Advanced networks are resource constrained and hence any solution proposed must be aware of efficient resource utilization. On the other hand, due to the open unguided wireless medium, newer kinds of security attacks are possible in such networks that are not possible in a traditional wired network infrastructure. To prevent security attacks and threats, secure algorithms must not increase much overhead in terms of computational complexity, bandwidth, memory and energy consumption. Theory of trust and light-weight cryptography will be explored here to encourage the users to propose novel security techniques to ensure equivalent secure system by adding low overheads to the systems. This Chapter deals with all these vital concepts.