Quote of the day—Senator Al Franken

Steve Jobs said to the press that ‘we build a database of cell tower hotspots that could be 100 miles away from where you are, those are not telling you anything about your location.’ Yet in a written statement, Apple explained that the very same data would help your iPhone calculate its location. How can those two statements be true at the same time? Does this data indicate anything about your location or doesn’t it?

Senator Al Franken
May 10, 2011
Senators press Apple, Google for answers about location tracking
[I know! I know!

While Apple is a direct competitor to my employer (Microsoft) with this product and it’s not in my best interest to defend them I feel compelled to say that in this particular instance Apple is getting a bum rap. I worked on this same feature in Windows Phone 7 and understand the problem very, very well.

The answer given wasn’t the best and that probably made it difficult for Franken to grasp the concepts. So I’ll try again. Almost for certain this is how it works. The phone obtains a collection of cell tower  locations and unique cell tower IDs in a particular geographical area. This area could be a rectangle that is 100 miles by 100 miles on a side. When the user requests their location the phone obtains the unique ID of the cell tower the phone is connected to. The ID is looked up in the collection of cell towers, just as someone’s name might be looked up in an address book. The location/address of the cell tower is then returned to the user as the best estimate of the user’s location.

As long as the cell tower IDs used for location lookup are not stored then the best that can be done by examination of the files on the phone is to see the different cell towers (and Wi-Fi) collections that were stored. As long as those collections were large (100 miles by 100 miles per collection) then the best that can be deduced is the user was someplace within that collection area. If the collection area is much smaller, say 100 feet by 100 feet (this could happen because Wi-Fi access points have much greater density that cell towers) then it becomes very important to make sure those collections are secure from snooping. If those collections are sometimes for a small geographical area and the files are not made secure then shame on Apple. They were being careless with the users privacy and should be chastised for that carelessness. But at this time I cannot conclude Apple screwed up.

So to answer Franken’s questions, those two statement can be true at the same time. The data does indicate your position within the geographical area of the hotspot locations. But that does not necessarily mean the location is know with the type of accuracy that a stalker would find particular useful–unless just knowing the city or zip code is sufficiently damaging.—Joe]


5 thoughts on “Quote of the day—Senator Al Franken

  1. You explained that really well. I’m sold

    –that’s definitely an issue I’ve seen, though, as a different kind of scientist (I do chemistry)–it’s often difficult for people “in the field” to explain what we do to laymen. Part of the issue is the use of jargon, but that can be overcome somewhat–part of it is that when we use words we often intend them to have a specific meaning that isn’t the most common usage–and I think it’s more that we get so used to thinking about what we do at a certain level & we forget that everyone else isn’t there. Or we take it to the other extreme and oversimplify too much and then people think we’re talking down to them. I struggle with this sort of thing every time I have to teach, especially freshman labs, and it seems to get harder every year.

  2. Cell tower triangulation can assist the cell phone in computing location. A list of cell towers, with their location, gives a smartphone user a “quick start” when using Map based software before the built in GPS receiver has time to acquire four satellites for necessary positioning. This is called “assisted GPS” or A-GPS. But for it to work you either need to to store the cell tower (and or wifi hotspot) location on the phone, or query that data very rapidly. Since it is quicker to store the data on the phone (doesn’t take much memory at all) that is a better option for consumers who want it to work “right now.”

    Google has used Android devices to map out every wifi access point ever accessed by an android device. This is a huge security risk, but it also helps with location triangulation (although I have no evidence that google has used their wifi database for location triangulation).

  3. @PT, of course. The encryption idea probably isn’t worth much though. If the cell phone OS can decrypt it without user intervention then that means the decryption key is stored on the cell phone. If the key can be secured away from “prying eyes” then the files themselves could also be secured. If the key can’t be secured then the encryption accomplished nothing. If the key is supplied by the user then it is a hassle to supply it upon each location request.

    The auto-delete is almost required. I know how WP7 does it (I designed and wrote that code) and I suspect iPhone and Android do something similar. The data becomes almost worthless after a few months because of the constant updating of cell towers and Wi-Fi access points. Also as you travel around the country you could consume a lot of storage space.

    @AM, technically it isn’t “triangulation” it is trilateration since only intersecting circles are used and no angle measurement are involved. But a lot of people call it triangulation anyway–sort of like clips and magazines.

  4. In my head I still call triangulation “intersection and resection”…. https//secure.wikimedia.org/wikipedia/en/wiki/Resection_%28orientation%29#Resection_versus_intersection

    Old habits die hard.

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