Rapid decryption of data by key synchronization and indexing

Abstract

A satellite broadcast conditional access system with key synchronization uses indexing of an authorization stream to quickly restart the decrypting process after short carrier fades and after carrier switches. The authorization stream includes cyphered seeds and index numbers which are sequentially sent to a group of receivers. The same authorization stream can also be broadcast multiple times to the group of receivers. A conditional access server selects a starting index number and increments the index number by a predefined value. The receivers have a memory to save the current index number for the authorization stream. Any receiver that loses its connection to the broadcast and thereafter reestablishes its connection can retrieve the latest index number being issued in the authorization stream and compare it with the stored index number. When the index numbers match or are within a defined threshold, the receiver will continue to decypher the seeds and decrypt the transport stream.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims the benefit of U.S. Provisional Application Ser. No. 60 / 482,235 filed Jun. 25, 2003.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT[0002]Not Applicable.BACKGROUND OF THE INVENTION[0003]1. Field of the Invention[0004]This invention relates generally to satellite broadcast systems and, more particularly, to a conditional access system for encrypting and decrypting data.[0005]2. Related Art[0006]A conditional access system is used to permit access to a transport stream only to subscribers who have paid for it. This is generally done by distributing the transport stream in encrypted form. Although any integrated receiver-decoder (IRD) that is connected to a satellite broadcast network can receive the encrypted transport stream, only the IRDs of those authorized subscribers are able to decrypt the encrypted transport stream. The IRD determines whether the encrypted transport stream should be decrypted an...

AI Technical Summary

Benefits of technology

[0010]It is in view of the above problems that the present invention was developed. The present invention is a satellite broadcast conditional access system with key synchronization that allows the IRDs to quickly restart the decrypting process after short carrier fades and after carrier switches when they are within the same protected network. The invention uses an indexed authorization stream allowing the IRDs to quickly decide, after restoration of the data link following a carrier fade or switch, whether their stored copies of the decrypting seeds are still current and correct. The invention also uses multiple transmissions of the cyphered seeds during each distribution period providing the IRD with multiple opportunities to receive the current seed.

[0011]For the first attribute, the index numbers on all the authorization streams are assigned in a manner such that the authorization stream may be identified and that the specific time epoch of those cyphered seeds may be determined. When a conditional access server program initializes, it randomly selects the starting index number from a domain of numbers, and applies this number to each and every authorization stream bearing a cyphered seed. Then, while in operation, it increments that index by a predefined value at each new distribution period, i.e., an odd / even flavor switch according to the preferred embodiment. The IRDs, in their turn, after reestablishing connection to the carrier-borne transport stream, may quickly retrieve the index numbers being issued in the authorization stream and compare them to the same for both flavors of the cyphered seeds it keeps in volatile storage. If those numbers match, then the IRD will then immediately decypher those seed(s) and restart decrypting on the transport stream knowing it is using the correct seed. This restart may commence very quickly after the authorization stream is detected, and that the IRD need not wait until its own messages are received and decyphered.

[0012]For the second attribute, the distribution of the cyphered seeds is repeatedly sent with considerable delay between the cyphered seed messages. This greatly reduces the likelihood that a carrier switch or a short fade could prevent the IRD from getting at least one copy of its own cyphered seed message during each distribution period.

Problems solved by technology

A well known problem concerning such conditional access systems is that the IRDs may suffer either carrier fades or be switched between carriers bearing the same instantiation of the service provider.

However, the magnitude of time delay in the recoveries, on a typical large network (12,000 satellite IRDs) can be extremely long, such as one or two minutes in legacy systems.

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