A SYSTEM FOR ENSURING ENCRYPTED COMMUNICATION AFTER HANDOVER

A FRAUDULENT INTRUDER CAN EAVESDROP ON A CALL BY REMOVING INFORMATION ABOUT AN ENCRYPTION ALGORITHM WHEN A MULTIMODE MOBILE STATION (100) SENDS (700,800) AN UNPROTECTED INITIAL SIGNALING MESSAGE CONTAINING THIS INFORMATION OVER THE RADIO INTERFACE TO THE MOBILE TELECOMMUNICATIONS SYSTEM. THE ATTEMPT CAN BE PRE-VENTED IN A UNIVERSAL MOBILE TELECOMMUNICATIONS SYSTEM (UMTS) COMPRISING AT LEAST TWO RADIO ACCESS NETWORKS PROVIDING MOBILE STATIONS WITH ACCESS TO AT LEAST ONE CORE NETWORK, A MULTIMODE MOBILE STATION (100), AND AT LEAST ONE CORE NETWORK. DURING CONNECTION SETUP WITH A FIRST RADIO ACCESS NETWORK (101), THE MULTIMODE MOBILE STATION (100) SENDS (700,800) AN UNPROTECTED INITIAL SIGNALING MESSAGE THAT INCLUDES INFORMATION ABOUT THOSE ENCRYPTION ALGORITHMS THAT THE MULTIMODE MOBILE STATION (100) SUPPORTS WHEN IT COMMUNICATES IN A SECOND RADIO ACCESS NETWORK (105).; THE FIRST RADIO ACCESS NETWORK (101) SAVES (701,801,900) SOME OR ALL THE INFORMATION OF IT. THEN IT COMPOSES (601,704,804,904) AND SENDS (704,804) AN INTEGRITY PROTECTED MESSAGE THAT INCLUDES INFORMATION ABOUT THE ENCRYPTION ALGORITHMS SUPPORTED BY THE MULTIMODE MOBILE STATION (100) IN THE SECOND RADIO ACCESS NETWORK (105).