National Science Foundation Stevens Center for Wireless Network Security

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National Science FoundationStevens Center for
Wireless Network Security
Energy Issues in Secure and Reliable Wireless
Multimedia Sensor Networking
Chetan NanjundaSatish BapatlaR.ChandramouliStev
en Institute of Technology
N. VijaykrishnanM.J. IrwinPenn State University
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Contents

• Energy Awareness
• Sensor Networks
• Security
• Error Control
• Optimizations
• Experimental results

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Energy Awareness

• Energy Sources
• Battery
• Solar (time variant)
• Energy consumption
• Computation
• Transmission
• Power consumption varies over time in wireless
  sensor networks
• Energy awareness spans several layers

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• SENSOR NETWORKS

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Constraints in Sensor Networks

• By design, sensors should be inexpensive
• Sensors are powered by a small battery, hence
  limited power will be available
• Battery replacement is an expensive process.
• sometimes not possible!!!
• The two basic resource constraints in a sensor
  are
• Memory
• Power

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Constraints in Sensor Networks

• Memory
• Operating system code space
• The network protocols requires the intervention
  of operating system
• Available code space
• Data processing, Security algorithms and Error
  control should be run in this available code space

• Power
• Power consumption is in three domains
• Sensing
• Data processing
• Communication

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• SECURITY

Information
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Avalanche Effect

• The bits in the ciphertext change with a
  probability of one half whenever a single input
  bit is complemented before encryption
• This is one of the important criterion for
  designing cryptographically good S-boxes

Example For a 128 bit AES encryption p1 ? AES ?
c1 p2 ? AES ? c2
if d(p1,p2) 1 ? d(c1,c2) 64
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Effect of Bit Errors

• Error Propagation Caused because of Avalanche
  effect

if d(c1,c2) 1 ? d(p1,p2) 64
i.e if one bit in the ciphertext gets corrupted
the whole message is lost!!

• This triggers several retransmissions
• Energy inefficient
• Error control strategies are important

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• ERROR CONTROL

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Optimizations in Error Control

• Adaptive Error Control.
• Feedback loop allows the transmitter to adapt the
  error coding according to the error rate observed
  at the receiver
• Example RCPC codes

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Optimizations in Error Control

• Viterbi Vs. List Viterbi
• Viterbi decoder
• Maximum likelihood decoder for convolution codes
• Has three basic parts
• Branch metric computation
• Path metric computation
• Trace back unit
• Probability of successful decoding is very high
  for random bit error rates lt 10-2 (average
  transmissions are below 1.1 at such BER)

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Optimizations in Error Control

• List Viterbi decoder
• Decodes M paths with ascending order of path
  metric
• The ith best path is the path with the ith least
  minimal metric
• This approach greatly reduces the number of
  retransmissions for error rates 10-2 , 10-1
• Power asymmetry in sensor networks can be
  exploited by list viterbi
• One of the important design criteria is to
  evaluate the tradeoff between computation and
  communication

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Data Dependent Optimizations

• Layered Multimedia Encoding
• Different layers have different level of
  priorities
• Layered multimedia can be integrated with the
  retransmission strategy to optimize transmission
  power
• The varying level of priority in these layers can
  be exploited to provide varying levels of
  security to optimize computational power

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Experimental Results

• Security
• AES (avalanche effect)
• Error Control
• List Viterbi (Distribution of Path search success
  for different error rates)
• Power Consumption
• Different Rounds of DES
• DES Vs. RC4
• Different Key Lengths of RC4
• Comparison of DES, IDEA, GOST

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Avalanche Effect
d(p1,p2) 1
P1-1
P2-1
Encryption
Encryption
A E S
P2-2
P1-2
A E S
P2-9
P1-9
one bit of plaintext was flipped at a random
position and the bit differences between original
cipher and the encrypted cipher was observed at
intermediate rounds
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Avalanche Effect In AES
one bit of plaintext was flipped at a random
position and the bit differences between original
cipher and the encrypted cipher was observed at
intermediate rounds
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Error Propagation
d(c1,c2) 1
C1-1
C2-1
Decryption
Decryption
A E S
A E S
C2-2
C1-2
C2-9
C1-9

• One bit in the cipher text was flipped in random
  position and the bit differences between the
  recovered plaintext and the ideal plaintext was
  observed at intermediate rounds

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Error Propagation Caused by Avalanche

• One bit in the cipher text was flipped in random
  position and the bit differences between the
  recovered plaintext and the ideal plaintext was
  observed at intermediate rounds

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Error Control Setup
DATA
CRC
RCPC
AES Enc
Puncturing matrix
Wireless Channel with Random Bit Error
Channel condition
List Viterbi
Received DATA
AES Dec

• CRC

• Packet Size 200bits
• 16bit CRC

• Convolution mother code rate 1/2

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Distribution of Successful Decoding Over Path
Search Depth
10-2 BER
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Distribution of Successful Decoding Over Path
Search Depth
(0.2) 10-1 BER
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Distribution of Successful Decoding Over Path
Search Depth
(0.4) 10-1 BER
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Distribution of Successful Decoding Over Path
Search Depth
(0.6) 10-1 BER
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Distribution of Successful Decoding Over Path
Search Depth
(0.8) 10-1 BER
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Distribution of Successful Decoding Over Path
Search Depth

• 10-1 BER

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Schematic Of H/W Setup
Read Voltage Current by GPIB
Labview
Vcc I cc
Power Supply
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DES Power Requirement for Different Rounds
power
(watts)
Number of Rounds
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Power Requirement for Different Key Lengths of RC4
power
(watts)
Key Length
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DES Vs. RC4 for Random Data
? DES
power
(watts)
? RC4
Random DATA
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Power Consumption Per Round
power
? IDEA
? DES
(watts)
?Gost
Key Length
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Overall Power Consumption
power
?Gost
? IDEA
(watts)
? DES
Key Length
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Questions??
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