say that the used by the majority of the world’s mobile-phone users can be listened in on with just a few thousand dollars worth of hardware and some free open-source tools.
In a presentation given Sunday at the in Berlin, researcher Karsten Nohl said that he had compiled 2 terabytes worth of data — cracking tables that can be used as a kind of reverse phone-book to determine the encryption key used to secure a GSM (Global System for Mobile communications) telephone conversation or text message.
While Nohl stopped short of releasing a GSM-cracking device — that would be illegal in many countries, including the U.S. — he said he divulged information that has been common knowledge in academic circles and made it “practically useable.”
Intercepting mobile phone calls is illegal in many countries, including the U.S., but GSM-cracking tools are already available to law enforcement. Knoll believes that criminals are probably using them too. “We have just basically copied what you can already buy in a commercial product,” he said.
The flaw lies in the 20-year-oldused by most carriers. It’s a 64-bit cipher called A5/1 and it is simply too weak, according to Nohl. Using his tables, antennas, specialized software, and $30,000 worth of computing hardware to break the cipher, someone can crack the GSM encryption in real time and listen in on calls, he said. If the attacker was willing to wait a few minutes to record and crack the call, the total cost would be just a few thousand dollars, he said.
There are about 3.5 billion GSM phones worldwide, making up about 80 percent of the , according to Post Views: 19