Designing Secure Sensor Networks

1. Designing Secure Sensor Networks - Elaine Shi & Adrian Perrig - 2005. 9. 13. HongKi Lee

2. Contents • Introduction • Threat and Trust Model • Security Requirements • Attacks and Countermeasures • Promising Research Directions • Conclusion

3. Introduction • Sensor networks will play an essential role in the upcoming age of pervasive computing => Security will be important for most applications • Security in sensor networks is complicated by the constrained capabilities of hardware and the properties • Severely constrained computation, memory, and energy resources • Susceptible to physical capture & compromise • Use wireless communication • Security also needs to scale to large-scale deployments

4. Threat and Trust Model • Outsider Attacks • Attack from unauthorized participant of the sensor network • Eavesdrop to steal private or sensitive information • Alter or spoof packets to infringe on the authenticity of communication • DoS attack such as jamming and battery depletion attack • Capture and physically destroy nodes • Benign node failures result from non-adversarial factors such as catastrophic climate events • Insider Attacks / Node Compromise • Node compromise is the central problem of sensor network • An authorized participant in the sensor network • Captured and reprogrammed by the attacker • Running some malicious code • Radio compatible with the sensor nodes

5. Threat and Trust Model • The Base Station as a Point of Trust • Base Station can act as a central trusted authority in protocol design • Much more powerful node with rich computational, memory, and radio resources • Assume that BS is physically protected or has tamper-robust hardware • Scalability is a major concern if use BS as a central trusted authority • BS act as a trusted intermediary to establish pairwise key • BS become a scalability bottleneck • to help set up d × n/2 keys (d : # of neighbors, n : # of nodes) • The nodes neighboring the BS suffer from higher communication overhead

6. Security Requirements • Desired Properties • Authentication • Secrecy • Availability • Service Integrity

7. Desired Properties • Robustness against Outsider Attacks • to protect eavesdropping or packet injection • robust to node failures • Resilience to Insider Attacks, Graceful Degradation with Respect to Node Compromise • mechanisms to deal with compromised nodes are required • mechanisms that are resilient to node compromise • gracefully degrades when a small fraction of nodes compromise • Realistic Levels of Security • security concerns of a sensor network and the level of security desired may differ according to application-specific needs

8. Authentication • To detect maliciously injected or spoofed packets • source authentication : verify the origin of a packet • data authentication : ensure data integrity • Almost all applications require data authentication • military and safety-critical applications • inject false data reports or malicious routing information • other applications, still risk-prone to go without authentication • people can meddle with the sensor network protocols solely out of mischief • Does not solve the problem of compromised nodes • intrusion detection techniques to find the compromised nodes and revoke their cryptographic keys network-wide

9. Secrecy • Ensuring the secrecy of sensed data for protecting from eavesdroppers • using standard encryption functions to protect • Encryption is not sufficient for protecting the privacy of data • Traffic analysis on the overheard ciphertext • Appropriate access control policies at the BS is needed • e.g. person locator application • Node compromise complicates the problem of secrecy • Sensitive data may be released by compromised node • If group shared key is used, it can eavesdrop and decrypt the communication between other nodes within its RF range

10. Availability • Be functional throughout its lifetime • DoS attacks often result in a loss of availability • In a manufacturing monitoring application • may cause failure to detect a potential accident and result in financial loss • In a battlefield surveillance application • may open a back door for enemy invasion. • Various attacks can compromise the availability • important to achieve graceful degradation in the presence of node compromise or benign node failures

11. Service Integrity • Above the networking layer, the sensor network usually implements several application-level services. • Secure data aggregation • to obtain a relatively accurate estimate of the real-world quantity being measured • to detect and reject a reported value that is significantly distorted by corrupted nodes • Time synchronization service • Current protocols assume a trusted environment • An open research problem • how to develop a time synchronization protocol that achieves graceful degradation in the presence of compromised nodes

12. Attacks and Countermeasures • On Secrecy and Authentication • On Availability • Stealthy Attacks against Service Integrity

13. On Secrecy and Authentication • Key Establishment and Management • Key establishment problem : how to set up secret keys between a pair of nodes in the network. • Global key stored on each sensor node prior to deployment • compromise one node : all communication links will be compromised • Public key cryptography • computational cost may be too high • may open up the network to DoS attacks • bogus message to perform signature verification =>Random key predistribution techniques • Further research is necessary to improve scalability, resilience to node compromise, memory requirements, and communication overhead

14. Broadcast/Multicast Authentication • Broadcast and multicast are indispensable for sensor networks • source authentication poses a new research challenge • digital signature • public key cryptography is too costly for sensor networks =>μTesla protocol • provides secure broadcast authentication assuming loose time synchronization between sensor nodes • asymmetry into symmetric key cryptography through delayed key disclosure and one-way function key chains

