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Continuous After-the-fact Leakage-Resilient Key Exchange (full version)

Janaka Alawatugoda, Colin Boyd, Douglas Stebila

Published Jan 1, 2014• 2 citations
OpenAlex

Abstract

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.

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Modelling After-the-fact Leakage for Key Exchange (full version)

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Security models for two-party authenticated key exchange (AKE) protocols have developed over time to prove the security of AKE protocols even when the adversary learns certain secret values. In this work, we address more granular leakage: partial leakage of long-term secrets of protocol principals, even after the session key is established. We introduce a generic key exchange security model, which can be instantiated allowing bounded or continuous leakage, even when the adversary learns certain ephemeral secrets or session keys. Our model is the strongest known partial-leakage-based security model for key exchange protocols. We propose a generic construction of a two-pass leakage-resilient key exchange protocol that is secure in the proposed model, by introducing a new concept: the leakage-resilient NAXOS trick. We identify a special property for public-key cryptosystems: pair generation indistinguishability, and show how to obtain the leakage-resilient NAXOS trick from a pair generation indistinguishable leakage-resilient public-key cryptosystem.

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Identity-based authenticated key exchange (ID-AKE) protocol is an important cryptographic primitive, which is used to establish a session key between two communication participants while authenticating each other. Indeed, most of the existing ID-AKE protocols do not concern with side-channel attacks in the sense that adversaries could obtain partial information of ephemeral/permanent secret keys of users. Recently, several leakage-resilient ID-AKE (LR-ID-AKE) protocols have been proposed to address such attacks. However, these LR-ID-AKE protocols have a restriction that the total leakage information during the life time of the LR-ID-AKE protocol must be bounded to some ratio of ephemeral/permanent secret keys. In this paper, the authors define a new adversary model, termed as identity-based continuous-leakage extended Canetti-Krawczyk (ID-CL-eCK) model. Using the key refreshing procedure (i.e., the multiplicative blinding technique) of permanent secret keys, the first LR-ID-AKE protocol resilient to continuous key leakage is proposed, and it possesses overall unbounded leakage property. Comparisons are given to demonstrate that the proposed protocol is better than the previously proposed ID-AKE protocols in terms of security models and leakage properties. Under the generic bilinear group model, security analysis is made to show that the proposed LR-ID-AKE protocol is secure against adversaries in the new ID-CL-eCK model.

IEEE Systems Journal•Feb 18, 2019•30 citations
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.
Security models for two-party authenticated key exchange (AKE) protocols have developed over time to prove the security of AKE protocols even when the adversary learns certain secret values. In this work, we address more granular leakage: partial leakage of long-term secrets of protocol principals, even after the session key is established. We introduce a generic key exchange security model, which can be instantiated allowing bounded or continuous leakage, even when the adversary learns certain ephemeral secrets or session keys. Our model is the strongest known partial-leakage-based security model for key exchange protocols. We propose a generic construction of a two-pass leakage-resilient key exchange protocol that is secure in the proposed model, by introducing a new concept: the leakage-resilient NAXOS trick. We identify a special property for public-key cryptosystems: pair generation indistinguishability, and show how to obtain the leakage-resilient NAXOS trick from a pair generation indistinguishable leakage-resilient public-key cryptosystem.
Recently, the Continuous After-the-Fact Leakage (CAFL) security model has been introduced for two-party authenticated key exchange (AKE) protocols. In the CAFL model, an adversary can adaptively request arbitrary leakage of long-term secrets even after the test session is activated. It supports continuous leakage even when the adversary learns certain ephemeral secrets or session keys. The amount of leakage is limited per query, but there is no bound on the total leakage. A generic leakage-resilient key exchange protocol π has also been introduced that is formally proved to be secure in the CAFL model. In this paper, we comment on the CAFL model, and show that it does not capture its claimed security. We also present an attack and counterproofs for the security of protocol π which invalidates the formal security proofs of protocol π in the CAFL model.
Security models for two-party authenticated key exchange (AKE) protocols have developed over time to prove the security of AKE protocols even when the adversary learns certain secret values. In this work, we address more granular leakage: partial leakage of long-term secrets of protocol principals, even after the session key is established. We introduce a generic key exchange security model, which can be instantiated allowing bounded or continuous leakage, even when the adversary learns certain ephemeral secrets or session keys. Our model is the strongest known partial-leakage-based security model for key exchange protocols. We propose a generic construction of a two-pass leakage-resilient key exchange protocol that is secure in the proposed model, by introducing a new concept: the leakage-resilient NAXOS trick. We identify a special property for public-key cryptosystems: pair generation indistinguishability, and show how to obtain the leakage-resilient NAXOS trick from a pair generation indistinguishable leakage-resilient public-key cryptosystem.
Abstract Typically, secure channels are constructed from an authenticated key exchange (AKE) protocol, which authenticates the communicating parties based on long-term public keys and establishes secret session keys. In this paper we address the partial leakage of long-term secret keys of key exchange protocol participants due to various side-channel attacks. Security models for two-party authenticated key exchange protocols have been developed over time to provide security even when the adversary learns certain secret values. This paper combines and extends the advances of security modelling for AKE protocols addressing more granular partial leakage of long-term secrets of protocol participants. Further, we fix some flaws in security proofs of previous leakage-resilient key exchange protocols.
Typically, secure channels are constructed from an authenticated key exchange (AKE) protocol, which authenticates the communicating parties based on long-term public keys and establishes secret session keys. In this paper we address the partial leakage of long-term secret keys of key exchange protocol participants due to various side-channel attacks. Security models for two-party authenticated key exchange protocols have developed over time to provide security even when the adversary learns certain secret values. This paper combines and extends the advances of security modelling for AKE protocols addressing more granular partial leakage of long-term secrets of protocol participants.
Identity-based authenticated key exchange (ID-AKE) protocol is an important cryptographic primitive, which is used to establish a session key between two communication participants while authenticating each other. Indeed, most of the existing ID-AKE protocols do not concern with side-channel attacks in the sense that adversaries could obtain partial information of ephemeral/permanent secret keys of users. Recently, several leakage-resilient ID-AKE (LR-ID-AKE) protocols have been proposed to address such attacks. However, these LR-ID-AKE protocols have a restriction that the total leakage information during the life time of the LR-ID-AKE protocol must be bounded to some ratio of ephemeral/permanent secret keys. In this paper, the authors define a new adversary model, termed as identity-based continuous-leakage extended Canetti-Krawczyk (ID-CL-eCK) model. Using the key refreshing procedure (i.e., the multiplicative blinding technique) of permanent secret keys, the first LR-ID-AKE protocol resilient to continuous key leakage is proposed, and it possesses overall unbounded leakage property. Comparisons are given to demonstrate that the proposed protocol is better than the previously proposed ID-AKE protocols in terms of security models and leakage properties. Under the generic bilinear group model, security analysis is made to show that the proposed LR-ID-AKE protocol is secure against adversaries in the new ID-CL-eCK model.