Analysis of Authentication and Key Establishment in Inter-generational Mobile Telephony

Second (GSM), third (UMTS), and fourth-generation (LTE) mobile telephony protocols are all in active use, giving rise to a number of interoperation situations. Although the standards address roaming by specifying switching and mapping of established security context, there is not a comprehensive specification of which are the possible interoperation cases. Nor is there comprehensive specification of the procedures to establish security context (authentication and short-term keys) in the various interoperation scenarios. This paper systematically enumerates the cases, classifying them as allowed, disallowed, or uncertain with rationale based on detailed analysis of the specifications. We identify the authentication and key agreement procedure for each of the possible cases. We formally model these scenarios and analyze their security, in the symbolic model, using the tool Prove if. We find two scenarios that inherit a known false base station attack. We find an attack on the CMC message of another scenario.