EPFL researchers win Internet Defense Prize for end-to-end encrypted collaborative documents at USENIX Security Symposium; 120 ms delay, scalable.

EPFL researchers win Internet Defense Prize for end-to-end encrypted collaborative documents at USENIX Security Symposium; 120 ms delay, scalable.

IC researchers win Internet Defense Prize for new encryption method - EPFL

IC researchers win Internet Defense Prize for new encryption method

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Researchers from the EPFL School of Computer and Communication Sciences have developed a new way to keep collaborative online documents end-to-end encrypted without compromising their usability. On August 12, 2026, the work was honored with the Internet Defense Prize at the USENIX Security Symposium.

End-to-end encryption (E2EE) has become the standard for protecting personal chats. However, sensitive data isn’t limited to personal communication channels, as collaborative online documents such as those used by Google Docs, Apple Notes, and Microsoft 365 also contain data that require confidentiality.

Many collaborative document services do not use E2EE for co-editing. Although the content is transmitted and stored in encrypted form, it must be decrypted on the providers’ servers to enable users to edit it together. This means that the respective service providers can access personal documents at any time.

“People already expect their private messages to be protected by end-to-end encryption,” explains Carmela Troncoso, an assistant professor at EPFL and the Max Planck Institute for Security and Privacy (MPI-SP). “However, collaborative documents can contain information that is just as sensitive, and should therefore benefit from the same level of protection.”

Now, researchers from EPFL, and the MPI-SP, as part of the CASA Cluster of Excellence, have developed a method that allows encrypted messaging technology to be applied to collaborative documents.

In their paper End-to-End Encrypted Collaborative Documents , Troncoso, along with Christian Knabenhans from EPFL and Zayd Maradni from MPI-SP, apply the principle of E2EE to collaborative documents by developing a model that uses Signal as an encrypted channel for synchronizing edits.

At its core, a collaborative document is based on a reconciliation mechanism that ensures all users always have access to a consistent version of the document. Existing solutions implement this mechanism either on the server side or on the client side. While security-focused approaches such as CryptPad encrypt communication between users, they do not offer fully transparent security guarantees.

“Today, collaborative documents are often encrypted in transit and at rest, but the provider still has to decrypt their contents to enable collaboration,” explains Knabenhans. “What’s missing is end-to-end protection that keeps the document confidential even from the service provider.”

To make their method as user-friendly as possible, the researchers first examined what requirements users have for collaborative documents. A practical system must enable unrestricted collaboration, meaning that multiple people should be able to edit and share documents simultaneously or at different times. In addition, users expect role-based access control that allows different permissions, such as reading, commenting, or editing.

A new approach to encrypted collaboration

In their approach, the researchers combine a mechanism for synchronizing edits with an end-to-end encrypted (E2EE) broadcast channel. This results in an end-to-end encrypted collaborative document (E2EE-CD).

“We realized that the core problem of collaborative documents is very similar to what secure messaging already solves: getting encrypted updates reliably to a group of people,” Knabenhans says. “Rather than building a new secure communication system from scratch, we asked whether we could use a mature solution like Signal and adapt it to synchronize document edits.”

In practical implementation, they use the cryptographic protocol of the Signal messenger (Signal Protocol). This protocol already fulfils key requirements such as E2EE and is used by millions of people worldwide every day; here the researchers are expanding the existing features of Signal chat to meet the requirements for collaborative documents. When a person creates a new document, a new Signal group is created. Other collaborators gain access by joining this group. All changes are then shared via the Signal group, converted into a transferable format, and applied to a local copy of the document.

In a series of experiments, the researchers tested various scenarios and evaluated the trade-off between usability and security. The system responded with a delay of about 120 milliseconds and proved to be scalable. The results show that an E2EE broadcast channel is sufficient for implementing secure collaborative document systems and lay the foundation for collaborative document systems that meet high security requirements while also being suitable for practical use.

