1. Security Considerations for Wireless Sensor Networks Prabal Dutta dutta.4@osu.edu (614) 975-3658 Security Considerations for Wireless Sensor Networks

2. Security Considerations for Wireless Sensor Networks Overview  Motivation  Basic Concepts  Confidentiality  Authentication & Non-repudiation  Integrity  Freshness  Challenges  Key Distribution Strategies  Constraints  Others  Take Away

3. Security Considerations for Wireless Sensor Networks Motivation  This Presentation  Introduction to security concepts for 1451.5 survey  In General  Wireless Sensor/Actuator Networks may be collecting sensitive data and controlling important assets that must be protected  Wireless is a broadcast medium so inherently insecure and subject to eavesdropping  Vulnerable to active attacks like message spoofing or message replays  Obscurity IS NOT security  MUST have security for a complete solution

4. Security Considerations for Wireless Sensor Networks Confidentiality  Allows communicating parties to keep secrets  Protects against eavesdropping  Implemented through encryption using ciphers  Private (“Shared”) Key (Symmetric Cipher)  Fast, small, efficient, but has a key distribution problem  Public Key (Asymmetric Cipher)  Solves key distribution, but computationally very expensive  But encryption is not enough – if the same message encrypts to the same cipher text – then replay attacks are possible (“freshness”)

5. Security Considerations for Wireless Sensor Networks Authentication & Non-repudiation  Related concepts that allow a message recipient to verify the authenticity of the message source  Allow a party to prove its identity  Protects against forgery or masquerade  If a priori knowledge of peer (and a shared secret) exists, then use of knowledge of shared secrets is sufficient  Otherwise, requires use of a digital signature from a trusted source (like a notary public)  Digital Signatures implemented using a member of the public key cryptography suite (e.g. DSA) - but computationally expensive

6. Security Considerations for Wireless Sensor Networks Integrity  Ensures that:  Messages are not accidentally corrupted by an imperfect communications channel  Message are not intentionally corrupted by an attacker during transmission  Typically implemented through cryptographic hashes that are similar to a CRC.  Hashes are considerably more complex than a CRC function, and therefore practically impossible to reverse engineer.  Common hashes include MD5 and SHA

7. Security Considerations for Wireless Sensor Networks Freshness  Ensures that:  Messages are current  Messages are ordered  Messages are not duplicates (replays) of a previously transmitted message  Weak freshness provides partial message ordering but no delay information  Strong freshness provides complete ordering and delay estimation  Implemented through sequence numbers, timestamps, etc.

8. Security Considerations for Wireless Sensor Networks Key Distribution Strategies  Shared Global Key (pre-deployment)  Frequently used  Compromised node compromises entire network  Shared Pair-wise Keys (pre-deployment)  Requires n(n-1)/2 ~ n^2 keys  Compromised node compromises entire network  New node requires n + 1 new keys n + 1 updates  Ad Hoc Pair-wise Keys (post-deployment)  Computationally expensive (D-H KE: 2.24 J in 5.75 sec on 206MHz SA [Hodjat] -> 1850 reps on CR2450 battery)  Vulnerable to DoS Attacks  Base Station Key Distribution Center (pre & post)  Pair-wise keys between nodes and BS (Kerberos-like)  Ad hoc pair-wise keys between nodes with BS help

9. Security Considerations for Wireless Sensor Networks Constraints  Limited source of energy  Limited computational resources  MHz  FLOPS  Code size  RAM size  Limited communications bandwidth  Asymmetric ciphers (e.g. RSA) and key exchange protocols (e.g. Diffie-Hellman) are computationally expensive

10. Security Considerations for Wireless Sensor Networks Other Challenges  Cipher Selection  Must be small, fast, and readily available  Global Clock Synchronization  Required for certain functions like freshness  Authenticated Broadcast [TESLA, TIK]  One node simultaneously broadcasts authenticated message to several other nodes  Also requires clock synchronization  Static vs. Mobile Nodes  Mobility adds another dimension of complexity to key distribution

11. Security Considerations for Wireless Sensor Networks Take Away  Many constraints & tradeoffs and nothing comes for free  Energy is biggest constraint  Key exchange is a major challenge  No “one-size-fits-all” solution  Active area of academic research  Berkeley, UCLA, Network Associates, others