Cryptography – Video cryptography – Video electric signal modification
Reexamination Certificate
1998-09-02
2001-10-16
Peeso, Thomas R. (Department: 2132)
Cryptography
Video cryptography
Video electric signal modification
C380S240000, C380S216000, C380S200000, C713S162000
Reexamination Certificate
active
06304659
ABSTRACT:
The present invention relates to a method and apparatus for including data within a digital television signal while providing protection against analysis of the destination of the data to the intended recipients.
A digital video broadcast (DVB) channel may be used to transmit datagrams to individual receivers, groups of receivers (multicast) or all receivers (broadcast) which have access to the broadcast channel within a Digital Video Broadcast/Motion Picture Expert Group 2 (DVB/MPEG-2) Transport Stream. Datagrams are prefixed with a header that contains a protocol-independent destination address within the data broadcasting network and a protocol identifier. If the destination addresses are clear (i.e. not encrypted) it is possible for the traffic of data being transmitted to receivers accessing the channel to be monitored and commercial information relating to this traffic may consequently be exposed.
European Patent No 0 679 029 proposes a method of increasing the security of data being transmitted to receivers by use of encryption keys. These keys, used by a transmitter to encode data, are transmitted to a receiver in encrypted form using either single or double encryption techniques. These keys are then decrypted at the receiver before being used to decrypt the transmitted data. However, in the method described the encrypted keys and the data are sent in data packets in which the address is in unencrypted form.
International Patent No WO 94/10802 describes a method of sending addressable data to a receiver having a unique identification number. The addressable data may contain various subscriber specific data such as, for example, program authorisation information. Again, the addresses used to identify the specific receivers in the transmitted data packet are not encrypted, allowing traffic analysis to be performed on the transmitted data packets which could result in such commercial information becoming exposed.
The present invention is concerned with a method and apparatus for protecting the destination addresses of data being transmitted over a digital video broadcasting channel.
According to one aspect of the invention, there is provided a method of receiving data addressed to one or more receivers each having an individual identifier wherein the data is included in a digital signal comprising destination addresses successively encrypted from a sequence of control words, and control messages containing the control words in encrypted form, address flags and control flags, the method comprising:
processing the control messages to construct receiver addresses from the control words and the receiver identifier;
directing the receiver addresses to update a receiver address register selected by the associated control flag in response to the transmitted control flags;
directing each destination address to be compared with the receiver address to one of the address registers selected by the associated address flag in response to the address flags and;
accepting each packet of data having a destination address matching the receiver address to which it was compared.
According to a second aspect of the present invention, there is provided apparatus for receiving data addressed to one or more receivers each having an individual identifier wherein the data is included in a digital signal comprising destination addresses successively encrypted from a sequence of control words, and control messages containing the control words in encrypted form, address flags and control flags, the method comprising:
processing means for processing the control messages to construct receiver addresses from the control words and the receiver identifier;
a first directing means for directing the receiver addresses to update a receiver address register selected by the associated control flag in response to the transmitted control flags;
a second directing means for directing each destination address to be compared with the receiver address to one of the address registers selected by the associated address flag in response to the address flags and;
accepting means for accepting each packet of data having a destination address matching the receiver address to which it was compared.
According to a third aspect of the invention, there is provided a method of creating a secure data-stream containing one or more data packets to be transmitted to one or more receivers each having an individual identifier, the method comprising the steps of;
allocating control messages comprising control flags and control words in encrypted form and multiplexing these with the data-stream;
encrypting the destination address in the header of the or each data packet using the receiver identifier and the control word as inputs;
allocating an address flag for inclusion within the or each data packet for use by a receiver in accepting or rejecting such a data packet.
REFERENCES:
patent: 4991207 (1991-02-01), Shiraishi et al.
patent: 5237610 (1993-08-01), Gammie et al.
patent: 5539823 (1996-07-01), Martin
patent: 5627892 (1997-05-01), Kauffman
patent: 0 679 029 A1 (1995-10-01), None
patent: WO 94/10802 (1994-05-01), None
Dallard Nigel Stephen
Gold Martin
Merry Paul Austin
Mountifield Anthony
Jack Todd
Ladas & Parry
Peeso Thomas R.
Tandberg Television ASA
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