“We’re very proud to receive the Internet Defense Prize and grateful that the community has recognized the potential of this work to make online collaboration more secure,” Troncoso says. “We hope this work will make end-to-end encryption a practical option for collaborative documents, giving people stronger privacy without sacrificing the features they expect from modern collaboration tools.”

Source: Computer and Communication Sciences | IC

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End-to-end encryption (E2EE) has become the standard for protecting personal chats. However, sensitive data isn’t limited to personal communication channels, as collaborative online documents such as those used by Google Docs, Apple Notes, and Microsoft 365 also contain data that require confidentiality. Many collaborative document services do not use E2EE for co-editing. Although the content is transmitted and stored in encrypted form, it must be decrypted on the providers’ servers to enable users to edit it together. This means that the respective service providers can access personal documents at any time. “People already expect their private messages to be protected by end-to-end encryption,” explains Carmela Troncoso, an assistant professor at EPFL and the Max Planck Institute for Security and Privacy (MPI-SP). “However, collaborative documents can contain information that is just as sensitive, and should therefore benefit from the same level of protection.” Now, researchers from EPFL, and the MPI-SP, as part of the CASA Cluster of Excellence, have developed a method that allows encrypted messaging technology to be applied to collaborative documents. Security meets usability In their paper End-to-End Encrypted Collaborative Documents , Troncoso, along with Christian Knabenhans from EPFL and Zayd Maradni from MPI-SP, apply the principle of E2EE to collaborative documents by developing a model that uses Signal as an encrypted channel for synchronizing edits. At its core, a collaborative document is based on a reconciliation mechanism that ensures all users always have access to a consistent version of the document. Existing solutions implement this mechanism either on the server side or on the client side. While security-focused approaches such as CryptPad encrypt communication between users, they do not offer fully transparent security guarantees. “Today, collaborative documents are often encrypted in transit and at rest, but the provider still has to decrypt their contents to enable collaboration,” explains Knabenhans. “What’s missing is end-to-end protection that keeps the document confidential even from the service provider.” To make their method as user-friendly as possible, the researchers first examined what requirements users have for collaborative documents. A practical system must enable unrestricted collaboration, meaning that multiple people should be able to edit and share documents simultaneously or at different times. In addition, users expect role-based access control that allows different permissions, such as reading, commenting, or editing. A new approach to encrypted collaboration In their approach, the researchers combine a mechanism for synchronizing edits with an end-to-end encrypted (E2EE) broadcast channel. This results in an end-to-end encrypted collaborative document (E2EE-CD). “We realized that the core problem of collaborative documents is very similar to what secure messaging already solves: getting encrypted updates reliably to a group of people,” Knabenhans says. “Rather than building a new secure communication system from scratch, we asked whether we could use a mature solution like Signal and adapt it to synchronize document edits.” In practical implementation, they use the cryptographic protocol of the Signal messenger (Signal Protocol). This protocol already fulfils key requirements such as E2EE and is used by millions of people worldwide every day; here the researchers are expanding the existing features of Signal chat to meet the requirements for collaborative documents. When a person creates a new document, a new Signal group is created. Other collaborators gain access by joining this group. All changes are then shared via the Signal group, converted into a transferable format, and applied to a local copy of the document. In a series of experiments, the researchers tested various scenarios and evaluated the trade-off between usability and security. The system responded with a delay of about 120 milliseconds and proved to be scalable. The results show that an E2EE broadcast channel is sufficient for implementing secure collaborative document systems and lay the foundation for collaborative document systems that meet high security requirements while also being suitable for practical use. “We’re very proud to receive the Internet Defense Prize and grateful that the community has recognized the potential of this work to make online collaboration more secure,” Troncoso says. “We hope this work will make end-to-end encryption a practical option for collaborative documents, giving people stronger privacy without sacrificing the features they expect from modern collaboration tools.” The paper “End-to-End Encrypted Collaborative Documents ,” was one of three co-winners of the prestigious 2026 USENIX Security Internet Defense Prize which comes with US$25,000, funded by Meta.