## 6 Security and Privacy Requirements of Healthcare Applications  
Based on the above application scenarios, security issues and regulatory laws, this section points out the paramount security and privacy requirements for healthcare applications using wireless medical sensor networks, as follows:  
1. Data confidentiality: Patient health data are generally held under the legal and ethical obligations of confidentiality. These health data should be confidential and available only to the authorized doctors or other caregivers. Thus, it is important to keep the individual health information confidential, so that an adversary cannot eavesdrop on the patient's information. Data eavesdropping may cause damage to the patient because the adversary can use the patient's data for many illegal purposes and hence, the patient's privacy is breached. Therefore, data confidentiality is an important requirement in healthcare applications using WMSNs. 2. Data authentication: Authentication services provide authorization, which is necessary for both medical and non-medical applications. In WMSN healthcare applications, authentication is a must for every medical sensor and the base-station to verify that the data were sent by a trusted sensor or not. 3. Strong user authentication: The major problem in a wireless healthcare environment is vulnerability of wireless messages to an unauthorized user, so it is highly desirable that strong user authentication should be considered, whereby each user must prove their authenticity before accessing any patient physiological information. Furthermore, strong user authentication, also known as two-factor authentication, provides greater security for healthcare applications using wireless medical sensor networks [78]. 4. Data integrity: Data integrity services guarantee at the recipient end that the data has not been altered in transit by an adversary. Due to the broadcast nature of the sensor network, the patient's information could be altered by an adversary; this could be very dangerous in the case of life-critical events. To verify the data integrity, one must have the ability to identify any data manipulation done by illegal parties. Thus, proper data integrity mechanisms ensure that the received data has not been altered by an adversary. 5. Key distribution: If two parties exchange information, they must share a session key and that key must be protected from others. A secure session key helps secure subsequent communication and safeguards data against various security attacks. Thus in order to preserve the patient's privacy, an efficient key distribution scheme is a major requirement in wireless healthcare applications [90]. 6. Access control: In healthcare application many users (such as doctors, nurses, pharmacists, insurance companies, lab staff, social workers, _etc._) are always directly involved with the patient's physiological data, so it is highly desirable that a role-based access control mechanism should be implemented in real-time healthcare applications that can restrict the access of the physiological information, as user's roles. For example, the HL7 Standard Development Organization uses a role-based access control model [91]. * Data availability: Availability ensures that services and information can be accessed at the time when they are required. Thus, medical sensor node availability ensures that the patient's data are constantly available to the caregiver. If a sensor node is captured by an adversary, then its data availability will be lost, thus it is required to maintain always-on the operation of the healthcare applications in the case of loss of availability. * Data freshness: In healthcare applications, data confidentiality and integrity are not enough if data freshness is not considered. Data freshness implies that the patient physiological signs are fresh or resent; and thus an adversary has not replayed the old messages.