Protocols for Secure Communication in Wireless Sensor Networks

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90 Chapter 3. A Security Model for Wireless Sensor Networks The simplest form of multipath communication is replication: the same message is sent over multiple paths in parallel. If at least one copy arrives at the destination, the message transmission has been successful, thus providing a good countermeasure against message dropping (denial-of-service) attacks. Attacks on the integrity of messages can, if not prevented, at least be detected if multiple copies of a message, but with different contents, arrive. Of course, this method does not provide any protection against eavesdropping. Nevertheless, it is suitable for a Diffie-Hellman key exchange [54] (without key authentication, but possibly with integrity protection). Shamir’s secret sharing scheme [165] allows the splitting of a message into n pieces, k of which are sufficient to reconstruct the original message. The scheme is secure against an adversary that manages to get hold of at most k −1 pieces of the message, which will not yield any information about the message at all. Of course, if the adversary obtains k pieces, the confidentiality of the message is broken. Apart from threshold confidentiality, Shamir’s scheme also achieves robustness against the loss of pieces if n > k. However, it comes at the cost of an n-fold increase in size, since each piece is as large as the original message. Rabin [147] has devised a more efficient method that retains reliability, but lacks the feature of not revealing any information. Having n disjoint paths available and using secret sharing, we can transmit each piece on an independent path. The adversary will not be able to reconstruct the message unless he can eavesdrop on at least k paths. When faced with such a constrained attacker, this method can preserve the confidentiality of a message. One can distinguish between node disjointness and link disjointness. In wireless sensor networks, we can generally say that nodes are more important than links. Link-centricity should be replaced by node-centricity for the following reasons. (1) If one link suffers a failure because of external forces, it is likely that all other links in a certain area are exposed to the same external forces and thus suffer the same failure. Thus, disjointness of geographically close links does not help in this case. (2) The bandwidth of links is limited by the computational capacity of the nodes, and not by wireless technology (as in the conventional case). (3) There are many links compared to nodes, which alone makes nodes somewhat more significant; for each node, there is a potentially large number of links – between 1 and N (network size). From a security perspective, disjointness of paths is desirable: two paths that share a common node are only as good as that common node allows. An example are public-key infrastructures without a central certification authority [152]. Here, trust in the authenticity of public keys is indirectly transferred over multiple hops and each certification path is only as good as its weakest
3.5. Approximating End-to-End Security 91 link, thus disjointness is required. For WSN, we should consider a different security model, which allows us to relax the disjointness condition. Considering a geometrically constrained attacker, the probability that a node is captured is high when one of its neighbours is captured. Therefore, if a node near one of the endpoints is captured, it is likely that the endpoint is captured as well. In this case, the connection is broken by definition. Thus, we can consider two paths as “disjoint” if all the shared nodes between them are close to the endpoints, thereby increasing the risk of security breaches only minimally. The most important task in a disjoint path setting is to find or set up disjoint paths in the first place. We will present a method, which takes the previous considerations into account, in Chapter 5. Remark Multipath communication is very common in the physical world, although multiple paths are used rather sequentially than in parallel. One popular example is the distribution of credit cards and their associated PIN numbers. Here, separate letters are used for sending the credit card itself and its PIN number, and one of them is sent with a delay of a few days. The underlying assumption is that under these conditions, it is unlikely that both letters can be intercepted by malicious parties. Another example is key distribution for e-banking. The keys are sent by paper mail, where endpoint verification is possible, while the actual banking statements etc. are sent via the Internet. 3.5.3 Assessing the Security Level When devising techniques that provide a level of security that is not equivalent to end-to-end security, it is helpful to be able to somehow quantify how close they are able to approximate end-to-end security. For wireless sensor networks, such a quantification is canonically based on the number of nodes that are able to communicate (or, generally, act) securely. For wireless sensor networks, we propose two measures: the fraction of node pairs that are able to communicate securely, and the number of nodes that are able to participate in agreement schemes. Secure Pairwise Communication A fundamental requirement in a communication system is that two hosts can communicate securely (w.r.t. confidentiality or authenticity) with each other. The probability with which a connection provides the required security properties is an indication of the security level the network provides. Related to
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Diss. ETH Nr. 18174 Protocols for S
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ii often ad hoc and transient natur
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iv Dieses Ziel kann durch kryptogra
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Contents 1 Introduction 1 1.1 Backg
