of the 10th IEEE Wireless Telecommunications Symposium (WTS 2011), New York, USA, April 2011.
• Y. El Hajj Shehadeh, and D. Hogrefe, “An Optimal Guard-Intervals Based Mech-anism for Key Generation from Multipath Wireless Channels,”in Proceedings of the 4th IEEE International Conference on New Technologies, Mobility and Secu-rity (NTMS 11), Paris, France, February 2011.
1.3 Organization
This dissertation is organized as follows:
Chapter 2 provides an overview of the different security services required in a digital communication system. It also reviews briefly some of the main mechanisms usually implemented to provide these services.
Chapter 3 gives an overview of wireless propagation and the multipath wireless channel. First, a brief review of the different phenomena affecting a wireless signal is given. Multipath, spatial diversity, and channel reciprocity are mainly discussed as they characterize the wireless channel as a common reciprocal secret source of information that can be leveraged to derive a secret key between two communicating wireless nodes.
After that, we review channel modeling and describe the channel model used in our simulations.
Chapter 4investigates secret key generation on the physical layer of wireless com-munications. We first review some related work and give a short information-theoretic background on key extraction from common randomness, reconciliation, and privacy amplification. After a description of the system model, we present our proposed key generation mechanisms and the simulation results that show the effectiveness of our proposed methods. Afterwards, we tackle some practical issues that affect the per-formance of secret key generation from wireless channels. Delay between channel estimates and mobility are mainly investigated. Then, an enhancement to the key generation mechanisms is proposed to ensure robustness against delay and mobility.
Finally, reconciliation and key verification are discussed.
Chapter 5 tackles the problem of misbehavior on the MAC layer in wireless net-works. We first review the basic medium access scheme used in IEEE 802.11 networks and highlight its vulnerability to misbehavior in addition to its bandwidth efficiency.
We mainly focus on backoff misbehavior which allows a selfish node to get an unfair share of the wireless channel. We review some of the related work on this topic and propose the Random Backoff Control (RBC) mechanism. This mechanism provides a countermeasure against MAC layer DoS attacks and ensures a fairer distribution of network resources. The second part of this chapter is concerned with the design of
8 Chapter 1. Introduction
an advanced and secure medium access scheme. A review of some of the related work on this topic is first given. Afterwards, we describe our proposed Self-Organized Dis-tributed Channel Access (SODCA) scheme. Distinctively from all proposed solutions, our novel medium access scheme is a distributed, efficient, secure and dynamic schedul-ing scheme. Nevertheless, it does not incur any additional overhead. The efficiency of SODCA is manifested through extensive simulations based on the OMNeT++ network simulator.
Chapter 2
Security Basics
Contents
2.1 Security Attacks . . . . 10
2.1.1 Passive Attacks . . . . 10
2.1.2 Active Attacks . . . . 10
2.2 Security Services . . . . 11
2.2.1 Authentication . . . . 11
2.2.2 Access Control . . . . 12
2.2.3 Data Confidentiality . . . . 12
2.2.4 Data Integrity . . . . 12
2.2.5 Nonrepudiation . . . . 13
2.2.6 Availability and Secure Distribution of Resources . . . . 13
2.3 Security Mechanisms . . . . 13
2.3.1 Cryptography . . . . 14
2.3.2 Diffie-Hellman Key Exchange . . . . 16
2.3.3 Hashing and Message Authentication. . . . 16
2.3.4 Digital Signatures . . . . 17
2.3.5 Public Key Infrastructure . . . . 18
2.4 Summary and Discussion. . . . 19
Securing communications has always been a big challenge faced by researchers and network engineers in developing standards, protocols and products. Attacks targeting the Internet, private networks and wireless communications have increased enormously over time while the skill and knowledge required to implement them have declined.
The wide spread of digital communications and its acceptance by users have been always threatened by the secrecy of the data transmitted and the privacy of the senders.
Users have now become more concerned about the security of their digital communi-cations and their privacy than ever. Users and organizations require different security services that guarantee the security and privacy of their communication. Secrecy of their data is one of the biggest requirements. Moreover, they require guarantees on the
10 Chapter 2. Security Basics
integrity and authenticity of their transmitted messages. Finally, continuous availabil-ity of the network is also an important required feature.
In this chapter, we investigate these different security requirements and the main mechanisms used. First, we discuss the different types of attacks that may threaten the security and privacy of users. After that, we discuss the different security services;
and finally we review some of the basic mechanisms that are being used to satisfy the different security and privacy requirements.
2.1 Security Attacks
2.1.1 Passive Attacks
A Passive attack targets eavesdropping on or monitoring data transmissions without tampering the transmitted messages. This type of attack is by its nature difficult to detect since the attacker listens only to the communication without any intervention. It is even more facilitated in wireless communication due to its broadcast nature. There-fore, security measures should be taken into account to prevent any adversary from accessing or reading the contents of the transmitted information.
2.1.2 Active Attacks
Active attacks have in general a bigger impact on the security and the privacy of communications. They are related to any act of modifying, tampering, eliminating or even creating messages.
An attacker may tamper or modify the transmitted messages so that they contain false information or become undecodable. He can also disrupt communications and eliminate transmitted messages. This may lead to a delay or disorder in the transmitted messages which might produce an unauthorized effect. Such modifications of messages may also lead the legitimate nodes to perform unauthorized actions or get compromised by the attacker and abused to perform larger scale attacks. Moreover, by modifying the contents of messages, an attacker can deplete the resources of a legitimate node.
Another form of active attacks is the masquerade attack, where an attacker pretends to be a different entity. By impersonating this entity, it might be able to have some privileges or access to more resources. For example, in a replay attack, an attacker captures passively messages transmitted by legitimate nodes and transmits them to appear as a legitimate node and get access to some network resources. Therefore, it is necessary to provide strong authentication of the identity of a node.
In addition, an attacker can inject false messages into the network that may lead to the disruption of communication (a Denial of Service attack (DoS) ) or may mislead the legitimate nodes into performing other actions that may exhaust their resources