LibEvLog is a library that provides interfaces for parsing and handling TCG2 (Trusted Computing Group 2) event logs, which are generated during the pre-boot phase of a system. These logs capture measurements of critical components and actions by recording hash values into Platform Configuration Registers (PCRs). Each event in the log includes metadata about the measurement, its type, and the resulting PCR value.
Event logs play a key role in remote attestation, where a system proves its integrity to a remote verifier. While PCR values alone are difficult to interpret, the accompanying event log offers detailed insights into what was measured and when. As described in the TCG specifications:
Attestation is used to provide information about the platform’s state to a challenger. However, PCR contents are difficult to interpret; therefore, attestation is typically more useful when the PCR contents are accompanied by a measurement log… The PCR contents are used to provide the validation of the measurement log.”
libevlog makes it easier to work with these logs by providing structured access to the data, enabling inspection, analysis, and validation of system measurements.
| Tool | Minimum Version |
|---|---|
| Clang-Format | 14 |
| CMake | 3.15 |
To configure the project, use the following command. This will default to using GCC as the toolchain and create a build directory named build/:
cmake -B build
To build the project, use:
cmake --build build
This will output libtl.a in the build directory.
For cross-compilation or selecting a different compiler, specify the target compiler using CC or CROSS_COMPILE:
CC=aarch64-none-elf-gcc cmake -B build -DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY
HASH_ALGORITHMThis CMake option controls which hash algorithm the library is compiled to support. Currently, the library is designed to support only a single algorithm at a time, chosen at compile time. The selection sets corresponding preprocessor definitions, which configure internal behavior for digest size and algorithm identifiers.
HASH_ALGORITHM | Defined Macro(s) |
|---|---|
SHA512 | TPM_ALG_ID=TPM_ALG_SHA512, TCG_DIGEST_SIZE=64U |
SHA324 | TPM_ALG_ID=TPM_ALG_SHA384, TCG_DIGEST_SIZE=48U |
| (default) | TPM_ALG_ID=TPM_ALG_SHA256, TCG_DIGEST_SIZE=32U |
These macros configure the internal logic of the library for the specified hash function.
Note: The current implementation only supports compiling with a single algorithm. However, the long-term goal is to allow users to specify and use multiple hash functions within the same build. This will enable more flexible and dynamic cryptographic functionality.
To build the library with SHA384 support:
CC=aarch64-none-elf-gcc cmake -B build -DHASH_ALGORITHM=SHA384 -DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY cmake --build build
To build the library with default SHA256:
CC=aarch64-none-elf-gcc cmake -B build -DHASH_ALGORITHM=SHA256 -DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY cmake --build build