A cryptographer has devised a way to monitor cellphone conversations by exploiting security weaknesses in the technology that forms the backbone used by most mobile operators. Karsten Nohl, chief scientist of Berlin-based Security Research Labs, said the attack works because virtually all of the world’s cellular networks deploy insecure implementations of GPRS, or general packet radio service. Some, such as those operated by Italy’s Wind or Telecom Italia, use no encryption at all, while Germany’s T-Mobile, O2 Germany, Vodafone, and E-Plus use crypto that’s so weak that it can easily be read by unauthorized parties.
He plans to release software on Wednesday at the Chaos Communication Camp 2011 that allows hobbyist hackers to snoop on GPRS traffic that uses no encryption. He will also demonstrate ways to use cryptanalysis to decrypt GPRS traffic that’s protected by weaker ciphers.
Nohl characterized most of the cryptographic protection offered by GPRS as “hopelessly out-dated.” For one thing, a lack of mutual authentication allows rogue base stations to harvest data from unsuspecting mobile phone users. And for another, short encryption keys make attacks with rainbow tables feasible.
