Trusted Device Mediates Trust Validation for Unknown Computing Platforms
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Solution Overview
Problem
Users cannot securely utilize unknown computing devices, such as public kiosks, for sensitive tasks due to the lack of control over the device's TPM and uncertainty about its trustworthiness, as existing mechanisms require communication with a certifying authority which may not be feasible in all scenarios.
Innovation Solution
A trusted device, which can be a portable storage device or a server, performs trust validation by examining the unknown device's event log and PCR values, using an encrypted volume and decryption key to establish trust, allowing the TPM to unlock the decryption key only if the device is deemed trustworthy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a TPM chip with PCRs is used to verify boot process integrity, then malicious code can be detected in controlled devices, but users cannot trust unknown devices like public kiosks because they cannot verify TPM integrity or know appropriate PCR values
Solution Approach 1:
The patent introduces a trusted device as an intermediary that carries a trusted volume containing validation software and expected PCR values. This trusted device mediates between the user and the unknown computing device, allowing trust validation without requiring the user to directly verify TPM integrity or know appropriate PCR values. The trusted device acts as a portable certificate authority that can validate any TPM-equipped device.
2Reliability
If direct communication with a certifying authority is required for trust validation, then trust relationships can be established, but users cannot use unknown devices in scenarios where such communication is not feasible
Solution Approach 1:
The trusted device contains all necessary validation capabilities locally, including the validation software and expected PCR values in the trusted volume. This allows the trusted device to perform self-service validation of unknown devices without requiring external communication with a certifying authority. The entire trust validation process is self-contained within the trusted device, making it operable in offline or isolated scenarios.
3Device complexity
If the TPM is assumed to be untampered in owned devices, then simple PCR verification suffices, but in unknown devices the user cannot be certain the TPM itself has not been tampered with
Solution Approach 1:
The patent implements preliminary sealing of the decryption key to the expected PCR values during the trusted volume creation process. This preliminary action binds the trusted volume to specific, known-good PCR values representing a trusted boot state. When validating an unknown device, the system compares the device's actual PCR values against these pre-established expected values, thereby verifying TPM integrity without requiring complex real-time analysis during the validation moment.
Data Source
AI summary
A transparent trust validation of an unknown platform can be performed by communicationally coupling it to a trusted device, such as a portable peripheral device carried by a user, or one or more remote computing devices. Information from the unknown platform can be obtained by boot code copied to it from the trusted device and such information can be validated by the trusted device. The trusted device can then provide an encrypted version of decryption key to the boot code which can request the Trusted Platform Module (TPM) of the unknown platform to decrypt and return the decryption key. If the information originally obtained from the unknown platform and validated by the trusted device was authentic, the TPM will be able to provide the decryption key to the boot code, enabling it to decrypt an encrypted volume comprising applications, operating systems or other components.