A system and a method include an onboard communication system configured to be disposed onboard a vehicle system and comprising one or more processors. The one or more processors may generate a session key that includes a shared secret key that is known by the onboard communication system and an off-board communication system, generate one or more encryption keys by hashing the session key with an identifier based on a cycle time that is known by the onboard communication system and the off-board communication system, generate one or more encrypted messages by encrypting one or more messages associated with one or more of the vehicle system or a route over which the vehicle system moves based on the one or more encryption keys, and communicate the one or more encrypted messages from the onboard communication system to the off-board communication system.