This repository accompanies the paper "ZEKRO: Zero-Knowledge Proof of Integrity Conformance" and provides a research implementation of the evaluated protocol.

This repository is organized as follows:

• swtpm: Contains a containerized implementation of IBM's Software TPM 2.0.
• zekro: Contains a containerized implmenetation of an example execution of the ZEKRO protocol which uses IBM's TPM 2.0 TSS.
• docker-compose.yml: Configuration file which spawns both zekro and swtpm and configures zekro to target the software TPM running inside swtpm.
• docker-compose-hwtpm.yml: Configuration file which spawns zekro and configures it to use a hardware TPM avilable on the host. Currently, this file assumes that the host system runs Linux and that the TPM device is exposed under /dev/tpm0.

To quickly run the provided compose configuration files, you need Docker and docker-compose installed.

To build and run the demonstrative application against IBM's Software TPM 2.0 from a terminal, simply change your current working directory to the base of this repository and execute the following command:

docker-compose -f docker-compose.yml up --abort-on-container-exit --force-recreate --build

If you have a hardware TPM available on your host system, then you can build and run the demonstrative application against your hardware TPM by executing the following command:

docker-compose -f docker-compose-hwtpm.yml up --abort-on-container-exit --force-recreate --build

Note that each of the configuration files includes environment variables and build arguments that can be adjusted to enable and disable TSS tracing (which outputs detailed information about the executed TPM commands) and control where and how timing information is logged. To enable or disable a build argument, set its value to either 1 (enabled) or 0 (disabled). These are the currently available arguments used during the build phase:

ENABLE_TIMINGS=1 # record execution time of each TPM command (1)
WRITE_TIMINGS_TO_FILE=1
WRITE_TIMINGS_TO_STDOUT=1
DEBUG_TSS=0 # output trace of TSS<->TPM communication
HWTPM=0 # use a hardware TPM (1) or software TPM (0)

By default, timing information is written to the /tmp/timings directory inside a running container (as determined by the TIMINGS_DIR environment variable), which bridges to the ./timings/ directory on the host. If you want to change the output directory on the host, simply modify the following line in the respective configuration file:

volumes:
  - /output/directory/on/host:/tmp/timings

It is also possible to directly build and run without Docker support using either an IDE (e.g., vscode) or directly in a terminal. For example, to build the demonstrative ZEKRO protocol using CMake from a terminal, change your working directory to the zekro subdirectory of this repository (where the zekro/CMakeLists.txt file is located) and then execute CMake (note here that we manually pass in the build arguments):

cmake -DENABLE_TIMINGS=1 -DWRITE_TIMINGS_TO_FILE=1 -DWRITE_TIMINGS_TO_STDOUT=1 -DVERBOSE=0 -DHWTPM=0 . && make

Once the program has been built, you can run it by executing:

./zekro

Note that if you do not use Docker, then the TIMINGS_DIR environment variable (which you must set manually on your system) directly determines the output directory of the timing information (when compiled to write to files). Furthermore, you need to correctly set up IBM's TPM 2.0 TSS on your host system before you can build correctly. Finally, unless you have a hardware TPM and compile the program to use the hardware TPM, you need to have IBM's Software TPM 2.0 up and running before executing the program.

The implementations provided in this repository are only research prototypes.

This library is licensed under either of the following licenses, at your discretion.

• Apache License Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

Unless you explicitly state otherwise, any contribution submitted for inclusion in this library by you shall be dual licensed as above (as defined in the Apache v2 License), without any additional terms or conditions.