Wireless Sensor Network Security

1. Security in Wireless Sensor Networks 14 Marks

WSNs are often deployed in open, unattended or hostile environments. Their wireless communication and limited hardware resources make them more vulnerable than conventional networks.

Protected Assets

• Sensor readings
• Node identity
• Encryption keys
• Routing information
• Control messages
• Network services
• Location and topology information

2. Need for WSN Security 7 Marks

• Wireless signals can be intercepted easily.
• Nodes may be physically captured.
• False readings may lead to incorrect decisions.
• Attackers may disrupt routing and communication.
• WSNs are used in military, industrial and healthcare applications.
• Location and identity information may be private.
• Compromised nodes may behave like legitimate nodes.
• Denial-of-service attacks can exhaust node batteries.

3. Security Goals and Requirements 14 Marks

Confidentiality

Only authorized entities should be able to read sensed data and control information.

Integrity

Data must not be modified, inserted or deleted without detection.

Authentication

The receiver must verify the identity of the sender.

Availability

Network services should remain accessible even during failures or attacks.

Freshness

Messages must be recent and not replayed from an earlier communication.

Non-Repudiation

A sender should not be able to deny an action or message where this property is required.

Access Control

Only authorized users and nodes may access network resources.

Data Privacy

Sensitive readings, identities and locations must be protected.

Secure Localization and Time Synchronization

Attackers must not be allowed to manipulate position or timing information.

4. Security Challenges in WSN 14 Marks

• Limited energy: Complex security operations consume battery power.
• Limited processing: Nodes cannot run very heavy cryptographic algorithms.
• Limited memory: Key tables and certificates must remain small.
• Wireless medium: Communication can be overheard or jammed.
• Unattended deployment: Nodes may be physically captured.
• Large scale: Thousands of nodes require scalable key management.
• Dynamic topology: Node failures and mobility change routes.
• No fixed infrastructure: Centralized security may not always be available.
• Broadcast communication: One malicious packet may affect many nodes.
• Insider attacks: A compromised node possesses valid credentials.
• Remote management: Secure updates and reconfiguration are difficult.
• Real-time requirements: Security must not introduce excessive delay.

5. Threat and Attack Model 14 Marks

Passive Attack

The attacker observes communication without changing network operation.

• Eavesdropping
• Traffic analysis
• Location monitoring

Active Attack

The attacker modifies, injects, drops or blocks messages.

• Jamming
• Packet modification
• False data injection
• Routing attacks

External Attack

Performed by an entity that is not an authorized network member.

Internal Attack

Performed by a compromised legitimate node. This attack is difficult to detect because the node may possess valid keys.

Node-Class Attacks

• Mote-class attacker: Has capability similar to ordinary sensor nodes.
• Laptop-class attacker: Has greater power, range, memory and processing capability.

6. Classification of Security Attacks 14 Marks

7. Physical-Layer Attacks 14 Marks

Jamming

An attacker transmits interfering radio signals to block legitimate communication.

Effects

• Packet loss
• Reduced availability
• Energy waste due to retransmission

Defences

• Frequency hopping
• Spread spectrum
• Channel switching
• Jamming detection
• Routing around the jammed region

Node Tampering

An attacker physically captures a node and extracts keys, modifies software or replaces hardware.

Defences

• Tamper-resistant packaging
• Key revocation
• Node-compromise detection
• Secure memory
• Self-destruction of sensitive keys after tamper detection

8. Data-Link and MAC-Layer Attacks 14 Marks

Collision Attack

The attacker causes interference during packet transmission, forcing retransmission.

Exhaustion Attack

The attacker repeatedly requests channel access or creates collisions to drain node batteries.

Unfairness Attack

A malicious node abuses MAC priorities or backoff rules to obtain more channel access.

Replay Attack

Old MAC frames are recorded and transmitted again.

Defences

• Error-correcting codes
• Rate limiting
• Small frame sizes
• Frame counters
• Authentication codes
• Time-division channel allocation
• Misbehavior detection

9. Network-Layer and Routing Attacks 14 Marks

Selective Forwarding

A malicious forwarding node drops selected packets while forwarding others.

Sinkhole Attack

An attacker advertises an attractive route and draws surrounding traffic through itself.

Wormhole Attack

Two attackers create a low-latency tunnel and replay packets between distant network regions.

Sybil Attack

One physical node presents multiple false identities.

Hello Flood Attack

A powerful attacker broadcasts HELLO packets, making distant nodes believe it is their neighbor.

Blackhole Attack

A malicious node attracts traffic and drops all received packets.

False Routing Information

The attacker changes route costs, sequence numbers or next-hop information.

