TPM Boot Attestation for Air-Gapped Edge Updates
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Solution Overview
Problem
Edge Computing Devices in distributed edge networks face challenges in maintaining operational availability and security in geographically remote, disconnected environments, including physical attacks, network attacks, and the need for secure software updates without remote connectivity.
Innovation Solution
Implementing a system that uses a Trusted Platform Module (TPM) with platform configurable registers (PCRs) to measure the boot chain, predict PCR values for system updates, and employ enhanced authorization and monotonic counters to ensure secure access to encrypted resources and allow updates in air-gapped environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If remote attestation is used to ensure device trustworthiness, then security is improved, but connectivity requirements increase
Solution Approach 1:
The system performs preliminary measurements of the boot chain and stores expected PCR values before the device operates in air-gapped mode. This allows the device to autonomously verify its own trustworthiness without needing real-time connectivity to a remote attester, resolving the contradiction between security verification and connectivity requirements.
Solution Approach 2:
The device uses local TPM measurements and predicted PCR values to self-verify its trustworthiness state. Instead of relying on external remote attestation services, the device autonomously determines whether it should be granted access to encrypted resources, enabling air-gapped operation while maintaining security.
2Reliability
If strict boot measurement verification is enforced, then security is improved, but system update flexibility deteriorates
Solution Approach 1:
The system dynamically updates the expected PCR values stored in the TPM when legitimate software updates are applied. Instead of enforcing static boot measurements, the system adapts the verification criteria to reflect the new trusted state, allowing continuous security verification while supporting system updates and evolution.
3Reliability
If continuous connectivity to Trusted Controller is required for security verification, then security is improved, but operational availability in remote locations deteriorates
Solution Approach 1:
The system performs security verification using locally stored predicted PCR values before connectivity is needed for other operations. This preliminary self-verification enables the device to maintain operational availability in remote locations while still ensuring security, as it does not require continuous connectivity to the Trusted Controller.
4Adaptability or versatility
If manual access to remote devices is limited, then deployment flexibility is improved, but ability to detect and respond to attacks deteriorates
Solution Approach 1:
The device continuously measures its boot chain state and compares actual PCR values against predicted values, providing feedback about its trustworthiness. When attacks are detected (mismatched PCR values), the system can respond by denying access to encrypted resources, enabling automatic attack detection and response without requiring manual access to remote devices.
Data Source
AI summary
A computer-implemented method for establishing trustworthiness of an Edge Computing Device may include predicting a platform configurable register (PCR) value for a system update to generate a predicted PCR value, and then storing the predicted PCR value. The method may further include running the system update by storing updated software on the Edge Computing Device, measuring one or more aspects of the updated software to generate a measured PCR value, comparing the measured PCR value with the predicted PCR value to determine that the measured PCR value matches the predicted PCR value. Responsive to determining that the measured PCR value matches the predicted PCR value, secret information may be transmitted. Predicting the PCR value may include using a TPM log to generate a pre-calculated hash of one or more changed parts of the updated software. Enhanced Authorization may be used to generate an authorization policy including the predicted PCR value.