Convenient signal blockers are devices that interrupt the connection between cell phones and active transmission towers, and are highly illegal. They are only used in prisons in Germany, for example, to avoid calls from smuggled cell phones.
Fortunately, anyone who fights against mobile phone users has bad cards: misery is expensive, hard to find and remarkable. In addition, due to their high transmission power, they can be attacked with relative ease, such as illegal amplifiers used by CB radio operators, the so-called burners.
But this effort is not entirely necessary, as demonstrated by the IT specialists of TU Berlin during the Usenix conference: in theory, eleven mobile phones and some open source software are enough to paralyze the entire network by a smaller operator of Mobile telephony in a big city like Berlin. Here is the conference summary.
The software is an open source baseband. The baseband is essentially the modem firmware installed in each mobile phone and smartphone and manages basic communications with the portable blocking network.
When a call arrives, the network operator begins a transmission, known as paging: all transmission towers near the possible receiver send a message that is received by all registered mobile phones. The message: "I have a call", complemented by a clear identification of the destination. If this message reaches the correct mobile phone, answer "here, here". The call is forwarded to the appropriate cell phone and reaches the recipient's cell phone.
The trick used by computer scientists: the manipulated baseband simply responds to each incoming call with the "I am here" signal, regardless of the actual recipient, and faster than the actual recipient. This means that calls cannot be found. The same goes for SMS messages. Theoretically, text messages could even be intercepted and read due to decrypted encryption of the GPS blocking standard. Particularly treacherous: in this way, criminals can also access mTAN for online banking.
By the way, this attack only works reliably in the GPS standard. The same trick could theoretically work for UMTS and LTE networks, but until now no hardware or software is required for a test.
With the continuous update of the blocker, it is more appropriate for people to solve several problems, so everyone must also pay attention to this data, so that many problems of life and work can be solved perfectly.