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3.4 Device Relationships

NIST platform security: roots of trust, firmware and secure enclaves SP 800-193
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first version loaded 3 Principles and Key Concepts part of 3

Title

Device Relationships

Control

Due to lack of capability or functionality, some platform devices may not have their own root(s) of trust to perform an update, detection, or recovery. We refer to devices needing assistance as symbiont devices and those lending assistance as host devices. A dependency may be established whereby a host device and a symbiont device jointly fulfill the guidelines for protection, detection and/or recovery that the symbiont device cannot fulfill independently. Such dependencies might leverage a secure communication channel or other techniques. To be effective at lending assistance, the host device needs to meet the guidelines itself for the mechanisms it helps convey to the symbiont device. Together, the host and symbiont device provide a CoT that implements the security guidelines for protection, detection and/or recovery.

There may be relationships between devices where the trust is implicit— that is, where trust is provided by the architecture of the system. A device may receive indication of unambiguous physical presence from a device where an implicit trust relationship already exists. The fact that the other device sent the message through a trusted path means that the device can trust the request.

The diagram in Figure 3 shows different aspects of the relationship between symbiont and host; this relationship can be within an isolation boundary or across isolation boundaries across devices. It also shows how different devices co-exist together with several roots of trust, several chains of trust and communication paths.

There may also be other relationships which do not imply nor require any level of trust. Consider a device responsible for receiving updates. That device may then propagate those updates to other devices. Since each device (or the symbiont device along with its host device) is responsible for verifying its own updates, there is no requirement for trust between the device distributing updates and the devices those updates are provided to. Figure 3: Trust Chains