IMSI CATCHING OVER WIFI NETWORKS: EXPOSING WIFI-OFFLOADING Introduction IMSI (International Mobile Subscriber Identity) catchers have been widely known in 3G mobile networks as a malicious device to intercept and eavesdrop mobile traffic and tracking users, considered a type of man-in-the-middle attacks. This type of attack has been aroused in wifi networks as well. Wifi networks that operate over 2G-4G protocols, better known as Wifi-offloading, has been an emerging concept adopted by mobile operators for several years to relieve the congested mobile data networks with additional capacity from the unlicensed Wifi spectrum. Wifi offloading architecture relies heavily on the mobile operator's infrastructure as the users are authenticated via their SIM/(U)SIM cards as the normal defined 3GPP mobile authentication mechanism. The architecture of wifi offloading solutions mainly consists of the wireless access point that the user attaches to and depends on the operator’s core ...