Beyond one server: Decentralizing secure group messaging

In May, WhatsApp made immoderate arguable changes to its presumption of service, leaving WhatsApp users with a choice: hold to the terms, oregon beryllium forced to leave.

Similarly, journalists and activists who are disquieted astir their messages being intercepted oregon spied on—especially successful countries with weaker escaped code guarantees—are faced with a prime regarding however the app handles their messages: hold to the terms, oregon permission the app.

"Right now, messaging app companies are successful complaint of users, erstwhile truly it should beryllium the different mode around," says Matthew Weidner, a Ph.D. pupil advised by CyLab's Heather Miller successful Carnegie Mellon University's Computer Science Department. "Users should person the state to take however their messages are handled."

That's wherefore Weidner argues that the services that radical messaging apps use—such arsenic end-to-end encryption oregon radical management—should beryllium de-centralized. That is, users shouldn't beryllium tethered to a azygous company's server, which leaves them astatine the mercy of the company.

In a caller survey presented astatine past week's ACM Conference connected Computer and Communications Security, Weidner defined a caller information protocol that could bring this thought of decentralization to fruition.

"The thought of our enactment is to springiness users the aforesaid security, but enactment a much flexible network, frankincense giving much powerfulness to users," says Weidner, who served arsenic the study's pb author. "If your connection thread is routed done 1 server and the institution raises the prices oregon shuts down, you could power to different server seamlessly."

Core to Weidner's enactment is what's called continuous radical cardinal statement (CGKA)—a previously-developed information protocol that allows a radical of individuals to articulation and permission a radical connection thread aft it's been created and not person to trust connected a connection radical manager. CGKA besides prevents the request to interest astir erstwhile oregon however agelong members of the radical are online. Typically, radical messages are routed done a azygous server that applies CGKA, but Weidner and his colleagues aimed to survey the grade to which unafraid messaging was imaginable for much flexible, decentralized networks. Thus, they specify decentralized CGKA, oregon DCGKA.

"What makes our insubstantial antithetic is we enactment successful a decentralized setting, wherever we don't needfully presume there's a cardinal server to way messages and assistance retired maintaining the group," Weidner says. "Instead, users tin nonstop messages to each different nevertheless they'd like."

A decentralized exemplary introduces respective challenges, Weidner says. Messages could beryllium delayed oregon delivered successful an inconsistent order, and with nary cardinal authority, determination is nary azygous root of truth. To lick this, messages are cautiously designed truthful they person the aforesaid effect nary substance what bid they are received in. That way, adjacent if thing uncommon but antithetic happens—like 2 users removing each different from the radical simultaneously—the full radical yet sees the aforesaid outcome.

How, then, does this play into the lives of journalists oregon activists trying to securely pass successful countries with weaker escaped code rights? Weidner says DCGKA provides a solution.

"If the journalists are utilizing a cardinal server tally by a institution to communicate, but it gets blocked oregon unopen down, they could power to a 'self-hosted' server that's physically successful 1 of their homes," Weidner says. "If that's blocked too, oregon if the full Internet is unopen down, they could power to utilizing a mesh web successful which adjacent devices link implicit Bluetooth. Even if immoderate messages get delayed oregon reordered during the transition, DCGKA volition proceed moving and providing security."

---

---

More information: Matthew Weidner et al, Key Agreement for Decentralized Secure Group Messaging with Strong Security Guarantees, Proceedings of the 2021 ACM SIGSAC Conference connected Computer and Communications Security (2021). DOI: 10.1145/3460120.3484542