A strengthened eCK secure identity based authenticated key agreement protocol based on the standard CDH assumption

An Authenticated Key Agreement (AKA) protocol enables two communicating parties to compute a session key with equal partnership, such that each entity is assured of the authenticity of its peer. Identity-based AKA (ID-AKA) protocols facilitate implicit authentication of the participating entities, without certificate verification. However, most of the existing ID-AKA schemes are proven secure based on the strong Gap Diffie-Hellman (GDH) assumption. Currently, there are no known implementation methods to realize the GDH assumption without using bilinear pairings. Further, none of the existing ID-AKA protocols have provable security against practical attacks due to intermediate result leakages. To this end, we propose a purely pairing-free ID-AKA protocol based on the Computational Diffie-Hellman assumption. The protocol offers provable security under the strengthened eCK (seCK) model that captures attacks resulting from intermediate result leakages. Comparative analysis with other ID-AKA protocols suggests that the proposed protocol satisfies stronger security requirements, without the gap assumption.