How To Detect And Find Rogue Cell Towers

Software defined radios are getting better and better all the time. The balaclava-wearing hackers know it, too. From what we saw at HOPE in New York a few weeks ago, we’re just months away from being able to put a femtocell in a desktop computer for under $3,000. In less than a year, evil, bad hackers could be tapping into your cell phone or reading your text message from the comfort of a van parked across the street. You should be scared, even though police departments everywhere and every government agency already has this capability.

These rogue cell sites have various capabilities, from being able to track an individual phone, gather metadata about who you have been calling and for how long, to much more invasive surveillance such as intercepting SMS messages and what websites you’re visiting on your phone. The EFF calls them cell-site simulators, and they’re an incredible violation of privacy. While there was most certinaly several of these devices at DEF CON, I only saw one in a hotel room (you catchin’ what I’m throwin here?).

No matter where the threat comes from, rogue cell towers still exist. Simply knowing they exist isn’t helpful – a proper defence against governments or balaclava wearing hackers requires some sort of detection system.. For the last few months [Eric Escobar] has been working on a simple device that allows anyone to detect when one of these Stingrays or IMSI catchers turns on. With several of these devices connected together, he can even tell where these rogue cell towers are.

A Stingray / cell site simulator detector
A Stingray / cell site simulator detector

Stingrays, IMSI catchers, cell site simulators, and real, legitimate cell towers all broadcast beacons containing information. This information includes the radio channel number, country code, network code, an ID number unique to a large area, and the transmit power. To make detecting rogue cell sites harder, some of this information may change; the transmit power may be reduced if a tech is working on the site, for instance.

To build his rogue-cell-site detector, [Eric] is logging this information to a device consisting of a Raspberry Pi, SIM900 GSM module, an Adafruit GPS module, and a TV-tuner Software Defined Radio dongle. Data received from a cell site is logged to a database along with GPS coordinates. After driving around the neighborhood with his rogue-cell-site detector sitting on his dashboard, [Eric] had a ton of data that included latitude, longitude, received power from a cell tower, and the data from the cell tower. This data was thrown at QGIS, an open source Geographic Information System package, revealing a heatmap with the probable locations of cell towers highlighted in red.

This device really isn’t a tool to detect only rogue cell towers – it finds all cell towers. Differentiating between a rogue and legitimate tower still takes a bit of work. If the heatmap shows a cell site on a fenced-off parcel of land with a big tower, it’s a pretty good bet that cell tower is legit. If, however, the heatmap shows a cell tower showing up on the corner of your street for only a week, that might be cause for alarm.

Future work on this cell site simulator detector will be focused on making it slightly more automatic – three or four of these devices sprinkled around your neighborhood would easily allow you to detect and locate any new cell phone tower. [Eric] might also tackle triangulation of cell sites with an RF-blocking dome with a slit in it revolving around the GSM900 antenna.

TiLDA MKπ, The EMF Camp 2016 Badge

The Scottish Consulate has stamped its last passport, the Dutch fire tower has belched its final flame, and the Gold Members Lounge has followed the Hacienda and the Marquee into clubland oblivion. EMF Camp 2016 is over, so all the 1500 or so attendees have left are the memories, photographs, and festival diarrhoea to remind them of their three days in the Surrey countryside.

Well, not quite all, there is the small matter of the badge.

In the case of EMF 2016 it was called TiLDA MKπ, and since there was a point earlier in the year when it seemed the badge might never see the light of day it represents a significant achievement from the EMF badge team.

The badge features an STM32L486VGT6 ARM Cortex M4 running at 80MHz, a 320×240 pixel colour LCD, magnetometer and accelerometer, and a CC3100 WiFi processor. The firmware provides a simple interface to an app store containing an expanding array of micropython apps from both the EMF Camp team and submitted by event attendees. As shipped the badge connects to one of the site networks, but this can be adjusted to your own network after the event. It’s been designed for ease of hacking, requiring only a USB connection and mounting as a disk drive without need for special software or IDE. A comprehensive array of I/O lines are brought out to both 0.1″ pitch pins and 4mm edge-mounted holes. At the EMF Camp closing speeches there was an announcement of a competition with a range of prizes for the best hardware and software uses for the badge.

shane-tweetThe TiLDA causes a sticky moment for our colleague, Tindie scribe Shane.
The TiLDA causes a sticky moment for our colleague, Tindie scribe Shane.

As is so often the case the badge was not without its teething troubles, as the network coped with so many devices connecting at once and the on-board Neopixel turned out to have been mounted upside down. Our badge seemed to have a bit of trouble maintaining a steady network connection and apps frequently crashed with miscellaneous Python errors, though a succession of firmware updates have resulted in a more stable experience. But these moments are part of the badge experience; this is after all an event whose attendees are likely to have the means to cope with such problems.

All the relevant files and software for the badge are fully open-source, and can be found in the EMF Camp GitHub repositories. We’ve put a set of images of the board in a gallery below if you are curious. The pinout images are courtesy of the EMF badge wiki.

We’ve featured EMF badges before, here’s our look at the EMF 2014 device.