A medical device of a medical system is configured for communicating with an external programmer over a wireless communications link. The medical device comprises a wireless communications module configured for receiving a first unencrypted version of a random number and a first encrypted version of the random number from the external programmer over the wireless communications link. The medical device further comprises control circuitry configured for performing an authentication procedure on the external programmer based on the first unencrypted version of the random number and the first encrypted version of the random number, and preventing the external programmer from commanding the medical device to perform an action unless the authentication procedure is successful.