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International Journal of Applied Cryptography

Session-StateReveal is stronger than eCKs EphemeralKeyReveal: using automatic analysis to attack the NAXOS protocol

Cas J. F. Cremers

Published Jan 1, 2010• 8 citations
Publisher

Abstract

In the paper, 'stronger security of authenticated key exchange' (LaMacchia et al., 2006, 2007), a new security model for authenticated key exchange protocols (eCK) is proposed. The new model is suggested to be at least as strong as previous models for key exchange protocols, such as the CK model (Canetti and Krawczyk, 2001; Krawczyk, 2005). The model includes a new notion of an EphemeralKeyReveal adversary query, which is claimed in e.g., LaMacchia et al. (2006), Okamoto (2007), and Ustaoglu (2008), to be at least as strong as the Session-StateReveal query. We investigate the relation between the two models by focusing on the difference in adversary queries. We formally model the NAXOS protocol and a variant of the eCK model, called eCK', in which the EphemeralKeyReveal query is replaced by the Session-StateReveal query. Using Scyther, a formal protocol analysis tool, we automatically find attacks on the protocol, showing that the protocol is insecure in the eCK' model. Our attacks prove that the Session-StateReveal query is stronger than the EphemeralKeyReveal query and that the eCK security model is incomparable to the CK model, disproving several claims made in the literature.

DOI
10.1504/ijact.2010.038304

Related papers

Session-state Reveal is stronger than Ephemeral Key Reveal: Attacking the NAXOS Authenticated Key Exchange protocol.

Cas J. F. Cremers

Abstract. In the paper “Stronger Security of Authenticated Key Ex-change ” [1,2], a new security model for authenticated key exchange pro-tocols (eCK) is proposed. The new model is suggested to be at least as strong as previous models for key exchange protocols. The model in-cludes a new notion of an Ephemeral Key Reveal adversary query, which is claimed in e. g. [2–4] to be at least as strong as the Session-state Reveal query. We show that Session-state Reveal is stronger than Ephemeral Key Reveal, implying that the eCK security model is incomparable to the CK model [5, 6]. In particular we show that the proposed NAXOS protocol from [1, 2] does not meet its security requirements if the Session-state Reveal query is allowed in the eCK model. We discuss the implications of our result for some related protocols proven correct in the eCK model, and discuss the interaction between Session-state Reveal and protocol transformations.

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A modified eCK model with stronger security for tripartite authenticated key exchange.

Qingfeng Cheng, Chuangui Ma, Fushan Wei

Since Bellare and Rogaway presented the first formal security model for authenticated key exchange (AKE) protocols in 1993, many formal security models have been proposed. The extended Canetti-Krawczyk (eCK) model proposed by LaMacchia et al. is currently regarded as the strongest security model for two-party AKE protocols. In this paper, we first generalize the eCK model for tripartite AKE protocols, called teCK model, and enhance the security of the new model by adding a new reveal query. In the teCK model, the adversary has stronger powers, and can learn more secret information. Then we present a new tripartite AKE protocol based on the NAXOS protocol, called T-NAXOS protocol, and analyze its security in the teCK model under the random oracle assumption.

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Analysis of Two Provably Secure Authenticated Key Exchange Protocols in the eCK Model

Xuexian Hu

The extended Canetti-Krawczyk(eCK) model proposed by LaMacchia et al.is currently regarded as the strongest security model for authenticated key exchange(AKE) protocols.In the eCK model,the adversary can make queries on the test session,and reveal both ephemeral private keys,both long-term keys,or one of each from the two different parties.In this paper,we analyze two AKE protocols designed in the eCK model based on the definition of eCK model.We propose ephemeral keys compromised attacks and long-term keys compromised attacks on one of them,and also propose ephemeral keys compromised attacks on the other one.The results of analysis show that both of them are insecure in the eCK model.

