SBAS Message Schemes to Support Inline Message Authentication

The international community is considering the addition of authentication signatures to the Satellite Based Augmentation System (SBAS) Minimum Operational Performance Standards (MOPS). Authentication would protect the user against the possibility of undesired integrity data being mistaken for genuine State provided signals. Several authentication schemes have been proposed over the past years, but recently a preference has been expressed for inline signatures (i.e., signatures that are interleaved with the correction and integrity messages, all in the same data stream). An important concern is whether there is sufficient bandwidth to add these new messages and will their addition negatively affect performance. We have proposed a method that achieves this goal and evaluate its performance. Further, our method ensures rigorous protection for the user by ensuring that unauthenticated data is discarded and cannot cause harm to the user, while maintaining the required Time-To-Alert of the SBAS integrity messages.