An IMSI catcher
is an eavesdropping device used for lawful interception of cellular phones and usually is undetectable for users of mobile phones. Such a virtual base transceiver station
(VBTS) is a device for identifying the International Mobile Subscriber Identity
(IMSI) of a nearby GSM mobile phone
its calls. It was patented and first commercialized by Rohde & Schwarz
The GSM specification requires the handset to authenticate to the network, but does not
require the network to authenticate to the handset. This well-known security hole can be exploited by an IMSI catcher.
The IMSI catcher masquerades as a base station
and logs the IMSI numbers of all the mobile stations
in the area, as they attempt to attach to the IMSI-catcher. It allows forcing the mobile phone connected to it to use no call encryption (i.e., it is forced into A5/0 mode), making the call data easy to intercept and convert to audio.
IMSI catchers are used in some countries by law enforcement
and intelligence agencies
, but based upon civil liberty and privacy concerns, their use is illegal in others. Some countries do not even have encrypted phone data traffic (or very weak encryption) rendering an IMSI catcher pointless.
Identifying an IMSI
Every mobile phone has the requirement to optimize the reception. If there is more than one base station of the subscribed network... Read More