Dear respected peers,
Today's global society strongly relies on collaborative document editing, which
plays an increasingly large role in sensitive workflows. While other
collaborative venues, such as secure messaging, have seen secure protocols
being standardized and widely implemented, the same cannot be said for
collaborative document editing. Popular tools such as Google Docs, Microsoft
Office365 and Etherpad are used to collaboratively write reports and other
documents which are frequently sensitive and confidential, in spite of the
server having the ability to read and modify text undetected.
Capsule is the first formalized and formally verified protocol standard that
addresses secure collaborative document editing. Capsule provides
confidentiality and integrity on encrypted document data, while also
guaranteeing the ephemeral identity of collaborators and preventing the server
from adding new collaborators to the document. Capsule also, to an extent,
prevents the server from serving different versions of the document being
A proposal of Capsule is available here:
In this paper, I provide a full protocol description of Capsule. I also provide
formal verification results on the Capsule protocol in the symbolic model.
Finally, I present a full software implementation of Capsule, which includes a
novel formally verified signing primitive implementation.
As it stands, Capsule is by no means a finalized protocol, and all that is
presented in the preprint linked above is preliminary and very open to
Capsule is by no means a protocol as involved or innovative as some others,
such as the Signal protocol. However, I believe that it is valuable to see such
a protocol solidly proposed and formalized, given that its targeted use case is
underserved despite its legitimacy.
I welcome your feedback on the current Capsule draft. I enjoy working on this
project and hope to make of it a good software soon. Let's discuss it and share
Sent from my computer
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