Obtaining IMSI by software-defined radio (RTL-SDR)

RTL-SDR is the cheapest and the most widespread software-defined radio devices which has the ability to receive GSM downlink signal. Soldering together clock generators of two such receivers with the help of Multi-RTL utility gives an opportunity to receive uplink traffic too. Obtaining personal data, namely IMSI of the user is carried out by modification of Multi-RTL so that it could work in real time and extraction of location update request and identity response from the traffic.