[linux-dvb] Re: CI and streaming

[Roberto Deza <rdeza@unav.es>]

Hi,

At 14.21 21-01-2004 +0200, Irek Defée wrote:

[CAM behaviour]
<...>
>This looks really bad. I thought that stream from the whole transponder
>stream is decrypted, not one program.

Normally, each program should be encrypted with different Control Words
(one could be subscribed to one package, don't covering all of the
programs in the transponder). The common descramblers (also the AV711x
used in TT DVB_FF cards) are cappable of this job, but there isn't 
interest on support this "feature" on a receiver and there is real 
interest (from the providers) on disalow it, for other uses (as 
simultaneus view, recording, etc).

>Does the receiver send to CAM
>PID values every time it want them decrypted???

I think that the CAM alone parse the DVB stream tables (CAT, PMT, etc),
getting the ECM sections, wich are sent to the Smartcard to get the
decrypted ControlWords, also the EMM sections (again sent to the 
Smartcard, for subscription management); all of this is "automatic" and 
builtin in the CAM firmware, driven from the receiver by some commands, 
which select the program to decode. I don't know the exact details of 
this commands, but the protocols are standard and you can see a 
implementation in current VDR :-).


Best regards:
--
Roberto Deza Asensio
Universidad de Navarra
Data Procesing Center


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