End-to-end encryption has become common in messaging apps, protecting conversations so that only the people involved can read them.
Now, researchers have developed a way to bring similar protection to shared online documents, potentially making collaborative work much more private.
The new approach was developed by researchers from the Max Planck Institute for Security and Privacy, EPFL and the CASA Cluster of Excellence.
It uses technology behind the Signal messaging service to allow several people to securely edit the same document without giving the service provider access to its contents.
Online tools such as Google Docs, Apple Notes and Microsoft 365 have made it easy for people to work together from different locations. But collaborative documents can contain highly sensitive personal, financial or business information.
Many services encrypt information while it is being transmitted or stored. However, the data may need to be decrypted on the provider’s servers so that changes from different users can be synchronized. As a result, the provider may technically be able to access the document.
End-to-end encryption, or E2EE, works differently. With E2EE, information remains encrypted between the people using a service, and even the service provider should not be able to read it.
The researchers wanted to determine whether this level of privacy could be combined with the features people expect from modern collaborative documents.
Their system, described in the paper “End-to-End Encrypted Collaborative Documents,” uses the Signal Protocol as a secure communication channel between collaborators.
When someone creates a document, the system creates a Signal group. Other people gain access to the document by joining that group. Changes made to the document are converted into a format that can be securely transmitted through the group. Each participant then applies those changes to a local copy stored on their own device.
This means the central service does not need to receive an unencrypted version of the document simply to coordinate everyone’s edits.
The researchers also considered usability. People need to be able to work on documents at the same time or at different times, while document owners may want to give participants different permissions, such as the ability to read, comment or edit.
Testing showed that the system could provide these collaborative features while maintaining strong encryption. In experiments involving different scenarios, it produced a response delay of about 120 milliseconds and was able to scale as collaboration increased.
The researchers say the findings demonstrate that an end-to-end encrypted broadcast channel can provide the foundation for secure collaborative document systems.
The work does not mean that existing services such as Google Docs or Microsoft 365 are immediately switching to Signal-based encryption. Instead, it demonstrates a possible architecture for future collaboration platforms.
As more personal and professional work moves into shared cloud documents, such technology could eventually make real-time online collaboration more private without sacrificing the convenience that has made these tools so popular.
