The Universal Mobile Telecommunications System (UMTS) represents an evolution in terms of capacity, data speeds and new service capabilities from second generation mobile networks. It also provides more secure wireless access security mechanisms. One of these mechanisms, the authentication and key agreement (AKA) protocol, is designed to help a foreign network to authenticate a roaming mobile user through authentication vectors generated by the authentication center (AuC) in the user’s home network. However, AKA has been criticized due to its introduction of sequence numbers and its vulnerabilities of redirection attacks and active attacks in corrupted networks. Moreover, since only the home network can generate authentication vectors to its subscribers, the AuC actually becomes the traffic bottleneck. This paper proposes an enhanced AKA based on vector combination (VCAKA) to eliminate the above drawbacks. Through vector combination, a size n array of authentication vectors can realize up to 2n??1 times mutual authentication instead of only n times in UMTS AKA. Hence, the traffic
for the home network to generate authentication vectors is exponentially decreased. Also, VC-AKA abandons the employment of sequence numbers and no more re-synchronization procedure needed as in UMTS AKA. Through security analysis and comparison with related work, we show that VC-AKA is more efficient and secure.