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Aggregation and Secure Aggregation

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.

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Aggregation and Secure Aggregation

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  1. Aggregation and Secure Aggregation

  2. Learning Objectives • Understand why we need aggregation in WSNs • Understand aggregation protocols in WSNs • Understand secure aggregation protocols in WSNs

  3. Prerequisites • Module 7 • Basic concepts of computer networks • Basic concepts of network security

  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 [Aggre_1] Section 1

  5. What is Aggregation?

  6. One Example of Aggregation - Count • Example: consider a query that counts the number of motes in a network of indeterminate size

  7. 1 2 3 4 5 Sensor # Time Goal: Count the number of nodes in the network. Number of children is unknown. Scenario: Count adopted from slides from S. Madden

  8. 1 2 3 Sensor # Time Goal: Count the number of nodes in the network. Number of children is unknown. Scenario: Count

  9. 1 2 3 4 Sensor # Time Goal: Count the number of nodes in the network. Number of children is unknown. Scenario: Count

  10. 1 2 3 4 5 Sensor # Time Goal: Count the number of nodes in the network. Number of children is unknown. Scenario: Count

  11. 1 2 3 4 5 Sensor # Time Goal: Count the number of nodes in the network. Number of children is unknown. Scenario: Count

  12. 1 2 3 4 5 Sensor # Time Goal: Count the number of nodes in the network. Number of children is unknown. Scenario: Count

  13. 1 2 3 4 5 Sensor # Time Goal: Count the number of nodes in the network. Number of children is unknown. Scenario: Count

  14. 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

  15. Data Aggregation Process • Sensor nodes are organized into a tree hierarchy rooted at the Base Station • Non-leaf nodes act as the aggregators

  16. Example Aggregation • Max, Min • Count, Sum • Average • Median

  17. Tiny Aggregation • Distribution phase • Aggregate queries are pushed down into the network • Collection phase • Aggregate values are continuously routed up from children to parents

  18. Energy Consumption

  19. Declarative Queries for Sensor Networks • Examples: SELECT nodeid, light FROM sensors WHERE light > 400 EPOCH DURATION 1s Sensors 1 • Time is partitioned into epochs of duration iA single aggregate value is produced to combine the readings of all devices during the epoch

  20. SELECT roomNo, AVG(sound) • FROM sensors • GROUP BY roomNo • HAVINGAVG(sound) > 200 • EPOCH DURATION 10s 3 • SELECTAVG(sound) • FROM sensors • EPOCH DURATION 10s 2 Rooms w/ sound > 200 Aggregation Queries

  21. 1 2 3 4 5 Illustration: Aggregation SELECT COUNT(*) FROM sensors Slot 1 Sensor # Slot # 1 Section 4.1 of TAG

  22. 1 2 3 4 5 Illustration: Aggregation SELECT COUNT(*) FROM sensors Slot 2 Sensor # 2 Slot #

  23. 1 2 3 4 5 Illustration: Aggregation SELECT COUNT(*) FROM sensors Slot 3 Sensor # 1 3 Slot #

  24. 1 2 3 4 5 Illustration: Aggregation SELECT COUNT(*) FROM sensors Slot 4 5 Sensor # Slot #

  25. 1 2 3 4 5 Illustration: Aggregation SELECT COUNT(*) FROM sensors Slot 1 Sensor # Slot # 1

  26. Flow Up the tree during an epoch How parents choose the duration of the interval in which they will receive values?

  27. 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 Section 7.1 of [Aggre_1]

  28. Secure Aggregation

  29. 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

  30. 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

  31. 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

  32. Integrity and Authenticity • CBC: Cipher Block Chaining

  33. 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?

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