Defences

• Authenticated routing messages
• Multipath routing
• Neighbor verification
• Geographical or temporal packet leashes
• Identity verification
• Trust and reputation systems
• Route monitoring

10. Transport-Layer Attacks 7 Marks

Flooding

The attacker repeatedly creates connection requests or sends excessive packets, consuming memory and energy.

Desynchronization

Forged control messages cause endpoints to repeatedly retransmit or reset communication state.

Defences

• Client puzzles
• Rate limitation
• Authentication
• Connection timeout
• Packet sequence verification

11. Application-Layer Attacks 7 Marks

• False-data injection: Fabricated sensor values are reported.
• Data aggregation attack: Aggregated values are altered.
• Malicious code: Unauthorized software is installed.
• Query attack: Expensive or repeated queries drain network resources.
• Privacy attack: Sensitive application information is disclosed.

Defences

• Secure code update
• Input validation
• Data authentication
• Anomaly detection
• Access control

12. Cryptography in Wireless Sensor Networks 14 Marks

Cryptographic Services

• Encryption for confidentiality
• Message Authentication Code for integrity and authentication
• Hash function for data verification
• Digital signature for authentication and non-repudiation
• Key agreement for establishing shared secrets

WSN Design Requirements

• Low computation cost
• Small memory requirement
• Low communication overhead
• Short key and message sizes
• Resistance to node capture
• Scalable key distribution

13. Symmetric-Key Cryptography 14 Marks

Advantages

• Fast execution
• Low energy consumption
• Small code and memory requirement
• Suitable for sensor nodes

Limitations

• Secret-key distribution is difficult.
• A captured node may expose shared keys.
• Large networks require scalable key management.

Examples

• AES
• Lightweight block ciphers
• Link-layer shared-key encryption

14. Asymmetric-Key Cryptography 14 Marks

Advantages

• Simplifies authentication and key establishment
• Supports digital signatures
• Does not require a pre-shared secret between every pair

Limitations

• Higher computation and energy cost
• Larger keys and messages
• May be difficult for very constrained nodes

Use in WSN

Elliptic Curve Cryptography is often preferred over traditional public-key approaches because it can provide comparable security with smaller keys.

15. Authentication, Integrity and Freshness 14 Marks

Message Authentication Code

A MAC is generated from message data and a secret key. The receiver recomputes it to verify integrity and authenticity.

Hash Function

A hash function creates a fixed-size digest. Any message modification normally changes the digest.

Freshness Mechanisms

• Sequence numbers
• Frame counters
• Nonces
• Timestamps
• Challenge-response protocols

Replay Protection

The receiver rejects packets carrying previously used sequence numbers, counters or nonces.

16. Key Management in WSN 14 Marks

Key Types

• Individual key: Shared between a node and base station.
• Pairwise key: Shared between two neighboring nodes.
• Cluster key: Shared among cluster members.
• Network or group key: Shared by many or all nodes.

Key-Distribution Approaches

• Single network-wide pre-shared key
• Pairwise pre-installed keys
• Random key pre-distribution
• Master-key-based establishment
• Public-key-based agreement

Requirements

• Scalability
• Low storage cost
• Resistance to node capture
• Key revocation
• Secure node addition
• Periodic key renewal

17. Secure Routing in WSN 14 Marks

Requirements

• Authentication of routing messages
• Protection against route modification
• Fresh route information
• Detection of malicious forwarding
• Resilience to node failure
• Low security overhead

Techniques

• Link-layer authentication
• Sequence numbers and timestamps
• Multipath routing
• Watchdog monitoring
• Trust-based route selection
• Bidirectional-link verification
• Geographical verification
• Secure neighbor discovery

Trade-Off

Strong security improves protection but may consume more energy, memory and bandwidth. Secure routing must balance protection with sensor-node constraints.

18. Secure Data Aggregation 14 Marks

Threats

• Aggregator modifies results.
• Compromised nodes send false readings.
• Attackers replay old data.
• Eavesdroppers learn private sensor values.

Protection Methods

• Authenticated aggregation
• Redundant aggregation paths
• Statistical outlier detection
• End-to-end integrity verification
• Encrypted aggregation
• Trust-based aggregator selection

19. Intrusion Detection in WSN 14 Marks

Detection Approaches

• Signature-based: Matches known attack patterns.
• Anomaly-based: Detects deviation from normal behavior.
• Specification-based: Detects violation of defined protocol rules.

