Even after the vomiting, I'm still unclear what they're actually doing.
It's either:
- A sort of locked-down build area, where they import some code, build it and package it up, and presumably put it into a locked-down repository
or:
- A way of adding a cryptographic signature or similar to the meta data in an OSS projects releases
It's some of both, and some more stuff.
It's a combination of a build environment that produces reproducible builds (meaning every time you do a build of a given source you get a bit-identical output -- this is not a property of most build systems[*]), plus signed metadata of source and reproducibly-built binaries, plus hosting of the above so that if you don't want to go to the effort of creating and checking the reproducible builds yourself you can just check against Google's system.
Note that all of this is harder than just "check the hash of the source code" because even if the source code is pristine changes can be injected by the build process. See Ken Thompson's classic Reflections on Trusting Trust.
Unless you're testing the code in some way to make sure it's at least vaguely doing the thing it claims, then it sort of doesn't matter how much you trust the build or delivery services - a well built bitcoin miner is still malware.
Sure, if you don't have a reason to trust the source code you can't trust the binary. Nothing can fix that. What this does do is let you know that if a bitcoin miner got slipped in, it was slipped into the upstream project, not at any point in the distribution path. You still have to rely on the upstream developers not to do that, and to notice if someone gives them a malicious patch, or that someone else notices the miner (or something worse) in the source code and raises a stink about it.
Then there's the issue of trust - do you trust Google to provide 'safe' builds?
All of the tools are public, open source, so you can independently recreate everything Google is doing. Obviously you'll have to generate your own signing keys.
No idea, couldn't penetrate the buzzword bingo business lingo.
There is hardly any of that in TFA. What there is a lot of is security jargon, especially related to build provenance. Unlike business buzzwords [**], the jargon terms all have precise meanings. If you really want to understand it, you should start by reading the SLSA specification.
[*] It actually looks like oss-rebuild works with build systems that don't quite support reproducibility by doing binary diffs and determining which differences are innocuous (e.g. the compiler embedded a build timestamp) and which might indicate that something is wrong.
[**] Actually, it's often true that business "buzzwords" also have precise meanings which are unknown to the people who deride them.