IMPROVEMENTS IN AND RELATING TO CRYPTOGRAPHY

A pairing method between a user device (1) and an operator device (2), the user device (1) being intended to receive conditional access data from the operator device (2), the user device having a user device identifier (UID), the operator having an operator device identifier (OID). The method comprises receiving, by the user device, a user device key (KUID) derived from a first cryptographically secure function and receiving, by the operator device, an operator key (KOID) derived from a second cryptographically secure function. The user device comprises a user device bilinear mathematical function (e(KUID, OID)) and the operator device comprises an operator bilinear mathematical function (e(UID, KOID)) which each define a pairing over an elliptic curve. The method includes generating, by the operator device (2), a pairing key (KD = e(UID, KOID)) between the user device (1) and the operator device (2), using the operator key (KOID) and the device identifier (UID) as variables of the operator mathematical function (e(UID, KOID)). The user device (1) generates the same pairing key (KD = e(KUID, OID)) using the user device key (KUID) and the operator device identifier (OID) as variables of the user device mathematical function e(KUID, OID).