Security is a matter of extensive research interest with widespread deployment of WSN (Wireless Sensor Network) in various real life applications. Unreliable wireless communication, physically insecure locations and resource exhaustion attacks render sensor vulnerable to several security breaches. Sensors are supposed to operate on battery in hostile and unattended environment over a longer span of time. Taking into consideration conflict in interest between security and energy consumption, effective security implementation is non-trivial in WSN. A number of security schemes were presented in literature for ad hoc networks. However, most traditional security solutions like public key cryptography and trusted third party schemes are infeasible in WSN due to resource stringent nature. Probabilistic key management scheme (PKMS) perfectly suites the requirement of WSN due to their low storage, computation and communication overhead over resource stringent nodes. However, most the earlier presented PKMSs are based on Erdos-Renyi (ER) model of random graphs. ER model doesn’t go along well with WSN due to their certain assumptions. In this paper, we present and implement a new PKMS scheme in TinyOS based on kryptograph model. Simulation results illustrate that scheme based on kryptograph model is more secure, memory efficient and connected when compared to scheme based on ER model.