Capsule: A Protocol for Secure Collaborative Document Editing

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.
This talk will introduce the Capsule protocol. We will also go over the formal verification results of Capsule in the symbolic model. We then give an overview of the software implementation of Capsule, which includes a novel formally verified signing primitive implementation.

Nadim Kobeissi is a researcher in applied cryptography more specifically and computer security more generally. He is an adjunct professor at NYU Paris and direct Symbolic Software, an applied cryptography consulting and software firm. He is slated to defend his Ph.D. thesis (completed at INRIA's PROSECCO lab and accredited by ENS Paris) in Fall 2018.