Each POI device holds unique secret and private keys for every function bearing on PIN protection, known only to that device and to HSMs at the fewest facilities operations need, so that disclosure of one device's key reveals nothing about another's; this covers key-protecting, firmware-authentication, application-authentication and display-prompt keys, and a POI private key exists nowhere else except transiently at external generation before injection.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.