100 lines
5.4 KiB
Markdown
100 lines
5.4 KiB
Markdown
# London Trashcan Spies
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We're not talking about kids hiding out in trashcans talking on
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walkie-talkies and giggling to each other.
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[Ars has reported on London trashcans][0] rigged to collect the [MAC
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addresses][1] of mobile devices that pass by. Since we do not often see
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mobile devices carrying themselves around, we may as well rephrase this as
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"collect the MAC addresses of people that pass by":
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> During a one-week period in June, just 12 cans, or about 10 percent of the
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> company's fleet, tracked more than 4 million devices and allowed company
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> marketers to map the "footfall" of their owners within a 4-minute
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> walking distance to various stores.
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[0]: http://arstechnica.com/security/2013/08/no-this-isnt-a-scene-from-minority-report-this-trash-can-is-stalking-you/
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[1]: http://en.wikipedia.org/wiki/MAC_address
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Your device's---er, *your*---MAC address is a unique identifier that, in
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the case of wireless networks, is used by the networks to state that a
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message is intended specifically for you---something that is necessary since
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wireless devices communicate through open air and, therefore, your device is
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[also able to pick up the communications of other devices][2]:
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> In IEEE 802 networks such as Ethernet, token ring, and IEEE 802.11, and in
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> FDDI, each frame includes a destination Media Access Control address (MAC
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> address). In non-promiscuous mode, when a NIC receives a frame, it
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> normally drops it unless the frame is addressed to that NIC's MAC address
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> or is a broadcast or multicast frame.
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Therefore, in such networks, a MAC address is required for communication. So
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why does your device freely give away such a unique identifier that can be
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used to track you? Consider that, when wireless is enabled (and, as [the Ars
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article][0] mentions, sometimes [even when it's not][3]), your device
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generally scans your surroundings in order to provide you with a list of
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networks to connect to. This list is generally populated when various access
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points broadcast their own information to advertise themselves so that you
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can select them to connect. However, some access points are hidden---they do
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not broadcast their information, which helps to deter unwanted or malicious
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users. To connect to these access points, you generally provide the name
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that the access point administrator has given to it (e.g. "mysecretap").
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Let's say you disconnect from mysecretap. Since the access point (AP) is not
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broadcasting itself, how does your device know when it is available again?
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It must attempt to ping it and see if it gets a response. With this ping is
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your MAC address. Since many devices conveniently like to connect
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automatically to known access points when they become available, it is
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likely that your device is pinging rather frequently.
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But what if you do not use hidden access points? Well, it is likely that the
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same issue still stands---what if the access point that you connected to was
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once listed but then becomes hidden? (Maybe the administrator of the access
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point allowed broadcasts for a period of time to allow people to connect
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easily, but then hid it at a later time.) Your device would need to account
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for that, and therefore, to be helpful, likely broadcasts pings for any
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access point you have connected to recently (where "recently" would depend
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on your device).
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Now, back to the [NSA][5]-wannabe-trashcans: At this point, all an observer
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must do is lay in wait for those broadcasts and record the MAC addresses. By
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placing these devices at various locations, you could easily track the
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movements of individuals, including their speed, destinations, durations of
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their visits, visit frequencies, favorite areas, dwellings, travel patterns,
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etc. Since devices may broadcast a whole slew of recent access points that
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it connected to, you could also see areas that the owner may have been to
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(oh, I see that you connected to the free wifi in that strip joint). You
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[could be evil][6].
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Turn off wireless on your device when you are not using it---especially when
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you are traveling. Ensure that your device [does not continue pinging access
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points when wireless is disabled][3].
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Better yet, fight back. Consider exploring how to spoof your MAC address,
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perhaps randomly generating one every so often. Consider the possibilities
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of activist groups that may pollute these spy databases by gathering a list
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of unique MAC addresses of passerbys for the purpose of rebroadcasting them
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at random intervals---which you could even do using long-range antennas
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targeted at these devices.[^7] If done properly to mimic models of common
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travel patterns, the data that these spy devices gather would become
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unreliable.[^8]
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Surveillance by any entity---be it [governments][5], corporations,
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individuals or otherwise---is not acceptable.
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[2]: http://en.wikipedia.org/wiki/Promiscuous_mode
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[3]: http://arstechnica.com/gadgets/2013/08/review-android-4-3-future-proofs-the-platform-with-multitude-of-minor-changes/3/#p15
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[4]: http://arstechnica.com/security/2013/08/diy-stalker-boxes-spy-on-wi-fi-users-cheaply-and-with-maximum-creep-value/
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[5]: /2013/06/national-uproar-a-comprehensive-overview-of-the-nsa-leaks-and-revelations
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[6]: http://renewlondon.com
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[^7]: Disclaimer: Please research your local laws.
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[^8]: Of course, it is important that such an activity in itself does not
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violate a person's privacy, and so such collection must be done in a manner
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that cannot in itself identify the person's travel patterns (e.g. by
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not storing information on what access point the data was collected from).
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