@startuml
skinparam ParticipantPadding 10
skinparam BoxPadding 10
box AP
participant RMM
participant BL31
endbox
box RSS
participant DelegAttest
participant InitAttest
participant MeasuredBoot
participant Crypto
endbox

== RMM Boot phase ==

RMM -> BL31: get_realm_key(\n\t**hash_algo**, ...)
BL31 -> DelegAttest: get_delegated_key
DelegAttest -> MeasuredBoot: read_measurement
Rnote over DelegAttest: Compute input\n\ for key derivation\n\ (hash of measurements)
DelegAttest -> Crypto: derive_key
Rnote over DelegAttest: Compute public key\n\ hash with **hash_algo**.
Rnote over Crypto: Seed is provisioned\n\ in the factory.
DelegAttest --> BL31: get_delegated_key
BL31 --> RMM: get_realm_key
Rnote over RMM: Only private key\n\ is returned. Public\n\ key and its hash\n\ must be computed.\n\
Public key is included\n\ in the realm token.\n\ Its hash is the input\n\ for get_platform_token
RMM -> BL31: get_platform_token(\n\t**pub_key_hash**, ...)
BL31 -> DelegAttest: get_delegated_token
Rnote over DelegAttest: Check **pub_key_hash**\n\ against derived key.
DelegAttest -> InitAttest: get_initial_token
Rnote over InitAttest: Create the token including\n\ the **pub_key_hash** as the\n\ challenge claim
InitAttest -> MeasuredBoot: read_measurement
InitAttest -> Crypto: sign_token
InitAttest --> DelegAttest:  get_initial_token
DelegAttest --> BL31: get_delegated_token
BL31 --> RMM: get_platform_token
Rnote over RMM: Platform token is\n\ cached. It is not\n\ changing within\n\ a power cycle.
@enduml