Method for monitoring the usage of a service by a communication device coupled to a tamper resistant module, in particular a smart card. A said service is transmitted from a resource able to communicate with said communication device by way of a network. The service comprises a plurality of encrypted data flow and its use comprises successive decryption steps of data flow by a respective first key EK, said first key EK being encrypted in the data flow and decrypted in the tamper resistant module by way of a second key KEK stored in said tamper resistant module or derived inside said module. The invention is characterized in that said method comprises the following steps: a. A counting step, in which a memory location stores a count of occurrences of decryption steps of said first key EK attached to a same service; b. A using step, in which said counter is used to prove the amount of data flow which has been decrypted.