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Recently, Chakraborty et al. (Cryptoeprint:2017:441) showed a novel approach of constructing several leakage-resilient cryptographic primitives by introducing a new primitive called leakage-resilient non-interactive key exchange (LR-NIKE). Their construction of LR-NIKE was only in the bounded-memory leakage model, and they left open the construction of LR-NIKE in continuous-memory leakage model. In this paper we address that open problem. Moreover, we extend the continuous-memory leakage model by addressing more realistic after-the-fact leakage. The main ingredients of our construction are a leakage-resilient storage scheme and a refreshing protocol (Dziembowski and Faust, Asiacrypt 2011) and a (standard) chameleon hash function (CHF), equipped with an additional property of oblivious sampling, which we introduce. We observe that the present constructions of CHF already satisfies our new notion. Further, our protocol can be used as a building block to construct leakage-resilient public-key encryption schemes, interactive key exchange and low-latency key exchange protocols in the continuous-memory leakage model, following the approach of Chakraborty et al. (Cryptoeprint:2017:441).

Security models for two-party authenticated key exchange AKE protocols have developed over time to capture the security of AKE protocols even when the adversary learns certain secret values. Increased granularity of security can be modelled by considering partial leakage of secrets in the manner of models for leakage-resilient cryptography, designed to capture side-channel attacks. In this work, we use the strongest known partial-leakage-based security model for key exchange protocols, namely continuous after-the-fact leakage $$\mathrm {eCK}$$$$\mathrm {CAFL\text {-}eCK}$$ model. We resolve an open problem by constructing the first concrete two-pass leakage-resilient key exchange protocol that is secure in the $$\mathrm {CAFL\text {-}eCK}$$ model.

Security models for two-party authenticated key exchange (AKE) protocols have developed over time to provide security even when the adversary learns certain secret keys. In this work, we advance the modelling of AKE protocols by considering more granular, continuous leakage of long-term secrets of protocol participants: the adversary can adaptively request arbitrary leakage of long-term secrets even after the test session is activated, with limits on the amount of leakage per query but no bounds on the total leakage. We present a security model supporting continuous leakage even when the adversary learns certain ephemeral secrets or session keys, and give a generic construction of a two-pass leakage-resilient key exchange protocol that is secure in the model; our protocol achieves continuous, after-the-fact leakage resilience with not much more cost than a previous protocol with only bounded, non-after-the-fact leakage.