  The Location Service (LCS) proposed by the telecommunication industry is an
architecture that allows the location of mobile devices to be accessed in
various applications. We explore the use of LCS in location-enhanced server
authentication, which traditionally relies on certificates. Given recent
incidents involving certificate authorities, various techniques to strengthen
server authentication were proposed. They focus on improving the certificate
validation process, such as pinning, revocation, or multi-path probing. In this
paper, we propose using the server's geographic location as a second factor of
its authenticity. Our solution, SALVE, achieves location-based server
authentication by using secure DNS resolution and by leveraging LCS for
location measurements. We develop a TLS extension that enables the client to
verify the server's location in addition to its certificate. Successful server
authentication therefore requires a valid certificate and the server's presence
at a legitimate geographic location, e.g., on the premises of a data center.
SALVE prevents server impersonation by remote adversaries with mis-issued
certificates or stolen private keys of the legitimate server. We develop a
prototype implementation and our evaluation in real-world settings shows that
it incurs minimal impact to the average server throughput. Our solution is
backward compatible and can be integrated with existing approaches for
improving server authentication in TLS.
