set of digital words 4 is shown in Figure 3. A subset of these data words is then selected, with the selection being in accordance with a random or pseudo-random number generator (not shown). At a simple level, the random number generator may supply a yes/no signal to determine whether a particular data word 4 is to be selected for the subset. The subset of data words 5 is shown in Figure 4.
- 7 -
The intervals between each selected data wor of the subset 5 are recorded and kept for use in a subsequent identification process. The intervals are usifelly in terms of the number of samples or number of words between the selected data words of the subset 5* In addition to the intervals, the most significant digit, which 'will generally be a one in the case of large valued positive samples, is stored, and the digits together with the intervals therebetween constitute a unique identifying pattern. f
In a subsequent identification process, a digitally encoded version of the source material, which may be the result of the original encoding process, or may be a result that is obtained after subsequent digital-to-
+ analogue and analogue-to-digital conversion processes,, is taken and is processed so as to obtain a new oveiH&led digital version, with the oversampling being at an integer multiple of the original sampling rate. This oversampling process is illustrated in Figure 5. The oversampled version is obtained by first applying _> digital- to-analogue conversion to the digitally encoded version being examined so as to obtain an analogue waveform 6. Then an analogue-to-digital conversion is made with-the analogue signal being sampled at a rate that is an integer multiple of the original sampling rate. In Figure 5 the sampling interval 7 of the oversampled1 digital data words 8 is one sixteenth that of the . original sampling interval (i.e. an oversampling rate of sixteen times the original) . It should be noted that it is possible to avoid the digital-to-analogue and analogue- to-digital conversion processes described above by applying direct digital interpolation techniques losi g digital computing means.
Figure 6 shows the next step in the identification process. After the oversampled digital representation of
the signal has been obtained, the most significant digit associated with each sample is stored as shown at 9. The stored digits are examined in order to determine whether groups of them that are separated by intervals as set out in the unique identifying pattern possess a degree of agreement with the digits constituting the other part of the unique identifying pattern. This comparison is carried out by a correlator 10 which compares groups of the digits 9 with those of the identifying sequence in an attempt to assess the degree of correlation thereof. If the degree of correlation exceeds some predetermined threshold value, then an identification is confirmed and an appropriate signal is transmitted on line 11.
The process of correlation is well known to those skilled in the art, as is the reliability of identifica- tion which can be obtained from considerations of elementary probability. If the threshold 12 is set such that the value of one in five of the data words exceeds the threshold, the identification sequence comprises forty digits, and the correlation threshold is a minimum of twentyfive agreements, then the probability of false identification as calculated by known statistical considerations is of the order of 4.5 x 10~
It will be appreciated that where there is no likelihood of digital to analogue conversion being applied to the source material, then the oversampling of the signal can be dispensed with and the identifying sequence of digits separated by intervals can be compared directly with the original digital version in order to effect identification. An important instance in which this direct approach can be applied is in the identification of computer software.
The identification information, i.e. the sequence of most significant digits and the intervals between those
digits, is signal dependant. In order for identification to be performed, this information must be provided within the identifying appraratus, which may even be remotely located. Where the most significant digits are all ones, all that is necessary is for the intervals between the most significant digits to be transmitted to the remotely located identifying apparatus. This can be done using standard methods of encryption, and the identification information can thereby be installed within a receiver, without the user having access to, or being able to obtain, the said identification seqence. After the identification sequence has been so installed in the receiver, it is then possible to apply the identification technique to prohibit or permit the playing or copying of the identified material, or to record this fact for billing purposes or to set it against some charge card.
Claims
1. A method of identifying a digitally encoded signal comprising a series of data words, the method being characterised by the steps of identifying certain data words according to a predetermined criteria relating to the value of the data words; selecting a subset of the identified data words; and storing a certain digit of each selected data word and the intervals between the successively selected data words as a unique identifying pattern.
2. A method according to Claim 1 characterised in that the subset of words is selected in accordance with the output from a random or pseudo-random number generator.
3. A method according to Claim 1 or Claim 2 characterised in that the certain digit which is stored is the most significant digit.
4. A method according to any of Claims 1 to 3 characterised in that the predetermined criteria comprises identifying those data words whose value is above a predetermined threshold level.
5. A method of identifying a digitally encoded signal comprising a series of data words, the method being characterised by the steps of taking a master version of the digitally encoded signal; identifying certain data words according to a predetermined criteria relating to the value of the data words; selecting a subset of the identified data words; storing a certain digit of each selected datεi word and the intervals between the successively selected _. r -&*s>' data words as a unique identifying pattern; , taking a copy of the digitally encoded signals; identifying the certain digit of each data word in accordance with the unique identifying pattern; comparing the identified certain digits and those of the identifying pattern; and indicating whether the degree of correlation between the identified certain digits and those of the identifying pattern exceeds a predetermined threshold value.
