SSH commit verification now supported
github.blog
github.blog
Seems to be a pretty new feature too; [1] claims it's from November 2021.
This isn't supported by GitHub yet but we're hopefully working towards that too.
The main piece that's platform specific is the Verified badges that you see in the UI + any CI checks.
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!
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!
(Using a burner has the problem that a valid-looking mail might have people legitimately try to reach out, which is not nice)
https://docs.github.com/en/authentication/managing-commit-si...
`ID+username@users.noreply.github.com`
Example: https://github.com/grncdr/dev-mode/commit/06376070aff042e9d5...
Maybe try removing and adding the public key from your account? That might trigger the system to scan all your commits and re-verify.
It does?
>Why shouldn't I be encouraged to have 2 or 4 or 10 identities if I want to?
What is stopping you?
At least the OpenPGP smart card specification kind of does, yes.
It uses a "single private key stored on the card" (ok, actually three keys) model, whereas FIDO (including SSH‘s security key implementation) uses key handles, which theoretically support an unlimited number of keys per authenticator.
You can achieve that yourself, for example, using Pass. Encrypt theoretically unlimited number of password and secret keys with the master password in the hardware token.
It can be, but it‘s essentially just a binary blob. It can also be entropy to deterministically re-derive a private or secret key from an internal root secret, or just a primary key to look up that key or entropy within the token.
> You can achieve that yourself, for example, using Pass.
How? With a hardware token, you can only do what its protocol allows you to in terms of key derivation.
That means that with a standard OpenPGP card, you will not be able to do key handle based key derivation, while with FIDO/CTAP you can.
You could obviously develop your own OpenPGP-compatible hardware token standard, but you‘d only be able to use it with a patched version of GPG, GPG agent etc, but a big advantage of OpenPGP smartcards (and even more so FIDO/CTAP tokens) is that they are widely supported without requiring driver installation.
Of course certain projects (especially if very critical or secure systems) definitely benefit from that but imagine you put your handwritten signature on every single step of your work (hint: you don't do that in the real World). You would never do so for normal internet activity like Google searches, Twitter or Facebook yet you want to sign your git commits with a signature undeniable connected to yourself, probably also connected to your real name.
If you just think that signing is just a "cool feature to have" then you should really educate yourself about implications of having a connected (real name?) identity on the internet.
[1] https://en.wikipedia.org/wiki/Plausible_deniability
[2] https://legaldictionary.net/plausible-deniability/
P.S.: I just wanted to make people think before activating this feature. Most GitHub code and repositories worked perfectly without it. Do you really need it? When yes, why?
Committing code is not like browsing facebook, or searching on google. Even then, your name is on any posts you're making on twitter or facebook, and i'm sure google knows what you're searching.
As a maintainer, why would you want people to be able to deny making a given commit? or have them come in completely anonymously?
How can this be proved? Even with signing, anyone can impersonate anyone.
PGP encrypted public messages is common even on the dark web.
1. Because you trust code for what it is and are willing to trade attribution surety for a lesser ask of contributors
2. Because you care about certain principles of anonymity and non-repudiation and want to respect them in your own plainly legitimate project.
3. Because your project is or risks becoming illegitimate in some jurisdiction and you want to protect your contributors as best you can.
It'd be nice if we can continue to respect these reasons as valid even while allowing other maintainers to exercise different policies.
1. This is not even a moderate ask; using ssh for git transactions is no more or less burdensome than https
2. As has been pointed out, there is no reason or reliable way to verify the identity of a creator's SSH key
3. Real-world example of such a project, or why this matters in the context of (2)?
GitHub exposes your public key via it's API. (Why? I have no idea. I call it a privacy violation) So, you need to create new github identity for every SSH identity that you wish to remain anonymous for, otherwise they just get tied together & one aspect of anonymity is lost.
How does that expose any more information than you do by pushing a commit with a GitHub account?
As a user of code published on Github, I sure as heck want there to be clear ownership and authorship of the code I use, and to be able to hold them accountable for malice. And there is lots malicious code on Github, trying to disguise itself as legit; Having a strong public persona isn't guarantee that my github code isn't malicious, but it does raise the stakes.
