Patent ID: 7881478

Claim:
Access control method of an encrypted program transmitted by an operator to a plurality of groups of subscribers, each group of subscribers having a group key KG, and each subscriber being able to receive from the operator an operating key KT, enciphered by the group key KG for decryption of the transmitted encrypted program, the method further comprising: linking the enciphered operating key KT to a random value R to generate a secret code; transmitting the secret code to subscribers in a first transmission, prior to transmission of the encrypted program, transmitting the encrypted program along with an entitlement control message (ECM), in a second separate transmission, wherein the ECM comprises a control word used to encrypt the encrypted program, and transmitting the random value R, after transmission of the secret code, to subscribers for calculation of the operating key KT, wherein the random value R is transmitted only when the operating key KT is used to decipher a control word necessary to decrypt the encrypted program, wherein each group of subscribers calculates the operating key KT using the group key KG stored on a decoder associated with the subscribers and the random R, and decrypts the encrypted program using the deciphered control word.