6. A method of identifying a digitally encoded signal comprising a series of data words, the method being characterised by the steps of taking a master version of the digitally (encoded signal; identifying certain data words according to a predetermined criteria relating to the value of the data words; selecting a subset of the identified data words; storing a certain digit of each selected data word and the intervals between the successively selected data words as a unique identifying pattern; taking a copy of the digitally encoded signals; producing an oversampled digital version of the digitally encoded signals; identifying the certain digit of each data word of the oversampled digital version; comparing groups of the identified certain digits with the stored identifying pattern; and indicating whether the degree of correlation between any groups of identified digits and the stored identifying pattern exceeds a predermined threshold value.
7. A method according to Claim 6 characterised in that the sampling rate of the oversampled digital version is an integer multiple of the sampling rate of the master digital version.
8. Appratus for identifying a digitally encoded signal comprising a series of data words, characterised in that the apparatus comprises means for identifying certain data words according to the predetermined criteria relating to the value of the data words; means for selecting a subset of the identified data words; and a memory means adapted to store a certain digit of each selected data word and data representing the intervals between the successively selected data words as a unique identifying pattern.
9. Apparatus according to Claim 8 characterised in that there is further provided a random or pseudo-random number generator, output from which is employed by the subset selecting means in order to select a subset of the identified data words in a random or pseudo-random manner.
10. Apparatus according to Claim 8 or 9 characterised in that the memory means is adapted to store the most significant digit of each selected data word.
11. Apparatus according to any of Claims 8 to 10 characterised in that the means for identifying certain data words comprises means for determining whether the value of a particular data word is above a predetermined threshold value.
12. Apparatus for identifying a digitally encoded signal comprising a series of data words, characterised in that the apparatus comprises means of for receiving and storing a unique identifying pattern comprising a series of digits and data representing the intervals between the data words containing the data digits; means for identifying a certain digit of each data word in accordance with the stored identifying pattern; means for comparing the identified certain digits and those stored as a part of the identifying pattern; and means for indicating whether the degree of correlation between the identified certain digits and those of the identifying pattern exceeds a predetermined threshold value.
13. Apparatus for identifying a digitally encoded signal comprising a series of data words, characterised in that the apparatus comprises means for receiving and storing a unique identifying pattern comprising a series of digits and data representing the intervals between the data words containing the digits; oversampling means adapted to produce an oversampled digital version of the digitally encoded signal; means for identifying a certain digit of each data word of the oversampled digital version; means for comparing groups of the identified certain digits with the stored identifying pattern; and means for indicating whether the degree of correlation between any groups of identified digits and the stored identifying pattern exceeds a * predetermined threshold value.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8903516.6 | 1989-02-16 | ||
| GB898903516A GB8903516D0 (en) | 1989-02-16 | 1989-02-16 | A signal security system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| WO1990009663A1 true WO1990009663A1 (en) | 1990-08-23 |
Family
ID=10651788
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/GB1990/000268 WO1990009663A1 (en) | 1989-02-16 | 1990-02-16 | Signal security system |
Country Status (2)
| Country | Link |
|---|---|
| GB (1) | GB8903516D0 (en) |
| WO (1) | WO1990009663A1 (en) |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS60211668A (en) * | 1984-04-05 | 1985-10-24 | Tokyo Electric Co Ltd | Information storage method of floppy disc storage medium |
| EP0171234A2 (en) * | 1984-08-10 | 1986-02-12 | McWHIRTER HOLDINGS PTY LIMITED | Circuitry for characterizing speech for tamper protected recording |
| JPS6151667A (en) * | 1984-08-21 | 1986-03-14 | Pioneer Electronic Corp | Pcm audio service system |
| EP0297242A2 (en) * | 1987-06-30 | 1989-01-04 | Kabushiki Kaisha Toshiba | Recording/reproducing system and method with record restriction function |
-
1989
- 1989-02-16 GB GB898903516A patent/GB8903516D0/en active Pending
-
1990
- 1990-02-16 WO PCT/GB1990/000268 patent/WO1990009663A1/en unknown
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS60211668A (en) * | 1984-04-05 | 1985-10-24 | Tokyo Electric Co Ltd | Information storage method of floppy disc storage medium |
| EP0171234A2 (en) * | 1984-08-10 | 1986-02-12 | McWHIRTER HOLDINGS PTY LIMITED | Circuitry for characterizing speech for tamper protected recording |
| JPS6151667A (en) * | 1984-08-21 | 1986-03-14 | Pioneer Electronic Corp | Pcm audio service system |
| EP0297242A2 (en) * | 1987-06-30 | 1989-01-04 | Kabushiki Kaisha Toshiba | Recording/reproducing system and method with record restriction function |
Non-Patent Citations (2)
| Title |
|---|
| PATENT ABSTRACTS OF JAPAN vol. 10, no. 212 (P-480)(2268) 24 July 1986, & JP-A-61 51667 (PIONEER ELECTRONIC CORPORATION) 14 March 1986, see the whole document * |
| PATENT ABSTRACTS OF JAPAN vol. 10, no. 74 (P-439)(2131) 25 March 1986, & JP-A-60 211668 (TOKYO DENKI K.K.) 24 October 1985, see the whole document * |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8903516D0 (en) | 1989-04-05 |
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