Abstract: The logic ruling the user and network authentication as well as the data ciphering in the GSM architecture has been inherited by the General Packet Radio Services (GPRS) and the Universal Mobile Telecommunication System (UMTS) as well. So, in all these systems, three nodes are involved in the corresponding processes; namely, the Mobile Station (MS), the Visitors Location Register (VLR), and the Home Location Register (HLR). Moreover, the methods of the conventional cryptography have been adopted by all the three systems. In this paper a description of the subscriber authentication is given, as well as of the data ciphering, as they are recommended by the Specifications regarding the aforementioned systems. Based on this analysis, we pinpoint the vulnerable points of the VLR-HLR and MS-VLR links, exposed to third party attacks, and we propose for their coverage asymmetric cryptography procedures, consisting of the transactions between the VLR-HLR, as well as the MS-VLR.