Cryptography – Video cryptography – Video electric signal modification
Reexamination Certificate
1999-02-04
2003-07-01
Darrow, Justin T. (Department: 2132)
Cryptography
Video cryptography
Video electric signal modification
C380S201000, C380S204000, C380S212000, C380S231000, C380S240000, C705S051000, C705S052000, C705S057000
Reexamination Certificate
active
06587561
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to broadcast systems in general, and in particular to data broadcast systems, especially to systems providing Conditional Access services.
BACKGROUND OF THE INVENTION
Systems for ensuring that, in a pay or subscription broadcast system, only those who have paid to receive broadcast content actually do receive the broadcast content are well-known in the art. Such systems, which often include many other features, are known as Conditional Access (CA) systems. Typically, pay broadcast systems generally broadcast encrypted material and utilize a CA system to deliver one or more appropriate decryption keys to authorized receivers only.
One CA system is described in U.S. Pat. Nos. 5,282,249 and 5,481,609, both to Cohen et al. The two Cohen et al. patents describe a scrambled television system. Scrambled television transmissions described in the Cohen et al. patents include both scrambled data representing television signals and coded control messages, also known in the art as ECMs. The ECMs of Cohen et al. include, in a coded form, data necessary for generating a control word (CW) which may be used to descramble the scrambled data representing television signals.
Data necessary for generating a control word is known in the prior art to take many different forms and may include, in general, at least any of the following: a control word; an encrypted control word which is intended to be decrypted before use; and a seed to a generating function such as, for example, a one-way function which generates the control word upon input of the seed. Throughout the present specification and claims the terms “control word generating information” and “CW generating information” are used interchangeably to designate data necessary for generating a control word in any appropriate form, as described above.
While the two patents to Cohen et al. describe an analog system, that is, a system in which analog television data streams are broadcast to television sets, it is appreciated that similar ECM methods may also be used for digital television data streams, it being appreciated that scrambling methods appropriate to digital data would be used in digital television data streams.
The system of Cohen et al. and other systems described in the art share a feature of broadcasting an ECM synchronous to, generally immediately before or in a data stream parallel to, the actual scrambled broadcast. Typically, such an ECM is valid for a brief duration, with a new ECM being broadcast, in synchrony with a scrambled broadcast scrambled according to a new key, a few seconds, such as 10 seconds, after the broadcast of the previous ECM. Some systems have been described in which a key is sent, whether by broadcasting or by other means such as by mail, with a lower frequency, even once a month. Such a system is described, for example, in U.S. Pat. Nos. 4,484,027 and Re 33,189 to Lee et al.
Patents describing systems related to encrypted broadcasting and/or key distribution in encrypted broadcasting systems include the following:
U.S. Pat. No. 4,228,321 to Flanagan describes a privacy transmission system with remote key control, in which key control signals are produced at the unscrambling location and are both used for unscrambling at that location and also transmitted to a scrambling location for use in scrambling.
U.S. Pat. No. 4,531,020 to Wechselberger et al describes a method for controlling the simultaneous broadcast of enciphered digital information signals, for example in a radio or television broadcast environment, to a plurality of subscribers using several levels of enciphering keys.
U.S. Pat. No. 4,531,021 to Bluestein et al describes enciphering digital information for transmission using a first key, common to all receivers, and a second key specific to one receiver of a small group of receivers.
U.S. Pat. No. 4,864,615 to Bennett et al describes a system for reproduction of secure keys by using distributed key generation data and a distributed encrypted prekey.
U.S. Pat. No. 4,866,770 to Seth-Smith et al describes a system for distributing video, audio, teletext, and data, in which system wide, individual decoder and group decoder control signals are transmitted as part of a composite signal. The group decoder control signal includes information relating to a group of decoders, while the individual decoder control signal includes information relating to the operation of individual decoders.
U.S. Pat. No. 4,944,006 to Citta et al describes a secure data packet transmission system utilizing a global encryption key as well as address keys for encrypting individually addressed bit packets.
U.S. Pat. No. 5,301,247 to Rasmussen et al. describes a method for ensuring secure communications, in which two keys are combined together to produce a session key.
U.S. Pat. No. 5,499,298 to Narasimhalu et al describes a method for controlled dissemination of digital information, in which encrypted digital information is decrypted by a tamper-proof controlled information access device, which access being provided according to conditions specified by an information provider.
In general, methods of transmitting a scrambled digital signal, including ECMs, are well known. Some systems use a composite signal, that is, an analog or digital signal including a plurality of components. Typically the plurality of components includes both a scrambled television signal component and an ECM component, the ECM component comprising a plurality of ECMs. Prior art references which discuss examples of this type of signal include the following: DVB ETR289, “Digital Video Broadcasting (DVB): Support for use of scrambling and conditional access (CA) within digital broadcasting systems”; and DVB SIM061, “Technical specification of DVB-Simulcrypt”, Apr. 1, 1997.
Other documents relating to broadcasting of digital information include the DVB Specification for Data Broadcasting, document SI-DAT 360 (TM 1779), Feb. 12, 1997; and ATSC Digital Television Standard, document A54, October 1995 and subsequent editions.
Other methods of transmitting a scrambled digital signal, particularly useful in a case where the signal includes sub-signals encoded according to various different methods, are described in “Common Interface Specification for Conditional Access and other Digital Video Broadcasting Decoder Applications”, DVB document A017, May 1996 and subsequent editions; and in “Common Interface Specification for Conditional Access and other Digital Video Broadcasting Decoder Applications”, CENELEC EN50221:1997.
The disclosures of all references mentioned above and throughout the present specification are hereby incorporated herein by reference.
SUMMARY OF THE INVENTION
The present invention seeks to provide an improved method for delivering a control word or key relating to an item. The present method is particularly useful in cases where the item is relatively short in duration and is transmitted asynchronously relative to an ECM stream; that is, time synchronization of the item and an associated ECM in the ECM stream cannot be guaranteed, typically because of the short duration of the item. The present method is also particularly useful in cases where the number of items is very large, and it may be impractical to assign a separate ECM stream to each item.
Cases of the types referred to may occur particularly in a data broadcast network, where a defined data item, such as a computer program or a multimedia item, is broadcast to subscribers or customers who have subscribed to or are otherwise authorized to receive the item. An item of this type may be of relatively short duration, such as between a fraction of a second and a few seconds, and there may be a very large number of items,
Existing methods of sending an ECM stream synchronized with a data stream, such as a data stream comprising a television program, are inadequate to provide for control word or key delivery in the cases described above, since state of the art ECM delivery mechanisms are not able to provide synchronization to the sub-second
Dallard Nigel Stephen
Sered Yishai
Darrow Justin T.
NDS Ltd.
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