In lab tests, Signal-based design encrypts shared documents end to end

A shared document can look private while still being readable by the company hosting it. Researchers from the Max Planck Institute for Security and Privacy, EPFL and the CASA Cluster of Excellence have now tested a different design: an online document whose contents remain end-to-end encrypted throughout collaboration, including when users edit it together.

The key move is to use Signal’s cryptographic protocol as an encrypted, asynchronous broadcast channel — a system for securely distributing changes without requiring a central server to read the document. When someone creates a file, the design creates a Signal group. Other collaborators join, and edits travel through that group before being applied to local copies of the document.

That approach targets the hardest part of shared editing: keeping everyone’s version consistent while allowing people to work at the same time or at different times. The model also includes role-based permissions, so a collaborator can be allowed to read, comment or edit. Existing security-focused tools such as CryptPad encrypt communication, the researchers say, but do not provide fully transparent security guarantees.

The experiments produced a response delay of about 120 milliseconds and showed that the system could scale across the tested scenarios. That is the practical promise: stronger privacy without giving up the basic behavior people expect from a collaborative document. The result remains a research design, however.

So what changes, concretely? A future document service could let a provider host synchronization without holding the keys needed to read the file. That would extend the privacy model already familiar from encrypted messaging to shared notes and business documents. The results lay the foundation for systems that combine high security requirements with practical use.