Aggregation and Secure Aggregation. Learning Objectives Understand why we need aggregation in WSNs...
-
Upload
austen-foster -
Category
Documents
-
view
247 -
download
0
description
Transcript of Aggregation and Secure Aggregation. Learning Objectives Understand why we need aggregation in WSNs...
Aggregation and Secure Aggregation
Learning Objectives
• Understand why we need aggregation in WSNs
• Understand aggregation protocols in WSNs• Understand secure aggregation protocols in
WSNs
Prerequisites
• Module 7• Basic concepts of computer networks• Basic concepts of network security
[Aggre_1] Section 1 4
Why do we need Aggregation?• Sensor networks – Event-based Systems• Example Query:
– What is the maximum temperature in area A between 10am and 11am?– Redundancy in the event data
• Individual sensor readings are of limit use• Forwarding raw information too expensive
– Scarce energy– Scarce bandwidth
• Solution– Combine the data coming from different sources
• Eliminate redundancy• Minimize the number of transmissions
• Aggregation: Summary
What is Aggregation?
I
C D
B
E
HA
F
G
Base Station
JK L M
NWireless Sensor Node
Data Transmission
Legend
v1 v2
v3
vi Sensor Measurement
f(v1, v2, v3)
One Example of Aggregation - Count
• Example: consider a query that counts the number of motes in a network of indeterminate size
adopted from slides from S. Madden
7
2
1
3
4
5
Scenario: Count
Goal: Count the number of nodes in the network.
Number of children is unknown.
1 2 3 4 5- - - - -
- - - - -
- - - - -
- - - - -
- - - - -
- - - - -
- - - - -
Sensor #
Time
2
1
3
Scenario: Count
Goal: Count the number of nodes in the network.
Number of children is unknown.
1 2 3 4 51 - - - -
- - - - -
- - - - -
- - - - -
- - - - -
- - - - -
- - - - -
Sensor #
Time
2
1
3
4
Scenario: Count
Goal: Count the number of nodes in the network.
Number of children is unknown.
1 2 3 4 51 - - - -
1 1 1 - -
1 + 2 1 1 - -
- - - - -
- - - - -
- - - - -
- - - - -
Sensor #
Time
2
1
3
4
5
Scenario: Count
Goal: Count the number of nodes in the network.
Number of children is unknown.
1 2 3 4 51 - - - -
1 1 1 - -
1 + 2 1 1 1 -
1 + 2 1 + ½
1 + ½
1 -
- - - - -
- - - - -
- - - - -
Sensor #
Time
2
1
3
4
5
Scenario: Count
Goal: Count the number of nodes in the network.
Number of children is unknown.
1 2 3 4 51 - - - -
1 1 1 - -
1 + 2 1 1 1 -
1 + 2 1 + ½
1 + ½
1 1
1+3 1+ ½ 1+ ½ 1+1 1
- - - - -
- - - - -
Sensor #
Time
2
1
3
4
5
Scenario: Count
Goal: Count the number of nodes in the network.
Number of children is unknown.
1 2 3 4 51 - - - -
1 1 1 - -
1 + 2 1 1 1 -
1 + 2 1 + ½
1 + ½
1 1
1+3 1+ ½ 1+ ½ 1+1 1
1+3 1+2/2
1+2/2
1+1 1
- - - - -
Sensor #
Time
2
1
3
4
5
Scenario: Count
Goal: Count the number of nodes in the network.
Number of children is unknown.
