Problems with the Static Root of Trust for Measurement

In 2011 the National Institute of Standard and Technology (NIST) released a draft of special publication 800155. This document provides a more detailed description than the Trusted Platform Module (TPM) PC client specification for content that should be measured in the BIOS to provide an adequate Static Root of Trust for Measurement (SRTM). In this paper we look at the implementation of the SRTM from a Dell Latitude E6400 laptop. We describe how the implementation of the SRTM on this system doesn’t meet all the requirements set forth by both the TPM PC client specification and the NIST guidance. We also show how a 51 byte patch to the SRTM can cause it to provide a forged measurement to the TPM indicating that the BIOS is pristine. If a TPM Quote is used to query the boot state of the system, this TPM-signed falsification will then serve as the root of misplaced trust. We also show how reflashing the BIOS may not necessarily remove this trust-subverting malware.