## 7 Related Works
The authentication is accomplished through the following steps: certificate generation; exchange of challenges; request of control coordinator (CTSS); base point distribution; confirmation of the reception of base point; and symmetric key generation. For detailed specifications the reader may refer to [90]. The authors proposed and analyzed two key distribution algorithms but they did not simulate or implement them in a real-time environment. [PERSON] _et al._[94] proposed an efficient security scheme for patient monitoring systems using wireless sensor networks. Their scheme uses a public key based infrastructure, and is composed of three main components: patient (PT), healthcare service system (HSS), and secure base stations (SBSs). A pseudo-inverse matrix is used to derive a pair-wise shared key, and a bilateral key handshaking method is used to establish secure communication between HSS and SBS or PT and SBS. Because SBS has prior knowledge of the secret keys of PTs and HSSs, any node PT in the network can establish secure PT-to-SBS communication or _vice versa_. In addition, their scheme provides data confidentiality (_i.e._, encryption and decryption). [PERSON] _et al._[95] proposed a software and hardware based real-time cardiac patient healthcare monitoring system known as tele-cardiology sensor network (TSN). TSN is specially designed for the U.S. healthcare community, and performs real time healthcare data collection for elderly patients in large nursing homes. In TSN, a patient's ECG signals are automatically collected and processed by small ECG sensors and transmitted wirelessly to an ECG server for further analysis. TSN is composed of a large number of wireless ECG communication units; each unit is called a mobile platform. In order to protect the patient privacy, TSN facilitates confidentiality (_i.e._, only source and destination can recognize the medical data, who has knowledge of secret keys), and integrity (_i.e._, no data is altered during the wireless communication). Further, to achieve the energy-efficiency cluster based routing is used. _Intra-cluster security_, skipjack block cipher cryptography algorithm used to protect patient physiological (_i.e._, ECG data), and an _inter-cluster security_ uses pre-distributed session keys. For multiple patients, cluster based routing used to reduce the patient-to-doctor routing overhead, and achieved efficiency. Their security scheme consumes 26 mJ (milli-joules) for data processing, 1,002 mJ for radio communication, and 11 mJ for memory accesses. For more details the reader may refer to [95]. [PERSON] _et al._[96] proposed another real time and secure architecture for health monitoring in smart homes using ZigBee technology. The proposed framework has the following features: (a) the ability to detect signals wirelessly within a body area sensor network (BSN); (b) low-power and reliable data transmission using ZigBee technology; (c) secure transmission of medical data over BSN; (d) efficient channel allocation over wireless networks, and (e) optimized analysis of data using an adaptive framework that maximizes the processing and computational capacity. A secure key management protocol used to establish secure session keys in body sensor networks because it provides cryptographic keys that facilitate security services, e.g., confidentiality, authentication, and data integrity. An authentication algorithm is used between the body sensors and the handheld device of the mobile patient. However, the authors provide security to physiological data, but they did not discuss which symmetric cryptosystem they have used, and did not analyze the energy efficiency for security services. [PERSON] _et al._[97] proposed a wearable context-aware system for ubiquitous healthcare. The proposed context-aware system is composed of wearable sensor systems, wearable computers and communication modules. The wearable sensors are connected to wearable computers via ZigBee communication.