A Technical University of Berlin telecommunications security research group has revealed that it was able to block local cell phones from receiving calls and text messages using a software modification on a GSM phone. As such, this method can be used as a telecommunications hack that prevents a specific network area from properly sending communication on to handsets.
The work was done by a team lead by Jean-Pieree Seifert who say the software modification can be used with any 2G GSM network, with this particular case having been performed using a variety of modified Motorola cell phones. The modification is said to be simple, and involves embedded software on the baseband processor.
With the modification - which is essentially flashing new firmware on the phone - the handset will respond to a cellular network faster than the phone a communication is actually intended for, thereby intercepting the call or text in the place of the phone that was supposed to receive it. In this case, the researchers didn't modify the phones in such a way that they receive the call or messages, however.
This was facilitated by the existence of open source baseband code, which resulted when the baseband code for a Vitelcom handset leaked, allowing the curious to decipher the functioning of what is typically proprietary information. The modified software was flashed to Motorola C1-series handsets, all of which run on a Calypso baseband processor from Texas Instruments.
The modified cell phones then work on the local cellular network in the area, each potentially able to block calls and messages to hundreds of cell phones. Says the researchers, as few as 11 of these modified phones could be used to take down a location area of E-Plus, the third-largest network in Germany. The solution to this problem isn't simple, however - GSM network protocols would need to be changed so that phones prove they're the proper intended recipient of information with the use of encrypted codes.
SOURCE: MIT Technology Review