Observed Indicators

• Abnormal packet-dropping rate
• Unusual traffic volume
• Repeated identity use
• Unexpected route changes
• Abnormal energy consumption
• False or inconsistent readings

Limitations

• False alarms
• Storage and computation cost
• Difficulty detecting insider attacks
• Communication overhead for cooperative detection

20. IEEE 802.15.4 Security 14 Marks

Security Services

• Data confidentiality
• Frame integrity
• Data-origin authentication
• Replay protection
• Access control support

AES-Based Protection

IEEE 802.15.4 uses the Advanced Encryption Standard with a 128-bit key for link-layer security operations.

Security Modes

• AES-CTR for confidentiality
• AES-CBC-MAC for authentication and integrity
• AES-CCM / CCM* for combined confidentiality and authentication

Frame Counter

A monotonically increasing frame counter helps detect replayed frames.

Security Level

The frame identifies the required combination of encryption and authentication-tag length.

Limitations

• Key establishment is not completely defined by the MAC standard.
• Security depends on correct key management.
• Link-layer protection does not automatically provide end-to-end security.
• Compromised nodes with valid keys remain dangerous.

21. ZigBee Security Architecture 14 Marks

Security Components

• Trust Center
• Network key
• Link key
• Master key or installation-based secret
• Frame counters
• AES-128 protection

Trust Center

The Trust Center controls device admission, distributes keys and manages network security policy.

Network Key

A shared key used to protect network-layer communication among ZigBee devices.

Link Key

A key shared between two devices for point-to-point application protection.

ZigBee Security Process

1. A device requests to join the network.
2. The Trust Center verifies or authorizes the device.
3. Security keys are established or transported.
4. Frames are encrypted and authenticated.
5. Frame counters prevent replay.
6. Keys may be updated when required.

Security Risks

• Weak default keys
• Insecure device joining
• Improper key transport
• Physical node capture
• Failure to update keys

22. IEEE 802.15.4 and ZigBee Security Comparison 14 Marks

23. WSN Security Best Practices 7 Marks

• Use unique device credentials.
• Avoid permanent network-wide default keys.
• Authenticate every control message.
• Use frame counters or nonces against replay.
• Rotate and revoke keys when necessary.
• Disable unused interfaces and services.
• Use secure boot and signed firmware updates.
• Monitor abnormal traffic and packet dropping.
• Protect nodes physically where possible.
• Apply least-privilege access control.
• Use secure routing and multipath protection.
• Balance security strength with energy constraints.

Unit 5 Quick Revision

• WSN security protects nodes, data, communication and services.
• Core goals are confidentiality, integrity, authentication, availability and freshness.
• WSNs face limited energy, open wireless links and physical capture.
• Attacks may be passive, active, external or internal.
• Jamming and tampering occur at the physical layer.
• Collision, exhaustion and unfairness affect the MAC layer.
• Sinkhole, wormhole, Sybil and selective forwarding affect routing.
• Symmetric cryptography is efficient but requires secure key distribution.
• Asymmetric cryptography supports authentication and key establishment.
• Message Authentication Codes provide integrity and authentication.
• Frame counters and nonces provide freshness and replay protection.
• Key management includes distribution, renewal and revocation.
• IEEE 802.15.4 uses AES-128-based link-layer security.
• ZigBee adds Trust Center, network keys and link keys.

Important RGPV Exam Questions

Long Answer Questions

1. Define WSN security and explain its need.
2. Explain security goals and requirements of Wireless Sensor Networks.
3. Discuss major security challenges in WSN.
4. Classify WSN attacks into passive, active, external and internal attacks.
5. Explain physical-layer attacks and their countermeasures.
6. Explain MAC-layer attacks in sensor networks.
7. Discuss network-layer attacks such as sinkhole, wormhole and Sybil.
8. Explain selective forwarding, Hello flood and blackhole attacks.
9. Discuss transport-layer and application-layer attacks.
10. Explain the role of cryptography in WSN security.
11. Compare symmetric and asymmetric cryptography for sensor networks.
12. Explain authentication, integrity and freshness mechanisms.
13. Discuss key-management requirements and approaches in WSN.
14. Explain secure routing mechanisms.
15. Write a detailed note on secure data aggregation.
16. Explain intrusion-detection approaches for WSN.
17. Explain IEEE 802.15.4 security architecture.
18. Explain ZigBee security architecture and the role of Trust Center.
19. Compare IEEE 802.15.4 and ZigBee security.

Short Answer Questions

1. Define confidentiality.
2. What is data freshness?
3. What is an insider attack?
4. Define jamming.
5. What is a sinkhole attack?
6. Define wormhole attack.
7. What is a Sybil attack?
8. Define selective forwarding.
9. What is a Message Authentication Code?
10. What is replay protection?
11. Define pairwise key.
12. What is a Trust Center?
13. What is a ZigBee network key?
14. What is a ZigBee link key?
15. Which encryption standard is used by IEEE 802.15.4?

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