The number of key custodians is kept to the minimum operations require. In particular: custodians for each component are designated in the fewest number necessary, such as a primary and a backup, and are employees or contracted personnel; each custodian and backup signs a key-custodian form recording the designation; the form gives the specific authorisation, the custodian's responsibilities for the keying material entrusted, the custodian's signature acknowledging them, an effective date and management's authorising signature; custodians who together could reach the threshold to form a key do not report directly to the same person, except in organisations too small for that, and the components held by a manager and that manager's direct reports never form a quorum or reveal anything about the key.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.