ACM Transactions on Computer Systems (TOCS)
Analysis of Key-Exchange Protocols and Their Use for Building Secure Channels
EUROCRYPT '01 Proceedings of the International Conference on the Theory and Application of Cryptographic Techniques: Advances in Cryptology
Universally Composable Notions of Key Exchange and Secure Channels
EUROCRYPT '02 Proceedings of the International Conference on the Theory and Applications of Cryptographic Techniques: Advances in Cryptology
Password Mistyping in Two-Factor-Authenticated Key Exchange
ICALP '08 Proceedings of the 35th international colloquium on Automata, Languages and Programming, Part II
Secure communications over insecure channels based on short authenticated strings
CRYPTO'05 Proceedings of the 25th annual international conference on Advances in Cryptology
Key exchange using passwords and long keys
TCC'06 Proceedings of the Third conference on Theory of Cryptography
Security analysis and enhancements of 3GPP authentication and key agreement protocol
IEEE Transactions on Wireless Communications
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In this work, we consider Authentication and Key Agreement (AKA), a popular client-server Key Exchange (KE) protocol, commonly used in wireless standards (e.g., UMTS), and widely considered for new applications. We discuss natural potential usage scenarios for AKA, attract attention to subtle vulnerabilities, propose a simple and efficient AKA enhancement, and provide its formal proof of security. The vulnerabilities arise due to the fact that AKA is not a secure KE in the standard cryptographic sense, since Client C does not contribute randomness to the session key. We argue that AKA remains secure in current deployments where C is an entity controlled by a single tamper-resistant User Identity Module (UIM). However, we also show that AKA is insecure if several Client's devices/UIMs share his identity and key. We show practical applicability and efficiency benefits of such multi-UIM scenarios. As our main contribution, we adapt AKA for this setting, with only the minimal changes, while adhering to AKA design goals, and preserving its advantages and features. Our protocol involves one extra PRFG evaluation and no extra messages. We formally prove security of the resulting protocol. We discuss how our security improvement allows simplification of some of AKA security heuristics, which may make our protocol more efficient and robust than AKA even for the current deployment scenarios.