1. Security Of Wireless Sensor Networks

2. Learning Objectives Understand the security threats faced by WSNs
Understand the security primitives used in WSNs
Understand TinySec

3. Prerequisites Module 2 Basic concepts of network security
Basic concepts of computer networks

4. Security Risks in Wireless Sensory Networks
Eavesdropping
Confidentiality
Packet Injection
Access control
Integrity
Jamming
Replay
Denial of Service K K
TinySec K
Fix the picture K
Adversary

5. Security Goals Access Control Message Integrity Confidentiality
Link layer protocol should prevent unauthorized parties from participating in the network
Message Integrity
Receiver should be able to detect the malicious modification of transmitted messages
Confidentiality
Keep transmitted messages secret from unauthorized parties
Replay Protection
Attacker can replay a legitimate message at some later time

6. Security Goals Performance Ease of use
Using cryptography will incur increased overhead in extra demands on the processor and RAM
Increased message length decreases the throughput and increased latency. It will also increase the power consumption
Ease of use
Higher level security protocols will rely on the link-layer security as a primitive
Transparent to applications

7. Security Primitives Message Authentication Codes (MACs)
A common solution to achieve authenticity and integrity
MAC can be viewed as “Cryptographically secure checksum”
Generated with a key shared by both sender and receiver
Difficult to forge without the key
Initialization Vectors (IV)
To achieve semantic security
An input to the algorithm to add variation to the encryption process

8. Block Ciphers Pseudorandom permutation (invertible)
DES, RC5, Skipjack, AES
Maps n bits of plaintext to n bits of ciphertext
Used to build encryption schemes and message authentication codes (MAC)

9. Mode of Operation
Block ciphers operate on blocks of plaintext and ciphertext
For example 64 bits
A cryptographic mode combines the basic ciphers, some sort of feedback, and some simple operations
Example Block Cipher modes
ECB, CBC, CFB, CTR, OFB

10. Cipher Block Chaining (CBC) Mode
The results of the encryption of previous blocks are fed back into the encryption of the current block.

11. Two Security Options - TinySec
Authenticated Encryption (TinySec-AE)
Data payload encrypted
Packets authenticated with a MAC
MAC computed over the encrypted data and the packet header
Authentication Only (TinySec-Auth)
Data payload is not encrypted

12. Encryption - TinySec TinySec IV format Encryption schemes
Tradeoff between long and short IV
How long is long enough?
The structure of IV is dst||AM||l||src||ctr
Encryption schemes
Stream cipher has a devastating failure mode: if the same IV is ever used, it is often possible to recover both plaintext
Block cipher is preferred
It is as robust as possible in the presence of repeated IV
MAC algorithms use a block cipher

13. Packet Format - TinySec

14. Keying Mechanisms - TinySec
Determines how cryptographic keys are distributed and shared throughout the network
Mechanisms
A single network-wide TinySec key among the authorized nodes
Nodes share a key for communication only if they need to communicate with each other (pair-wise)
Neighboring nodes to share a TinySec key

15. Assignment
1. Please list five attack scenarios for wireless sensor networks
2. How does TinySec provide “Authenticated encryption” and “Authentication only” mechanisms?
3. What is a block cipher?