Quote:
Originally Posted by Kymmy
??? Sorry but I always thought the card is just a simple PIC and has nothing to do with the full encryption but is normally just a carrier of the user key/details (which can be encrypted in thier own right and why the card needs changing if the main or master keys are updated) which when combined with the main key enables the decryption of the signal.. If so how can an electron microscope be used when a simple reader will do  |
The cards decrypt control messages which provide information the box needs to decrypt data, plus they also decrypt the individual subscriber addressable control messages.
Quote:
|
The data stream is scrambled with an 8-byte secret key, called the control word. Knowing the value of the control word at a given moment is of relatively little value, because it changes very frequently, about every 10 seconds.
|
Quote:
|
In order for the receiver to unscramble the data stream, it must be permanently informed about the current value of the control word. In practise, it must be informed slightly in advance, so that no viewing interruption occurs. Encryption is used to protect the control word during transmission to the receiver: the control word is encrypted as an entitlement control message (ECM). The CA subsystem in the receiver will decrypt the control word only when authorised to do so; that authority is sent to the receiver in the form of an entitlement management message (EMM). The EMMs are specific to each subscriber, as identified by the smart card in his receiver, or to groups of subscribers, and are issued much less frequently than ECMs, perhaps at monthly intervals.
|
http://video.aol.co.uk/video-detail/...ard/1526516239
The reason VM can use Nagra 1 and 3 simultaneously is that the control word will be encrypted with both schemes. It is this control word that the encryption is there to protect, strongly obfuscating / scrambling the actual digital TV signal is easy, it's protecting the control word while simultaneously ensuring that authorised users receive the up to date word every few seconds that's the tough part.
A smartcard has more than enough processing power to decrypt 8 bytes every 10 seconds or so.
The cards hold record of what the customer is authorised to use (which package they are on), and they decrypt control words appropriately to ensure that that subscriber has the access they are authorised for. Reverse engineer what the card holds, how it holds it, and what it does with it and you've just undone the encryption. This is what they will be targetting as the existing dodgy receivers already have the capability to descramble the signals once they have the appropriate keys / algorithms to decrypt the control words as they come down.