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+Title: Visualizing GSM radio chatter using gr-gsm and Hopglass
+Tags: english, debian, personvern, surveillance
+Date: 2017-09-29 10:20
+
+<p>Every mobile phone announce its existence over radio to the nearby
+mobile cell towers.  And this radio chatter is available for anyone
+with a radio receiver capable of receiving them.  Details about the
+mobile phones with very good accuracy is of course collected by the
+phone companies, but this is not the topic of this blog post.  The
+mobile phone radio chatter make it possible to figure out when a cell
+phone is nearby, as it include the SIM card ID (IMSI).  By paying
+attention over time, one can see when a phone arrive and when it leave
+an area.  I believe it would be nice to make this information more
+available to the general public, to make more people aware of how
+their phones are announcing their whereabouts to anyone that care to
+listen.</p>
+
+<p>I am very happy to report that we managed to get something
+visualizing this information up and running for
+<a href="http://norwaymakers.org/osf17">Oslo Skaperfestival 2017</a>
+(Oslo Makers Festival) taking place today and tomorrow at Deichmanske
+library.  The solution is based on the
+<a href="http://people.skolelinux.org/pere/blog/Easier_recipe_to_observe_the_cell_phones_around_you.html">simple
+recipe for listening to GSM chatter</a> I posted a few days ago, and
+will show up at the stand of <a href="http://sonen.ifi.uio.no/">Åpen
+Sone from the Computer Science department of the University of
+Oslo</a>.  The presentation will show the nearby mobile phones (aka
+IMSIs) as dots in a web browser graph, with lines to the dot
+representing mobile base station it is talking to. It was working in
+the lab yesterday, and was moved into place this morning.</p>
+
+<p>We set up a fairly powerful desktop machine using Debian
+Buster/Testing with several (five, I believe) RTL2838 DVB-T receivers
+connected and visualize the visible cell phone towers using an
+<a href="https://github.com/marlow925/hopglass">English version of
+Hopglass</a>.  A fairly powerfull machine is needed as the
+grgsm_livemon_headless processes converting the radio signal to data
+packages is quite CPU intensive.</p>
+                                       
+<p>The frequencies to listen to are identified using a slightly
+patched scan-and-livemon (to set the --args values for each receiver),
+and the Hopglass data is generated using the
+<a href="https://github.com/petterreinholdtsen/IMSI-catcher/tree/meshviewer-output">patches
+in my meshviewer-output branch</a>.  For some reason we could not get
+more than four SDRs working.  There is also a geographical map trying
+to show the location of the base stations, but I believe their
+coordinates are hardcoded to some random location in Germany, I
+believe.  The code should be replaced with code to look up location in
+a text file, a sqlite database or one of the online databases
+mentioned in
+<a href="https://github.com/Oros42/IMSI-catcher/issues/14">the github
+issue for the topic</a>.
+
+<p>If this sound interesting, visit the stand at the festival!</p>