## 7 Related Works
The wearable sensor system has two types of sensor, _i.e._, a watch type sensor and a chest belt type sensor. Wearable computers, e.g., PDAs, are used to collect the sensors' data. ZigBee technology is used for communication between the wearable sensors and PDAs. A wireless local area network (LAN) with 802.11b (Wi-Fi) is used for communication between PDAs and healthcare service providers on the Internet. [PERSON] _et al_[98] proposed a strong privacy-preserving scheme against global eavesdropping for eHealth systems known as SAGE. The system achieves content oriented privacy and contextual privacy against a strong global adversary. The content oriented privacy applies if a malevolent user has the capability to disclose a patient's data while data is being transmitted on wireless channels by observing and manipulating it. If not, then content oriented privacy is achieved. The contextual privacy stated that if a malicious user has the ability to link the data source (_i.e._, patient) and the destination (_i.e._, doctor/central server) of a message, then there is a contextual privacy breach. The functions of SAGE include system settings, patient registration, patient health information transmission and patient health information collection. The basic idea of SAGE is that a patient information database (PIDB) receives the personal health information (PHI) from patient's body sensors (e.g., accelerometer, blood pressure, oxygen saturation, and temperature sensors); it broadcasts the PHI to all physicians. Then only the applicable physician has access to the patient's PHI. In this system, all PHI information's are stored in the PIDB at the eHealth center. To achieve access control, only registered patients can store their data and only legal physicians can retrieve patients' data from the PIDB. Authors have proposed elliptic curve cryptography based privacy solution and demonstrate a formal proof for the proposed solution against strong eavesdropping. For more details refer to [98]. [PERSON] _et al._[99] proposed a secure health monitoring (SHM) using medical wireless sensor networks. SHM provides security services such as confidentiality, authenticity, and integrity to the patient data at low computation and communication cost. The proposed scheme has the following components: (a) the ability to detect ECG signals wirelessly within the patient body, (b) low-power and reliable data transmission using Telos-B technology. In SHM, the confidentiality is achieved by PingPong-128 stream cipher cryptography, and authentication and integrity are achieved by PingPong-MAC, _i.e._, message authentication code. Further, the proposed SHM consumes 1.1 KB RAM, 17.4 KB ROM and 19.2 ms CPU computation time. [PERSON] _et al._[100] proposed an adaptive fault-tolerant communication scheme, named as AFTCS, for body sensor networks. AFTCS provide reliable data transmission for critical sensors by reserving channel bandwidth according to the amount of human physiological data, the external environment and the system itself. As we have seen in this section, significant research has been conducted in order to secure healthcare applications using wireless medical sensor networks. It is obvious that extensive security and privacy research is needed in wireless healthcare application, which can fill the security gaps that we have discussed in the above sections.