The GSM phone network is based on technology which is over 20 years old. As a result it is now possible to eavesdrop phone calls using four $15 Motorola handsets, a medium-end computer and a 2TB hard drive.
Karsten Nohl and Sylvain Munaut gave a live demonstration of this new hack last week at the 27th annual Chaos Communication Congress in Berlin. The whole process takes about 20 seconds, enabling phone conversations and SMS messages to be recorded and decrypted.
This new GSM attack is based on research that was revealed at the 2009 Berlin conference where, with $4000 of equipment, phone calls could be intercepted and recorded. Previously to that, commercially available equipment capable of eavesdropping on other people’s phone calls would have cost more than $50,000.
The problem lies with the GSM encryption algorithm A5/1 which is now decades-old and has known weaknesses. By using a 2TB rainbow table the encryption can be easily broken.
The hack uses ‘silent’ or ‘broken’ SMS messages that do not show up on the phone to gather information about the phones location and other unique numbers needed to employ the hack.