Interoperability in End-to-End Encrypted Messaging
Len J, Ghosh E, Grubbs P, Rösler P (2026)
Publication Type: Conference contribution
Publication year: 2026
Publisher: Association for Computing Machinery, Inc
Pages Range: 15-25
Conference Proceedings Title: CSLAW 2026 - Proceedings of the 2026 Symposium on Computer Science and Law
Event location: Berkeley, CA
ISBN: 9798400724473
Abstract
The Digital Markets Act (DMA) is a nascent European Union regulation which entered into force in November 2022. One of its most controversial provisions is a requirement that so-called "gatekeepers"offering end-to-end encrypted messaging apps, such as WhatsApp, implement "interoperability"with other messaging apps: in essence, encrypted messaging across service providers. This requirement represents a fundamental shift in the design assumptions of existing encrypted messaging systems, most of which are designed to be centralized. Despite some design proposals by standards groups and companies (such as Meta), there is as of yet limited understanding of how much sacrifice in privacy (especially, metadata privacy) is required to make interoperability work.In this paper, we take an initial step in this direction. We break down the DMA's effects on the design of encrypted messaging systems into three main areas: identity, or how to resolve identities across service providers; protocols, or how to establish a secure connection between clients on different platforms; and abuse prevention, or how service providers can detect and take action against users engaging in abuse or spam. For each area, we identify key security and privacy requirements. We then do a deep-dive on the reference design for WhatsApp interoperability that was recently released by Meta, and observe that its privacy guarantees are fairly weak. Finally, we propose our own design for an interoperable encrypted messaging system.
Authors with CRIS profile
Involved external institutions
University of North Carolina at Chapel Hill
United States (USA) (US)
Microsoft Corporation
United States (USA) (US)
University of Michigan
United States (USA) (US)
United States (USA) (US)
Microsoft Corporation
United States (USA) (US)
University of Michigan
United States (USA) (US)
How to cite
APA:
Len, J., Ghosh, E., Grubbs, P., & Rösler, P. (2026). Interoperability in End-to-End Encrypted Messaging. In CSLAW 2026 - Proceedings of the 2026 Symposium on Computer Science and Law (pp. 15-25). Berkeley, CA, US: Association for Computing Machinery, Inc.
MLA:
Len, Julia, et al. "Interoperability in End-to-End Encrypted Messaging." Proceedings of the 5th ACM Symposium on Computer Science and Law, 2026, Berkeley, CA Association for Computing Machinery, Inc, 2026. 15-25.
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