In multi-hop cellular networks, data packets have to be relayed hop by hop from a given mobile station to a base station and vice-versa. This means that the mobile stations must accept to forward information for the benefit of other stations. In this paper, we propose an incentive mechanism that is based on a charging/rewarding scheme and that makes collaboration rational for selfish nodes. We base our solution on symmetric cryptography to cope with the limited resources of the mobile stations. We provide a set of protocols and study their robustness with respect to various attacks. By leveraging on the relative stability of the routes, our solution leads to a very moderate overhead.

Using Wireless Mesh Networks (WMNs) to offer Internet connectivity is becoming a popular choice for Wireless Internet Service Providers as it allows a fast, easy and inexpensive network deployment. However, security in WMNs is still in its infancy as very little attention has been devoted so far to this topic by the research community. In this paper, we describe the specifics of WMNs and we identify three fundamental network operations that need to be secured.

A hybrid ad hoc network is a structure-based network that is extended using multi-hop communications. Indeed, in this kind of network, the existence of a communication link between the mobile station and the base station is not required: A mobile station that has no direct connection with a base station can use other mobile stations as relays. Compared with conventional (single-hop) structure-based networks, this new generation can lead to a better use of the available spectrum and to a reduction of infrastructure costs. However, these benefits would vanish if the mobile nodes did not properly cooperate and forward packets for other nodes. In this paper, we propose a charging and rewarding scheme to encourage the most fundamental operation, namely packet forwarding. We use "MAC layering" to reduce the space overhead in the packets and a stream cipher encryption mechanism to provide "implicit authentication" of the nodes involved in the communication. We analyze the robustness of our protocols against rational and malicious attacks. We show that -using our solutioncollaboration is rational for selfish nodes. We also show that our protocols thwart rational attacks and detect malicious attacks.

Wi-Fi networks have a very strong potential: They are easy to deploy, they use unlicensed frequencies and they provide internet connectivity that is several times faster than by cable modem. However, two major problems still need to be solved: the lack of a seamless roaming scheme and the variable quality of service experienced by the users. The reputation-based solution presented in this paper solves both problems: It allows a mobile node to connect to a foreign Wireless Internet Service Provider (WISP) in a secure way while preserving its anonymity and it encourages the WISPs to provide the users with good QoS. We analyze the robustness of our solution against various attacks and we prove by means of simulations that our reputation model indeed encourages the WISPs to behave correctly. We also propose a simple mechanism that allows the WISPs to predict the QoS they are able to offer to the (mobile) clients.

In recent years, wireless Internet service providers (WISPs) have established thousands of WiFi hot spots in cafes, hotels and airports in order to offer to travelling Internet users access to email, web or other Internet service. However, two major problems still slow down the deployment of this kind of networks: the lack of a seamless roaming scheme and the variable quality of service experienced by the users. This paper provides a response to these two problems: We present a solution that, on the one hand, allows a mobile node to connect to a foreign WISP in a secure way while preserving its anonymity and, on the other hand, encourages the WISPs to provide the users with good QoS. We analyse the robustness of our solution against various attacks and we prove by means of simulations that our reputation model indeed encourages the WISPs to behave correctly.