Using an RTL-SDR as a Simple IMSI Catcher

Over on YouTube user Keld Norman has uploaded a video showing how he uses an RTL-SDR with gr-gsm and a Python script to create a simple IMSI catcher. IMSI stands for International mobile subscriber identity and is a unique number that identifies a cell phone SIM card in GSM (2G) mobile phone systems. For security IMSI numbers are usually only transmitted when a connection to a new cell tower is made. More advanced IMSI-catchers used by governmental agencies use a fake cell tower signal to force the IMSI to always be revealed. This way they can track the location of mobile phones as well as other data like who or when you are calling.

In the video Keld uses a Python script called IMSI-Catcher. This script displays the detected IMSI numbers, country, and mobile carrier on a text display. The video description shows how to install GR-GSM and the IMSI-Catcher script on Ubuntu.

IMSI-Catcher Python Script
IMSI-Catcher Python Script
How to make a simple $7 IMSI Catcher

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Most things are made that way so agencies can easy get access. It`s secure for 99.99% ppl but not for them.
Same thing goes for SSL browser encryption, they have some kind of master key + some mathematical hole in header, they give them key for decoding secured transfer in real time. Again, it`s safe for ordinary ppl but not for them. They even force ppl to vote for that in us senat not other TKIP encryption.


I can’t help but wonder what is going to happen at the N.S.A. when it finds out that a twenty dollar dongle is decoding things that they thought were secure ??????????????????? You know how they are when people are having to much fun .

Beer It

Broken by design, comes to mind.

The information just before “Known-plaintext attacks” says it all.

J Austin

Who ever said that the NSA think that GSM is secure? Didn’t you read about the Americans listening to Angela Merkel’s cell phone?


It’s a joke to suggest the NSA ever thought phones were secure.


2G imsi catcher is not required. 2G is a dead technology worldwide.


literally billions of people still use 2g.


2G is dead down under.