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Security in Wireless Sensor Networks. Group Meeting Fall 2004 Presented by Edith Ngai. Outline. Wireless Sensor Networks (WSN) Security in WSN Key Management Approaches Straight Forward Approach Basic Probabilistic Approach Deployment-based Approach Conclusion References.

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Security in wireless sensor networks l.jpg

Security in Wireless Sensor Networks

Group Meeting

Fall 2004

Presented by Edith Ngai

Outline l.jpg

  • Wireless Sensor Networks (WSN)

  • Security in WSN

  • Key Management Approaches

    • Straight Forward Approach

    • Basic Probabilistic Approach

    • Deployment-based Approach

  • Conclusion

  • References

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Wireless Sensor Networks

  • A sensor network is composed of a large number of sensor nodes

  • Sensor nodes are small, low-cost, low-power devices that have following functionality:

    • communicate on short distances

    • sense environmental data

    • perform limited data processing

  • The network usually also contains “sink” node which connects it to the outside world

Berkeley Motes

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  • WSN can be used to monitor the conditions of various objects / processes

    • Military: battlefield surveillance, biological attack detection, targeting

    • Ecological: fire detection, flood detection, agricultural uses

    • Health related: human physiological data monitoring

    • Miscellaneous: car theft detection, inventory control, home applications

  • Sensors are densely deployed either inside or very close to the monitored object / process

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Security in WSN

  • Main security threats in WSN are:

    • Radio links are insecure – eavesdropping / injecting faulty information is possible

    • Sensor nodes are not temper resistant – if it is compromised the attacker obtains all security information

  • Protecting confidentiality, integrity, and availability of the communications and computations

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Why Security is Different?

  • Sensor Node Constraints

    • Battery

    • CPU power

    • Memory

  • Networking Constraints and Features

    • Wireless

    • Ad hoc

    • Unattended

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Key Management: Goals

  • The protocol must establish a key between all sensor nodes that must exchange data securely

  • Node addition / deletion should be supported

  • It should work in undefined deployment environment

  • Unauthorized nodes should not be allowed to establish communication with network nodes

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Key Management Problem

Secure Channels

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  • Trusted-server schemes

    • Finding trusted servers is difficult

  • Public-key schemes

    • Expensive and infeasible for sensors

  • Key pre-distribution schemes

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Key Pre-distribution

  • Loading Keys into sensor nodes prior to deployment

  • Two nodes find a common key between them after deployment

  • Challenges

    • Memory/Energy efficiency

    • Security: nodes can be compromised

    • Scalability: new nodes might be added later

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Straight Forward Approach

  • Single mission key is obviously unacceptable

  • Pairwise private key sharing between every two nodes is impractical because of the following reasons:

    • it requires pre-distribution and storage of n-1 keys in each node which is n(n-1)/2 per WSN

    • most of the keys would be unusable since direct communication is possible only in the nodes neighborhood

    • addition / deletion of the node and re-keying are complex

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Basic Probabilistic Approach

  • Proposed by Eschenauer and Gligor

  • Relies on probabilistic key sharing among nodes of WSN

  • Uses simple shared-key discovery protocol for key distribution, revocation and node re-keying

  • Three phases are involved: key pre-distribution, shared-key discovery, path-key establishment

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Eschenauer-Gligor Scheme

Key Pool


Each node


selects m keys






  • When |S| = 10,000, m=75

    • Pr (two nodes have a common key) =0.50

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Observations and Objectives




Problem: How to pick a large key pool while maintaining high connectivity? (i.e. maintain resilience while ensuring connectivity)

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Deployment-based Scheme

  • Proposed by Du, et. al (IEEE Infocom 2004)

  • Improves Random Key Predistribution (Eschenauer and Gligor) by exploiting Location Information

  • Studies a Gaussian distribution for deployment of Sensor nodes to improve security and memory usage

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Deployment-based Scheme

  • Groups select from key group S (i,j)

  • Probability node is in a certain group is (1 / tn).

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Step 1 : Key Pre-distribution - Key Sharing Among Key Pools -























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Step 1 : Key Pre-distribution - Key Sharing Among Key Pools -

  • Determining |Sc|

    • When |S| = 100,000, t = n = 10, a = 0.167, b = 0.083

      |Sc| = 1770

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Step 2: Shared-key Discovery

  • Takes place during initialization phase after WSN deployment. Each node discovers its neighbor in communication range with which it shares at least one key

  • Nodes can exchange IDs of keys that they poses and in this way discover a common key

  • A more secure approach would involve broadcasting a challenge for each key in the key ring such that each challenge is encrypted with some particular key. The decryption of a challenge is possible only if a shared key exists

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Step 3: Path-key Establishment

  • During the path-key establishment phase path-keys are assigned to selected pairs of sensor nodes that are within communication range of each other, but do not share a key

  • Find secure path by using flooding method

    • Limit the lifetime of the flooding message to three hops to reduce flooding overhead

  • Share random key K by using secure path

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Local Connectivity

  • With 100 keys, location management improves local connectivity from 0.095 to 0.687

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Network Resilience

  • What is the damage when x nodes are compromised?

    • These x nodes contain keys that are used by the good nodes

    • What percentage of communications can be affected?

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  • Robust security mechanisms are vital to the wide acceptance and use of senor networks for many applications

  • Security in WSN is quite different from traditional (wired) network security

  • Various peculiarities of WSN make the development of good key scheme a challenging task

  • We have discussed several approaches to key management in WSN

References l.jpg

  • I. F. Akyildiz, W. Su, Y. Sankarasubramaniam, and E. Cyirci. Wireless Sensor Networks: A Survey. Computer Networks, 38(4):393-422, 2002.

  • L. Eschenauer and V. Gligor. A Key-Management Scheme for Distributed Sensor Networks. In Proc. of ACM CCS’02, November 2002.

  • H. Chan, A. Perrig, and D. Song. Random Key Predistribution Schemes for Sensor Networks. In 2003 IEEE Symposium on Research in Security and Privacy.

  • W. Du, J. Deng, Y. Han, S. Chen, and P. Varshney. A Key Management Scheme for Wireless Sensor Networks Using Deployment Knowledge. IEEE Infocom 2004.