Witness Protocol — Cross-Agent Tamper Detection

reference

Witness Protocol

The witness protocol provides cross-agent tamper detection via PubSub-broadcast Signed Tree Heads (STHs).

How agents participate

  1. Each agent subscribes to the tenant’s audit chain PubSub topic
  2. STH updates are broadcast every 60 seconds
  3. Agents cache the latest STH locally
  4. On every API request, agents include the X-Loopctl-Last-Known-STH header with their cached position and signature prefix

Divergence detection

If an agent’s cached STH doesn’t match the server’s record for that position, a divergence is detected. This means someone rewrote the chain — which requires compromising every connected agent’s memory simultaneously.

Custody halt

On divergence, the tenant’s custody operations are halted until an operator clears the halt via break-glass with WebAuthn.

See Chain of Custody for the full trust model. See Break Glass for emergency procedures.