In this paper we investigate and provide solutions for security threats in the context of hybrid networks consisting of a cellular base station and mobile devices equipped with dual cellular and ad-hoc (802.1 Ib) cards. The cellular connection is used for receiving services (i.e. Internet access) from the base station, while the ad-hoc links are used to improve the quality of the connection. We provide detailed descriptions of several attacks that arbitrarily powerful adversaries, whether outsiders or insiders, can mount against well-behaved members of the network. We introduce a secure routing protocol called JANUS, that focuses on the establishment of secure routes between the base station and mobile devices, and the secure routing of the data. We show that our protocol is secure against the attacks described and experimentally compare the message over-head introduced by JANUS and UCAN.
