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Chapter 1. Secrecy Capacity of Independent Parallel Channels

Ensuring the confidentiality of communications is fundamental to securing any network. This requirement becomes particularly important for wireless systems, where eavesdropping is facilitated by the broadcast nature of the wireless medium. Rather than physically guard the communication medium to provide confidentiality, the traditional approach is to employ cryptographic algorithms to ensure that only legitimate users can correctly interpret the messages, while all other entities fail to glean any useful information.
Zang Li, Roy Yates, Wade Trappe

Chapter 2. Obtaining Secrecy through Intentional Uncertainty

The tremendous popularity of wireless medium for communications is mainly because of the broadcast nature, which allows access to multimedia and information without restriction on the user’s location. However, guaranteeing secure communication in a wireless medium is made difficult by the same broadcast nature, which makes it easy to eavesdrop on an ongoing communication, while making it nearly impossible to detect eavesdropping. The time-varying and unreliable nature of the wireless channels poses further difficulties. However, the same physical properties, which have a detrimental effect on reliability in communication, provide an opportunity to enhance the secrecy of communication, if used carefully.
Satashu Goel, Rohit Negi

Chapter 3. Distributed Secret Sharing over the Gaussian Interference Wiretap Channel

In the process of secret sharing, a single secret is encoded into multiple entities called shares. These shares possess the special properties that they jointly contain no information about the original secret unless a sufficient quantity of them are available for decoding [19]. There has been a recent trend in applying secret sharing to mobile ad hoc networks [21] because the process of encoding and decoding does not require the use of keying and key management. Furthermore, secret sharing is inherently robust to limited degrees of insider attacks, in which partial knowledge of shares become available to an attacker. However, in many other network scenarios, secret sharing is deemed unsuitable for two reasons. First, each user is required to create multiple shares leading to excessive overhead and unnecessary bandwidth expansion in the network. Second, the routing of the shares to the destination(s) must remain as separated as possible so that enough of them do not easily fall into the hands of a restricted enemy who may then successfully decode the original secret. Spatially-restricted enemies can be thwarted somewhat through the use of mobility of intermediate network nodes that provide avenues for different shares to be sent along non-overlapping routes [21].
William Luh, Deepa Kundur

Chapter 4. Cooperative Jamming: The Tale of Friendly Interference for Secrecy

In wireless communications, interference is generally regarded as an undesired phenomenon. In multiuser systems, interference management and avoidance are essential for acceptable system performance [1, 2]. In systems including cognitive radios with secondary spectrum privileges, a system objective is detecting the channel occupancy in an intelligent way to limit interference to primary users [3].
Xiang He, Aylin Yener

Chapter 5. Hybrid-ARQ Schemes for Reliable and Secret Wireless Communications

Hybrid automatic retransmission request (HARQ) schemes are revisited for a block fading wire-tap channel. Here, two legitimate users communicate over a block-fading channel in the presence of a passive eavesdropper who intercepts the transmissions through an independent block-fading channel. In this model, the transmitter obtains a 1-bit ACK/NACK feedback from the legitimate receiver via an error-free public channel. Both reliability and confidentiality of secure HARQ protocols are studied by joint consideration of channel coding, secrecy coding, and retransmission protocols. In particular, the error and secrecy performance of repetition time diversity (RTD) and incremental redundancy (INR) protocols are investigated based on Wyner code sequences. These protocols ensure that the confidential message is decoded successfully by the legitimate receiver and is kept completely secret from the eavesdropper for a set of channel realizations. It is illustrated that there exists a family of rate-compatible Wyner codes which ensure a secure INR protocol. Next, it also defines the connection outage and the secrecy outage probabilities that characterize the tradeoff between the reliability of the legitimate communication link and the confidentiality with respect to the eavesdropper's link, respectively. For a given connection/secrecy outage probability pair, an achievable throughput of secure HARQ protocols is derived for a block-fading channel. Finally, both asymptotic analysis and numerical calculations demonstrate the benefits of HARQ protocols to throughput and secrecy.
Xiaojun Tang, Predrag Spasojević, Ruoheng Liu, H. Vincent Poor

