A receiver/decoder or IRD (Integrated receiver/decoder) is in charge of receiving the broadcast signals, these signals being scrambled so that only the authorized IRD can have access to them. These signals form a plurality of services, each service representing a channel with audio, video and control data.
In order to descramble a service, the control data contain entitlement messages ECM in which the key (control word) to decrypt the audio and video data is transported as well as the access conditions. These ECM are also encrypted with a so-called “transport key”. In the IRD, a security module is in charge of the security operations and in particular of the decryption of the ECM. The security module contains the transport key and decrypt the ECM. The access conditions are then compared with the access rights stored in the security module and if the access conditions are met, the control word is returned to the descrambler for descrambling the audio and video.
Security modules, as mentioned above, can be implemented in a variety of manners such as on a microprocessor card, on a smartcard or any electronic module in the form of a badge or key. These modules are generally portable and detachable from the receiver/decoder and are designed to be tamper-proof. The most commonly used form has electrical contacts but contactless versions of type ISO 14443 also exist. Another implementation of the security module exists where it is directly soldered inside the receiver/decoder, a variation of this being a circuit on a socket or connector such as a SIM module. Yet another implementation is to have the security module integrated on a chip which has another function e.g. on the de-scrambling module or on the microprocessor module of the receiver/decoder. The security module can also be implemented in software.
The transport key as well as the access rights are updated regularly by the management center by sending management messages EMM, these messages being encrypted by a key pertaining to the targeted security module.
The condition to receive without interruption the services is to receive the new keys (e.g. transport key) or new rights on time even if the IRD is not used by the user. This is why, the majority of IRD have in fact a false power down mode, the full functionalities staying on for receiving the messages sent by the management center. Only the user interaction in turn into idle, such as the screen. We will name this mode “active/standby state” for the rest of the description.
A first solution to avoid keeping the IRD in active/standby state is described in the document WO01/97518A1 in which the IRD pass from the active state to the active/standby state when the user activate the power down mode, this active/standby state allowing to receive the messages until the update of the IRD is done. At that time, the IRD pass to a complete standby state.
Another solution is described in the document US 2006/0004661 in which the receiver comprises a wake up logic to activate the receiver when the same is supposed to receive a message. After a pre-programmed time, the wake up logic send a signal to the receiver to go back into standby mode. This solution is based on a synchronization between the head-end and the receiver. The wake up time should be known by the head-end and the time window defined by the wake up logic should be used to send the messages to this receiver.