[linux-dvb] Re: Kernel OOPS

[Ralph Metzler <rjkm@metzlerbros.de>]

Andrew de Quincey writes:
 > 
 > > > > And, unless there is a hardware or firmware CSA descrambler on the
 > > > > card, you will never be able to decrypt pay-tv in a legal way.
 > > > > IANAL, but I don't think that anyone can write a CSA descrambler under
 > > >
 > > > GPL.
 > > >
 > > > That's incorrect. You don't needs to implement CSA, the MPEG-2 transport
 > > > stream from the demodulator is physically routed through the CAM, which
 > > > implements CSA. Thus, it can be done in a perfectly legal way.
 > >
 > > Hm, interesting. Are you sure? Afaik the CSA is implemented in the AV7110
 > > of the full-featured cards. So I would have expected that CSA has to be
 > > implemented in the driver of the budget cards, not in the CAM.
 > > Maybe I'm wrong.
 > 
 > Pretty sure; by my reading (and Robert's I think) of CENELEC EN50221, you feed 
 > an encrypted stream to the CAM module, and it outputs a decrypted stream. The 
 > CAM is treated as a "black box"; you just send control signals at it to 
 > choose which PIDs to decode etc... well, I'll find out if who is right in a 
 > few days :)

You are definitely right. E.g. KNC cards work fine by leaving
the decoding to the CAMs and without any CSA in software. 

Also compare with the specs of "CI-CAM chip" suppliers like SIDSA
which say they implement CSA. The CSA in the AV7110 or other "STB
chips" is only for embedded software CAMs as many receivers offer them
(mostly with VIACCESS). 

I think it is not even possible to get a software license from the 
patent holder (totally apart from the question if this kind of algorithm
patent is really valid in Europe). 
The whole thing is of course silly since the weak point never ever
was the CSA (and obscurity would not help secure that if there were
any weakness) but stupid errors in the card programming or other leaks.
On the other hand, CSA in software is slow and better left to special
purpose hardware anyway.


Ralph


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