Patent ID: 7822205

Claim:
A method of controlling pairing between a removable security module and a host apparatus connected to the removable security module, the pairing method securing data exchanged between the removable security module and the host apparatus by using a unique pairing key, the method comprising: verifying the pairing between the removable security module and the host apparatus and using the unique pairing key when the pairing between the removable security module and the host apparatus has been already carried out, wherein, when the pairing between the removable security module and the host apparatus has not been carried out, the method includes, searching for a free location among locations reserved for the unique pairing key in the removable security module and wherein, when a free location is absent, the method further includes performing at least one of reading an activity counter associated with each location of the removable security module, said activity counter being incremented each time a location is used for pairing, and finding a lowest value activity counter to determine the location to be used for a pairing procedure, and reading a chronology counter associated with each location of the removable security module, said chronology counter being incremented each time a location is used for pairing, and finding a lowest value chronology counter to determine the location to be used for a pairing procedure, initiating the pairing procedure by transmitting a cryptogram contained in the host apparatus, the cryptogram including an identifier identifying the host apparatus and the unique pairing key, and the cryptogram being encrypted by a secret key common to a plurality of removable security modules, the plurality of removable security modules including the removable security module, decrypting the cryptogram with the removable security module and extracting the identifier of the host apparatus and the unique pairing key from the cryptogram, and storing the unique pairing key in the removable security module, the unique pairing key used to pair with the host apparatus.