Waraxe IT Security Portal

talianiami · Beginner

1 – GSM
GSM is the world’s largest mobile phone network. It is used by over 2 billion people
across more than 212 countries. GSM was designed in 1982 and became live in 1991.
A typical GSM network contains Base Stations, a Base Station Concentrator, various
databases (MSC, VLR, …), switches and terminals. Various different signal protocols
(including SS7) are used to transfer the information between the key elements of the
network.
The air interface works on 4 main frequency bands. The range of the wireless signal can
exceed 35km.
Today’s Mobile Phones (MS) are incredible powerful signal transceivers. They operate
on two 32-bit CPU’s at over 350 MHz.
2 – Receiving GSM signals
Various Nokia mobile phones have been shipped by accident with maintenance
functionality. These phones can be configured from a normal PC to receive any GSM
data from the broadcast channel. These phones cost between $1-5 USD and are available
on E-bay. Other commercial products like the Sagem trace mobile or Ericsson phones can
be used as well.
The USRP is a software defined radio and can receive and transmit any kind of data
between 0 and 3 GHz. We have developed a software module to receive and decode
GSM signals. The USRP costs $750 USD.
There exists a wide range of commercial testing and interception equipment from
resellers all around the world. Some of these products are tailored for tapping GSM
conversations.
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