Chapter 6. Secret Communication Under Channel Uncertainty

This chapter reviews recent results on the secrecy capacity for wire-tap channels, in which the channels to a legitimate receiver and to an eavesdropper have multiple states. Several classes of wire-tap channels that fall into this category are introduced and discussed including the parallel wire-tap channel, the fading wire-tap channel, the compound wire-tap channel, and the wire-tap channel with side information. Open problems and future directions under this topic are also discussed.
Yingbin Liang, H. Vincent Poor, Shlomo Shamai (Shitz)

Chapter 7. Cooperative Secrecy in Wireless Communications

The broadcast nature of wireless communications leads to two concepts: cooperation and secrecy. The over-heard information may be used to cooperate and improve the achievable rates. At the same time, the over-heard information forms the basis for information leakage and potential lack of secrecy. Both cooperation and secrecy are vibrant current research fields on their own right. More recently, the question whether cooperation and secrecy are opposing objectives or if they can co-exist and even support each other has received significant attention. In this chapter, we review our own and other researchers' works on cooperation, secrecy and the interaction of the two. Our emphasis will be to summarize the current state of the knowledge in each case and describe the main methodologies being used.
Sennur Ulukus, Ersen Ekrem

Chapter 8. Source Coding under Secrecy Constraints

Distributed compression involves compressing multiple data sources by exploiting the underlying correlation structure of the sources at separate noncooperating encoders, while decoding is done jointly at a single decoder. Recent years have witnessed an increasing amount of research on the theoretical and practical aspects of distributed source codes, which find applications in distributed video compression, peer-to-peer data distribution systems, and sensor networks. In many practical scenarios, limited network resources such as power and bandwidth, or physical limitations of the devices as in the case of sensor networks, pose challenges in terms of network performance and security. Oftentimes, the data aggregated in distributed compression systems may have commercial value as in the case of warehouse inventory monitoring systems, may contain sensitive information as in the case of distributed video surveillance systems, or might infringe personal privacy concerns as in the case of human body sensors measuring various health indicators. In all these scenarios, it is essential to develop distributed compression and communication protocols which exploit the limited power and bandwidth resources efficiently as well as satisfying the security requirements. Our goal in this chapter is to review fundamental limitations and tradeoffs for the overall performance optimization taking into account the quality and the security considerations jointly.
Deniz Gündüz, Elza Erkip, H. Vincent Poor

Chapter 9. Secret Key Extraction from Level Crossings over Unauthenticated Wireless Channels

Many of the risks associated with securing wireless systems stem from challenges associated with operating in a mobile environment, such as the lack of a guaranteed infrastructure or the ease with which entities can eavesdrop on communications. Traditional network security mechanisms rely upon cryptographic keys to support confidentiality and authentication services. However, in a dynamic mobile wireless environment, with peer-to-peer associations being formed on-the-fly between mobile entities, it is difficult to ensure availability of a certificate authority or a key management center. Since such scenarios are likely to become more prevalent, it is necessary to have alternatives for establishing keys between wireless peers without resorting to a fixed infrastructure.
Suhas Mathur, Wade Trappe, Narayan Mandayam, Chunxuan Ye, Alex Reznik

Chapter 10. Secret Key Generation Among Multiple Terminals with Applications to Wireless Systems

The security of most existing cryptosystems relies on the (unproven) difficulty in solving a computational problem, e.g., factoring large integers or computing discrete logarithms in certain groups (cf. e.g.,[11]). This notion of security is called computational complexity security, as it is based on the assumption that an adversary has restricted computational power and lacks “efficient algorithms.„ However, this assumption is being weakened with the development of efficient algorithms as well as the increase in computational power of modern computers (e.g., quantum computer).
Chunxuan Ye, Alex Reznik

Chapter 11. Secret Key Agreement Techniques based on Multipath Propagation Characteristics

