On Energy Efficiency of Elliptic Curve Cryptography for Wireless Sensor Networks

Energy efficiency is a primary concern in Wireless Sensor Networks (WSN). This is due to the fact that WSNs are powered battery, and hence the life of WSNs becomes limited by the battery life. Efforts to replace depleted batteries are not feasible if WSNs are often deployed with thousands of sensor nodes, possibly in inaccessible, hostile, hazardous, or remote territories. Though WSNs are energy-constrained, adequate level of security is often desired in many applications of WSNs that guarantees data integrity and confidentiality. However, security protocols introduce extra energy overhead to a sensor node due to additional processing and communications associated with the protocols. Thus it is important to seek security protocols and solutions for WSNs that are energyefficient but also effective. Security is commonly implemented through symmetric key cryptography which requires a key exchange mechanism to establish a key between the communicating parties. One well known key exchange protocol that has been found to be suitable for WSNs is the Elliptic Curve Diffie-Hellman (ECDH) key exchange protocol. In this work, we determine energy requirements of ECDH for various key sizes in order to aid the selection of a security level for the key exchange protocol while maintaining the best possible energy efficiency for WSNs. Particularly, we study energy requirements of TinyECC software package for the ECDH key exchange protocol used in Imote2 sensor nodes for key sizes of 128 bits, 160 bits, and 192 bits as recommended by NIST (National Institute of Standards and Technology). Our study shows very favorable results for the 160-bit key ECDH exchange algorithm.