[messaging] Capsule: A Protocol for Secure Collaborative Document Editing

Nadim Kobeissi nadim at nadim.computer
Mon Aug 13 10:20:29 PDT 2018

Hello everyone,

I've updated the draft of my paper on the Capsule secure collaborative
document editing protocol with substantial improvements, more details and
many corrections:

Anyone interested in this topic will, I think, find this updated paper to
be a more rewarding and worthwhile read.

Best regards,

Sent from my computer

On Wed, Mar 7, 2018 at 9:00 PM Nadim Kobeissi <nadim at nadim.computer> wrote:

> 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 collaborated on.
> A proposal of Capsule is available here:
> https://eprint.iacr.org/2018/253
> 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
> suggestions.
> 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 our opinions!
> Sincerely,
> Nadim
> Sent from my computer
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