Patent attributes
A passive keyless entry system for an electronic lock, comprises a lock installation including a lock controller, and an RF transmitter and receiver, and a fob with a controller, and an RF transmitter and receiver. The fob generates messages to unlock the lock in an unlock event. The controllers share a secret specifying parameters for a sequence of messages to be exchanged bidirectionally between the installation and the fob, the parameters changing between each unlock event and an immediately subsequent unlock event. For each unlock event one of the controllers generates and sends a first message of the message sequence, in accordance with the specified parameters. The other controller causes transmission of a second message of the sequence in accordance with the specified parameters, in response to receiving the first message. At least one message of the sequence comprises a plurality of frames, each frame including a particular sequence of bits, adjacent frames being separated by an inter-frame interval. Adjacent messages in the sequence being separated by an inter-message interval. The specified parameters are such that a given message of the sequence includes a first inter-frame interval, and the inter-message interval between said given message of the sequence and the immediately preceding or immediately subsequent message is no longer than said first inter-frame interval.
