What it proves — and what it does not.

WHO — the account. PRESENT — the device’s own local user-verification approved the use of its key for this operation (not that a named person is there or acting freely). TOGETHER — two independent devices produced compatible observations of the same physical event. NOW — it was created at the moment of the operation and did not exist before it.

Replay of a recording of a past ceremony is addressed: each ceremony is bound to a fresh challenge tied to that one operation. This is validated on real hardware.

A live relay between two places at the same instant is a harder problem. KeyPulse is designed to raise the cost and change the nature of that attack. It does not claim to make it impossible. This is an active area of research and it has a first-class limitations page.

The design minimises data. Each integrator gets an opaque, non-correlatable reference for the same user, so third parties cannot link a user across services. KeyPulse’s own infrastructure necessarily holds that mapping — it never learns civil identity, but it is not “fully anonymous”.

A high-value financial transaction · A change of administrator rights · Access to critical infrastructure · An irreversible operation · A validation that requires several people

KeyPulse is a layer, not a replacement. It is strongest where a physical proof of co-presence has real value. The KeyPulse column is the target for Secure Chain; cells marked “research” are open problems, not shipped properties.

● established · ◐ partial / by implementation · ○ not provided · ⧗ open research

For each threat: what is demonstrated today, what is an engineering goal, and what is genuinely open. We would rather you learn this here than discover it later.