Journal of Wuhan University•Jan 1, 2010•0 citations

Stronger Security of Authenticated Key Exchange

Brian A. LaMacchia, Kristin Lauter, Anton Mityagin

Recent work by Krawczyk [10] and Menezes [14] has highlighted the importance of under-standing well the guarantees and limitations of formal security models when using them to prove the security of protocols. In this paper we focus on security models for authenticated key exchange (AKE) protocols. We observe that there are several classes of attacks on AKE protocols that lie outside the scope of the Canetti-Krawczyk model. Some of these additional attacks have already been considered by Krawczyk [10]. In an attempt to bring these attacks within the scope of the security model we extend the Canetti-Krawczyk model for AKE security by providing significantly greater powers to the adversary. Our contribution is a more compact, integrated, and comprehensive formulation of the security model. We then introduce a new AKE protocol called NAXOS and prove that it is secure against these stronger adversaries. 1

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Comparing SessionStateReveal and EphemeralKeyReveal for Diffie-Hellman protocols

Berkant Ustaoğlu

Both the “eCK” model, by LaMacchia, Lauter and Mityagin, and the “CK01” model, by Canetti and Krawczyk, address the effect of leaking session specific ephemeral data on the security of key establishment schemes. The CK01-adversary is given a SessionStateReveal query to learn session specific private data defined by the protocol specification, whereas the eCK-adversary is equipped with an EphemeralKeyReveal query to access all ephemeral private input required to carry session computations. SessionStateReveal cannot be issued against the test session; by contrast EphemeralKeyReveal can be used against the test session under certain conditions. On the other hand, it is not obvious how EphemeralKeyReveal compares to SessionStateReveal. Thus it is natural to ask which model is more useful and practically relevant. While formally the models are not comparable, we show that recent analysis utilizing SessionStateReveal and EphemeralKeyReveal have a similar approach to ephemeral data leakage. First we pinpoint the features that determine the approach. Then by examining common motives for ephemeral data leakage we conclude that the approach is meaningful, but does not take into account timing, which turns out to be critical for security. Lastly, for Diffie-Hellman protocols we argue that it is important to consider security when discrete logarithm values of the outgoing ephemeral public keys are leaked and offer a method to achieve security even if the values are exposed.

•Jan 1, 2009•0 citations

An eCK-secure Authenticated Key Exchange Protocol Without Random Oracles

Daisuke Moriyama, Tatsuaki Okamoto

Two-party key exchange protocol is a mechanism in which two parties communicate with each other over an insecure channel and output the same session key.A key exchange protocol that is secure against an active adversary who can control and modify the exchanged messages is called authenticated key exchange (AKE) protocol.LaMacchia, Lauter and Mityagin presented a strong security definition for public key infrastructure (PKI) based two-pass protocol, which we call the extended Canetti-Krawczyk (eCK) security model, and some researchers have provided eCK-secure AKE protocols in recent years.However, almost all protocols are provably secure in the random oracle model or rely on a special implementation technique so-called the NAXOS trick.In this paper, we present a PKI-based two-pass AKE protocol that is secure in the eCK security model.The security of the proposed protocol is proven without random oracles (under three assumptions), and does not rely on implementation techniques such as the NAXOS trick.

