Cryptography – Video cryptography – Copy protection or prevention
Reexamination Certificate
1998-01-28
2001-01-23
Swann, Tod R. (Department: 2767)
Cryptography
Video cryptography
Copy protection or prevention
C380S239000
Reexamination Certificate
active
06178242
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the production and recording of digital data streams, particularly scrambled digital data streams such as scrambled digital television data streams.
BACKGROUND OF THE INVENTION
Systems for scrambling a television data stream are well-known in the art. One such system is described in the following U.S. Pat. No. 5,282,249 to Cohen et al.; U.S. Pat. No. 5,481,609 to Cohen et al. Scrambled television data streams described in the Cohen et al. patents comprise both scrambled data representing television signals and coded control messages, also known as ECMs. The ECMs of Cohen et al. comprise, in a coded form, data necessary for generating a control word (CW) which may be used to descramble the scrambled data representing television signals.
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. Generally, the scrambling techniques used for scrambling analog television signals such as, for example, the well-known “cut-and-rotate” technique, are chosen for their applicability to analog signals. In scrambling of digital television signals other scrambling techniques, well-known in the art, are used, the techniques being more appropriate to digital signals such as, for example, applying the well-known DES algorithm to the digital television signals.
Methods of transmitting a scrambled digital signal, including ECMs, are described in the MPEG-2 standard, ISO/TEC 13818-6, Jul. 12, 1996 and subsequent editions.
Recording of analog television signals such as, for example, recording using a VCR, is well-known in the art and VCR equipment is widely commercially available from a variety of manufacturers. Recording of digital television signals is also known. A consumer digital VCR is described, for example, in the article “A Consumer Digital VCR for Digital Broadcasting” by Okamoto et al., published in
IEEE Transactions on Consumer Electronics
, Vol. 41, No. 3, August 1995, pp. 643-649.
U.S. Pat. No. 5,574,787 to Ryan describes an apparatus and method for copy protection for video platforms in which a specially adapted video recorder, playback device, or set top decoder is used to protect copyright material.
European patent application EP 0 714 204 A2, assigned to LG Electronics, Inc., describes a method for copy protection in digital video systems.
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 system for producing and recording digital data streams, and particularly for protecting recorded digital data streams including digital television data.
The prior art digital recording systems referred to above do not fully address the problem of recording a scrambled digital data stream. The term “digital data stream”, as used throughout the present specification and claims, refers in a broad sense to any stream of digital data transmitted continuously at least during a particular period of time, and particularly includes broadcast digital data such as broadcast digital television signals. The term “scrambling” in all of its forms, as used throughout the present specification and claims, refers to any method of scrambling, encoding, or encrypting data, many such methods being well-known in the art.
A digital VCR such as that described by Okamoto et al. records and reproduces a digital bit stream; that is, the digital VCR of Okamoto et al. records and produces whatever bits are presented thereto. Thus, the digital VCR of Okamoto et al. could record and reproduce a scrambled digital data stream. In the system of Okamoto et al., however, problems could arise in descrambling the recorded data stream such as, for example, for playing on a television.
As is well known in the art, security functions in scrambled television systems are typically controlled by a removable security element such as a removable smart card. Furthermore, it is well known in the art that, in actual practice, operators of scrambled television systems periodically replace the removable security elements found in consumer home systems in order to change the security and scrambling behavior of the system.
After replacement of the removable security element or, typically, after a limited transition period following replacement of the removable security element, broadcasts scrambled with methods applicable to the previous removable security element can not be descrambled using the present removable security element. Typically, therefore, if a recording were made on a system such as that described by Okamoto et al. of a broadcast from a digital system using techniques similar to those described by Cohen et al. and in the MPEG-2 standard, both referred to above, the recording would become unusable as soon as a change of removable security elements was carried out by the scrambled television system operator. The present invention seeks to provide apparatus and methods for recording digital data streams which, in addition to having other features, overcome the problem of unusability of recordings after a change of removable security elements.
There is thus provided in accordance with a preferred embodiment of the present invention a method for producing an output scrambled digital data stream from an input scrambled digital data stream, the input scrambled digital data stream including a plurality of control messages (ECMs), each ECM including coded information for generating a control word (CW) associated with the ECM and being encoded using an ECM key, the input scrambled digital data stream also including a plurality of segments of scrambled digital data, each segment of scrambled digital data being associated with one of the plurality of ECMs and being scrambled using the CW associated with the ECM, the method including replacing each of the plurality of ECMs with a corresponding transformed ECM (TECM), each corresponding TECM including coded information for generating the CW associated with the corresponding ECM and being encoded using a TECM key, thus producing the output scrambled digital data stream, wherein the ECM key is replaced with a new ECM key at an ECM key change time, and the TECM key is not replaced at the ECM key change time.
Further in accordance with a preferred embodiment of the present invention the step of replacing includes performing the following steps iteratively for each one of the plurality of ECMs: receiving the one ECM and the segment of scrambled digital data associated therewith, generating the associated CW from the one ECM using the ECM key, generating a transformed ECM (TECM) including coded information for generating the associated CW and being encoded using a TECM key, outputting the TECM, and outputting the segment of scrambled digital data associated with the ECM.
There is also provided in accordance with another preferred embodiment of the present invention a method for recording, on a recording medium, a broadcast scrambled digital data stream to produce a scrambled digital recording, the broadcast scrambled digital data stream including a plurality of control messages (ECMs), each ECM including coded information for generating a control word (CW) associated with the ECM and being encoded using an ECM key, the broadcast scrambled digital data stream also including a plurality of segments of scrambled digital data, each segment of scrambled digital data being associated with one of the plurality of ECMs and being scrambled using the CW associated with the ECM, the method including receiving the broadcast scrambled digital data stream, and recording on the recording medium a scrambled digital data stream including a plurality of transformed ECMs (TECMs) and the plurality of segments of digital data, wherein each of the plurality of ECMs is replaced with a corresponding TECM, each corres
Coddington Trevor Quick
Limbach & Limbach LLP
NDS Limited
Swann Tod R.
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