| 摘要 |
In order to trigger a device for example a vehicle locking system or an automated teller system, the device generates signals from a code (e.g. a PIN) (101) and selects one of those signals for transmission (102), different signals being selected at different times. The selection is normally random. A separate unit, carried by an authorised user, receives the signal (201) from the device and generates further signals (202) (second signals) from that initial signal, and a code (e.g. the PIN) stored in the unit. One of the second signals is then selected by the unit (300) and transmitted (203). The device also generates the plurality of second signals using the signal that it has transmitted and the initial code (103). Therefore, it can compare a received signal with the stored signals (105). If they agree, then the device determines that it has received a valid signal, and is triggered (108). If the device receives any other signal, it will not correspond to one of the plurality of second signals and thus the signal received will be determined as invalid (107). Hence, the security of the system is high. |
