Abstract
Constraint specific wireless sensor networks need energy efficient and secure communication mechanisms. In this paper we propose Lightweight Security protocol (LSec) that fulfils both requirements. LSec provides authentication and authorization of sensor nodes with simple secure key exchange scheme. It also provides confidentiality of data and protection mechanism against intrusions and anomalies. LSec is memory efficient that requires 72 bytes of memory storage for keys. It only introduces 74.125 bytes of transmission and reception cost per connection.