Reducing False Synchronizations in 3G-WLAN Integrated Networks

Authentication in 3G encompasses a mechanism, which ensures that the authentication vectors (AVs) are used only once. To achieve this, the employed mechanism maintains counters at both sides (mobile station and network) and verifies that the provided AVs are among the last α generated. However, there are many cases in which the mobile station receives AVs that have not been previously used, but the employed mechanism rejects them as outdated. This phenomenon, called false synchronization, causes signaling overhead and delays, and increases the cost of the network use. False synchronizations are more frequent in 3G-WLAN integrated networks. The frequency of false synchronizations decreases with α, while at the same time the risk of a replay attack increases. This paper aims at analytically determining an appropriate value of α, which balances effectively in 3G-WLANs the tradeoff between the rate of false synchronizations and exposure to adversaries exploiting compromised AVs. This is done by determining a threshold value of α beyond which the further reduction in false synchronizations is marginal, while the potential for a replay attack is constantly increasing and substantial. To this end, an analytical model based on a four dimensional Markov chain is developed whose accuracy is verified through simulations.