Abstract:
A semiconductor circuit for use in a system for receiving and decrypting broadcast signals such as pay television comprises an input and stores for receiving a decryption key in two portions named mother and daughter portion. The splitting of the key into two portions allows a common main or mother portion to be sent broadcast to a large number of subscribers and for separate daughter portions to be sent to each subscriber or group of subscribers depending upon, for example, entitlements for which the subscribers have paid. The semiconductor circuit is arranged to retrieve the mother portion and a relevant daughter portion to construct a complete decryption key.
Abstract:
A method which determines the validity of information contained in a data stream, said information falling within a predetermined range when valid, said method comprises the steps of selecting a first part of said of said information, said first part being more significant than a remainder of said information; comparing said first part with one or more corresponding parts of one or more values defining said predetermined range. Determining from said comparing step if said information is or could be within said predetermined range.