Cryptology ePrint Archive: Report 2019/1363

Multi-Device for Signal

Sébastien Campion and Julien Devigne and Céline Duguey and Pierre-Alain Fouque

Abstract: Nowadays, we spend our life juggling with many devices such as smartphones, tablets or laptops, and we expect to easily and efficiently switch between them without losing time or security. However, most applications have been designed for single device usage. This is the case for secure instant messaging (SIM) services based on the Signal protocol, that implements the Double Ratchet key exchange algorithm. While some adaptations, like the Sesame protocol released by the developers of Signal, have been proposed to fix this usability issue, they have not been designed as specific multi-device solutions and no security model has been formally defined either. In addition, even though the group key exchange problematic appears related to the multi-device case, group solutions are too generic and do not take into account some properties of the multi-device setting. Indeed, the fact that all devices belong to a single user can be exploited to build more efficient solutions. In this paper, we propose a Multi-Device Instant Messaging protocol based on Signal, ensuring all the security properties of the original Signal.

Category / Keywords: cryptographic protocols / Secure Instant Messaging, Ratcheting, Multi-Device

Original Publication (with major differences): ACNS2020

Date: received 26 Nov 2019

Contact author: celine duguey at irisa fr

Available format(s): PDF | BibTeX Citation

Version: 20191127:081651 (All versions of this report)

Short URL: ia.cr/2019/1363