The devices surrounding us become smarter and can autonomously form a network without requiring our intervention. However, our needs can be even better accommodated when the networked devices cooperate and complement each other’s capabilities. One of the initial steps towards achieving a cooperative platform of smart devices is the discovery of resources and capabilities within the network. Today’s operational service discovery protocols carry simple text-based uniform resource identifiers that are not expressive enough. Machines cannot comprehend the meaning of a new service that is not in their knowledge base. In addition to being more expressive, service discovery protocols must compensate the diversity to improve cooperation between the devices that use different application protocols and operate on different communication interfaces. In this paper, we propose the Smart Discovery Protocol (SDP) which outperforms the operational service discovery protocols with three main features: (1) more expressive semantic representation of the services, (2) operating in the network layer to deal with diversity, and (3) unifying existing service discovery protocols. SDP represents services with ontologies as some recently proposed semantic service discovery protocols. It further enhances the success of semantic representations by creating a unified platform that can carry legacy discovery services. In this respect, the novelties of SDP are as follows: firstly, it operates in the network layer and consequently abstracts both the application layer and communication interfaces. Secondly, SDP unifies the legacy service discovery protocols by integrating their simple text-based service representations in one message. The underlying transport mechanism of SDP is designed as an add-on to the Neighbor Discovery Protocol (NDP) of the IPv6 standard. The metadata is carried in the payload of ICMPv6 packets. Simple text-based representations of other service discovery protocols are embedded in type-length-value options of NDP. Authenticity of the devices is ensured by the IPv6 Secure Neighbor Discovery protocol. Unlike previous semantic approaches on service discovery, we have implemented our protocol on real hardware. The results demonstrate the feasibility of carrying semantic representations of the services and integration of other service discovery protocols.@en

The Internet of Things (IoT) represents the concept of cognitive networked devices that measure their environment and act on it intelligently. For instance, health sensors monitor vital human signs and inform their owner; smart meters measure the energy consumption and relay the information in real time to energy providers and consumers; and smart thermostats optimize heating while reducing costs. Though most IoT devices are designed to work alone, collective operation advances their capabilities. In a smart building application, for instance, several devices from temperature and presence sensors to heating and lighting appliances, cooperate to maximize energy efficiency and comfort. From the application perspective, presence sensors feed lighting and heating appliances with information; from the networking perspective, all these sensors and actuators relay each other's traffic for connectivity (if the medium is wireless). Without cooperation context awareness fails and wireless multi-hop networks collapse. Unfortunately, when the altruistic act of cooperation is costly, devices become selfish. For a battery-powered device, forwarding a neighbor's packet increases its energy consumption and consequently, decreases its lifetime. Therefore, that device does not cooperate and refrains from forwarding foreign packets. When all nodes in a wireless network follow the same reasoning, none of the packets are relayed, and consequently the network gets disconnected. In this thesis, first, we investigate the mechanisms and incentives for cooperation and reveal that social relations such as family and friendship are crucial. Then, we automate cooperation mechanism for devices based on social relations. Advancing ``smart'' IoT devices by making them ``social'' is becoming a hot topic in IoT research. It is argued that social devices can share their data and assist each other without requiring human intervention and consequently, improve their management. But, what is the meaning of a social device? Being a social device does not necessarily mean assisting all others by sharing data and forwarding packets. A social device has its own identity and social profile such that it is aware of its owner. The criterion of assisting others is its owner's preferences, which are embedded in social relations. As we prove in the thesis, consumers desire to know to whom they assist, suggesting that peers should be inside the circle of trusted social relations. Social relations are crucial for cooperation, now the question is: how can we automate cooperation decisions based on social relations? Without automation, consumers cannot manage all their devices' interactions. The reason is that IoT imposes the challenge of scaling up to billions of devices such that each person will be equipped with tens of devices. Our solution is a decentralized architecture where every device is identified by a URI that points to the social profile of that device. Ownership relations are declared in this social profile. When a resource server (e.g., light bulb, temperature sensor) receives a request from a client device (e.g., smartphone), the resource server crawls the client's and its owner's social profile. If the resource server discovers a social relation that grants access, it responds positively to the client's request. Unlike centralized approaches, our decentralized proposal protects privacy, provides end-to-end security, and can operate without an Internet connection. The drawback of our approach is the complexity of searching decentralized social profiles especially for indirect relations such as friend-of-a-friend. For unconstrained devices, we limit the search space based on proximity. In an access point (AP) scenario, the AP overhears WiFi beaconing messages from clients to discover their existence. For constrained devices, the whole search operation is delegated to a more resourceful cloud service. Our solutions for social network integration depend on secured identity information. Unfortunately, highly constrained devices that have less than 20~KBs of memory cannot be protected from identity-related attacks. These constrained devices can neither punish their defector neighbors nor reward only cooperators. They either cooperate always and are exploited by free-riders or defect always and disrupt network traffic. In this thesis, we offer adaptability to these devices via meta-strategies that only require local information. Devices overhear the traffic in their neighborhood and practice the best local strategy (defection or cooperation). We show that even if free-riders change their identities, meta-strategies protect them against exploitation while still promoting cooperation throughout the network. All in all, in this thesis we make a few stepts towards the goal of autonomous cooperation in IoT; and in particular we show that 1. social relations are crucial in cooperation decisions, 2. decentralized social-device networks (proposed in this thesis) can automate cooperation and provide secure-by-default IoT systems, 3. constrained devices that are vulnerable to identity-change attacks can protect themselves by observing the traffic in their neighborhood.@en

