Security mechanisms for positioning systems - enhancing the security of eLoran

The Positioning, Navigation and Timing (PNT) infrastructure becomes more and more important. Today, most PNT systems are based on the Global Positioning System (GPS). This dependency on GPS makes the PNT infrastructure very vulnerable. Therefore, a backup for GPS is needed in case of attacks on GPS or system failures. One of the most promising backups for GPS is the Long Range Navigation System (LORAN). To be able to be an independent backup for GPS, LORAN is currently being upgraded to enhanced LORAN (eLoran). Civil navigation systems are very vulnerable to jamming and spoofing attacks, as no security countermeasure is used to prevent these attacks. But because these systems are used in more and more critical applications, the threat of attacks and therefore the need for security mechanisms increases. The development of eLoran is a great opportunity to embed security mechanisms into the design of eLoran to make eLoran a secure positioning system. In this thesis, efficient security mechanisms for eLoran are discussed. A modified version of the TESLA authentication algorithm, called adjusted TESLA, is proposed for the eLoran data channel. The main modification is to embed the transmission time of each key into the one-way chain generation. With this modification it can be shown that a key size of 80 bit can provide sufficient security for many years. Furthermore, it is possible to use this key on its own to authenticate the most important information in eLoran, the source of the signal and the transmission time of the signal. In this way, it is not necessary to use a MAC to prevent signal-synthesis attacks. But message authentication is only one step towards a secure positioning system. Only signal-synthesis and counterfeit correction message attacks can be prevented using adjusted TESLA. Other attacks like selective-delay and relaying attacks are still possible. Therefore, additional countermeasures against these attacks are discussed in the last chapter. A new method, called colliding signals, is introduced that can prevent signal-synthesis attacks. Although this method seems to be impracticable for eLoran, it can be a powerful tool in other terrestrial positioning systems.