  The reliability of information in participatory sensing (PS) systems largely
depends on the accuracy of the location of the participating users. However,
existing PS applications are not able to efficiently validate the position of
users in large-scale outdoor environments. In this paper, we present an
efficient and scalable Location Validation System (LVS) to secure PS systems
from location-spoofing attacks. In particular, the user location is verified
with the help of mobile WiFi hot spots (MHSs), which are users activating the
WiFi hotspot capability of their smartphones and accepting connections from
nearby users, thereby validating their position inside the sensing area. The
system also comprises a novel verification technique called Chains of Sight,
which tackles collusion-based attacks effectively. LVS also includes a
reputation-based algorithm that rules out sensing reports of location-spoofing
users. The feasibility and efficiency of the WiFi-based approach of LVS is
demonstrated by a set of indoor and outdoor experiments conducted using
off-the-shelf smartphones, while the energy-efficiency of LVS is demonstrated
by experiments using the Power Monitor energy tool. Finally, the security
properties of LVS are analyzed by simulation experiments. Results indicate that
the proposed LVS system is energy-efficient, applicable to most of the
practical PS scenarios, and efficiently secures existing PS systems from
location-spoofing attacks.
