Security Of Wireless Sensor Networks

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

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

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

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

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

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

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)

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

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

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

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

Packet Format - TinySec

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

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?