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Contents ix 3.3.1 Basic Assumptions
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Contents xi 6.3 Performance Evaluat
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Chapter 1 Introduction 1.1 Backgrou
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1.3. Contributions 3 on the other h
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1.4. Thesis Outline 5 • Mario Str
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Chapter 2 Wireless Sensor Networks
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2.1. Applications of Wireless Senso
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2.1. Applications of Wireless Senso
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2.2. Sensor Node Characteristics 13
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2.3. Related Network Types 21 zero,
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2.3. Related Network Types 23 • P
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2.3. Related Network Types 25 PAN,
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2.4. Related Device Types 27 in con
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2.4. Related Device Types 29 ports
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2.5. Sensor Network Models 31 both
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2.5. Sensor Network Models 33 are a
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2.6. Simulation of Sensor Networks
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2.6. Simulation of Sensor Networks
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Page 81 and 82: 3.1. Attack Paths 67 field (cf. [17
Page 83 and 84: 3.1. Attack Paths 69 modules [63].
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Page 87 and 88: 3.2. Attack Objectives 73 • Timel
Page 89 and 90: 3.2. Attack Objectives 75 Critical
Page 91 and 92: 3.2. Attack Objectives 77 Actors A
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Page 109 and 110: 3.7. Summary 95 Location-constraine
Page 111 and 112: Chapter 4 Key Establishment Shared
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Page 137 and 138: 4.6. Related Work 123 pc = 0.33 Du-
Page 139 and 140: 4.6. Related Work 125 Probability o
Page 141 and 142: 4.7. Summary 127 The security of th
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5.3. Properties of Tree Paths 141 b
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5.3. Properties of Tree Paths 143 a
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5.3. Properties of Tree Paths 145 n
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5.3. Properties of Tree Paths 147 F
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5.3. Properties of Tree Paths 149 D
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5.4. Security Evaluation 151 compro
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5.5. Related Work 153 width usage a
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5.5. Related Work 155 separation. F
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Chapter 6 Integrity-Preserving Comm
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6.1. Authentication and Integrity P
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6.2. Basic Interleaved Authenticati
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6.3. Performance Evaluation 175 A B
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6.3. Performance Evaluation 177 We
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6.4. Security Evaluation 179 Bandwi
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6.4. Security Evaluation 181 a sens
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6.4. Security Evaluation 183 Number
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6.4. Security Evaluation 185 We ass
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6.4. Security Evaluation 187 Paths
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6.4. Security Evaluation 189 ity of
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6.4. Security Evaluation 191 of the
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6.4. Security Evaluation 193 The se
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6.5. Extended Interleaved Authentic
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6.6. Comparing Interleaved and Mult
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6.7. Applications 209 Psi 1 0.8 0.6
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6.7. Applications 211 codes are att
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6.7. Applications 213 domain. The r
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6.9. Summary 215 simulations and by
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Chapter 7 Conclusion This work prop
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7.1. Secure Communication in Wirele
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7.2. Future Work 221 7.1.4 Shortcut
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Bibliography [1] Specification of t
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Bibliography 225 1st European Works
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Bibliography 227 [41] Rohan Chitrad
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Bibliography 229 [64] L. Eschenauer
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Bibliography 231 [85] Yahoo! Inc. D
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Bibliography 233 [105] Kristof Van
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Bibliography 235 [126] Anne Marie M
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Bibliography 237 [150] Sylvia Ratna
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Bibliography 239 [172] Thanos Stath
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Bibliography 241 [192] Eric W. Weis
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Curriculum Vitae Harald Vogt Person
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