Thesis

1. INTRODUCTION
privacy at the same time in an efficient way, as the applications are delay sensitive. To make things
even worse, the network is very heterogenous, different vehicles can have different equipment and
abilities, so no unique solution can solve every problem.
When defining the key vulnerabilities and challenges of vehicular ad hoc networks, it is crucial
to first define and characterize the possible attackers. In many papers [Raya and Hubaux, 2007;
Hu et al., 2005] the attacker can be characterized as follows:
Insider vs. Outsider: The key difference between an insider and an outsider attacker is that
an insider poses legitimate and valid cryptographic credentials, while an outsider does not
have any valid credentials. It is obvious that an insider attacker can mount stronger attacks,
then an outsider.
Malicious vs. Rational: The main goal of a malicious attacker is to disrupt the normal operation
of the network without any further goal, while a rational attacker wants to make some
profit with his attack. In general, it is easier to handle a rational attacker, because his steps
can be foreseen easier.
Active vs. Passive: A passive attacker only eavesdrops the messages of the vehicles, while an
active attacker can send, modify, or delete messages.
Local vs. Global: A local attacker mounts his attack on a small area (or on some non continuous
small areas), while a global attacker has influence on broader areas.
In the following, some basic and sophisticated attacks are presented to give the reader an idea
about the threats in vehicular ad hoc networks.
An insider attacker can diffuse bogus information to affect the behavior of other drivers. The
source of the information can be a cheated sensor reading or a modified location data.
In wireless networking, the wormhole attack [Hu et al., 2006] consists in tunneling packets
between two remote nodes. Similarly, in VANETs, an attacker that controls at least two entities
remote from each other and a high speed communication link between them can tunnel packets
broadcasted in one location to another, thus disseminating erroneous (but correctly signed)
messages in the destination area.
According to [Kroh et al., 2006] the following security concepts must be used in a vehicular
ad hoc network to handle most of the possible attacks: identification and authentication concepts,
privacy concepts, integrity concepts, access control and authorization concepts. The concepts are
introduced in Section 3.8 with a special attention on providing privacy to the users of the system.
In Chapter 3, the privacy of VANETs is analyzed, especially the privacy provided by pseudonyms
considering outsider rational passive local attackers. A pseudonym change algorithm is
provided as well considering an outsider rational passive global attacker.
1.3 Introduction to Wireless Sensor Networks
The following description of Wireless Sensor Networks (WSNs) and the related security problems
is based on [Akyildiz et al., 2002; Chan and Perrig, 2003; Li et al., 2009; Lopez, 2008; Perrig et
al., 2004; Sharma et al., 2012; Yick et al., 2008]. The interested reader can get a broader view and
deeper understanding on WSNs by reading the cited papers instead of only relying on this short
introduction.
A sensor network is composed of a large number of sensor nodes, which are typically densely
deployed. One sensor node consists of some sensor circuits which can measure some environmental
variable, central processing unit which is typically a microcontroller, and radio circuit which
enables the communication with other nearby nodes. The goal of a wireless sensor network can
be one of many applications: military applications (e.g. battlefield surveillance), environmental
applications (e.g. forest fire detection), critical infrastructure protection (e.g. surveillance of water
pipes), health applications (e.g. drug administration in hospitals), home applications (e.g. smart
environment).
4