1. Aggregation and Secure Aggregation

2. [Aggre_1] Section 12 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

3. What is Aggregation?

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

5. adopted from slides from S. Madden 5 2 1 3 4 5 Scenario: Count Goal: Count the number of nodes in the network. Number of children is unknown. 12345 ----- ----- ----- ----- ----- ----- ----- Sensor # Time

6. 2 13 Scenario: Count Goal: Count the number of nodes in the network. Number of children is unknown. 12345 1---- ----- ----- ----- ----- ----- ----- Sensor # Time

7. 2 13 4 Scenario: Count Goal: Count the number of nodes in the network. Number of children is unknown. 12345 1---- 111-- 1 + 211-- ----- ----- ----- ----- Sensor # Time

8. 2 13 45 Scenario: Count Goal: Count the number of nodes in the network. Number of children is unknown. 12345 1---- 111-- 1 + 2111- 1 + ½ 1- ----- ----- ----- Sensor # Time

9. 2 13 45 Scenario: Count Goal: Count the number of nodes in the network. Number of children is unknown. 12345 1---- 111-- 1 + 2111- 1 + ½ 11 1+31+ ½ 1+11 ----- ----- Sensor # Time

10. 2 1 3 4 5 Scenario: Count Goal: Count the number of nodes in the network. Number of children is unknown. 12345 1---- 111-- 1 + 2111- 1 + ½ 11 1+31+ ½ 1+11 1+31+2/ 2 1+11 ----- Sensor # Time

11. 2 1 3 4 5 Scenario: Count Goal: Count the number of nodes in the network. Number of children is unknown. 12345 1---- 111-- 1 + 2111- 1 + ½ 11 1+31+ ½ 1+11 1+31+2/ 2 1+11 1+41+2/ 2 1+11 Sensor # Time

12. 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

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

14. Example Aggregation Max, Min Count, Sum Average Median

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

16. Energy Consumption

17. Declarative Queries for Sensor Networks Examples: SELECT nodeid, light FROM sensors WHERE light > 400 EPOCH DURATION 1s 1 EpochNodeidLightTempAccelSound 01455xxx 02389xxx 11422xxx 12405xxx Sensors Time is partitioned into epochs of duration i A single aggregate value is produced to combine the readings of all devices during the epoch

18. Aggregation Queries SELECT roomNo, AVG(sound) FROM sensors GROUP BY roomNo HAVING AVG(sound) > 200 EPOCH DURATION 10s Rooms w/ sound > 200 3 2 SELECT AVG(sound) FROM sensors EPOCH DURATION 10s EpochAVG(sound) 0440 1445 EpochroomNoAVG(sound) 01360 02520 11370 12520

19. Section 4.1 of TAG Illustration: Aggregation 12345 11 2 3 4 1 1 2 3 4 5 1 Sensor # Slot # Slot 1 SELECT COUNT(*) FROM sensors

20. Illustration: Aggregation 12345 11 22 3 4 1 1 2 3 4 5 2 Sensor # Slot # Slot 2 SELECT COUNT(*) FROM sensors

21. Illustration: Aggregation 12345 11 22 313 4 1 1 2 3 4 5 3 1 Sensor # Slot # Slot 3 SELECT COUNT(*) FROM sensors

22. Illustration: Aggregation 12345 11 22 313 45 1 1 2 3 4 5 5 Sensor # Slot # Slot 4 SELECT COUNT(*) FROM sensors

23. Illustration: Aggregation 12345 11 22 313 45 11 1 2 3 4 5 1 Sensor # Slot # Slot 1 SELECT COUNT(*) FROM sensors

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

25. 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

26. Secure Aggregation

27. 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

28. 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

29. 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 –P 1 |P 2 : Concatenation of message P 1 and P 2 –MAC(K, P): Message Authentication Code (MAC) of message P using key K –X 0 : seed of the LCG –a, b, m: Parameters of the LCG

30. Integrity and Authenticity CBC: Cipher Block Chaining