Acumen: A Platform for Encrypted and Accountable Collaborative Editing

Modern-day collaborative editing tools must reconcile a prominent tension between user privacy and collaboration: encrypting user data prevents an application server from processing user edits. We present Acumen, a cryptographic system for real-time collaborative applications based on conflict-free replicated data types (CRDTs). Acumen is the first system to provide strong snapshot consistency, enabling untrusted users to create verifiable document snapshots used to invite new collaborators. Acumen also provides confidentiality, integrity, fork-causal consistency, and ensures that invited users do not learn the previous edit history of the document. We achieve these properties through the use of cryptographic accumulators and a novel secure garbage collection mechanism. Our evaluation shows that Acumen can support 25 users each simultaneously typing 60 WPM with negligible degradation in latency and availability.