What is IMSI :

IMSI is also known as International Mobile Subscriber Identity (IMSI). IMSI is a globally unique number for each subscriber. The IMSI number consists of 15 digits, first 3 digits are Mobile Country Code (MCC), 2 digits are Mobile Network Code (MNC) and the last 10 digits are Mobile Subscriber Identification Number (MSIN). The IMSI number is stored in the Subscriber Identity Module (SIM).

Generations of Mobile Phone :

1G :

1G is a first-generation mobile network that was introduced in 1979. The radio signals used by 1G networks are analog and without encryption (no encryption). Text messaging was not yet possible on 1G networks.

2G :

2G is a second-generation cellular telecommunications network that was launched commercially in 1991 on the GSM standard. 2G networks are radio signals that have been digitized, and the data is encrypted (weak encryption such as a5/1, a5/3, etc.).

The 2G network features are such as data (GPRS, EDGE), SMS, MMS, voice mail, and call forwarding were implemented. Also, Later 2.5G and 2.75G were introduced and both implemented improved techniques for data transfer such as GPRS and EDGE. In general, the Global System for Mobile Communication (GSM) is used for most mobile phone protocols.

3G :

3G is a third-generation mobile network that was introduced in May 2001. 3G networks are radio signals that are digitized and the data is encrypted (strong encryption).

3G network features are internet speed up to 2 Mbps such as increased bandwidth and data transfer rates, Send/receive large email messages, Large capacities, and broadband capabilities.

3G mobile networks support Global Positioning System (GPS), mobile television (LIVE TV), and video conferencing.

4G :

4G is a fourth-generation mobile network that was introduced in 2009. 4G networks have better encryption standards (very strong encryption).

4G network features are internet speed up to 100 Mbps such as Support interactive multimedia, voice, video, wireless internet, and other broadband services. High speed, high-capacity and low-cost per bit. Global mobility, service portability, scalable mobile networks.

5G :

5G is the fifth-generation mobile network that was commercially launched in 2018. 5G network Internet speeds up to 10Gbps and beyond improving speed, 5G is expected to achieve IoT (Internet of Things) in a big way.

Architecture of GSM :

What is an IMSI Catcher :

An IMSI catcher or international mobile subscriber identity-catcher is a telephone eavesdropping device used for intercepting cellular mobile phone traffic and tracking location data of mobile phone users.

IMSI Catcher operates on a fake mobile phone tower between the target mobile phone and the real towers of the service provider, it is considered a man-in-the-middle (MITM) attack.

The 3G or 4g wireless cellular network mutual authentication required from both the handset and the network. However, but may be able to downgrade 3G and LTE to non-LTE network services which do not require mutual authentication Click here!.

Required Hardware and Software :

Hardware :

USB DVB-T key (RTL2832U) with antenna (less than 15$) or HackRF one or USRP.

Software & OS :

GR-GSM or Sigintos.

How to install GR-GSM:

Debian-based distributions (Ubuntu, Kali Rolling Edition etc.) :

sudo apt install python3-numpy python3-scipy python3-scapy

sudo apt-get install -y \
    cmake \
    autoconf \
    libtool \
    pkg-config \
    build-essential \
    python-docutils \
    libcppunit-dev \
    swig \
    doxygen \
    liblog4cpp5-dev \
    gnuradio-dev \
    gr-osmosdr \
    libosmocore-dev \
    liborc-0.4-dev \
    swig

Then download the gr-gsm's source and build it with following commands :

 git clone https://git.osmocom.org/gr-gsm
 cd gr-gsm
 mkdir build
 cd build
 cmake ..
 mkdir $HOME/.grc_gnuradio/ $HOME/.gnuradio/
 make
 sudo make install
 sudo ldconfig
                                

Installation from packages on Debian Testing and Ubuntu 18.04+ :

 sudo apt-get install gr-gsm

How to install Kalibrate :

 sudo apt-get update
 git clone https://github.com/steve-m/kalibrate-rtl
 cd kalibrate-rtl
 ./bootstrap && CXXFLAGS='-W -Wall -O3'
 ./configure
 make
 sudo make install
                                

How to find gsm frequency’s

kal -g 40  -s GSM900

How to install IMSI Catcher :

 sudo apt install python-numpy python-scipy python-scapy
 git clone https://github.com/Oros42/IMSI-catcher.git

Capturing or Intercept of GSM traffic :

 grgsm_livemon

Capturing of GSM traffic :

Capturing and Sniff calls, SMS of GSM traffic :

Detection of IMSI Catcher :

There are different applications available, which help to find the IMSI Catcher in your location. Once it is installed on the mobile, it will automatically detect the IMSI Catcher. Applications contain a database of all the cell towers of mobile carriers in different countries and regularly update this list.

● Android IMSI-Catcher Detector.

● SnoopSnitch.

● Cell Spy Catcher.

● GSM Spy Finder.

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