Two More Efficient Variants of the J-PAKE Protocol

in ACNS 2016 (2016, June)

Recently, the password-authenticated key exchange protocol J-PAKE of Hao and Ryan (Workshop on Security Protocols 2008) was formally proven secure in the algebraic adversary model by Abdalla et al. (IEEE ... [more ▼]

Recently, the password-authenticated key exchange protocol J-PAKE of Hao and Ryan (Workshop on Security Protocols 2008) was formally proven secure in the algebraic adversary model by Abdalla et al. (IEEE S&P 2015). In this paper, we propose and examine two variants of J-PAKE - which we call RO-J-PAKE and CRS-J-PAKE - that each makes the use of two less zero-knowledge proofs than the original protocol. We show that they are provably secure following a similar strategy to that of Abdalla et al. We also study their efficiency as compared to J-PAKE's, also taking into account how the groups are chosen. Namely, we treat the cases of subgroups of finite fields and elliptic curves. Our work reveals that, for subgroups of finite fields, CRS-J-PAKE is indeed more efficient than J-PAKE, while RO-J-PAKE is much less efficient. On the other hand, when instantiated with elliptic curves, both RO-J-PAKE and CRS-J-PAKE are more efficient than J-PAKE, with CRS-J-PAKE being the best of the three. We illustrate this experimentally, making use of recent research by Brier et al. (CRYPTO 2010). Regardless of implementation, we note that RO-J-PAKE enjoys a looser security reduction than both J-PAKE and CRS-J-PAKE. CRS-J-PAKE has the tightest security proof, but relies on an additional trust assumption at setup time. We believe our results can be useful to anyone interested in implementing J-PAKE, as perhaps either of these two new protocols may also be options, depending on the deployment context. [less ▲]

On Password-Authenticated Key Exchange Security Modeling

in Stajano, Frank; Mjolsnes, Stig; Jenkinson, Graeme (Eds.) et al Technology and practice of passwords: 9th International Conference, PASSWORDS 2015, Cambridge, UK, December 7-9, 2015, Proceedings (2016, March)

Deciding which security model is the right one for Authenticated Key Exchange (AKE) is well-known to be a difficult problem. In this paper, we examine definitions of security for Password-AKE (PAKE) in ... [more ▼]

Deciding which security model is the right one for Authenticated Key Exchange (AKE) is well-known to be a difficult problem. In this paper, we examine definitions of security for Password-AKE (PAKE) in the style proposed by Bellare et al. at Eurocrypt 2000. Indeed, there does not seem to be any consensus, even when narrowing the study down to this particular authentication method and model style, on how to precisely define fundamental notions such as accepting, terminating, and partnering. The aim of this paper is to begin addressing this problem. We first show how definitions vary from paper to paper. We then propose and thoroughly motivate a definition of our own, and use the opportunity to correct a minor flaw in a more recent and more PAKE-appropriate model proposed by Abdalla et al. at Public Key Cryptography 2005. Finally, we argue that the uniqueness of partners holding with overwhelming probability ought to be an explicitly required and proven property for AKE in general, but even more so in the password case, where the optimal security bound one aims to achieve is no longer a negligible value. To drive this last point, we exhibit a protocol that is provably secure following the Abdalla et al. definition, and at the same time fails to satisfy this property. [less ▲]

What Public Keys Can Do for Three-Party, Password-Authenticated Key Exchange

in Sokratis; Agudo, Isaac (Eds.) Public Key Infrastructures, Services and Applications: 10th European Workshop, EuroPKI 2013, Egham, UK, September 12-13, 2013, Revised Selected Papers (2014, September)

We study three-party, password-authenticated key exchange protocols where the trusted third party has a high-entropy private key to which corresponds a public key. In this scenario we can maintain the ... [more ▼]

We study three-party, password-authenticated key exchange protocols where the trusted third party has a high-entropy private key to which corresponds a public key. In this scenario we can maintain the user-friendliness of password authentication while provably achieving security properties that ordinary password-authenticated key exchange protocols cannot, namely resistance against key compromise impersonation and a special form of internal state revealing. We define security models tailored to our case and illustrate our work with several protocols. [less ▲]