Published by guardian.co.uk, Irish Times
Photo: Girish Gupta
Karsten Nohl and his team of 24 hackers began working on the security algorithm for GSM (Global System for Mobiles) in August.
Developed in 1988, the system prevents the interception of calls by forcing phones and base stations to change frequencies constantly. Most of the UK's mobile phones use the GSM system and the breach represents a potential threat to the security of mobile phone communication.
Nohl claims that armed with the code, which has been published online, and a laptop with two network cards, an eavesdropper could be recording phone calls within 15 minutes.
"This shows that existing GSM security is inadequate," Nohl told the Chaos Communication Congress, an international annual meeting of hackers taking place in Berlin this week.
Nohl insisted that he had deciphered the code to force the global telecommunications industry to upgrade its security.
Nohl told the Guardian that important negotiations involving politicians or business leaders could easily be intercepted and they should invest in further encryption software to protect their privacy. "If there is anything secret going on using GSM, this should be of concern."
The GSM Association, which represents the interests of the worldwide mobile communications industry, played down the security threat and said Nohl's activity was "highly illegal".
"We consider this research, which appears to be motivated in part by commercial considerations, to be a long way from being a practical attack on GSM," said Claire Cranton, a spokeswoman. "To do this while supposedly being concerned about privacy is beyond me."
Nohl, who has a doctorate in computer engineering from the University of Virginia, insisted his work was purely academic. "We have written advice from our lawyers stating that our research is within the legal realm," he said. "Obviously the data we produce could of course be used for illegitimate purposes."
Simon Bransfield-Garth, the chief executive of London-based encryption software firm Cellcrypt, said: "The code that has been cracked is for the 21-year-old 64-bit A5/1 GSM algorithm. In 2007 the GSM Association developed a 128-bit version, A5/3. However, most network operators have not invested to make the required upgrade.
"We said in August when this project began that the code would be broken within nine to 12 months. This is a very significant step."