| 摘要 |
The present invention aims at providing a way to speed-up the channel change, in particular for encrypted contents with verification of the access rights. According to the present invention, a method is proposed for controlling access to a plurality of channels by a receiver/decoder (STB) comprising a security module (SC), each channel being encrypted by a specific channel control word (CW1, CW2), each channel having a channel identifier (ID1, ID2) and transporting entitlement messages ECM containing at least the current channel control word and the channel access conditions, this method comprising the steps of:
- tuning to a first channel having a first channel identifier (ID1),
- transmitting the first channel identifier (ID1) to the security module (SC),
- receiving first entitlement messages ECM1 containing a first control word (CW1),
- transmitting the first entitlement messages ECM1 to the security module (SC),
- decrypting the first entitlement messages ECM1 and verifying the channel access conditions,
- if the access conditions are met, returning the first control word (CW1) to the receiver/decoder (STB),
- storing of the first control word (CW1) and the first channel identifier (ID1) by the security module (SC),
- tuning to a second channel having a second channel identifier (ID2),
- transmitting the second channel identifier (ID2) to the security module (SC),
- calculating, by the security module (SC), the second control word (CW2) by the following steps:
- calculating a root control word (RK) with an inverse cryptographic function F -1 using the first control word (CW1) and the first channel identifier (ID1),
- calculating the second control word (CW2) with the cryptographic function F using the root control word (RK) and the second channel identifier (ID2),
- returning the second control word (CW2) to the receiver/decoder (STB). |
