A secure element for providing hardware isolation of a mission critical subsystem, the secure element comprising: a memory configured to include a whitelist, a blacklist and a secure element logic; and a processor coupled to the memory and an unsecure path, the processor configured to: verify at least one of an execution image used by an electronic control unit using a digital signature; perform actuation operation received across the unsecure path that modifies the state of the mission critical subsystem; determine if a diagnostic operation received across the unsecure path that request state information of the mission critical subsystem is a trusted operation in the mission critical subsystem by comparing the diagnostic operation to a blacklist; when the diagnostic operation is not found in the blacklist, determine the diagnostic operation to be a trusted operation and perform the diagnostic operation; store information used to determine which of the diagnostic operation and the actuation operation received across the unsecure path are performed; and flash the execution image of the electronic control unit when the execution image of the electronic control unit is received across the unsecure path, wherein the secure element is interposed between an unsecure bus and the electronic control unit, and the electronic control unit is interposed between the secure element and the mission critical subsystem, wherein the blacklist is stored using a data structure which is a tree for storing words with common prefixes, and wherein the secure element uses a list of measurements of allowed electronic control unit execution image to be loaded at boot-time of the electronic control unit. a memory configured to include a whitelist, a blacklist and a secure element logic; and a processor coupled to the memory and an unsecure path, the processor configured to: verify at least one of an execution image used by an electronic control unit using a digital signature; perform actuation operation received across the unsecure path that modifies the state of the mission critical subsystem; determine if a diagnostic operation received across the unsecure path that request state information of the mission critical subsystem is a trusted operation in the mission critical subsystem by comparing the diagnostic operation to a blacklist; when the diagnostic operation is not found in the blacklist, determine the diagnostic operation to be a trusted operation and perform the diagnostic operation; store information used to determine which of the diagnostic operation and the actuation operation received across the unsecure path are performed; and flash the execution image of the electronic control unit when the execution image of the electronic control unit is received across the unsecure path, wherein the secure element is interposed between an unsecure bus and the electronic control unit, and the electronic control unit is interposed between the secure element and the mission critical subsystem, wherein the blacklist is stored using a data structure which is a tree for storing words with common prefixes, and wherein the secure element uses a list of measurements of allowed electronic control unit execution image to be loaded at boot-time of the electronic control unit. verify at least one of an execution image used by an electronic control unit using a digital signature; perform actuation operation received across the unsecure path that modifies the state of the mission critical subsystem; determine if a diagnostic operation received across the unsecure path that request state information of the mission critical subsystem is a trusted operation in the mission critical subsystem by comparing the diagnostic operation to a blacklist; when the diagnostic operation is not found in the blacklist, determine the diagnostic operation to be a trusted operation and perform the diagnostic operation; store information used to determine which of the diagnostic operation and the actuation operation received across the unsecure path are performed; and flash the execution image of the electronic control unit when the execution image of the electronic control unit is received across the unsecure path, wherein the secure element is interposed between an unsecure bus and the electronic control unit, and the electronic control unit is interposed between the secure element and the mission critical subsystem, wherein the blacklist is stored using a data structure which is a tree for storing words with common prefixes, and wherein the secure element uses a list of measurements of allowed electronic control unit execution image to be loaded at boot-time of the electronic control unit.