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No power on the Reader screenshot
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No card inserted screenshot
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Secret key encryption and smart cards are used for example in pay TV applications. Sometimes this is referred to as "conditional access" television. Television programs (usually premium movies, football or soccer matches and adult content) are encrypted using a secret key. To make it difficult for Eve to obtain this key, the secret key is changed every few minutes or sometimes even every few seconds. This way, even if Eve can successfully use a brute force attack to guess the key, she only has a very small portion of the television program. Alice has a set-top box and a smart card that allows her to decrypt the television programs. The set-top box passes the decrypted television program on to the television. Originally these boxes were designed to be placed on top of the television set, hence the name.
Special messages, called Entitlement Control Messages (ECMs), are sent along with the program. These messages contain the secret keys. Of course the ECMs themselves are also encrypted, this time using a key stored on the smart card. Alice's set-top box receives the ECMs and passes them on to the smart card. The smart card decrypts the ECMs and extracts the secret keys contained therein. This allows the set-top box to decrypt the television program.
The keys needed to decrypt the ECMs can be programmed on the smart card in advance. By regularly changing these keys, Alice is forced to purchase a new smart card every month or so. If Eve manages to make a copy of the smart card, or to extract the keys from it, she will only be able to watch the programs for the rest of that particular month.
Another option is to regularly send out so-called Entitlement Management Messages (EMMs) that contain the keys needed to decrypt the ECMs. The EMMs themselves are then encrypted with keys stored on the smart card. The service provider then every month simply sends out a new EMM. This provides much greater flexibility, and Alice does not have to go to the store every month. Every smart card can now have a different key. The service provider sends out different EMMs for all the smart cards in the system. Every EMM thus is readable only by one smart card. If the service provider thinks a particular smart card has been copied illegally, he simply does not send out a new EMM for that particular smart card.
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