## 3 Consumer Products and Active Implantable Medical Devices
### Security and attacks in Consumer Products
For an observed network flow, researchers specifically correlated packet size, inter-packet timing, and packet rate with individual media items - all without knowledge of packet contents. We note that the highly specific purpose of the SlingBox Pro eased the task at hand for two reasons. First, researchers knew apriori the type of traffic they'd be concerned with (e.g. encoded and compressed movies). Secondly, the device's specific purpose ensured that researchers did not need to filter out extraneous traffic (e.g. web downloads) during their sniffing and analysis. Obvious solutions for preventing side channels include padding and attenuating signals. _Padding_ emitted signals with random noise would prevent that signal from being identified; however, issues of energy consumption remain. For example, the aforementioned attack against the SlingBox Pro could have been prevented by padding the VBR compressed media streams with random data. The problem here is that the goal of VBR compression is to reduce bandwidth usage, whereas padding media streams with random data would increase bandwidth usage. _Signal attenuation_ would use metal shielding to prevent wireless signals from crossing physical boundaries. The economics of massive scale attenuation are hard to justify, as it might require wrapping whole buildings in shielding. **Device fingerprinting attacks** occur when side channels are used to _fingerprint_ (or uniquely identify) a wireless device. Such unique identification can be used to track a device even if the device takes proactive steps to ensure its anonymity. By simple measurement of a device's physical layer signal characteristics (such as the signal strength, angle of arrival, and time of arrival), invasive localization techniques might be able to track a wireless device's location without appropriate end-user consent, thereby violating the user's location privacy. Because such device fingerprinting is independent of MAC and IP addresses, malicious user tracking may be possible even if a device takes proactive steps (such as frequently changing its MAC and IP addresses) to ensure its anonymity. Fingerprinting attacks can be mitigated by introduction of random communication delays, use of periodic transmissions, introduction of signal attenuation, and use of randomly varying resistors in transceiver hardware (e.g. to randomly alter that signal's physical layer characteristics) [38, 39]. Other common methods for protecting location privacy in the face of such device fingerprinting attacks are based on the concepts of _mixed zones_ and _anonymous identifiers_[40, 41, 42]. In these methods, neighboring wireless devices sometimes enter a completely _silent_ state wherein nothing is transmitted by any device. This silent state can be entered whenever a specified time period elapses or whenever a device enters a certain geographic area. At the conclusion of the silent state, all wireless devices adopt new identities (e.g. new MAC addresses and IP addresses). Since during the silent period the localization system cannot track mobile devices, it may be hard for a localization system to associate the new device identities and locations with the old (e.g. before the silent period) device identities and locations. In this way, the silent state creates a mixed zone that breaks any attempt by a localization system to continuously track a user's location, and hence protects the location privacy of users. Unfortunately, such methods have severe implications in that they limit the ability of _all_ localization systems to function-even trusted ones. Similarly, the long disruptions on communication introduced by such methods may be unacceptable. Many further attacks are possible on consumer products. These attacks include spoofing, phishing, eavesdropping, and wormholes, all of which are described in detail in subsection 2.4. Some manufacturers have proposed strategies for low cost improvements to consumer device security.