As a human who has seen what happens when people commit mistakes, we're very emotionally bad at dealing with mistakes. "Who broke the vase?" is a tough question to ask. "Who broke the build" can carry the same weight - Both very little, and very much, depending on when it's asked and how expensive the vase was. I'd like to think that making mistakes will be easier in a merkle-tree structured world; That as a collective, we will learn to do a better job of helping people admit their mistakes, come forward with them, and say "I made that mistake, and have learned from it". The internet has proven that false again and again.
In two important ways - People are unwilling to forgive, and people are unwilling to admit. Past minor mistakes haunt people forever all the time. Look at things like "Has Justine Landed Yet?"[1].
A malicious liar (We'll call them Eve) will deny, refute, and plain old lie in the face of whatever. There can be incredibly convincing evidence (A RSA-Key Verified Git Signature, for example) of... whatever, and it will be written off as "Harassment" by friends of Eve. Further: There's plenty of actual malice that passes itself off as not. Rapists say "She clearly wanted it, she got wet" - Criminals do that at all levels, making up excuses for why their victims deserved it.
Regardless - It is a sea change to be held accountable for your code. I do want it, but I do not believe that SSH key verification will achieve that. I think it will be a significant change when it does happen, though, and one with significant consequences.
[1]https://www.nytimes.com/2015/02/15/magazine/how-one-stupid-t...
Having your real name on the GitHub account but not having a commit sig is not really that strong deniability anyway.
If your thinking about some situation where you are being legally hounded because of code (e.g. DMCA, tornado cash situation etc) they will subpoena your hardware and likely find enough evidence that you can't plausibly deny writing the code anyway. GitHub logs may show you the upload was with a SSH key or http auth associated with you anyway.
For non legal situations, I suspect most observers won't really believe that a non-signed upload could have been done by someone else. Especially if it's to a repo only you have upload permission to or something.
In most engineering or engineering adjacent fields you are doing this, btw. Yes, in software too.
Websites from Google search result are verified by my browser via HTTPS certs. On twitter or facebook, users usually trust the centralized authnz systems hosted by the platform to verify content ownership. But out of box, git allows you to use whatever name/email on your commit, so that's a problem.
In my whole career, there were 3 times that I got questioned about "why did you introduce this line of code, which caused some production issue?" and turned out to be results of someone junior developer's rebase/amend or whatnot. I pointed out that I always sign my commits and those unsigned ones were not mine. Without signature I really could not tell whether I was the author or not, since some commits are months/years old.
I believe those altered commits were honest mistakes without malicious intention, and our organization has blameless culture. But I still want to let my coworkers know that I am not the one who caused this problem. Signing commits helps a lot in these situations and clears misunderstanding, and I believe more or less impacted my performance review and bonus (my performance would probably not be as good if I had to own those incidents).
CI/CD tools are getting better each day, a commit can mean a lot more than "a snapshot of the code base", like, it could have been a checkpoint of the state of the production environment (IaC, GitOps ... etc). You already have your name on the commit, so why not offer a way for others to verify you are really who you say you are?
And I should probably clarify, that the identity of a git commit does not have to be linked to a human in real life. It's just a way to verify that a commit is really from author X and not Y.
Systems are typically unsecured until someone starts abusing it. GitHub has obviously foreseen this possibility which is why they have the infrastructure in place to restrict freedom in the interest of security. The day someone starts aggressively misusing that feature, they could take it away just like that.
Edit: Turns out this still uses gpg? I think?
Anytime you use that public key (for example, to SSH into a server) that session is linked to your identity via git commits (this doesn't actually matter for github, as github exposes all your SSH keys via its API anyways).
However, the OpenSSH team were very careful to design their signature feature so that what is signed is always different from any possible SSH login.
Now, of course if you sign a text document which says "I want Bill to have all my stuff" but you meant, you know, Bill at work, can keep my stapler and that cool glow-in-the-dark mug, because I'm leaving next week and I can't be bothered to box it all up and take it, whereas your 2nd cousin William tries to persuade a judge it's a legal Will, and so your untimely death in a car crash should result in him inheriting everything instead of your bereaved wife and six year old daughter - well, that OpenSSH can't do anything about.
