PROSPA: Open Service Authentication

PROSPA is a pilot study supported by the UK Space Agency (UKSA) which is investigating innovative solutions for key management within the Galileo Public Regulated Service (PRS). The PROPSA project is led by Astrium UK with major contributions from NSL. The objective of PROSPA is to demonstrate the proof of concept for a Galileo open service authentication system using PRS signals. PROSPA uses “snippets”, time sliced subsections of the encrypted PRS signals, which are distributed to authorised user receivers over a communications link. The received snippets are then used to authenticate the received Open Service signals. PROSPA gives all the benefits of PRS including, authenticity, anti-spoofing and access control but without the drawback of classified key distribution to the user receivers. It is a cost-effective way of providing an authenticated Open Service to government authorised users, and could therefore provide benefits to public services and user groups which would otherwise not have used PRS. The final PROSPA system will include a snippet generator located at secure centres. The snippet generator will essentially be a PRS receiver. Snippets of the encrypted PRS signal are generated by a proprietary algorithm which does not reveal the encrypted code. As the snippets contain only small sections of the PRS signal that have already been transmitted globally by the Galileo satellites, they are unclassified. The snippets are checked in the service centre using a snippet validation receiver and if confirmed good they are distributed to the user receivers via a communications channel. The user receivers can then authenticate the open service signals by performing a time aligned correlation with the PRS snippet. A strong correlation shows that the PRS signal is present and hence the signal is authentic and suitable for use. One of the key objectives of PROSPA is to keep the communication capacity required by each user receiver similar to that of a telephone call. A major driver for this objective is the ability to utilise existing communications networks for snippet distribution, for example, 3G. Furthermore, it is expected that standard commercial encryption and user authentications can be used for the delivery of snippets from the secure server. The PROSPA proof of concept demonstration uses an RF simulation of the Galileo PRS and Open Service signals. The PRS is emulated with a random stream of chips that is unknown to the receiver. As the signals have been designed in advance, the snippets are pre-loaded on to an FTP server. An Android terminal (tablet or smart phone) retrieves the snippets and provides them to the user receiver via Bluetooth. The receiver then provides an authenticated navigation solution back to the terminal. Although currently in the early stages the initial results are very promising; good correlations have already been achieved with relatively small snippet files. Future work will include a technology demonstrator which will provide potential user groups with a first approximation of the capabilities of the system and open up opportunities for early experimentation with the Galileo Public Regulated Service (PRS) in a wide range of governmental applications.