S ecurity I N W IRELESS S ENSOR N ETWORKS Prepared by: Ahmed ezz-eldin

1. Security IN WIRELESS SENSOR NETWORKS Prepared by: Ahmed ezz-eldin

2. Key Management Approaches • "Pairwise key establishment"is the fundamental security service allowing nodes to communicate in cryptographic way • Due to limited resources we can't use any of: -Public-Key-Cryptography -Key-Distribution-Center used in traditional networks. • Instead, we use: Key Pre(before deployment) - schemes

3. Key Pre-distribution Schemes • Symmetric-key schemes: "one key for encryption and decryption" 1-Unique Random key. 2-Networkwide shared key. 3-Probabilistic key pre-distribution. 4-Polynomial based key pre-distribution. • Public-key schemes: "one key for encryption, while the other for decryption" 1-Elliptic Curve Cryptography.

4. Unique Random Key • Each node is assigned unique random key. • To communicate with any node, must use its key. • Introduces huge storage overhead: network of n nodes, each must store (n-1) keys.

5. Networkwide Shared Key • Master/Global key used by all nodes. • Compromise of even a single node would reveal the secret key and allow decryption of all traffic. • One variant is to establish a set of link keys with other neighbor nodes, then erase the master key. • Does not allow new nodes to be deployed.

6. Probabilistic Key Pre-distribution • Setup server generates large pool of random keys each is assigned unique ID. • Each node randomly picks subset of keys from the key pool and their Ids. • Any 2 nodes can communicate with each other if share a common key.

7. After deployment, two nodes need to communicate, send list of key IDs they hold, and use common keys for communication. • The probability of sharing at least one common key is as follows: S : key Pool size. S': Subset size at node. • If don't have a common key .... need to find number of other nodes to help establish a session key ( called path key ).

8. This technique needs less memory and can guarantee a high probability of sharing common key between two nodes. • But small number of compromised nodes will disclose a large fraction of secrets, as single key may be shared by more than two nodes. • For more security, q-composite scheme is proposed, where two nodes setup pairwise key iff they share at least q-common keys.

9. Polynomial key Pre-distribution • The Setup server randomly generates a bivariate t-degree polynomial over finite field Fq, where f(x,y)=f(y,x). • For node with id i, setup server will compute polynomial share of f(x,y)->f(i,y) which is pre-loaded for node i.

10. Nodes i and j, can compute common key f(i,j) as follows: -node i evaluates f(i,y) at point j gets f(i,j). -node j evaluates f(j,y) at point j gets f(j,i). • Each node needs "(t+1)log q" storage places to store polynomial f(i,x). • Large mathematical overhead. • However, no communication overhead, as what is needed is the id of the other node.

11. Elliptic Curve Cryptograhy • ECC is a lightweight type of public key cryptography. • Usually used in heterogeneous sensor networks. • Sensor network contains nodes, gateways and base-station. • Gateways are powerful in terms of energy, computation and memory. • Before deployment, server generates and pre-loads keys based on ECC into senosr and gateways as follows:

12. Sensor node is pre-loaded with: Unique id. Its own public and private keys. Public key of all gateways in the network. • Gateway is pre-loaded with: Unique id. Its own public and private keys. Public key of the base station. public key of all sensor nodes in the network. • Sensor nodes are randomly deployed. • Gateways are deployed such that each node can hear form at least one gateway.

14. Each gateway Gj broadcasts message Bj to all sensor nodes. • Each node selection will be based on Signal-to-Noise-Ratio. • Each sensor node ni can verify the message using the public key of the gateway.

15. Sensor node sends a session-key request to the gateway node, holding list of its neighbors ni'. • Gateway sends the ECC encrypted pairwise key between the node i and its neighbor node I'. • Node i decrypts the message received.

16. Assuming that gateways are tamper proof. • An adversary is unable to impersonate the identity of any node except by capturing it. • Obviously capturing node ni reveals: Its (PUi , PRi ) Pubic key of all gateways Reveals no info of links not communicate directly with it. • Capturing node does not effect the security of the rest nodes, as no reveal for private keys of other nodes.

17. References *"A Key Management Scheme for Cluster Based Wireless Sensor Networks" 2008 IEEE/IFIP International Conference. *"Security in wireless sensor networks" communication of the ACM june 2004/Vol 47. *"Security for wireless sensor networks" Advances in information security springer. *"Analyzing the Key Distribution from Security Attacks in Wireless Sensor" Piya Techateerawat and Andrew Jennings. *"Secure Clustering and symmetric key establishment in heterogeneous wireless sensor newtorks"Research article Reza Azarderskhsh and Arash reyhani. *"Cryptography and Security in Wireless Sensor Networks" Pyrgelis Apostolos, University of Patras. *”Security and Privacy in Sensor Networks” Haowen Chan and Adrian Perrig, Carnegie Mellon University.