The motivation of this chapter is to study the issues related to secure communication among sensor nodes. Sensor nodes are usually of limited computational ability having low CPU power, a small amount of memory, and constrained power availability. Thus the standard cryptographic algorithms suitable for state of the art computers may not be efficiently implemented in sensor nodes. In this regard we study the strategies that can work in constrained environments. First we present a basic introduction to the security issues in distributed wireless sensor networks. As implementation of public key infrastructure may not be recommendable in low end hardware platforms, we describe key predistribution issues in detail. Further we study some specific stream ciphers for encrypted communication that are suitable for implementation in low end hardware.