Systems and methods for obtaining authentication vectors issued, for use by a mobile communication terminal, by a Home Location Register (HLR) that serves a cellular communication network independently of any cooperation with the cellular network. Further to obtaining the authentication vectors, a terminal is caused to communicate over a WiFi WLAN using an encryption key derived from the obtained authentication vectors, e.g., per the EAP-SIM or EAP-AKA protocol. Since the encryption key is known, communication from the terminal is decrypted. The authentication vectors may be obtained by (i) an “impersonating” Visitor Location Register (VLR) server that does not serve the cellular network; (ii) an interrogation device which, by imitating a legitimate base station serving the cellular network, solicits the mobile communication terminal to associate with the interrogation device; or (iii) an SS7 probe, which obtains authentication vectors communicated from the HLR server to other entities on the SS7 network.