# SAM-PAY: A Location-Based Authentication Method for Mobile Environments +
## 1 Introduction
Even the use of biometric identification solutions is not 100% secure because there is always a chance for a false positive or negative. Other proposals introduced the idea of combining several authentication methods in order to obtain a more reliable user identification [9; 14; 15; 16]. Potentially, several factors should be employed to authenticate the user, including username/password, biometrics, behavioral characteristics, and location information, which must be protected for integrity against intentional attacks aimed to forge or spoof it. For instance, in [9], the probability that a user is at a certain location is used as a measure to parameterize the authentication level of the user. To combat identity theft, [17] proposed in 2005 an authentication architecture and system combining a physical location cross-check, a method for assuring uniqueness of location claims, and a centralized verification process. The above mentioned work extensively discusses necessary checks regarding the personal device used in the authentication process, like device irregularities, theft, and cloning, and proposes that all identity verifications be funneled through a centralized point. This component allows to check that no \"irregularities\" have occurred for the personal device in question (based on ongoing device monitoring). Moreover, determining and securely asserting that a user is at a certain location is not trivial, as no single location-sensing technology has emerged as a clear winner in all kinds of environments. The Global Positioning System (GPS) is the de facto location technology for wide outdoor areas, but it does not work in covered areas or indoors, and it can be spoofed (as explained in Section 2). For indoor environments, many technologies have been proposed, but the data obtained from the different technologies should be combined to obtain a more complete picture of the physical environment and to determine the location with higher accuracy [18]. To mitigate these problems, a possible solution would be to use a specialized ground component, such as the Galileo Local Element (LE). These LEs are part of the overall Galileo definition, and the Galileo Program has foreseen the development of some selected experimental local elements [19]. Alternatively, for some critical services, the Open Service Navigation Message Authentication (OSNMA) could be employed. OSNMA is a data authentication function for Galileo Open Service worldwide users and is freely accessible. It provides (satellite) receivers with the assurance that the received Galileo navigation message is coming from the system itself and has not been modified. Even though OSNMA has been tested in some recent projects, e.g., in the ROOT project [20; 21], it is still not widely exploited on a large scale because not every (user) device can be equipped with an OSNMA-aware receiver. To authenticate remote users, we propose a method--named SAM-PAY (Secure Authentication Method for Payments)--which combines the usage of \"classical\" authentication methods (like static passwords and one-time passwords) with the location information provided by the GPS/EGNOS (European Geostationary navigation Overlay System) satellite networks and certified by a terrestrial component, namely the Galileo Local Element (LE). SAM-PAY is based on three authentication factors: where a person is and when, i.e., the location of the user associated with the time information; something the user has, i.e., a specialized device used for localization and security purposes named User Terminal (UT); and something the user knows, i.e., a static PIN (Personal Identity Number) used to obtain access to the UT and a one-time password used to perform payment operations. The location/positioning information used in SAM-PAY is calculated by the UT and is certified by the ground component named Local Element. We used the SAM-PAY authentication mechanism to design and implement a prototype self-service at gas stations.