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Apparatus and method for local encryption control of a global transport data stream
| Details |
Inventors: Thatcher, William Bradford; Wasilewski, Anthony J.;
Assignee: Scientific-Atlanta, Inc. (Norcross, GA)
Primary Examiner: Gregory; Bernarr E.
Assistant Examiner:
Attorney, Agent or Firm: Massaroni; Kenneth M., Barnhardt, III; Hubert J., Gardner; Kelly A.
An encryption control system to process an input transport data stream into an output transport data stream includes an input demultiplexer, a first secure microprocessor, a second secure microprocessor and an output multiplexer. The input transport data stream includes first entitlement managment message data. The input demultiplexer culls the first entitlement managment message data from the input transport data stream, the first entitlement management message data including an encrypted multi-session key. The first secure microprocessor processes the first entitlement management message data to recover the multi-session key by decrypting the encrypted multi-session key using a first algorithm. The second secure microprocessor re-encrypts the multi-session key using a second algorithm and formats second entitlement management message data based on the first entitlement management message data with the re-encrypted multi-session key substituted for the encrypted multi-session key. The output multiplexer provides the output transport data stream based on the input transport data stream with the second entitlement management message data substituted for the first entitlement management message data. |
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DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS FIG.
4 is a format diagram of a representative transport data stream.
Video and audio data are prepared in the form a packetized elementary stream having a header, a presentation time stamp, and the video itself.
The packetized elementary stream is allocated into the payload section of one or more transport packets.
Transport packets are preferably 188 bits in length.
Transport packets preferably include a synchronization block and prefix data followed by payload data.
Standards referred to as MPEG-2 (actually ISO/IEC 13818-1), incorporated herein by reference, define particular embodiments of the transport data stream.
Multiplexer/encryptor 64 combines individual transport packets 62 into a frame of data 60.
Of particular interest to the present invention are entitlement management messages EMM and entitlement control messages ECM.
These messages are multiplexed into the transport data stream TDS.
Entitlement management messages are addressed to a specific decoder or group of decoders.
Entitlement control messages are broadcast to all decoders.
Seed data encrypted under a multi-session key is included in the data transmitted in the entitlement control message.
Entitlement control message ECM is sent repeatedly at a high rate, for example, ten times a second.
Multi-session key MSK, encrypted under a secret serial number, is included in entitlement management message EMM.
The entitlement management message is addressed to the decoder that has stored in it the secret serial number used to encrypt the multi-session key.
Entitlement management messages are sent infrequently, for example, once per month.
In practical use, the entitlement management message is sent many times per month to each decoder so that the decoder will have the opportunity to decrypt and store the multi-session key for the upcoming session (e.
g.
, next month).
At a particular point in time the entitlement control message will provide data indicating the switch over to the new multi-session key which was received from an earlier entitlement management message
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Communications 
