Multi-Server Authenticated Key Exchange Protocol

Hua Guo, Yi Mu, Xiyong Zhang +1 more

Ting-Chieh Ho, Yuh‐Min Tseng, Sen‐Shan Huang

Saraswathi Shunmuganathan

Yuhao Han, Libin Wang

Transport Layer Security (TLS) protocols are essential for ensuring the confidentiality, integrity, and authentication of data communications. Mutual authentication between client and server is crucial in high-security scenarios such as finance and government. However, existing TLS protocols typically rely on certificate-based public key infrastructures (PKI) for client authentication, which increases deployment complexity and introduces risks associated with third-party trust. In contrast, password-authenticated TLS protocols use memorable passwords for client authentication, offering advantages in simplicity and usability. Nonetheless, such protocols remain vulnerable to server compromise and fail to provide sufficient security against quantum adversaries.To address these challenges, we propose a novel TLS protocol based on asymmetric password-authenticated key exchange (PAKE). The protocol employs an asymmetric PAKE mechanism wherein only password-derived information is stored on the server, while the client derives its private key from the password. This design effectively mitigates the risk of server leakage attacks. The protocol further integrates two types of post-quantum secure key encapsulation mechanisms (KEMs): an OW-ChCCA (One-Way Checkable against Chosen-Ciphertext Attacks) secure KEM for server key exchange and authentication, and an OW-PCA (One-Way Plaintext-Checkable Attacks) secure KEM for binding the client’s password-derived private key to enable client authentication. Both KEMs support multi-user, multi-challenge settings and admit tight, post-quantum secure instantiations.Furthermore, this paper provides a formal security analysis of the proposed protocol within an optimized multi-stage key exchange model. By combining the random oracle and ideal cipher models with a game-based proof methodology, we demonstrate that the protocol achieves mutual authentication and forward secrecy, while also providing tight security bounds and post-quantum resilience. This work thus presents a promising solution for constructing post-quantum password-authenticated TLS protocols.

Ren Ishibashi, Kazuki Yoneyama

Authenticated Key Exchange (AKE) is a cryptographic protocol to share a common session key among multiple parties. At ISC 2021, Liu, Tang, and Zhou proposed a modular multi-factor AKE framework resilient to a characteristic attack called server compromise impersonation based on big data in the bounded-retrieval model and concrete post-quantum big data-based AKE schemes. They also formulated a security model (LTZ model) that captures perfect forward secrecy, key compromise impersonation, and server compromise impersonation. However, the LTZ model does not consider the compromise of ephemeral secret keys, and their schemes rely on the random oracle model. In this paper, we extend the LTZ model (LTZ-eCK model) to capture the compromise of ephemeral secret keys and propose a generic construction of big data-based AKE resilient to both server compromise impersonation and ephemeral key leakage in the standard model. Our generic construction allows us to achieve the post-quantum big data-based AKE scheme (from isogenies, lattice, etc.) in the LTZ-eCK model without random oracles.

Zuowen Tan