Cryptology ePrint Archive: Report 2015/1092

Post-quantum key exchange - a new hope

Erdem Alkim and Léo Ducas and Thomas Pöppelmann and Peter Schwabe

Abstract: In 2015, Bos, Costello, Naehrig, and Stebila (IEEE Security & Privacy 2015) proposed an instantiation of Ding's ring-learning-with-errors (Ring-LWE) based key-exchange protocol (also including the tweaks proposed by Peikert from PQCrypto 2014), together with an implementation integrated into OpenSSL, with the affirmed goal of providing post-quantum security for TLS.

In this work we revisit their instantiation and stand-alone implementation. Specifically, we propose new parameters and a better suited error distribution, analyze the scheme's hardness against attacks by quantum computers in a conservative way, introduce a new and more efficient error-reconciliation mechanism, and propose a defense against backdoors and all-for-the-price-of-one attacks. By these measures and for the same lattice dimension, we more than double the security parameter, halve the communication overhead, and speed up computation by more than a factor of 8 in a portable C implementation and by more than a factor of 27 in an optimized implementation targeting current Intel CPUs. These speedups are achieved with comprehensive protection against timing attacks.

Category / Keywords: public-key cryptography / Post-quantum key exchange, Ring-LWE, high-speed software, vectorization

Original Publication (with minor differences): USENIX Security 2016

Date: received 10 Nov 2015, last revised 10 Jul 2019

Contact author: newhope at cryptojedi org

Available format(s): PDF | BibTeX Citation

Note: Fixed several typos and details in the failure analysis (Section D).

Version: 20190710:103122 (All versions of this report)

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