In some cases, such as in movie theaters, calls are made on jammer phones. Some places even ban phone calls; So signal jammers can be installed in prisons. They block radio frequencies and prevent residents from using prohibited phones. This "misfortune" is illegal in private hands and is costly, energy-intensive and inefficient. In the wrong hands, they also pose a security risk, as they can hamper emergency calls.
As computer scientists at the Technical University of Berlin have shown, even commercial mobile phones can be converted into jamming stations by changing their software. In doing so, they drew attention to a widespread security breach. The research team, led by Nico Golde of the Institute for Software Technology and Theoretical Computing, replaced the software on the phone and then used it to exploit a vulnerability in the GMS radio standard. The computer scientists presented their findings at the 22nd Usenix Security Symposium in Washington in mid-August.
Optimized open source software runs on modified phones. That's how they trick the radio masts, instead of flooding frequencies in small areas with false signals like gsm jammer. Blocked phones prevent text messages and calls from reaching recipients throughout the area: they pretend to have a false identity and answer questions on behalf of others.
Because even before a phone call is made, radio towers send status messages over hundreds of square kilometers. This process is called paging. "A notification that a call is waiting is sent to all phones in the area," said Nicogold, the lead author of the study. "It contains an identification number. With it, every phone can check if an incoming call is coming from that device."
However, corded phones can answer these questions faster than other cell phones, thus keeping them away from calls and texts. For the transmission mast, the actual recipient appears to have been notified. But he found nothing there. In the best case, only calls are lost and no calls are established. In the worst case, text messages can even be intercepted and read due to encryption cracking and lack of authentication.
So far, computer scientists have only tested their methods against the more than 20-year-old GSM standard, which many modern smartphones also use when necessary. The researchers write that communication between machines and the future Internet of Things is also threatened by this security flaw. Even new UMTS or LTE networks may be vulnerable. "Many GSM protocols have been replicated for them: paging mechanisms exist in the third and fourth generation mobile radio standards," Golde said. "A similar attack is likely to happen here." However, until now, there has been a lack of suitable hardware, especially software.
