Aggregation and Secure Aggregation Why do we need

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Aggregation and Secure Aggregation

Aggregation and Secure Aggregation

Why do we need Aggregation? • Sensor networks – Event-based Systems • Example Query:

Why do we need Aggregation? • Sensor networks – Event-based Systems • Example Query: – What is the maximum temperature in area A between 10 am and 11 am? – 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 2

What is Aggregation?

What is Aggregation?

One Example of Aggregation - Count • Example: consider a query that counts the

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

Sensor # 1 2 3 4 5 Goal: Count the number of nodes in

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

Sensor # 1 2 3 Goal: Count the number of nodes in the network.

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

Sensor # 1 2 3 4 Goal: Count the number of nodes in the

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

Sensor # 1 2 3 4 5 Goal: Count the number of nodes in

Sensor # 1 2 3 4 5 Goal: Count the number of nodes in the network. Number of children is unknown. Scenario: Count 1 2 3 4 5 1 - - 1 1 1 - - 1+2 1 1 1 - 1+2 1+½ - - - - Time

Sensor # 1 2 3 4 5 Goal: Count the number of nodes in

Sensor # 1 2 3 4 5 Goal: Count the number of nodes in the network. Number of children is unknown. Scenario: Count 1 2 3 4 5 1 - - 1 1 1 - - 1+2 1 1 1 - 1 1 1+2 1+½ 1+3 1+ ½ 1+1 1 - - - - - Time

Sensor # 1 2 3 4 5 Goal: Count the number of nodes in

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

Sensor # 1 2 3 4 5 Goal: Count the number of nodes in

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

Count Example – A Better Scheme • Each leaf node in the tree reports

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

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

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

Tiny Aggregation • Distribution phase – Aggregate queries are pushed down into the network

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

Energy Consumption

Declarative Queries for Sensor Networks • Examples: 1 SELECT nodeid, light FROM sensors WHERE

Declarative Queries for Sensor Networks • Examples: 1 SELECT nodeid, light FROM sensors WHERE light > 400 EPOCH DURATION 1 s Sensors Epoch Nodeid Light Temp Accel Sound 0 1 455 x x x 0 2 389 x x x 1 1 422 x x x 1 2 405 x x x • Time is partitioned into epochs of duration i A single aggregate value is produced to combine the readings of all devices during the epoch

Aggregation Queries SELECT AVG(sound) Epoch 0 AVG(sound) 440 FROM sensors 1 445 2 EPOCH

Aggregation Queries SELECT AVG(sound) Epoch 0 AVG(sound) 440 FROM sensors 1 445 2 EPOCH DURATION 10 s FROM sensors Epoch room. No AVG(sound) 0 1 360 0 2 520 GROUP BY room. No 1 1 370 HAVING AVG(sound) > 200 1 2 520 3 SELECT room. No, AVG(sound) EPOCH DURATION 10 s Rooms w/ sound > 200

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

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

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

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

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

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

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

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

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

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

Flow Up the tree during an epoch How parents choose the duration of the

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

Topology Maintenance and Recovery • How to address the unreliable nature of WSNs in

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]

Secure Aggregation

Secure Aggregation

Secure Aggregation • It is challenging to design suitable security mechanisms for Wireless Sensor

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

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,

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

Integrity and Authenticity • CBC: Cipher Block Chaining

Integrity and Authenticity • CBC: Cipher Block Chaining