KSII Transactions on Internet and Information Systems•Jan 1, 2011•11 citations
In the paper, 'stronger security of authenticated key exchange' (LaMacchia et al., 2006, 2007), a new security model for authenticated key exchange protocols (eCK) is proposed. The new model is suggested to be at least as strong as previous models for key exchange protocols, such as the CK model (Canetti and Krawczyk, 2001; Krawczyk, 2005). The model includes a new notion of an EphemeralKeyReveal adversary query, which is claimed in e.g., LaMacchia et al. (2006), Okamoto (2007), and Ustaoglu (2008), to be at least as strong as the Session-StateReveal query. We investigate the relation between the two models by focusing on the difference in adversary queries. We formally model the NAXOS protocol and a variant of the eCK model, called eCK', in which the EphemeralKeyReveal query is replaced by the Session-StateReveal query. Using Scyther, a formal protocol analysis tool, we automatically find attacks on the protocol, showing that the protocol is insecure in the eCK' model. Our attacks prove that the Session-StateReveal query is stronger than the EphemeralKeyReveal query and that the eCK security model is incomparable to the CK model, disproving several claims made in the literature.
Abstract. In the paper “Stronger Security of Authenticated Key Ex-change ” [1,2], a new security model for authenticated key exchange pro-tocols (eCK) is proposed. The new model is suggested to be at least as strong as previous models for key exchange protocols. The model in-cludes a new notion of an Ephemeral Key Reveal adversary query, which is claimed in e. g. [2–4] to be at least as strong as the Session-state Reveal query. We show that Session-state Reveal is stronger than Ephemeral Key Reveal, implying that the eCK security model is incomparable to the CK model [5, 6]. In particular we show that the proposed NAXOS protocol from [1, 2] does not meet its security requirements if the Session-state Reveal query is allowed in the eCK model. We discuss the implications of our result for some related protocols proven correct in the eCK model, and discuss the interaction between Session-state Reveal and protocol transformations.
Since Bellare and Rogaway presented the first formal security model for authenticated key exchange (AKE) protocols in 1993, many formal security models have been proposed. The extended Canetti-Krawczyk (eCK) model proposed by LaMacchia et al. is currently regarded as the strongest security model for two-party AKE protocols. In this paper, we first generalize the eCK model for tripartite AKE protocols, called teCK model, and enhance the security of the new model by adding a new reveal query. In the teCK model, the adversary has stronger powers, and can learn more secret information. Then we present a new tripartite AKE protocol based on the NAXOS protocol, called T-NAXOS protocol, and analyze its security in the teCK model under the random oracle assumption.
The extended Canetti-Krawczyk(eCK) model proposed by LaMacchia et al.is currently regarded as the strongest security model for authenticated key exchange(AKE) protocols.In the eCK model,the adversary can make queries on the test session,and reveal both ephemeral private keys,both long-term keys,or one of each from the two different parties.In this paper,we analyze two AKE protocols designed in the eCK model based on the definition of eCK model.We propose ephemeral keys compromised attacks and long-term keys compromised attacks on one of them,and also propose ephemeral keys compromised attacks on the other one.The results of analysis show that both of them are insecure in the eCK model.
Recent work by Krawczyk [10] and Menezes [14] has highlighted the importance of under-standing well the guarantees and limitations of formal security models when using them to prove the security of protocols. In this paper we focus on security models for authenticated key exchange (AKE) protocols. We observe that there are several classes of attacks on AKE protocols that lie outside the scope of the Canetti-Krawczyk model. Some of these additional attacks have already been considered by Krawczyk [10]. In an attempt to bring these attacks within the scope of the security model we extend the Canetti-Krawczyk model for AKE security by providing significantly greater powers to the adversary. Our contribution is a more compact, integrated, and comprehensive formulation of the security model. We then introduce a new AKE protocol called NAXOS and prove that it is secure against these stronger adversaries. 1
Both the “eCK” model, by LaMacchia, Lauter and Mityagin, and the “CK01” model, by Canetti and Krawczyk, address the effect of leaking session specific ephemeral data on the security of key establishment schemes. The CK01-adversary is given a SessionStateReveal query to learn session specific private data defined by the protocol specification, whereas the eCK-adversary is equipped with an EphemeralKeyReveal query to access all ephemeral private input required to carry session computations. SessionStateReveal cannot be issued against the test session; by contrast EphemeralKeyReveal can be used against the test session under certain conditions. On the other hand, it is not obvious how EphemeralKeyReveal compares to SessionStateReveal. Thus it is natural to ask which model is more useful and practically relevant. While formally the models are not comparable, we show that recent analysis utilizing SessionStateReveal and EphemeralKeyReveal have a similar approach to ephemeral data leakage. First we pinpoint the features that determine the approach. Then by examining common motives for ephemeral data leakage we conclude that the approach is meaningful, but does not take into account timing, which turns out to be critical for security. Lastly, for Diffie-Hellman protocols we argue that it is important to consider security when discrete logarithm values of the outgoing ephemeral public keys are leaked and offer a method to achieve security even if the values are exposed.
Two-party key exchange protocol is a mechanism in which two parties communicate with each other over an insecure channel and output the same session key.A key exchange protocol that is secure against an active adversary who can control and modify the exchanged messages is called authenticated key exchange (AKE) protocol.LaMacchia, Lauter and Mityagin presented a strong security definition for public key infrastructure (PKI) based two-pass protocol, which we call the extended Canetti-Krawczyk (eCK) security model, and some researchers have provided eCK-secure AKE protocols in recent years.However, almost all protocols are provably secure in the random oracle model or rely on a special implementation technique so-called the NAXOS trick.In this paper, we present a PKI-based two-pass AKE protocol that is secure in the eCK security model.The security of the proposed protocol is proven without random oracles (under three assumptions), and does not rely on implementation techniques such as the NAXOS trick.