Cryptography – Video cryptography – Video electric signal modification
Reexamination Certificate
2000-08-11
2004-03-30
Darrow, Justin T. (Department: 2132)
Cryptography
Video cryptography
Video electric signal modification
C380S210000, C380S211000, C380S230000, C380S239000, C705S051000, C705S052000, C705S055000, C705S058000
Reexamination Certificate
active
06714650
ABSTRACT:
The present invention relates to a method and apparatus for transmission and recording of scrambled digital data, for example broadcast audio and/or visual data.
Transmission of scrambled or encrypted digital data is well-known in the field of pay. TV systems, where scrambled audiovisual information is broadcast e.g. by satellite to a number of subscribers, each subscriber possessing a decoder or receiver/decoder capable of descrambling the transmitted program for subsequent viewing.
In a typical conditional access system for pay TV, scrambled digital data is transmitted together with a control word for descrambling the digital data, the control word itself being encrypted by a first key and transmitted in encrypted form in an ECM message. The scrambled digital data and encrypted code word are received by a decoder possessing an equivalent of the first key necessary to decrypt the encrypted control word and thereafter descramble the transmitted data. Usually, the control word changes every 10-15 seconds. A paid-up subscriber will receive on a monthly basis an EMM message including the exploitation key necessary to decrypt the encrypted control words so as to permit viewing of the broadcast programs.
With the advent of digital technology, the quality of the transmitted data has increased many times over. A particular problem associated with digital quality data lies in its ease of reproduction. Where a descrambled program is passed via an analogue link (e.g. the “Peritel” link) for viewing and recording by a standard VCR the quality remains no greater than that associated with a standard analogue cassette recording. The risk that such a recording may be used as a master tape to make pirate copies is thus no greater than with a standard shop-bought analogue cassette.
By way of contrast, any descrambled digital data passed by a direct digital link to one of the new generation of digital recording devices (for example, a DVHS recorder) will be of the same quality as the originally transmitted program. It may thus be reproduced any number of times without any degradation of image or sound quality. There is therefore a considerable risk that the descrambled data will be used as a master recording to make pirate copies, either further digital copies or even simple analogue VHS copies.
PCT/US97/07981, which represents the closest prior art document, discloses a system of copyright control, in which authorisation messages are included with a broadcast program. A receiver/decoder makes a decision to record the program or not based on this message, the program usually being recorded in clear on the video cassette. The system operates in parallel with a conventional conditional access system and in all embodiments the transmitted scrambled program is descrambled in the decoder before being recorded.
EP 0763936 discloses another method of copyright control, again using a system of authorisation messages in parallel with a conventional access control system. In order to permit replaying of a scrambled recording after the end of a subscription month (and a subsequent change in exploitation key), the system stores that month's EMM message in the smart card of the decoder. This may lead to significant information storage problems in the smart card.
It is an object of the present invention to enable a secure system for transmission and recordal of data permitting authorised recording of transmitted digital data, whilst minimising the risk of pirate copies of such recordings being made by unauthorised third parties and avoiding the problems with the known systems.
According to the present invention there is provided a system for transmission and recording of digital data, comprising a transmission means adapted to prepare and transmit at least one control word encrypted by a first key together with digital data scrambled by that control word characterised in further comprising a digital recording device adapted to receive and record the transmitted scrambled digital data together with the encrypted control word on a digital support, the digital recording device further including an access control unit adapted to decrypt the control word and thereafter descramble the digital data during playback.
In this way, the data in question will be recorded in the scrambled form in which it was transmitted directly on the digital support medium, and may only be accessed thereafter in conjunction with the recording device and associated access control unit, thereby providing a secure system for recordal whilst avoiding the problems with the known methods.
The access control unit may be permanently integrated in the recording device. However, in some embodiments it may be envisaged that the access control unit is incorporated in a discrete module, for example as a smart card on SIM card, insertable in the recording device to permit decryption and descrambling of the recorded data upon playback.
Whilst the recording device may include the means necessary to receive the transmitted digital data, the system may also comprise a separate receiver/decoder adapted to receive the transmitted digital data and encrypted code word and to communicate this information to the recording device for subsequent recordal.
In this embodiment, the receiver/decoder may be a standard type as known from the field of digital television broadcast and adapted to receive broadcast audio and/or visual data (scrambled and in clear) as well as data sent, for example, via a modem link to the receiver/decoder. The receiver/decoder may also be integrated with other devices such as digital television, DVHS recorder etc.
Broadly speaking, the system may function in two possible modes of operation; a cyclical transmission mode and a transmission on demand mode. In the case of a cyclical transmission mode, the transmission means is adapted to repetitively transmit the scrambled digital data and encrypted code word.
In such a mode, the control word for the data is preferably encrypted by a first key associated with the identity of the data being transmitted. For example, in the case where a number of pieces of music are being transmitted in a repeating cycle, the control word or words needed to descramble the data for each recording are encrypted by a key specific to that particular piece of music. The number of control words needed may depend on the length of the piece of music.
The equivalent of the key needed to decrypt the control word may be communicated to the access control means in a number of ways, for example, simply by transmission “in clear” over a telephone network or the like. Preferably, however, the first key is encrypted by a second key before communication to the access control unit.
In such an embodiment, the system may further comprise a key encryption apparatus adapted to encrypt the equivalent first key by a second key before communication to the recording device, the access control unit possessing an equivalent of the second key so as to permit the decryption of the first key and, thereafter, the decryption of the control word and subsequent descrambling of the transmitted data
The key encryption apparatus may be integrated with the transmission means and the associated circuitry for scrambling the transmission etc. However, it may equally be associated with a separate database and server containing a list of keys associated with each access control means and recording device.
In the case where the system comprises a receiver/decoder unit, the receiver/decoder unit may be adapted to request a first key from the key encryption apparatus, the key encryption apparatus thereafter transmitting the encrypted first key to the receiver/decoder for subsequent communication to the recording device and access control module.
For example, the key encryption apparatus may respond to a request received from the receiver/decoder via a modem channel by returning information on this channel. Alternatively, the information may be communicated to the transmission means for subsequent communication, for example, in a broadcast transmissio
Benardeau Christian
Maillard Michel
Canal + Societe Anonyme
Darrow Justin T.
Rosenthal & Osha L.L.P.
LandOfFree
Recording of scrambled digital data does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Recording of scrambled digital data, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Recording of scrambled digital data will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3211318