Constructing a transport stream

Abstract

A plurality of sets of primary product keys is established or generated, each set containing at least two different primary product keys. One primary product key of each set is made available to each receiver or group of receivers, such that each receiver or group of receivers is provided with a different combination of said primary product keys. For each set of primary product keys, the plurality of receivers or groups of receivers is provided with a different primary entitlement control message corresponding to each primary product key of said set, each such primary entitlement control message distributing a primary control word for recovery through decryption using the corresponding primary product key. The primary control words can then be used for purposes such as tracing compromise of the conditional access system, or arranging for differently fingerprinted content to be decoded at different receivers or groups of receivers.