1. SPINS: Security Protocols for Sensor Networks Adrian Perrig, Robert Szewczyk, Victor Wen, David Culler, and J.D. Tygar – University of California, Berkeley Presented By: Kimberly Yonce

2. Outline  Wireless Sensor Networks  SPINS Building Blocks SNEP TESLA  Related Work  Limitations/Future Work/Comments

3. Wireless Sensor Networks (WSN)  A wireless network consisting of spatially distributed autonomous devices using sensors to cooperatively monitor different locations.  Types of Sensors: temperature, sound, vibration, pressure, motion, and light.

4. WSN Applications  Habitat monitoring ZebraNet: Animals are equipped with tracking nodes that contain GPS to monitor position and speed of movement and light sensors to indicate current environment.

5. WSN Applications  Fire Detection SmokeNet: Sensors monitor smoke detection in a building. Sensors worn by firefighters monitor heart rate and air tank level as well as their location.

6. WSN Applications  Medical Uses Vital Sign Monitoring Patient Tracking Emergency Triage Stroke Rehabilitation

7. WSN Applications  Military Uses Military Vehicle Tracking Mine Fields Sniper Localization  Traffic Monitoring  Intrusion Detection

8. Sensor Network at UC Berkeley

9. Sensor Hardware

10.  SmartDust  TinyOS  CPU: 8-bit, 4MHz  Storage: 8 KB instruction flash, 512 bytes RAM, 512 bytes EEPROM  916 MHz radio  Bandwidth: 10 Kbps  OS Code Space: 3500 bytes  Available Code Space: 4500 bytes

11. WSN Challenges  Severely resource-constrained environments: Processing power Storage Bandwidth Energy

12. Is Security Possible?  RSA Performs operations on 2 large prime numbers N (modulus of the public and private keys) is recommended to be at least 2048 bits long  Digital Signatures High communication overhead of 50-1000 bytes per packet High overhead to create and verify the signatures

13. Is Security Possible?  DES 64 bit block size Key length 56 bits 512-entry Sbox table 256-entry table for various permutations  AES 128 bit fixed block size Key size of 128, 192, or 256 bits 800 bytes of lookup tables

14. WSN Communication Patterns  Sensor Readings Node to Base Station  Specific Requests Base Station to Node  Reprogramming Network, Routing Beacons Base Station broadcast to all Nodes

15. Sensor Network Security Requirements  Data Confidentiality  Data Authentication  Data Integrity  Data Freshness Weak Freshness Strong Freshness

16. SPINS Building Blocks  SNEP Data confidentiality Two-party data authentication Integrity Freshness  TESLA Authentication for data broadcasts

17. SNEP  Low communication overhead  Uses MAC to achieve two-party authentication and data integrity  A shared counter between sender and receiver helps ensure semantic security

18. SNEP with Strong Freshness

19.  TESLA  TESLA authenticates initial packet with a digital signature. TESLA uses only symmetric mechanisms.  Instead of disclosing a key in each packet, a key is disclosed once per epoch.  TESLA restricts number of authenticated senders.  Broadcast from Base Station vs. Broadcast from a node

20. Cryptography Implementation  Block Cipher RC5 – small code size and high efficiency  Variable block size (32, 64, or 128 bits)  Key Size (0 to 255)  # of Rounds (0 to 255)  Modular additions and XORs  Feistal like structure

21. Encryption Function  Counter (CTR) Mode Same function for encryption and decryption Stream cipher in nature

22. MAC Generation

23. Key Setup

24. Evaluation  Code Size  RAM Requirements

25. Evaluation  Energy Costs

26. Related Work  Carman, Kruus, and Matt analyze a variety of approaches for key agreement and distribution in sensor networks.  TEA by Wheeler and Needham or TREYFER by Yuval are smaller alternatives as symmetric ciphers.  Karlof and Wagner investigate security goals for routing in sensor networks.  Deng et al. analyze attacks against the base station.

27. Limitations/Future Work  TESLA requires loose time synchronization between nodes  Counter must be updated at sender and receiver  Information leakage through covert channels  Only ensure that a compromised sensor does not reveal the keys of all the sensors in the network

28. Limitations/Future Work  Does not consider DoS  Does not achieve non-repudiation  Relies on the base station being trusted, and therefore does not consider attacks on the base station itself.

29. Questions/Comments