## 1 Introduction
### Problem Statement  
The development of a wireless healthcare application offers many novel challenges, such as, reliable data transmission, node mobility support and fast event detection, timely delivery of data, power management, node computation and middleware [25-32]. Further however, deploying new technologies in healthcare applications without considering security often makes patient privacy vulnerable [8,33-36]. For instance, the patient's physiological vital signals are very _sensitive_ (_i.e._, if a patient has some embarrassing disease), so any leakage of individual disease data could makes him/her embarrassed. In fact sometimes revealing disease information can result in a person losing his/her job,  
Figure 2: Healthcare application using wireless medical sensor networks.  
or make it impossible for him/her to obtain insurance protection [37]. Further, wireless medical sensor networks cover a broad range of healthcare applications, such as physiological data monitoring, and activity monitoring in health-clubs, location tracking for athlete, _etc._ Consequently, WMSNs share individual data with physicians (in a doctor-patient relationship), insurance companies (as insurance protection), and health-coaches (as sports team trainers) or with family (as relatives' support) [38]. Therefore unauthorized collection and use of patient data by potential adversaries (such as insurance agents, for political reasons, rival coaches, personal enemies _etc._) can cause life-threatening risks to the patient, or make the patient's private matters publically available [37]. For example, in a simple scenario, a patient's body sensors transmit his/her body data to a nurse/caregiver; it may happen that an attacker is also eavesdropping the patient data while the data is transmitting, and consequently the patient's privacy is breached. Later that attacker can post the patient data on s social site (FaceBook or Twitter, _etc._), and thus pose risks to the patient's privacy, as depicted the Figure 3. Indeed wireless healthcare can offer many advantages to patient monitoring, but the physiological data of an individual are highly vulnerable, so security and privacy become some of the big concerns for healthcare applications, especially when it comes to adopting wireless technology. More importantly, a healthcare provider is subjected to strict civil and criminal penalties (_i.e._, either fine or imprisonment) if HIPAA rules [39] are not followed properly. Thus a patient security and privacy is the central concern in healthcare applications.  
Moreover, traditional security mechanisms needed unlimited resources, so they cannot be directly applied to the extremely resource-constrained sensor nodes. While WMSNs' security requirements are the same as those of traditional networks, namely availability, confidentiality, integrity, authentication, data freshness and non-repudations, thus resource conscious security protocols have emerged as one of the critical issue in healthcare applications using wireless medical sensor networks. There are other survey studies on security and privacy issues in wireless healthcare applications [8,33-36,40-43]. However, these studies discuss limited information about these security issues, so we can conclude that the topic of security in wireless medical sensor networks has not been properly investigated yet, which provides ample avenues to explore secure wireless healthcare applications.  
Figure 3: Risks to patient privacy.