Abstract
The scope of this survey is to examine and thoroughly evaluate the cluster-based Group Key Agreement (GKA) protocols for Wireless Sensor Networks (WSNs). Towards this goal, we have grouped the WSNs application environments into two major categories (i.e., infrastructure-based and infrastructureless) and have examined: a) which of the cluster-based Group Key Agreement (GKA) protocols that appear in the literature are applicable to each category, and b) to which degree these protocols will impact the systems' performance and energy consumption. In order to answer these questions we have calculated the complexity of each protocol and the energy cost it will add to the system. The evaluation of all discussed protocols is presented in a generalized way and can therefore serve as a reference point for future evaluations and for the design of new, improved GKA protocols.

Abstract
The adoption of Wireless Sensor Networks (WSNs) in the healthcare sector poses many security issues, mainly because medical information is considered particularly sensitive. The security mechanisms employed are expected to be more efficient in terms of energy consumption and scalability in order to cope with the constrained capabilities of WSNs and patients’ mobility. Towards this goal, cluster-based medical WSNs can substantially improve efficiency and scalability. In this context, we have proposed a general framework for cluster-based medical environments on top of which security mechanisms can rely. This framework fully covers the varying needs of both in-hospital environments and environments formed ad hoc for medical emergencies. In this paper, we further elaborate on the security of our proposed solution. We specifically focus on key establishment mechanisms and investigate the group key agreement protocols that can best fit in our framework.

Abstract
Wireless sensor networks are expected to make a significant contribution in the healthcare sector by enabling continuous patient monitoring. Since medical services and the associated to them information are considered particularly sensitive, the employment of wireless sensors in medical environments poses many security issues and challenges. However, security services and the underlying key management mechanisms cannot be seen separately from the efficiency and scalability requirements. Network clustering used in both routing and group key management mechanisms can improve the efficiency and scalability and therefore can also be envisioned in medical environments. This paper introduces a general framework for cluster-based wireless sensor medical environments on the top of which efficient security mechanisms can rely. We describe two different scenarios for infrastructure and infrastructure- less application environments, covering this way a wide area of medical applications (in-hospital and medical emergencies). We also examine the existing group-key management schemes for cluster-based wireless networks and discuss which protocols fit best for each proposed scenario.

Abstract
Research on wireless sensor networks targeting to medical environments has gathered a great attention. In this context, the most recent and perhaps the most promising complete scheme is the CodeBlue hardware and software combined platform, developed in the context of the self-titled Harvard's University project. CodeBlue relies on miniature wearable sensors to monitor real-time patients' vital activities and collecting data for further processing. Apart from the essential query interface for medical monitoring, CodeBlue offers protocols for hardware discovery and multihop routing. This paper contributes to the CodeBlue security, which until now is considered as pending or left out for future work by its designers. We identify and describe several security issues and attack incidents that can be directly applied on CodeBlue compromising its trustworthiness. We also discuss possible solutions for both internal and external attacks and the key-management mechanisms that these solutions presume.

Abstract
This paper evaluates the performance of a hybrid WLAN-3GPP network architecture for delivering subscribers' certificates. Two main categories of simulation scenarios are implemented and evaluated based on the underlying access network technology used; 802.11b and UMTS. Each of the scenarios is categorized further in numerous sub-cases. Results showed that AC acquisition when deployed in large scale between several heterogeneous networks is feasible within acceptable time limits.