A control system for an unmanned vehicle includes a control processing unit which receives input signals from one or more sensors and supplies output signals to one or more actuators. Processing modules are divided into a plurality of successively linked stages. In a first stage, multiple processing modules produce substantially equivalent payload data when operating correctly. Message cryptography units generate cryptographically signed messages containing the payload data. In a second stage, a voting cryptography unit receives and examines the cryptographically signed messages, and applies voting logic to derive a validated payload data for use by the respective processing module of the second stage.