17-11-2012, 04:39 PM
Security Issues in Mobile Ad Hoc Networks - A Survey
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Abstract
In this paper, we discuss security issues and their current solutions in the mobile ad hoc
network. Owe to the vulnerable nature of the mobile ad hoc network, there are numerous
security threats that disturb the development of it. We first analyze the main vulnerabilities in
the mobile ad hoc networks, which have made it much easier to suffer from attacks than the
traditional wired network. Then we discuss the security criteria of the mobile ad hoc network
and present the main attack types that exist in it. Finally we survey the current security
solutions for the mobile ad hoc network.
Introduction
In recent years, the explosive growth of mobile computing devices, which mainly include
laptops, personal digital assistants (PDAs) and handheld digital devices, has impelled a
revolutionary change in the computing world: computing will not merely rely on the
capability provided by the personal computers, and the concept of ubiquitous computing
emerges and becomes one of the research hotspots in the computer science society [1]. In the
ubiquitous computing environment, individual users utilize, at the same time, several
electronic platforms through which they can access all the required information whenever and
wherever they may be [2]. The nature of the ubiquitous computing has made it necessary to
adopt wireless network as the interconnection method: it is not possible for the ubiquitous
devices to get wired network link whenever and wherever they need to connect with other
ubiquitous devices. The Mobile Ad Hoc Network is one of the wireless networks that have
attracted most concentrations from many researchers.
Vulnerabilities of the Mobile Ad Hoc Networks
Because mobile ad hoc networks have far more vulnerabilities than the traditional wired
networks, security is much more difficult to maintain in the mobile ad hoc network than in the
wired network. In this section, we discuss the various vulnerabilities that exist in the mobile
ad hoc networks.
Lack of Secure Boundaries
The meaning of this vulnerability is self-evident: there is not such a clear secure boundary in
the mobile ad hoc network, which can be compared with the clear line of defense in the
traditional wired network. This vulnerability originates from the nature of the mobile ad hoc
network: freedom to join, leave and move inside the network.
In the wired network, adversaries must get physical access to the network medium, or even
pass through several lines of defense such as firewall and gateway before they can perform
malicious behavior to the targets [6]. However, in the mobile ad hoc network, there is no need
for an adversary to gain the physical access to visit the network: once the adversary is in the
radio range of any other nodes in the mobile ad hoc network, it can communicate with those
nodes in its radio range and thus join the network automatically.
Threats from Compromised nodes Inside the Network
In the previous subsection, we mainly discuss the vulnerability that there is no clear secure
boundaries in the mobile ad hoc network, which may cause the occurrences of various link
attacks. These link attacks place their emphasis on the links between the nodes, and try to
perform some malicious behaviors to make destruction to the links. However, there are some
other attacks that aim to gain the control over the nodes themselves by some unrighteous
means and then use the compromised nodes to execute further malicious actions. This
vulnerability can be viewed as the threats that come from the compromised nodes inside the
network.
Since mobile nodes are autonomous units that can join or leave the network with freedom, it
is hard for the nodes themselves to work out some effective policies to prevent the possible
malicious behaviors from all the nodes it communicate with because of the behavioral
diversity of different nodes. Furthermore, because of the mobility of the ad hoc network, a
compromised node can frequently change its attack target and perform malicious behavior to
different node in the network, thus it is very difficult to track the malicious behavior
performed by a compromised node especially in a large scale ad hoc network. Therefore,
threats from compromised nodes inside the network are far more dangerous than the attacks
from outside the network, and these attacks are much harder to detect because they come
from the compromised nodes, which behave well before they are compromised.
Lack of Centralized Management Facility
Ad hoc networks do not have a centralized piece of management machinery such as a name
server, which lead to some vulnerable problems. Now let us discuss this problem in a more
detailed manner.
First of all, the absence of centralized management machinery makes the detection of attacks
a very difficult problem because it is not easy to monitor the traffic in a highly dynamic and
large scale ad hoc network [7]. It is rather common in the ad hoc network that benign failures,
such as path breakages, transmission impairments and packet dropping, happen frequently.
Therefore, malicious failures will be more difficult to detect, especially when adversaries
change their attack pattern and their attack target in different periods of time. For each of the
victims, because it can only observe the failure that occurs in itself, this short-time
observation cannot produce a convincing conclusion that the failure is caused by an adversary.
However, we can easily find from a system point of view that the adversary has performed
such a large amount of misbehaviors that we can safely conclude that all of the failures
caused by this adversary should be malicious failure instead of benign failure, though these
failures occur in different nodes at different time. From this example we find that lack of
centralized management machinery will cause severe problems when we try to detect the
attacks in the ad hoc network.
Security Solutions to the Mobile Ad Hoc Networks
We have discussed several vulnerabilities that potentially make the mobile ad hoc networks
insecure in the previous section. However, it is far from our ultimate goal to secure the mobile
ad hoc network if we merely know the existing vulnerabilities in it. As a result, we need to
find some security solutions to the mobile ad hoc network. In this section, we survey some
security schemes that can be useful to protect the mobile ad hoc network from malicious
behaviors.
Security Criteria
Before we survey the solutions that can help secure the mobile ad hoc network, we think it
necessary to find out how we can judge if a mobile ad hoc network is secure or not, or in
other words, what should be covered in the security criteria for the mobile ad hoc network
when we want to inspect the security state of the mobile ad hoc network. In the following, we
briefly introduce the widely-used criteria to evaluate if the mobile ad hoc network is secure.
Availability
The term Availability means that a node should maintain its ability to provide all the designed
services regardless of the security state of it [4]. This security criterion is challenged mainly
during the denial-of-service attacks, in which all the nodes in the network can be the attack
target and thus some selfish nodes make some of the network services unavailable, such as
the routing protocol or the key management service [5].