With the proliferation of WiFi-enabled devices, people expect to be able to use them everywhere, be it at work, while commuting, or when visiting friends. In the latter case, home owners are confronted with the burden of controlling the access to their WiFi router, and usually resort to simply sharing the password. Although convenient, this solution breaches basic security principles, and puts the burden on the friends who have to enter the password in each and every of their devices. The use of social networks, specifying the trust relations between people and devices, provides for a more secure and more friendly authentication mechanism. In this paper, we progress the state-of-the-art by abandoning the centralized solution to embed social networks in WiFi authentication; we introduce EAP-SocTLS, a decentralized approach for authentication and authorization of WiFi access points and other devices, exploiting the embedded trust relations. In particular, we address the (quadratic) search complexity when indirect trust relations, like the smartphone of a friend's kid, are involved. We show that the simple heuristic of limiting the search to friends and devices in physical proximity makes for a scalable solution. Our prototype implementation, which is based on WebID and EAP-TLS, uses WiFi probe requests to determine the pool of neighboring devices and was shown to reduce the search time from 1 minute for the naive policy down to 11 seconds in the case of granting access over an indirect friend.@en

Cooperation is the foundation of wireless ad hoc networks with nodes forwarding their neighbors' packets for the common good. However, energy and bandwidth constraints combined with selfish behaviour lead to collapsed networks where all nodes defect. Researchers have tried to incentivize or enforce the nodes for cooperation in various ways. However, these techniques do not consider the heterogeneous networks in which a diverse set of nodes with different cognitive capabilities exist. Furthermore, in ad hoc networks identity is a fuzzy concept. It is easy to forge multiple identities and hide defective behaviour. Moreover, the nature of the wireless medium is always ambiguous due to collisions, interference and asymmetric links. In all this uncertainty, having complete information about the intentions of the nodes and acting on it is not straightforward. Backed by evolutionary game theory and multi-agent systems research, we adapt and modify two meta strategies to embrace this uncertainty. These modified meta strategies, Win Stay Loose Shift and Stochastic Imitate Best Strategy, do not require strict identity information and only depend on nodes' own capabilities. Nodes monitor the traffic in their neighbourhood by using a two-hop overhearing method, and decide whether they should be cooperative or defective. We show that nodes are able to discover and use the best strategy in their locality and protect themselves against the exploitation by free riders who devise Sybil attacks by changing their identities.@en