FIELD: physics, computer engineering.
SUBSTANCE: invention relates to computer engineering. A method of controlling access to a set of channels using a receiver/decoder comprising a security module (SC), each channel being encrypted by a specific channel control word (CW1, CW2), each channel having a channel identifier and transmitting access control messages ECM containing at least the current channel control word and the channel access conditions. The method comprises the following steps: tuning to a first channel having a first channel identifier (ID1); transmitting the ID1 to the SC; receiving first access control messages ECM1 containing a first control word (CW1); transmitting the first access control messages ECM1 to the SC; decrypting the first access control messages ECM1 and verifying the channel access conditions; if the access conditions are met; transmitting the CW1 to the receiver/decoder; storing of the CW1 and the ID1 in the SC; tuning to a second channel having a second channel identifier ID2; transmitting the ID2 to the SC; calculating, by the SC, the second control word (CW2) by performing the following steps: calculating a root control word (RK) with an inverse cryptographic function F-1 using the CW1 and the ID1; calculating the CW2 with the cryptographic function F using the RK and the ID2; transmitting the CW2 to the receiver/decoder.
EFFECT: reducing channel switching time when a user selects another channel.
9 cl, 3 dwg
