New-Tech Europe Magazine | June 2016

Figure 5 Intel TXT

CPU provides protected partitions for hardened access to memory. The platform controller hub (PCH) enforces memory protection policy and provides protected data transfer to graphics hardware and input/output devices. The PCH also interfaces to the trusted platform module (TPM), a hardware device that generates and stores cryptographic keys, stores the platform state during the secure boot process, and supports reporting or attestation of the secure state of the system. Figure 5 shows the steps for a secure Intel TXT boot process. Measure and Extend: 1. After system reset, the BIOS boot block acts as the core root of trust for measurement (CRTM), and

measures the system BIOS, the first initially untrusted component. The measurement is a hash value of BIOS code, and is stored in one of the TPM’s platform configuration registers (PCRs). The storage operation is actually a concatenation of the existing PCR contents with the new measurement information, which means the stored value reflects any changes made to the system since the last boot. This process is called extension. 2. The BIOS measures the hardware and the master boot record, and extends the PCR. 3. The master boot record measures a pre-loader for Intel TXT, Loader 1, and extends the PCR. The pre-loader prepares memory for instructions

that initiate trusted execution.

Verify: 4. Loader 1 verifies the authenticated code module (ACM). The digitally signed by Intel that verifies a list of applications that can be run next. 5. The ACM verifies Loader 2, which verifies platform configuration registers, system management mode code, and the operating system loader. Execute: 6. Operating system loader prepares for and then launches the operating system. TPM operation: 7. The secure operating system can

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