Consistent Synchronous Group Off-The-Record Messaging with SYM-GOTR

Authors: Michael Schliep (University of Minnesota), Eugene Vasserman (Kansas State University), Nicholas Hopper (University of Minnesota)

Volume: 2018
Issue: 3
Pages: 181–202
DOI: https://doi.org/10.1515/popets-2018-0027

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Abstract: We describe SYM-GOTR, a protocol for secure Group Off-The-Record (GOTR) messaging. In contrast to previous work, SYM-GOTR is the first protocol to offer confidential, authenticated, and repudiable conversations among a dynamic group with the additional properties of message unlinkability and the guarantee that all users see the same conversation, while providing efficient use of network and CPU resources. SYM-GOTR achieves these properties through the use of a novel optimistic consistency check protocol that either determines that all users agree on a transcript with constant-size messages or identifies at least one user that has not followed the protocol. We provide an implementation of SYM-GOTR as a Java library along with a plugin for the Jitsi instant messaging client. We analyze the performance of SYM-GOTR in a real world deployment scenario and discuss the challenges of providing a usable implementation without compromising the security of the conversation.

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