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:
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There is already some built-in method to confirm that a file is the product of a GitHub workflow
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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
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If there is another, perhaps more standard method, to prove that the executable is built from a specific source code.
A reproducible build is more than an automated build. It is a build process which enables any third party to build a binary that is bit-by-bit identical (see https://reproducible-builds.org/docs/definition/).
So if I would build a specific release/commit of your application on my PC (given an identical development environment, i.e. same version dependencies, compiler, etc.) it MUST result in a bit-by-bit identical binary to the one you built on your development machine and the one the github workflows built.
All these binaries would result in the same hash (and thus be verifiable by the same signature files).
Other than a signed binary from a trusted developer/organization, there is (IMHO) no way for a non-tech savvy user to gauge the trustworthiness of a binary they download from the internet, and even then a signing key might have been lost or broken (see the recent Microsoft debacle w.r.t. AD signing key misuse).
Thanks a lot. I have been evangelized by you and the other commenters. I see now that reproducible builds is the solution.
I now understand better the value of reproducible builds, and the more I think about it the more I realize that it is very bad that something as sensitive as a crypto wallet executable that does not follow the reproducible build standard has been going around. I do trust that the devs are not being malicious, but it is essential to have a good way to verify. Even the original github workflow is failing to build now, and new flags need to be passed to npm while building due to some openssl changes, so I'm not sure that anyone can actually reproduce the build today and get the same hash.
I'll read more about how to do it properly, and I'll try to create a Reproducible Build fork if I can actually pull it off.