Security in resource-limited environments poses a great challenge as the nodes comprising such a network are severely limited in processing power and storage. Various security protocols have been proposed for sensor networks and RFID that try to mitigate this problem but they provide security on a point-to-point basis which is weak and easily vulnerable to a number of attacks. In this paper, we discuss architecture for a resource limited environment that enables these networks to achieve better security and reliability while being simple and efficient. Based on the architecture we develop non-cryptographic security mechanisms using state machines for providing basic security services including authenticity and confidentiality. We also introduce the concept of Security Fusion where strong system level security properties are synthesized from weak point-to-point security properties. The strengths of these techniques are analysed so as to offer comparisons with conventional techniques.