A smart card (1) interfaces with a smart card reader (2) to generate an authentication message (PSRQ), which is sent to a PIN servicing centre (5, 6). If the authentication message (PSRQ) is validated by the PIN servicing centre (5, 6), a validation response message (PSRS) is sent back to the user (3). The user (3) enters the validation response message (PSRS) on the reader (2), which authenticates the validation response message (PSRS) with the smart card (1); the PIN servicing function may then be performed. The smart card cryptographic messages are generated internally and solely by the smart card (1)—the reader (2) acts merely as an input mechanism into the smart card (1) or as an output mechanism from the smart card (1) to the display (10). The reader (2), therefore, does not need to contain any customer information or be personalised by the card issuer.