Privacy zones are an important concept in the OpenBikeSensor ecosystem. They are used in the sensor device itself, but also on the Data Portal, to mask your location in certain areas.
This is a crucial privacy feature. Since uploaded data may become published in the Open Data repository, users may (or actually should) choose to configure these privacy zones to protect their privacy. A bad actor might otherwise be able to find out from the data where they live, work, or frequently hang out.
NoteThe Data Portal does not yet support privacy zones. But we’re working on it, and the way it is described here matches what will be possible.
How privacy zones work
A privacy zone can be configured in the sensor device itself, changing its recording activity, and in the Data Portal, which then uses it to filter data before publishing. Depending on how you use your sensor and what your level of concern is, you might choose either or both of these options.
A privacy zone is a circular area, defined by a center point and the radius, around which data is masked. You should set up multiple of these zones at relevant locations, so that bad actors cannot identify where your tracks start and end:
- Your home
- Your workplace
- Your friends’ homes
- Anywhere you frequently ride your bike or regularily hang out
There are 4 modes of operation for the OpenBikeSensor:
Which one to choose
The settings inside the OBS are applied as it records the data. So anything not recorded due to a privacy zone and the privacy setting will never be available to anyone, not even you, when you take out the SD card from the sensor and transfer the files to your computer.
If you want to have your own data, but not publish them, consider putting the privacy zones into the Data Portal instead. While this means you have to trust the Data Portal software to do its job properly (and nobody will guarantee that it does, but we promise to try our hardest), it allows you to download the unmasked data from the portal yourself.
A third option is to never upload the data from your OBS directly, but instead move the track files to your computer and use a script to privatize the data before you upload it from there to the Data Portal.
The safest option of course is to never upload your data at all. But then, what are we building a sensor for?
One more difference between configuring the privacy zones in the OpenBikeSensor versus the Data Portal is that the sensor does not retroactively apply the privacy settings. So if you forget a location, or did not choose the right recording mode before you went for a ride, the data is already stored in the track. The Data Portal however reapplies your privacy zones whenever you change them, to all your past (and future) tracks. Though you have to remember that once your data is published into the Open Data repository, anybody might have downloaded a copy already, and you will never be able to take that back. You should always review your settings before you publish!
Why we shift privacy zones
If you publish multiple tracks with anonymized data, anybody will be able to reconstruct the privacy zone from the published data. The tracks going from and to the private place inside the privacy zone will be cut off at the boundary of the zone. If you ride your bike into different directions, away from your private point, it is possible to mathematically redefine the circle that you used to cut off the tracks.
Therefore, it’s not advisable to put your privacy’s center point right on the location you don’t want others to know. In the OpenBikeSensor, you have the option to manually shift your privacy zone into a random direction. You should only do this once for each zone. You can also use any external map tool and manually find center coordinates for your privacy zone that seem reasonable to you, but are not exactly your private location.
In the Data Portal you can place the circle manually on map, in a way that it contains your private locations. Or you provide the actual private location and let the app choose a random offset. Both ways allow you to visually review your shifted zone before saving.
By the way, for the same reason as above, you should not change the offset of your privacy zones too often. Otherwise, it’s possible to reconstruct many circles from the data, all of which will contain your private location. This would defeat the purpose of shifting the privacy zone in the first place, as it reduces the size of the area that probably contains your private location. Kind of counter-intuitively, it reduces security instead of adding to it!