The main piece that's platform specific is the Verified badges that you see in the UI + any CI checks.
What the sigstore project does is having an oauth portal which can authenticate one of your online identities. It uses this to sign a temporary certificate for you with it's root CA. This certificate is what you use to sign commits and artifacts with.
https://docs.sigstore.dev/fulcio/certificate-issuing-overvie... has a good overview of how the certificate issuing works.
With Gitsign, by default a new keypair is generated per signing event (i.e. per commit) and never hits disk. The cert in the commit signature holds the public key, which we can check against Rekor (https://docs.sigstore.dev/rekor/overview) to verify it was valid at the time of signing.
If you have the time, https://www.youtube.com/watch?v=PVhRQFS9Njg is a great deep dive into how Sigstore works in general!
This is all based on public key cryptography. In public key cryptography, there are actually 2 keys, a public key and a private key. Sites like get hub and the repose can store the public keys, while into while individual users keep their private key's secret. Anyone with the public key can verify a signature, but only an individual with the private key can create the equivalent signature.
The trick is to determine if a given public key corresponds to an individual. There are various methods to try to address that.
I hope that helps!
This isn't supported by GitHub yet but we're hopefully working towards that too.