And if it is, many of the underlying cryptographic algorithms (like A5/1) can be broken in real time. For one, encryption isn’t always required. IMSI catchers will usually try to force communication over 2G, since the 2G protocol suffers from a number of security holes that make spying easier. Some IMSI catchers even jam the 4G/3G frequencies with white noise to eliminate real cell towers as connection options. Current IMSI catchers overcome this by masquerading as a neighboring tower or by operating at a higher-priority frequency. But in the 4G (LTE) era, phones are designed to maintain a connection with their current cell tower if the signal strength is above a certain threshold and to connect to neighboring cell towers if a connection is lost. Accordingly, an IMSI catcher needed to just broadcast (or appear to broadcast) a much stronger signal than the cell towers around it. In the 2G (GSM) era, this was simple enough, since phones were designed to connect to the tower with the highest signal strength and since base stations were not required to verify their identities to phones. Today, anyone with a software-defined radio (SDR) and a computing device running an open-source base station program (like OpenBTS) can effectively operate an IMSI catcher.Īn IMSI catcher is designed to mimic a real cell tower in order to trick one or more smartphones (or other cellular-enabled devices) within a given area into connecting to it. How IMSI Catchers WorkĪt a basic level, an IMSI catcher – also known as a cell-site simulator, fake cell tower, rogue base station, StingRay or dirtbox, to name a few of its many descriptors – consists of two main parts: a radio frontend for sending and receiving radio waves and a network backend for simulating a cellular core network.
With such low barriers to entry, it’s no longer just the bad guys who need to be worried about these devices.
Once used solely by law enforcement as a way of finding the international mobile subscriber identity (IMSI) linked to a criminal suspect’s SIM card for investigative purposes, now just about anyone can acquire or build an IMSI catcher to intercept a target’s communications. two years earlier, shining light on the prevalence of these types of spying devices. In September 2019, attribution was given to Israel for the IMSI catchers discovered in Washington, D.C.
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