key_get_instantiation_authkey
extern struct key *key_get_instantiation_authkey(key_serial_t target_id);
instkey = key_get_instantiation_authkey(id);
authkey = key_get_instantiation_authkey(id);
instkey = key_get_instantiation_authkey(keyid);
instkey = key_get_instantiation_authkey(keyid);