Patent ID: 7779455

Claim:
A method for monitoring usage of a service by a communication device coupled to a smart card, said service being transmitted from a resource able to communicate with said communication device by way of a network, said service comprising a plurality of encrypted data flow, the use of said service comprising successive decryption steps of data flow using a first key, said first key being encrypted in the data flow and decrypted in the smart card by way of a second key stored in said smart card, the method comprising: a counting step, in which a memory location stores a count of occurrences of decryption steps of said first key attached to the service, wherein the counting step comprises: receiving the first key encrypted by way of the second key; determining whether the first key corresponds to a previously stored encrypted key; when the first key corresponds to the previously stored encrypted key: sending, to the communication device, a previously stored decrypted version of the previously stored encrypted key without performing the decryption of the received encrypted first key; when the first key does not correspond to the previously stored key: incrementing the counter; decrypting the received encrypted first key to obtain a new decrypted first key to be used for decrypting data flow; and storing the received encrypted first key and the new decrypted first key; and a using step, in which said counter is used to determine a service fee for use of said service.