1 2 3 4 51 - - - -
1 1 1 - -
1 + 2 1 1 1 -
1 + 2 1 + ½
1 + ½
1 1
1+3 1+ ½ 1+ ½ 1+1 1
1+3 1+2/2
1+2/2
1+1 1
1+4 1+2/2
1+2/2
1+1 1
Sensor #
Time
Count Example – A Better Scheme
• Each leaf node in the tree reports a count of 1 to their parents
• Interior nodes sum the count of their children, add 1 to it, and report that value to their parent
Data Aggregation Process
• Sensor nodes are organized into a tree hierarchy rooted at the Base Station
• Non-leaf nodes act as the aggregators
Example Aggregation
• Max, Min• Count, Sum• Average• Median
Tiny Aggregation
• Distribution phase– Aggregate queries are pushed down into the
network• Collection phase
– Aggregate values are continuously routed up from children to parents
Energy Consumption
Time v. Current Draw During Query Processing
0
5
10
15
20
0 0.5 1 1.5 2 2.5 3Time (s)
Cur
rent
(mA
) Snoozing
Processing
Processingand Listening
Transmitting
Declarative Queries for Sensor Networks
• Examples:SELECT nodeid, lightFROM sensorsWHERE light > 400EPOCH DURATION 1s
1 EpochEpoch NodeidNodeid LightLight TempTemp AccelAccel SoundSound
0 1 455 x x x
0 2 389 x x x
1 1 422 x x x
1 2 405 x x x
Sensors
•Time is partitioned into epochs of duration iA single aggregate value is produced to combine the readings of all devices during the epoch
Aggregation Queries
SELECT roomNo, AVG(sound)FROM sensorsGROUP BY roomNoHAVING AVG(sound) > 200EPOCH DURATION 10s
Rooms w/ sound > 200
3
2SELECT AVG(sound)FROM sensorsEPOCH DURATION 10s
Epoch AVG(sound)0 4401 445
Epoch roomNo AVG(sound)0 1 3600 2 5201 1 3701 2 520
Section 4.1 of TAG
Illustration: Aggregation
1 2 3 4 5
1 1
2
3
4
1
1
2 3
4
51
Sensor #
Slot
#
Slot 1SELECT COUNT(*) FROM sensors
Illustration: Aggregation
1 2 3 4 5
1 1
2 2
3
4
1
1
2 3
4
5
2
Sensor #
Slot
#
Slot 2SELECT COUNT(*) FROM sensors
Illustration: Aggregation
1 2 3 4 5
1 1
2 2
3 1 3
4
1
1
2 3
4
5
31
Sensor #
Slot
#
Slot 3SELECT COUNT(*) FROM sensors
Illustration: Aggregation
1 2 3 4 5
1 1
2 2
3 1 3
4 5
1
1
2 3
4
5
5Sensor #
Slot
#
Slot 4SELECT COUNT(*) FROM sensors
Illustration: Aggregation
1 2 3 4 5
1 1
2 2
3 1 3
4 5
1 1
1
2 3
4
51
Sensor #
Slot
#
Slot 1SELECT COUNT(*) FROM sensors
Flow Up the tree during an epoch
How parents choose the duration of the interval in which they will receive values?
Section 7.1 of [Aggre_1]
Topology Maintenance and Recovery
• How to address the unreliable nature of WSNs in TAG?– Each node maintains a fixed size of its neighbors –
Select a better parent node– If a node does not hear from its parent for some
time, it assumes that its parent has failed
Secure Aggregation
Secure Aggregation
• It is challenging to design suitable security mechanisms for Wireless Sensor Networks (WSNs)– Stringent resource constraints on energy,
processing power, memory, bandwidth, etc.• WSNs need lightweight secure mechanisms• We introduce an LCG-based secure
aggregation scheme– Efficiency and simplicity
Security Goals
• Security Goals– Confidentiality
• Sensor data/readings cannot be disclosed to attackers– Integrity
• If an adversary modifies a data message, the receiver should be able to detect this tampering
– Authenticity• Ensures that data messages come from the intended sender
• Assumptions– The existence of a key management scheme– WSN nodes can negotiate the key and trust setup
LCG-based Security Protocols• Basic Hop by Hop Message Transmission
• Notations– A, B, C…: Sensor Nodes– E(P, K): Encryption of plaintext
message P using key K– P1|P2: Concatenation of message
P1 and P2
– MAC(K, P): Message Authentication Code (MAC) of message P using key K
– X0: seed of the LCG– a, b, m: Parameters of the LCG
DBE
HA
F
G
I
Base Station
J
C
E(PA | MAC(PA, KAH), KAH)
E(PB | MAC(PB, KBH), KBH)
E(AggrH | MAC(AggrH, KHJ), KHJ)
E(PB | MAC(PB, KCH), KCH)
E(PB | MAC(PB, KDH), KDH)
Integrity and Authenticity
• CBC: Cipher Block Chaining
Assignment
• 1. Why do we need aggregation in wireless sensor networks?
• 2. What is the basic idea of TAG?• 3. What is the basic idea of LCG-based secure
aggregation in wireless sensor networks?