A process for broadcasting conditional access programs which permits a progressive access. Scrambled program data is transmitted along with partial access checking messages and complete access checking messages such that subscribers having a partial access right may descramble portions of the scrambled data corresponding to information regarding only the identity of the conditional access programs, and subscribers having a complete access right may descramble the remainder of the scrambled data and view the conditional access programs. The conditional access programs may be television pictures, radio programs, or data broadcasts.
A process for the transmission and reception of scrambled conditional access programs, which are synchronously transmitted with entitlement control messages (ECM), with a reduced program switching time. The entitlement control messages (ECM) have check words, which are changed after a period of time called a phase, for descrambling the conditional access programs. The process includes transmitting main check messages (ECMp) for a main access program at a first frequency (Fp) and transmitting secondary check messages (ECMs) for secondary programs at a lower, second frequency (Fs). The secondary check messages (ECMs) are transmitted between two successive transmission of the main check messages (ECMp) such that all of the secondary check messages (ECMs) for each of the secondary programs are transmitted in a single phase. Therefore, a check word for any program is quickly acquired and program switching time is reduced.
According to the invention, the chip card issues a first certificate comprising its letter of credentials (Crc), an exponential (X), an optional message (M), these quantities being signed. The security module verifies the signature and in return issues a second certificate containing its letter of credentials (Crm), an exponential (Y), an optional message (M'), a cryptogram (C), these quantities being signed. A common secret key is constituted between the card and the security module by the exponentials and allows the card to interpret the cryptogram addressed to it and to act in accordance therewith.