I have forked a project’s source code on GitHub. The program takes a private key as an input and that key must never leave the client. If I want to share a pre-built executable as a release it is essential that I can prove beyond reasonable doubt that it is built from the published source.

I have learned about how to publish the releases by using a Workflow in the GitHub actions such that GitHub itself will build the project and then repare a release draft with the built files as well as the file hashes…

However, I noticed that the release is first drafted, and at that point I have the option to manually swap the executable and the hashes. As far as I can tell, a user will not be able to tell if I swapped a file and its corresponding hashes. Or, is there a way to tell?

One potential solution that I have found is that I can pipe the output of the hashing both to a file that is stored and also to the publicly visible logs by using “tee”. This will make it such that someone can look through the logs of the build process and confirm that the hashes match the hashes published in the release.

Like this:

I would like to know whether:

  • There is already some built-in method to confirm that a file is the product of a GitHub workflow

  • The Github Action logs can easily be tampered by the repo owner, and the hashes in the logs can be swapped, such that my approach is still not good enough evidence

  • If there is another, perhaps more standard method, to prove that the executable is built from a specific source code.

  • HousePantherEnglish
    2•1 year ago

    Yes, there is no avoiding that. But it’s a way of saying that the executable was built by you.

    • MaxOP
      1•1 year ago

      Thanks. In the future I work using the Reproducible Builds practices and use OpenBSD to sign my builds.

      In the immediate situation I want to know whether there is a way to use GitHub as my trusted third-party builder. I would like to share something with people - some of who might not have the skills to replicate the build themselves, but I still would like to be able to point them to something that is easy to understand and give them argument.

      My current argument is: “See, in the github logs you can see that github generated that hash internally during the workflow, and it matches the hash of the file that you have downloaded. So this way you can be sure that this build really comes from this source code, which was only changed here and there”. Of course I need to make absolutely sure that my argument is solid. I know that I’m not being malicious, but I don’t want to give them an argument of trust and then find out that I have mislead them about the argument, and that it was in fact possible to fake this.