But you would be correct to assume it is not safe in general to use keys for unrelated purposes, and only the (documented and justified) choice by OpenSSH reverses that assumption for the SSH tools.
Nope, it uses your SSH agent. It's super confusing because the git config key is `gpg.format` (which you set to `ssh`), but I promise it works without GPG installed.
I suspect this confusing name is because when support for signing commits was originally added to git it only supported GPG, and a bad choice on the parameter name was made.
This below doc indicates "no" but if not then, when?
> To set your SSH signing key in Git, paste the text below, substituting the contents of your clipboard [which contains the public key] for the key you'd like to use. Since the key contains spaces, you must wrap it in quotes:
https://docs.github.com/en/authentication/managing-commit-si...
Or am I missing something?
So far, we trust GitHub that a certain repo is under control of a certain individual or organization.
We trust Twitter that a tweet was done by Elon Musk and not by Joe Doe. We trust Instagram, that Sue really got a like from that famous influencer and did not fake it. We trust HN, that I wrote this comment.
But if signing these things would become the norm, commits, tweets, likes and posts would become eternal. Independent of any central authorities.
Unfortunately, it will probably not become popular. As there is nothing to gain for the author of a commit by signing it.
All of the recent focus on supply chain security could result in signed commits becoming more routine.
The problem is that unless there is a big stick, like a cybersecurity insurance company saying "unless you use U2F keys for 2FA, you are not covered", there is no incentive to change.
I mean, if you heard the horror stories of how a particular ex President's twitter password was incredibly insecure without even two factor auth you'd understand that users just don't care about anything even close to security.
I still long for the old days of tech when you at least had to figure out how a 56K modem worked to use it. You at least had to respect the ancient wizardry or incur the wrath of the Code Gods.
The amount of people using 1Password / Elliptical Curve Encryption / MFA in 2022 is effectively zero because everything has be ultra optimized for ease of use.
AFAICT, the new thing here is that you can use SSH instead of GPG to sign commits, which should hopefully make it easier for people to adopt.
It helps avoiding spam, as its only used for just confirming the author.
Sure, you might trust Facebook, and so knowing that React 18.0 was indeed signed by Facebook is interesting. But then React depends on leftpad, is-odd, reversearray, ... by random devs. What security do you gain by verifying the random signatures from random devs?
Unless there is a way for Facebook to sign those transitive dependencies, vouching for them in a way that you can check. That would be something. But their authors signing them does nothing.
git config --global "gpg.ssh.program" "C:/Program Files/OpenSSH/ssh-keygen.exe"
The only thing I could see it really preventing is a malicious employee making a commit with obviously bad code in someone else's name, but with branch protections enabled, it wouldn't go to prod without someone else catching it.
You are massively overconfident about the protections code review provides. But even if you _are_ confident in code reviews, you can push code to someone else's PR under their name, then approve it yourself and ship it yourself.
It also opens up social engineering vectors. Create a PR by CEO/CTO/Senior Security Engineer/whatever, with some critical sounding bug fix impacting $BIG_CLIENT, then you DM someone "hey, $IMPORTANT_PERSON needs this shipped ASAP, can you help us out with a quick +1?"
Of course, who knows how long that bad code could sit in prod before it gets noticed is a toss-up, and preventing it from happening is going to be infinitely better than just logging it.
Got any other scenarios that commit signing would solve?
i.e What happens if I push a SSH signed commit to a Gitlab or Bitbucket remote or mirror the repository? How do the commits appear to a client that does not understand SSH signatures?
It's always possible some program handles this badly, but I've been signing with ssh pretty much since the day it was added to git (before it was in a release) and never experienced any problems or complaints.
git config --global "gpg.ssh.program" "C:/Program Files/OpenSSH/ssh-keygen.exe"
EDIT: Interestingly, updating gave me a neat suggestion to use:
git config --global --add --bool push.autoSetupRemote true
I had upgraded git to get `git switch`