IEEE Spectrum has an article on Karsten Nohl’s efforts to lead an open-source GSM hacking project: Open-Source Effort to Hack GSM, IEEE Spectrum, 30 November 2009.
If you’re still using a cellphone based on early digital standards, you better be careful what you say. The encryption technology used to prevent eavesdropping in GSM (Global System for Mobile communications), the world’s most widely used cellphone system, has more security holes than Swiss cheese, according to an expert who plans to poke a big hole of his own.
Karsten Nohl, chief research scientist with H4RDW4RE, a Sunnyvale, Calif.-based security research firm, is mounting what could be the most ambitious attempt yet to compromise the GSM phone system, which is used by over 3 billion people around the world. Others have cracked the A5/1 encryption technology used in GSM before, but their results have remained secret. However, Nohl, who earned a Ph.D. in computer science at the University of Virginia and is a member of Germany’s Chaos Computer Club (CCC), intends to go one big step further: By the end of the year, he plans to make the keys available to everyone on the Internet.
GSM cracking has a long history, which began in the late 1990s in academic circles and has since sprouted a handful of commercial businesses. Today, these companies legally sell GSM call-interception solutions–which are relatively expensive–mostly to government intelligence agencies. In general, supplying and using this software is illegal in the wider market, but no one can say for certain how many groups have illegally gained access to the technology.
That’s the point Nohl hopes to drive home: The A5/1 algorithm is a broken 64-bit encryption technology, a relic of the Cold War era, when laws prohibited the export of strong encryption technology from the United States. It needs to be replaced–ideally by the much stronger, 128-bit A5/3 system, which is already being used in newer-generation digital cellular systems, such as Universal Mobile Telecommunications System (UMTS). “If you go from the 64 bits of the A5/1 cipher to the 128 bits of A5/3,” says Nohl, cracking requires an amount of memory storage that is beyond what “is available on earth.”
A big problem with plugging the GSM encryption hole, according to the security expert, is that operators are unwilling to admit that a problem even exists. Many want to avoid spending additional money on upgrading aging and amortized GSM infrastructure, he says. The GSM Association, which represents the interests of GSM mobile operators around the world, says only that it is aware of various eavesdropping projects. In the same breath, it points to the complexities of identifying and recording calls from RF signals.