Securing

Wireless Sensor Networks

Wenliang (Kevin) Du

Department of Electrical Engineering and Computer Science Syracuse University Excerpted from http://www.cis.syr.edu/~wedu/Research/slides/Purdue04.ppt

1

Overview • Overview of Wireless Sensor Networks (WSN).

• Security in wireless sensor networks.

– Why is it different? • Our work on key pre-distribution in WSN – Deployment-based scheme (INFOCOM’04) – Pair-wise Scheme (ACM CCS’03) • Summary.

2

Wireless Sensors Berkeley Motes 3

Mica Motes • Mica Mote : – Processor: 4Mhz – Memory: 128KB Flash and 4KB RAM – Radio: 916Mhz and 40Kbits/second.

– Transmission range: 100 Feet • TinyOS operating System: small, open source and energy efficient.

4

Spec Motes 5

Wireless Sensor Networks (WSN) Sensors Deploy 6

Applications of WSN • Battle ground surveillance – Enemy movement (tanks, soldiers, etc) • Environmental monitoring – Habitat monitoring – Forrest fire monitoring • Hospital tracking systems – Tracking patients, doctors, drug administrators.

7

Securing WSN • Motivation: why security?

• Why not use existing security mechanisms?

– WSN features that affect security.

• Our work: – Two key management schemes.

8

Why Security?

• Protecting confidentiality , integrity , and availability of the communications and computations • Sensor networks are vulnerable to security attacks due to the broadcast nature of transmission • Sensor nodes can be physically captured or destroyed 9

Why Security is Different?

• Sensor Node Constraints – Battery, – CPU power, – Memory.

• Networking Constraints and Features – Wireless, – Ad hoc, – Unattended.

10

Sensor Node Constraints • Battery Power Constraints – Computational Energy Consumption • Crypto algorithms • Public key vs. Symmetric key – Communications Energy Consumption • Exchange of keys, certificates, etc.

• Per-message additions (padding, signatures, authentication tags) 11

Constraints (Cont.) Public Key Encryption • Slow – 1000 times slower than symmetric encryption • Hardware is complicated • Energy consumption is high Processor MIPS R4000 MC68328 Energy Consumption (mJ/Kb) RSA/E/V RSA/D/S AES 0.81

16.7

0.00115

42 840 0.0130

12

Memory Constraints • Program Storage and Working Memory – Embedded OS, security functions (Flash) – Working memory (RAM) • Mica Motes: • 128KB Flash and 4KB RAM 13

Objectives of Our Research • Long-term Goals – Study how WSN’s constraints/features affect the design of security mechanisms.

– Develop security mechanisms for WSN.

• Current Projects – Key Management Problems – Data Fusion Assurance 14

Key Management Problem 15

Key Management Problem Sensors Deploy 16

Key Management Problem Sensors Deploy Secure Channels 17

Approaches • Trusted-Server Schemes – Finding trusted servers is difficult.

• Public-Key Schemes – Expensive and infeasible for sensors.

• Key Pre-distribution Schemes 18

Key Pre-distribution    Loading Keys into sensor nodes deployment prior to 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 19

Naïve Solutions   Master-Key   Approach Memory efficient, but low security.

Needs Tamper-Resistant Hardware.

Pair-wise Key    Approach N-1 keys for each node (e.g. N=10,000).

Security is perfect.

Need a lot of memory and cannot add new nodes.

20

Eschenauer-Gligor Scheme Each node randomly selects m keys Key Pool S A B C D E • When |S| = 10,000, m=75 Pr (two nodes have a common key) = 0.50

1  9925

C

75 10000

C

75  1  0 .

57  0 .

43 21

Establishing Secure Channels A B C D E 22

Exercise 7 • Write a program to calculate the probability: – Input: • G=(V,E) • Pr (two nodes have a common key) =  – Output: • Let E’  E denote the subset of secure channels, calculate the probability that G=(V,E’) is a connected graph.

– Due: June 4 th 23

Example 1 •  =1/2 24

1 8  1 8 1 8   1 8 8  1 8  1 2 25

Example 2 •  =2/3 ( 2 3  2 3  1 3  3 )  ( 2 3  2 3  2 3  1 )  20 27 26

3 1 2 2 3 3 1 Input Format • |V|=3 • Undirected edges (1,2) (2,3) (3,1) • Note: the given graph may not be complete.

27