## 3 Security and Privacy Issues
### Security Threats
[PERSON] _et al._[64] have used geo-positioning to locate the patient and caregiver in their project called SMART (Scalable Medical Alert Response Technology). As the authors support localization system for the patients and medical staff, if an adversary constantly receives the persons' radio signals and analyze them, then he/she gains details of those persons' locations, which could directly infringe a person's privacy. Activity Tracking Threats  
An adversary can obtain someone's health status while he/she is busy exercising in a health-club. Based on a sensor's captured data a malevolent user can guess the current activity of a patient and he may send the wrong exercise tips to the patient that could cause them severe pain. Considering another example, an athlete is being monitored using a wireless sensor network while he/she is practicing in the club [65]. Medical sensors are placed on the athlete's body, which sense health data, e.g., heart-rate, time and location, and send health feed back to the base station [10], so it might be possible for an adversary to modify the athlete's health data, which may bring the athlete under suspicion in doping tests that could even spoil the athlete's career. Denial-of-Service (DoS) Threats  
In [66] [PERSON] stated that \"a denial-of-service attack is any event that diminishes or eliminates a network's capacity to perform its expected function.\" Denial-of-service threat could be even more disruptive in healthcare applications because such a network needs always-on patient health monitoring (_i.e._, in-home, in-hospital, ambulatory _etc._). As DoS threats are harmful to every application, we have directly adopted DoS from [66]. A list of denial-of-service attacks is shown in Table 2. \begin{table}
\begin{tabular}{l l} \hline \hline
**Layers** & **Attacks** \\ \hline
**Physical layer** & Jamming, Node tampering \\
**Link layer/medium access control** & Collision, exhaustion, and unfairness \\
**Network and routing layer** & Neglect and greed, homing, misdirection, spoofing, \\
**Transport layer** & Folding and De-synchronization \\
**Application layer** & Overwhelming sensors, reprogramming attack \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Denial-of-service attacks at each network layers. * Physical layer: Jamming and tampering are the most common attacks on the physical layer. In jamming, generally, an attacker can squeeze the communication using high radio frequency (RF) signals, which disturb the network functionality. For example, medical sensor networks are small networks that squeeze early. Tampering is also known as a type of physical attack. A malevolent user steals the medical sensor and electronically interrogates it to extract the patient information from the sensor more. * Link/medium access control layer: This layer suffers mainly from collision, exhaustion, and unfairness attacks. In collision attacks, an adversary simultaneously transmits the packets at same frequency, resulting in packet collision and degradation of the network performance. In exhaustion attacks the battery source is self-sacrificing, since wireless nodes most of the time maintains the channel active. In unfairness attacks, network performance degrades because medium access control layer priority is generally disrupted according to the application requirements. * The network and routing layer: Routing-disturbance attacks lead to DoS threats in multi-hop medical sensor environments. Generally, the routing attacks involve spoofing; altering routing paths or replaying packets; selective forwarding; sinkhole; warm-hole, _etc_. * Transport layer: It controls end-to-end links, and suffers mainly from two popular types of attacks, namely, flooding attacks and de-synchronization attacks. Flooding attacks generally are used to drain the memory resources by sending the control signals. In de-synchronized attack, attacker may disturbs the established link between two legitimate two ends nodes (_i.e._, body sensor and base station) by re-synchronizing their transmission.