A survey of survivability in mobile ad hoc networks <s> I. INTRODUCTION <s> In recent years, mobile computing has enjoyed a tremendous rise in popularity. The continued miniaturization of mobile computing devices and the extraordinary rise of processing power available in mobile laptop computers combine to put more and better computer-based applications into the hands of a growing segment of the population. At the same time, the markets for wireless telephones and communication devices are experiencing rapid growth. Projections have been made that, by the year 2002, there will be more than a billion wireless communication devices in use, and more than 200 million wireless telephone handsets will be purchased annually. The rise of wireless telephony will change what it means to be “in touch”; already many people use their office telephone for taking messages while they are away and rely on their mobile telephone for more important or timely messages. Indeed, mobile phones are used for tasks as simple and as convenient as finding one’s associates in a crowded shopping mall or at a conference. A similar transformation awaits mobile computer users, and we can expect new applications to be built for equally mundane but immediately convenient uses. Much of the context for the transformation has to do with keeping in touch with the Internet. We expect to have “the network” at our disposal for the innumerable little conveniences that we have begun to integrate into our professional lives. We might wish to download a roadmap on the spur of the moment so that we can see what is available in the local area. We might wish to have driving suggestions sent to us, based on information from the global positioning system (GPS) in our car, using the services offered by various web sites. The combination of sufficiently fast and inexpensive wireless communication links and cheap mobile computing devices makes this a reality for many people today. In the future, the average traveler is likely to take such services for granted. <s> BIB001 </s> A survey of survivability in mobile ad hoc networks <s> I. INTRODUCTION <s> Large-scale peer-to-peer systems face security threats from faulty or hostile remote computing elements. To resist these threats, many such systems employ redundancy. However, if a single faulty entity can present multiple identities, it can control a substantial fraction of the system, thereby undermining this redundancy. One approach to preventing these "Sybil attacks" is to have a trusted agency certify identities. This paper shows that, without a logically centralized authority, Sybil attacks are always possible except under extreme and unrealistic assumptions of resource parity and coordination among entities. <s> BIB002 </s> A survey of survivability in mobile ad hoc networks <s> I. INTRODUCTION <s> Security in mobile ad hoc networks is difficult to achieve, notably because of the vulnerability of wireless links, the limited physical protection of nodes, the dynamically changing topology, the absence of a certification authority, and the lack of a centralized monitoring or management point. Earlier studies on mobile ad hoc networks (MANETs) aimed at proposing protocols for some fundamental problems, such as routing, and tried to cope with the challenges imposed by the new environment. These protocols, however, fully trust all nodes and do not consider the security aspect. They are consequently vulnerable to attacks and misbehavior. More recent studies focused on security problems in MANETs, and proposed mechanisms to secure protocols and applications. This article surveys these studies. It presents and discusses several security problems along with the currently proposed solutions (as of July 2005) at different network layers of MANETs. Security issues involved in this article include routing and data forwarding, medium access, key management and intrusion detection systems (IDSs). This survey also includes an overview of security in a particular type of MANET, namely, wireless sensor networks (WSNs). <s> BIB003
T HE INCREASING popularity of wireless portable devices, such as laptops, PDAs, wireless telephones or wireless sensors, has highlighted the importance of mobile ad hoc networks and ubiquitous computing. Nowadays, due to Internet service facilities and the convenience of portability, many people employ mobile networking in their professional and domestic activities. Mobile ad hoc network (MANET) is formed by a set of mobile hosts which communicate among themselves by means of the air. Those hosts establish dynamically the network without relaying on a support infrastructure and cooperate to forward data in a multi-hop fashion without a central administration  - BIB003 . MANETs were initially proposed for military applications and currently their use has been enlarged. Examples of application include emergency disaster relief, military battle field communication, sensing or controlling a region, sharing information during a lecture or conference, and so on BIB001 . MANET's hosts must ensure functionalities and guarantees provided by support structures in wired networks. Routing, access control and node authentication are examples of network functionalities that must be performed by node coopera- tion. Nevertheless, those hosts present characteristics, such as constraint resources (processing, memory, bandwidth, energy and others), mobility and wireless communication that limit their capacity to execute dense activities and increase the complexity on providing network management, control and security. Due to their communication type and constraint resources, MANETs are vulnerable to diverse types of attacks and intrusions. Wireless communication, for example, is susceptible to interferences and interceptions. Portability has made devices each time smaller, with resource limitation, and thus easy targets for overload attacks  ,  . The fully network decentralization, absence of support infrastructure and dynamic topology increase the vulnerability to many attacks such as impersonation, Sybil BIB002 , selective forwarding, blackhole, wormhole  ,  , among others. Many solutions have been proposed for security problems on ad hoc networks  , BIB003 ,  ,  . In general, these solutions apply preventive or reactive approaches using mechanisms to protect basic protocols or applications. Essentially, the solutions use specialized hardware, cryptographic primitives, mechanisms for overhearing neighbor communication or protocols designed for path diversity  . However, techniques and mechanisms are used for a specific goal, being effective to one given case, but inefficient to others. Moreover, all existent techniques and mechanisms are themselves incapable of individually defending against all types of attacks and intrusions. Due to solution restrictions and MANETs characteristics, researchers have focused on designing security mechanisms for achieving network survivability. Survivability is commonly defined as the ability of a system to fulfill its mission, in a timely manner, in the presence of attacks, failures or accident  . The term system has a wide sense and could characterize networks, means of communication or services, and mission represents the abstract goals and requirements of the system. The contributions of this survey are the following: (i) the contextualization of survivability to attacks, considering a design perspective resiliency-oriented; (ii) the proposal of a new classification of defense lines, suggesting that survivability to attacks can be reached when all defense lines work cooperatively; (iii) the identification of survivability key properties and requirements for MANETs; (iv) the investigation of survivable initiatives organized on three groups: route discovery, data transmission and key management. The survey concludes that current initiatives continue only using preventive and reactive mechanisms, being specialized to one network layer, protocol The rest of the survey is organized as follows. Section II defines survivable systems, presenting survivability concepts and key properties, as well as a classification of defense lines considering those concepts. Section III summarizes MANETs characteristics, security issues and conventional countermeasures. Section IV analyzes the survivability requirements for MANETs, taking into account their essential services. Section V describes and categorizes in three groups the survivable initiatives for MANETs. Finally, Section VI concludes the survey and gives future directions.