15. On Availability • Jamming and Packet Injection • Physical layer : interfering RF signals to impede communication • draining the nodes’ battery => frequency hopping & spread spectrum communication • Link-layer : jamming exploits properties of medium access control • malicious collisions or unfair share of the radio resource =>design secure medium access control protocols • error correcting codes, rate limitation, small frames • Networking layer : inject malicious packets =>authentication to enable the receiver to detect malicious packets =>message freshness through nonces to detect replayed packets

16. The Sybil Attack • malicious node illegitimately claims multiple identities • MAC layer : dominating fraction of the shared radio resource • Routing layer : lure network traffic to go through the same physical malicious entity • with high probability a Sybil identity will be selected as the next hop • “sinkhole” is created and selective forwarding by attacker => Leverage the key predistribution process • associate each node’s identity with the keys assigned to it • spoofing identity can succeed only when it has the corresponding keys • otherwise, it either fails to establish a communication link with the network or fails to survive validation

17. Miscellaneous Attacks against Routing • Routing availability is sacrificed if an intended recipient is denied the message • With compromised nodes, a simple attack is to drop packets or perform selective forwarding • Spreading bogus routing information, creating sinkholes or wormholes, and Hello flooding is more sophisticated attacks =>Multipath routing is a possible defense • Use multiple disjoint paths to route a message • unlikely that every path is controlled by compromised nodes

18. Stealthy Attacks against Service Integrity • To make the network accept a false data value • False data value => false aggregation result • Examples of stealthy Attack • corrupted sensor/aggregator • report significantly biased or fictitious values • Sybil attack • one compromised node to have greater impact on the aggregated result • DoS attacks • legitimate nodes cannot report their sensor readings to the base station • Consider time synchronization • Disseminate false timing information to desynchronize nodes => A Secure Information Aggregation (SIA) protocol • Study on stealthy attack in the data aggregation context and proposed SIA robust to the stealthy attack

19. Promising Research Directions • Code Attestation • Secure Misbehavior Detection and Node Revocation • Secure Routing • Secure Localization • Efficient Cryptographic Primitives

20. Code Attestation • Coping with compromised nodes is the most difficult challenge => Use code attestation to validate the code running on each sensor • Detect compromised nodes by verifying their memory content • Hardware : vision of a new trusted computing age • Equipped with trusted hardware (developed by TCG, NGSCB) • Build attestation mechanisms exploiting the trusted hardware • remote party can verify the code running on a device • reduce cost, enhance efficiency, and minimize energy consumption is essential • code attestation through pure software means • So far little research has been done in this aspect • A promising research direction

21. Secure Misbehavior Detection and Node Revocation • Detect and revoke compromised nodes in a timely fashion • Use a distributed voting system to tackle the problem • Potential problems • Malicious nodes can slander legitimate nodes • Cast votes against legitimate nodes • Malicious node can make a legitimate node look bad to other legitimate nodes • Pretend to be a victim to make a legitimate node look bad ☞ Limit each node to m potential votes

22. Secure Routing • Should enable communication despite adversarial activities • So far routing protocols for sensor networks assume a trusted environment • Secure routing protocols for ad hoc networks • Prevents tampering of routing protocol by compromised nodes • Prevents a large number of types of DoS attacks • Utilizes efficient symmetric key primitives • Still be too heavyweight for sensor networks • Sensor networks are differ from an ad hoc network • Usually immobile • Traffic patterns : data-centric =>Secure routing protocol well suited to sensor networks is required

23. Secure Localization • Two aspects of Securing localization problem • Sensor node can accurately determine its geographic coordinates in an adversarial environment • Malicious node cannot claim a false position to the infrastructure • Securing location determination • Prerequisite for secure geographic routing • Help to solve the wormhole attack and the Sybil attack • for Wormhole attack : a route consists of two consecutive nodes that are distant in geographic location is suspicion on the integrity of route • for Sybil attack : a concentration of nodes in a small geographic area is suspicious • an important building block to secure sensor networks

24. Efficient Cryptographic Primitives • Traditional security solutions are often too expensive for sensor networks • SPINS protocol suite • Leveraging efficient block ciphers to perform a variety of cryptographic operations • TinySec: Link layer security for tiny devices • Trading off efficiency and security • More research in this domain is necessary • Especially in exploring the use of efficient asymmetric cryptographic mechanisms for key establishment and digital signatures

25. Conclusion • Sensor networks will play an important role in critical military applications as well as pervade our daily life • However, security concerns constitute a potential stumbling block to the impending wide deployment of sensor networks • Several exciting research challenges remain before we can trust sensor networks to take over important missions