Paper 2023/386

Interoperability in End-to-End Encrypted Messaging

Julia Len, Cornell Tech
Esha Ghosh, Microsoft Research
Paul Grubbs, University of Michigan
Paul Rösler, FAU Erlangen-Nürnberg

The Digital Markets Act (DMA) is a nascent European Union regulation adopted in May 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. Technologists have not really begun thinking about the myriad security, privacy, and functionality questions raised by the interoperability requirement; given that the DMA’s interoperability mandate may take effect as soon as mid-2024, it is critical for researchers to begin understanding the challenges and offering solutions. 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, summarize existing proposals, and examine whether proposals meet our security and privacy requirements. Finally, we propose our own design for an interoperable encrypted messaging system, and point out open problems.

Available format(s)
Cryptographic protocols
Publication info
end-to-end encryptionsecure messaginginteroperability
Contact author(s)
jlen @ cs cornell edu
Esha Ghosh @ microsoft com
paulgrub @ umich edu
paul roesler @ fau de
2023-03-24: approved
2023-03-17: received
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Creative Commons Attribution


      author = {Julia Len and Esha Ghosh and Paul Grubbs and Paul Rösler},
      title = {Interoperability in End-to-End Encrypted Messaging},
      howpublished = {Cryptology ePrint Archive, Paper 2023/386},
      year = {2023},
      note = {\url{}},
      url = {}
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