A vehicle includes a controller. The controller is configured to send a nonce encrypted according to a symmetric encryption key. The nonce is sent responsive to receiving a pair request over a personal area network from a nomadic device outside the vehicle. The controller is further configured to initialize a secure connection using a random key and permit vehicle access according to data received via the secure connection. The initialization is responsive to receiving a concatenation of the random key and an incrementation of the nonce encrypted with the symmetric encryption key.