Zero-knowledge for real teams, not just the threat-model essay
Security · 7 min read · Published 2026-04-12 by Ahsan Tariq
Zero-knowledge collapses in practice the moment five humans need the same key. Here is how Ranbval kept the guarantee alive.
The single-user zero-knowledge story is easy: derive a key from a password, seal everything, never upload the password. It falls apart the moment a teammate needs access. Ranbval uses per-member envelopes. When you invite a teammate, their device generates an asymmetric key pair on first login. You or an admin re-wrap the project's data encryption keys for their public key. The Ranbval server never sees either password-derived key — it just moves around tiny per-person ciphertext envelopes. Adding a member is a local re-wrap, not a secret share. Removing a member rotates the DEK and re-wraps for the remaining set — past exports stay valid, new data does not leak backwards. Lost-device flow uses a recovery kit, not a backend master key that could be subpoenaed. If Ranbval gets breached, attackers get ciphertext. If an individual laptop gets breached, the blast radius is one project, one device, one audit trail — not your entire key inventory.
