CardSharing: What it is, what it is for and how it works
If we have satellite pay-TV, we can see that our decoder somewhere has a card inserted permanently. This card is the one that allows us to see the channels correctly since in the background it tells the receiver what we can see or not. As it does? basically offering the ability to decrypt the contracted channels. This card is basically a small computer, comparable to the SIM card of cell phones, only in this case the communication with the satellite is unidirectional. How can we share a card between several decoders? That is the big question, for this, we must understand what they are for and how they work.
If we all receive the same signal, then how do we remotely cut or modify our service?
What the company simply does is transmit an order to "damage" a certain card through the satellite. The receiver determines if the card is the one they have, and irreversibly “disables” it. This message is transmitted through an EMM (Entitlement Management Message), which is basically a type of message whose content is directly associated with a particular client or a subgroup of them.
Conditional Access
In the context of satellite television, Conditional Access (I am referring in particular to DVB-CA) is a defined standard for transmission encryption, whose access is conditioned by the use of smart cards that companies deliver with their equipment. .
The television signal received from the satellite is encrypted in two parts. The first part is where the content, image, sound, etc. comes from. and the second part is where the decryption key is located for the first part, this part is contained in a message known as ECM (Entitlement Control Message). Smart cards are the ones that provide the ability to decrypt this last message to deliver the key to the receiver's video processor and so, then we can see the video correctly.
So in simple, conditional access works like this:
1. The receiver tunes the channel and gets the ECM message
2. The ECM message is sent to the smart card
3. The smart card returns a key
4. The key is sent to the video processor and it is decrypted
5. Then comes a new ECM message and we go back to 1.
Card Sharing
As its name says, CardSharing is a practice that consists of sharing a smart card between several receivers, since this is the critical part of the decryption process, that is, steps 2 and 3 above. In the case of Nagra 2, this process managed to be emulated with software, but in the case of Nagra 3, it has not been possible so it is necessary to transmit the ECM message somewhere where there is a card capable of decrypting.
IKS or Internet Key Sharing
In particular, this name is given to Card Sharing in which steps 2 and 3 outlined above are performed via the internet. Step 1 is performed locally on the IKS server, in general providers have at least one dedicated receiver for each channel, from which a key table is generated that is shared at the request of the different clients.
SKS or Satellite Key Sharing
In this case, stage 1 is equivalent to IKS, however stages 2 and 3 occur unidirectionally through a satellite, so it is necessary to transmit the complete table of keys for all channels, and it is the “dongle” the responsibility for returning a particular key at the request of the receiver, according to the tuned channel.
