IMSI Catcher

Radio Signal sniffing and Wireless network hacking is currently gaining popularity. RTL SDR a powerful radio sniffer can be used to capture radio signals to hack the GSM network. A Few cases have been reported in which radio sniffing tools and some specially designed operating systems for radio signal sniffing are being used by malicious hackers to steal sensitive data by capturing SMS and Phone Calls.

GSM Catcher

It is a very easy task to capture ongoing phone calls and SMS using IMSI Catcher. Dragon OS, GR GSM with a few radio signal listening tools like Hack RF or RTL SDR can be used to accomplish the task of capturing GSM Cell Phone traffic.

Now let’s understand the real technique behind hacking GSM Network. Before we dive deeper into this topic, first of all, we need to understand how what is GSM works and how RTL SDR will come in handy while hacking the GSM network traffic.

What is GSM and IMSI?

GSM stands for global system for mobile communication which is used for wireless cellular networks worldwide to facilitate phone calls and SMS services. IMSI is used in GSM services as an Identifier that uniquely identifies users on the GSM or any other mobile network. It stands for international mobile subscriber identity. IMSI is a 15-digit unique number attached to each user using GSM and the universal mobile telecommunication system.

The IMSI number is allotted to each valid user registered in the telecom network and stored in the SIM card of the user. An IMSI number uniquely identifies a user internationally. IMSI includes MCC, MNC, and MSIN which makes it possible to identify the home network of the user and each mobile network service provider in the country.

How Attackers Hack GSM Network?

To protect the identity of GSM subscribers, the phone rarely transmits IMSI numbers to the cell tower. It is transmitted only when a new connection has to be established to receive or send a phone call or message. In the event of a user trying to establish a phone connection with another party, the hacker eavesdrops on the GSM network using network sniffing tools like RTL SDR and captures their IMSI number and other critical information to reveal their identity and location. A Few advanced IMSI catchers can mimic cellular towers and force a GSM phone to expose the user’s IMSI number.

Tools and Software Used by a Hacker to Sniff Sniffing Radio Signal

A lot of tools are available to hack into the cellular network but few are more popular and specialized in hacking GSM and Radio Signal. Dragon OS which comes preinstalled with various GSM Sniffing and IMSI Catcher scripts are widely used by network security specialist to analyze the wireless network as well as hackers to hack the radio signals.

Dragon OS

Dragon OS is a Debian Linux-based operating system that supports multiple Radio sniffing Hardware devices like RTL SDR and Hack-RF.

GR-GSM is another command-line package that consists of a set of tools capable of capturing gsm transmissions. It uses any hardware that works with SDR software to accomplish the task of capturing the signal.

You can use another graphical tool that will help you tune in to the different radio frequencies available around you. I’m talking about SDRSharp, a tool developed by AirSpy for Windows users, which uses RTL SDR to navigate different frequencies band of the electromagnetic spectrum.


AirSpy will help you discover and listen to the full bandwidth of available radio frequencies around you. You may be able to sniff ongoing voice communications over Walkie-Talkie used by Police Officers and industrial workers to communicate over Radio signals. Since our RTL-SDR Devices have a limited capacity that may limit picking every signal but definitely, you should get enough understanding of capturing radio frequencies to eavesdrop on the communication between two unknown parties.

What else can be Hacked Using RTL-SDR and HackRf?

Not only GSM communication but also other services that use the electromagnetic bandwidth to send and receive information can be compromised. Ham Radio, AM, FM, GPS, DTH services, and all other systems can be hacked using RTL-SDR and other powerful SDR Hardware like HackRf. Voice communication between Cabin crew members of the flight with the ground staff can be captured since they too use the radio signals. A Hacker or a network security officer just needs to tune such available SDR hardware sharply to record the communication. Military and detectives use modulation techniques to hide their messages so here we may feel difficult to carve the actual message from the captured signal. However, these secure communications can be captured and decrypted to compromise secure communication between them.

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