Beyond one server: Decentralizing secure group messaging

guest · Nov 24, 2021

Beyond one server: Decentralizing secure group messaging
November 24, 2021
https://techxplore.com/news/2021-11-server-decentralizing-group-messaging.html

In May, WhatsApp made some controversial changes to its terms of service, leaving WhatsApp users with a choice: agree to the terms, or be forced to leave.

"Right now, messaging app companies are in charge of users, when really it should be the other way around," says Matthew Weidner, a Ph.D. student advised by CyLab's Heather Miller in Carnegie Mellon University's Computer Science Department. "Users should have the freedom to choose how their messages are handled."
That's why Weidner argues that the services that group messaging apps use—such as end-to-end encryption or group management—should be de-centralized. That is, users shouldn't be tethered to a single company's server, which leaves them at the mercy of the company.
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In a new study presented at last week's ACM Conference on Computer and Communications Security, Weidner defined a new security protocol that could bring this idea of decentralization to fruition.

"The idea of our work is to give users the same security, but support a more flexible network, thus giving more power to users," says Weidner, who served as the study's lead author. "If your message thread is routed through one server and the company raises the prices or shuts down, you could switch to another server seamlessly."
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Core to Weidner's work is what's called continuous group key agreement (CGKA)—a previously-developed security protocol that allows a group of individuals to join and leave a group message thread after it's been created and not have to rely on a message group manager.

Typically, group messages are routed through a single server that applies CGKA, but Weidner and his colleagues aimed to study the extent to which secure messaging was possible for more flexible, decentralized networks. Thus, they define decentralized CGKA, or DCGKA.
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Key Agreement for Decentralized Secure Group Messaging with Strong Security Guarantees

In this paper we adapt secure group messaging for decentralized networks that have no central authority. Servers may still optionally be used, but they are trusted less.

In the face of device compromise our protocol achieves forward secrecy and post-compromise security. We evaluate the performance of a prototype implementation, and demonstrate that our protocol has practical efficiency.
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