**4. Conclusion**

This chapter has presented a comprehensive survey of several cryptographic and key management schemes in the current literature on WSNs. Various symmetric key and public key cryptographic approaches for WSNs have been discussed and their relative merits and demerits have been highlighted. The key management protocols were categorized into three broad categories, network topology-based schemes, deterministic key distribution schemes, and probabilistic key distribution schemes. For the network topology-based schemes, the distribution or centralization of the key management task is dependent on the network architecture. In the centralized key distribution schemes, the production, distribution, and revocation of keys are all under the control of one entity under a centralized key management scheme. However, in distributed key management schemes, the tasks of key generation, distribution, and revocation are delegated to a group of nodes in the network. While the distributed key management schemes are more secure and robust, these schemes involve higher overheads of computing, communication, and storage in comparison to their centralized counterparts. In deterministic key distribution schemes, a shared key between any randomly chosen nodes is either present or absent. On the contrary, in the probabilistic key distribution schemes, the availability of a shared key between a pair of nodes is given by probability. Several key distribution schemes of both types, deterministic, and probabilistic have been discussed in this chapter. The schemes have been compared on the types of keys used and the overhead of computation, communication, and memory, the schemes involve. Some open problems for future research directions are also discussed.

*A Survey of Cryptography and Key Management Schemes for Wireless Sensor Networks DOI: http://dx.doi.org/10.5772/intechopen.112277*
