## Cryptology ePrint Archive: Report 2018/760

Strongly Secure Authenticated Key Exchange from Supersingular Isogenies

Xiu Xu and Haiyang Xue and Kunpeng Wang and and Man Ho Au and Bei Liang and Song Tian

Abstract: This paper aims to address the open problem, namely, to find new techniques to design and prove security of supersingular isogeny-based authenticated key exchange (AKE) protocols against the widest possible adversarial attacks, raised by Galbraith in 2018. Concretely, we present two AKEs based on a double-key PKE in the supersingular isogeny setting secure in the sense of CK$^+$, one of the strongest security models for AKE. Our contributions are summarised as follows. Firstly, we propose a strong $\textsf{OW-CPA}$ secure PKE, $\mathsf{2PKE_{sidh}}$, based on SI-DDH assumption. By applying modified Fujisaki-Okamoto transformation, we obtain a $[\textsf{OW-CCA}, \textsf{OW-CPA}]$ secure KEM, $\mathsf{2KEM_{sidh}}$. Secondly, we propose a two-pass AKE, $\textsf{SIAKE}_2$, based on SI-DDH assumption, using $\mathsf{2KEM_{sidh}}$ as a building block. Thirdly, we present a modified version of $\mathsf{2KEM_{sidh}}$ that is secure against leakage under the 1-Oracle SI-DH assumption. Using the modified $\mathsf{2KEM_{sidh}}$ as a building block, we then propose a three-pass AKE, $\textsf{SIAKE}_3$, based on 1-Oracle SI-DH assumption. Finally, we prove that both $\textsf{SIAKE}_2$ and $\textsf{SIAKE}_3$ are CK$^+$ secure in the random oracle model and supports arbitrary registration. We also provide an implementation to illustrate the efficiency of our schemes. Our schemes compare favourably against existing isogeny-based AKEs. To the best of our knowledge, they are the first of its kind to offer security against arbitrary registration, wPFS, KCI and MEX simultaneously. Regarding efficiency, our schemes outperform existing schemes in terms of bandwidth as well as CPU cycle count.

Category / Keywords: public-key cryptography / authenticated key exchange, key encapsulation mechanism, supersingular elliptic curve isogeny, post quantum

Original Publication (with minor differences): IACR-ASIACRYPT-2019

Date: received 18 Aug 2018, last revised 12 Dec 2020

Contact author: haiyangxc at gmail com

Available format(s): PDF | BibTeX Citation

Note: Correct the definition of Corrupt in the security model.

Short URL: ia.cr/2018/760

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