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Flow for Integrity Measurement

In assessing the measurements, the TAA references a set of properties. These properties represent attributes and measurements for the BIOS and the operating system and virtual machine monitors. These measurements are referred to as golden measurements or whitelists, and are:

• Provided and verified and validated through certificates by the original equipment manufacturer (OEM))

• Provided and vouched for by an ISV Service

• Collected by an authenticated administrator on first boot in an isolated or enclave type of environment

The process for carrying out the integrity measurement and verification is as follows:

1. When a new instance of a BIOS or an operating system or virtual machine monitor is made available, an initial set of trusted measurements (golden measurements) is taken on the image. These measurements are provided either through third parties such as an OEM, operating system, virtual machine monitor supplier, or through a trusted whitelist service provider to the trust authority, It may also be generated at initial provisioning by system administrators.

2. An RTM such as Intel TXT is used to take the measurement of the software components during server or device boot.

3. The measurements are stored in the TPM. A log from which the measurements can be reconstructed is stored in memory for transmission to the verifier to allow reconstruction of the measurements.

4. The TAA generates an authenticated request for measurements from the server/device, in response to an action by any requester, or the endpoint device requesting a service. This action follows the attestation protocol previously described. The trust agent receives this request and passes it to the TPM to obtain a TPMQuote for the requested PCR measurments. TPMQuote, along with the measurement log, are packaged as an integrity report, using the TCG Integrity Reporting Schema.

5. The trust agent transmits the data to the TAA's verifier. The TAA verifies the signature over the hashes by inspecting both the public key used to sign them and the signature itself, which will ensure that the nonce sent to the trust agent is the same one as the one used in the TPMQuote. It then compares those signed measurements with the golden measurements obtained earlier. There is more than a simple comparison.

Depending upon the sophistication of the verifier, it can use the system measurement log (SML) to re-compute the aggregate measurements from the individual measurements, and then verify them against the golden measurements.

6. The results of the comparison, collated with other such comparisons from other machines and digitally signed, may be displayed via a user interface, such as a management console or dashboard, to the administrator or it can be provided through an API to an automated enforcement, policy engines, and orchestrators. Solutions use the results to apply, manage, enforce, and report on the trust level of the systems.

 
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