Cryptography – Key management – Having particular key generator
Patent
1997-02-18
1999-07-06
Cain, David
Cryptography
Key management
Having particular key generator
H04N 7167
Patent
active
059206250
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
This invention relates to a method of and apparatus for transmitting or receiving an encrypted signal, and in particular television signals that are access controlled by being scrambled in some manner.
DESCRIPTION OF THE PRIOR ART
Access control systems have become important to, for example, satellite television broadcasters, since they enable them to limit which geographical territories a programme can be viewed in: this may be important for compliance with scheduling or copyright obligations. Also, access control enables broadcasters to ensure that only viewers with paid-up subscriptions can continue to watch the access controlled television channels. Furthermore, it enables various pay-per-view features to be implemented.
Scrambling (encrypting) television signals is a well established technique that may be used wherever those signals are meant for only a limited sub-set of potential recipients. There are a number of different approaches to scrambling. One of the better established is the `cut & rotate` method, originally developed by Westinghouse. In `cut & rotate`, as applied to a PAL European standard television picture signal, each of the active picture lines of the 625 picture lines of a single picture frame is cut at a different point; the two segments of each line are then swapped over and the join between the two re-arranged segments smoothed over. Such a line is said to be `scrambled`; the television broadcaster who wishes to transmit such scrambled pictures may incorporate some form of `cut & rotate` engine or device (active line rotation unit) at the transmitting station so that the picture signals that are transmitted are scrambled. A frame of such scrambled lines can be received by a viewer's receiver, but it appears completely unintelligible unless that receiver can perform an exact inverse of the scrambling process. This would involve cutting each active picture line at the correct `cut-point` and rotating the segments of each line so that it was re-assembled in its original, unscrambled state. The receiver needs to know where each `cut-point` is.
If the `cut-point` data were included with the picture signal it would (a) take up a considerable amount of transmission bandwidth and (b) would enable a pirate to design a receiver that could work out where the cut-points were, thus defeating the entire purpose of a limited access system. Therefore, cryptographic techniques are used that enable the `cut-point` data to be generated internally from data that is transmitted with the picture signal. The data that is transmitted itself gives no clues to the `cut-point` data.
There are a number of different cryptographic techniques that have been employed for this purpose. One such technique is described in European Patent Application No. 9030131.9 in the name of News Data Security Products Limited, which discloses a keyless cryptographic process that has become widely used in the United Kingdom as part of the VideoCrypt system. This process will be described in greater detail in a subsequent part of this specification.
This invention is not limited to any one scrambling method. In digital television audio and data signals may be included in this scrambling. For illustrative convenience the `cut & rotate` method will be used in the examples that follow. Likewise, it is not limited to any one cryptographic process for the generation of cut points. For illustrative convenience the VideoCrypt process will be used in the examples that follow. The skilled implementer will readily envisage the application of the inventive techniques disclosed in this specification to other forms of scrambling, such as direct encryption of a digitally encoded signal, as well as other forms of cryptographic process.
Once a broadcaster has decided to use a particular cryptographic process, also commonly referred to as an `encryption system`, for a particular channel, then it is committed to using only that particular encryption system for that channel. This is because those wishing to view that channel
REFERENCES:
patent: 5003596 (1991-03-01), Wood
patent: 5134656 (1992-07-01), Kudelski
patent: 5164897 (1992-11-01), Bellisio
IEEE 1991 International Conference on Consumer Electronics, Jun. 5, 1991, Rosemont, Illinois, pp. 76-77, XP000288214, Digest by Jasjit S. Saini entitled VideoCrypt--An Open Architecture Pay TV System.
18th International Television Symposium and Technical Exhibition, May 10, 1993, Montreux, Switzerland, pp. 733-742, XP000379321, Article by Aleksander T. Futro entitled Smart Card for Conditional Access: A Marketing And Security Tool.
Veronica Satellite, No. 48, Nov 27, 1993, Hilversum, Netherlands, Extract entitled Experiment Met De Twee Videocrypten--Leng's Multicrypt.
Tele-Satellit, vol. 14, No. 97, Feb., 1994, Munich, Germany, p. 29, Extract entitled Digitrona `Advertisement--Konverter VCI-II`.
Cain David
Irdeto BV
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