Technology allows criminals to attempt to evade being tracked by changing their mobile phone’s ID code and by regularly dumping their SIM cards.
However, researchers at Dresden University of technology have identified that the radio signal from each mobile phone contains an unalterable digital fingerprint and that this can potentially be used to provide law enforcement with a more simple way of tracking the handset itself.
The method of tracking the mobile phone can identify individual GSM mobile phones and is based upon unique characteristics within the radio signal of the device.
The mobile phone consists of a collection of components including power amplifiers, oscillators and signal mixers and all of which can produce signal inaccuracies. For example, a phone’s resistance can vary from between 0.1 and 20 per cent of its stated value depending upon the quality of the component.
These component fluctuations mean that when analogue signals are converted into digital phone signals the stream of data broadcast by the handset contains error patterns that are unique to that phone’s unique mix of components.
During tests on 13 handsets within their lab, Dresden University were able to identify the handset with 97.6% accuracy from the signal sent by it to the network, however, they state that this is the first step in this type of remote mobile phone forensics and detection.
The method does not alter the device or signal, instead it relies upon passive detection of the signal from a mobile phone and cannot be detected itself. This work was performed on 2G based phones, however, there are believed to be similar unique defects within each handset with 3G and 4G functionality.
The unique method has been welcomed but forensic specialists say that it is demanding, however, could assist in identifying the use of a handset even if different SIM cards are used within it.
Identifying a mobile phone from its radio frequency fingerprint is similar to identifying a digital camera when the image itself does not contain the serial number, imperfections in the camera lens that are detectable within the image can allow for the source device to be identified.
6th August 2013
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