Universally Composable Notions of Key Exchange and Secure Channels.

Ran Canetti, Hugo Krawczyk

Ran Canetti, Shai Halevi, Jonathan I. Katz +2 more

Eduarda S. V. Freire, Julia Hesse, Dennis Hofheinz

Ran Canetti, Hugo Krawczyk

Recently, Canetti and Krawczyk (Eurocrypt'2001) formu- lated a notion of security for key-exchange (ke) protocols, called SK- security, and showed that this notion suffices for constructing secure channels. However, their model and proofs do not suffice for proving more general composability properties of SK-secure ke protocols. We show that while the notion of SK-security is strictly weaker than a fully-idealized notion of key exchange security, it is sufficiently robust for providing secure composition with arbitrary protocols. In particular, SK-security guarantees the security of the key for any application that desires to set-up secret keys between pairs of parties. We also provide new definitions of secure-channels protocols with similarly strong com- posability properties, and show that SK-security suffices for obtaining these definitions. To obtain these results we use the recently proposed framework of uni- versally composable (UC) security. We also use a new tool, called non- information oracles, which will probably find applications beyond the present case. These tools allow us to bridge between seemingly limited indistinguishability-based definitions such as SK-security and more pow- erful, simulation-based definitions, such as UC security, where general composition theorems can be proven. Furthermore, based on such compo- sition theorems we reduce the analysis of a full-fledged multi-session key- exchange protocol to the (simpler) analysis of individual, stand-alone, key-exchange sessions.

Lawrence Roy, Jiayu Xu

A Password-Authenticated Key Exchange (PAKE) protocol allows two parties to agree upon a cryptographic key, when the only information shared in advance is a low-entropy password. The standard security notion for PAKE (Canetti et al., Eurocrypt 2005) is in the Universally Composable (UC) framework. We show that unlike most UC security notions, UC PAKE does not imply correctness. While Canetti et al. has briefly noticed this issue, we present the first comprehensive study of correctness in UC PAKE: We show that TrivialPAKE, a no-message protocol that does not satisfy correctness, is a UC PAKE; We propose nine approaches to guaranteeing correctness in the UC security notion of PAKE, and show that seven of them are equivalent, whereas the other two are unachievable; We prove that a direct solution, namely changing the UC PAKE functionality to incorporate correctness, is impossible; Finally, we show how to naturally incorporate correctness by changing the model—we view PAKE as a three-party protocol, with the man-in-the-middle adversary as the third party. In this way, we hope to shed some light on the very nature of UC-security in the man-in-the-middle setting.

Zhong Yan-tao

The Internet of things (IoT) has experienced rapid development these years, while its security and privacy remains a major challenge. One of the main security goals for the IoT is to build secure and authenticated channels between IoT nodes. A common way widely used to achieve this goal is using authenticated key exchange protocol. However, with the increasing progress of quantum computation, most authenticated key exchange protocols nowadays are threatened by the rise of quantum computers. In this study, we address this problem by using ring-SIS based KEM and hash function to construct an authenticated key exchange scheme so that we base the scheme on lattice based hard problems believed to be secure even with quantum attacks. We also prove the security of universal composability of our scheme. The scheme hence can keep security while runs in complicated environment.