As we walk around with mobile phones in our pockets, there are multiple radios each with identifiers that can be captured and recorded just through their normal operation. Bluetooth and Wifi devices have MAC addresses and can advertise their presence to other devices merely by sending traffic, or by probing for devices to connect to if they’re not connected.
I found a simple tool, probemon that allows for anyone with a wifi card to track who is at which location at any given time. You could deploy a few of these with Raspberry Pis or even go even cheaper with a number of ESP8266.
In the news recently was a report from TfL about their WiFi data collection. Sky News reported that TfL “plans to make £322m by collecting data from passengers' mobiles”. TfL have later denied this but the fact remains that collecting this data is trivial.
I’ve been thinking about ideas for spoofing mass amounts of wireless devices making the collected data useless. I’ve found that people have had success in using Scapy to forge WiFi frames. When I have some free time I plan to look into some kind of proof-of-concept for this.
On the underground, this is the way to do this, but above ground I’ve also heard of systems that use the TMSI from 3G/4G, not WiFi data, to identify mobile phones. You’ll have to be a bit more brave if you want to forge these (please do not, unless using alternative licensed frequencies, you may interfere with mobile service and prevent 999 calls).
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