As information society progresses, wireless communications such as cellphone and WLAN (Wireless Local Area Network) systems will become more widely and rapidly accepted as the means to communicate. Unfortunately, there are many perceived weaknesses inherent in the security of wireless communications– largely due to the fact that the signals are transmitted through the air and are easily captured by third parties. Examples of such threats are found in eavesdropping of transmitted data on a radio channel, illegal and/or unauthorized access to public WiFi networks, and so on. In fact, security for wireless systems has been recognized as a major technical challenge that needs to be addressed in order for wireless systems to be the basis for many future applications.
Hideichi Sasaoka, Hisato Iwai

Chapter 12. Secret Communication over Fading Channels

The broadcast nature of any wireless communication network provides a natural eavesdropping and intervention capability to an adversary. Anyone with a tuned receiver within a radius that permits adequate signal to interference and noise ratio (SINR) may eavesdrop. Thus, effecting efficient key generation and renewal algorithms to ensure confidentiality, integrity, and authentication for every wireless link is essential for impenetrability.
B. Azimi-Sadjadi, A. Kiayias, A. Mercado, B. Yener

Chapter 13. Fingerprints in the Ether: Channel-Based Authentication

Most wireless systems lack the ability to reliably identify clients without employing complicated cryptographic tools. This introduces a significant threat to the security of wireless networks, as the wireless channel is a broadcast medium, i.e., intruders can access wireless networks without a physical connection. One serious consequence is that spoofing attacks (or masquerading attacks), where a malicious device claims to be a specific client by spoofing its MAC address, becomes possible. Spoofing attacks can seriously degrade network performance and facilitate many forms of security weakness.
Liang Xiao, Larry Greenstein, Narayan Mandayam, Wade Trappe

Chapter 14. Message Authentication: Information Theoretic Bounds

The goal of message authentication is to ensure that an accepted message truly comes from its acclaimed transmitter. It has wide applications in ecommerce and other areas. For example, when a stock broker receives a trading instruction for an account, he or she needs to verify that it is the owner of the account, and not someone else, who sends the instruction.
Lifeng Lai, Hesham El Gamal, H. Vincent Poor

Chapter 15. Trusted Cooperative Transmissions: Turning a Security Weakness into a Security Enhancement

Since the invention of wireless telegraphy, the effort to improve wireless channel capacity has never stopped. In the last decade, significant advancement has been made and this advancement has featured two milestones. The first milestone is Multiple-Input-Multiple-Output (MIMO) techniques, which create spatial diversity by taking advantage of multiple antennas and improvesthe wireless channel capacity by an amount on the order of the number of antennas on a wireless device. The second milestone is cooperative transmission. Instead of relying on the installation of multiple antennas on one wireless device, cooperative transmission achieves spatial diversity through physical layer cooperation. In cooperative transmission, when the source node transmits a message to the destination node, the nearby nodes that overhear this transmission will “help” the source and destination by relaying the replicas of the message, and the destination will combine the multiple received waveforms so as to improve the link quality. In other words, cooperative transmission techniques utilize nearby nodes as virtual antennas, and mimic the effects of MIMO in achieving spatial diversity.
Yan Lindsay Sun, Zhu Han

Chapter 16. Modulation Forensics for Wireless Digital Communications in Frequency-Selective Fading Channels

Within the past decades, the explosive development of wireless communication technologies facilitates the transmissions of all types of information over wireless medium: voice, multimedia, data with confidential content, military command and control, no matter where the receivers are. However, the broadcast nature of wireless media also allows everyone within the network to listen to others’ signal. From the national security point of view, any suspicious damaging activities should be under surveillance, and friendly signals should be securely transmitted and received, whereas hostile signals must be located, identified and jammed. Thus, it is crucial to develop a forensic scheme that is able to decode the information from the received signals only. The very first step of communication forensic detector is to determine which kind of modulation is in use, which is an intermediate step between signal detection and demodulation.
W. Sabrina Lin, K. J. Ray Liu
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