Tech-savvy criminals try to evade being tracked by changing
their cellphone's built-in ID code and by regularly dumping SIM cards. But
engineers in Germany have discovered that the radio signal from every cellphone
handset hides within it an unalterable digital fingerprint – potentially giving
law enforcers a simple way of tracking the handset itself.
Developed by Jakob Hasse and colleagues at the Technical
University of Dresden the tracking method exploits the tiny variations in the
quality of the various electronic components inside a phone.
"The radio hardware in a cellphone consists of a
collection of components like power amplifiers, oscillators and signal mixers
that can all introduce radio signal inaccuracies," Hasse says. A phone's
resistance, for instance, can vary between 0.1 and 20 per cent of its stated
value depending on the quality of the component.
The upshot of these errors is that when analogue signals are
converted into digital phone ones, the stream of data each phone broadcasts to
the local mast contains error patterns that are unique to that phone's peculiar
mix of components. In tests on 13 handsets in their lab, the Dresden team were
able to identify the source handset with an accuracy of 97.6 per cent.
"Our method does not send anything to the mobile
phones. It works completely passively and just listens to the ongoing
transmissions of a mobile phone – it cannot be detected," Hasse says.
Their research, funded by the EU and the German government,
was performed on 2G phones. But "defects are present in every radio
device, so it should also be possible to do this with 3G and 4G phones,"
Hasse says.
The novel method is welcome but technically demanding, say
forensics specialists.
"Serious criminals are extremely adept in using
single-use phones and dumping SIM cards so new capabilities like this would
certainly help law enforcement," says Nick Furneaux of forensics security
company CSItech in Bristol, UK.
"Identifying a phone from its radio frequency
fingerprint is certainly not far-fetched. It is similar to identifying a
digital camera where the image metadata does not provide a serial number. From
underlying imperfections in the lens, which are detectable in the image, the
source camera can be identified," Furneaux says.
William Webb, CEO of the UK-based Weightless Special
Interest Group , which is engineering ways to use unused TV frequencies for
broadband transmission, says the method is plausible but boosting the handset
recognition rate to 100 per cent will be the team's overarching challenge.
"If they can't do this it could lead to hundreds of thousands of
mis-tracked calls, privacy invasions and wrongly disconnected mobiles," he
warns.
No comments:
Post a Comment