4 ms·
Do you have reason to believe there's a problem with the gpg signatures in their repo?
by prutschman 6y ago
Do you have reason to believe there's a problem with the gpg signatures in their repo?
- bigiain 6y agoThe GPG sigs that are also published over MITMable unencrypted http? http://archive.canonical.com/dists/xenial/Release.gpg http://archive.canonical.com/dists/xenial/Release.gpg Yeah, I believe I see a problem there...
- theamk 6y agoWhich problem do you see? It's just a signature, they cannot be forged without a corresponding private key.
- AnthonyMouse 6y agoThe entire point of signatures is that you don't have to trust the channel that delivers them. The root of trust is the private key that comes with the operating system install ISO, but that you can download over HTTPS or have it delivered as physical media etc.
- jasonjayr 6y agoBut the public signing key, that's already installed via presumably verified initial media is already there, so unless their private key is compromised, which would be a bigger deal ....
- bigiain 6y ago> installed via presumably verified initial media This is not a universally correct assumption. How does this chain of trust bootstrap for a first time (or stand alone) user who downloads Ubuntu from a non-Ubuntu system? If I've got MITM, I can change both the ISO (with the totally-not-verified public key) as well as the gpg sig to match using a private key I know (and gave you the public key to).
- warkdarrior 6y agoSure. And how does a TLS connection for the ISO download solve this problem? You would need to make sure that the TLS connection is to the correct server. How do you check it is the right server? Probably by checking the hostname against some webpage and the TLS certificate against some CA roots in your browser. How you get the right hostname? How do you know the CA roots in your browser are correct? How do you know your browser executable and config are correct?
- bigiain 6y agoThere's an extremely wide range of adversaries between "potentially capable of MITMing a network I use" and "potentially capable of screwing with my OS/browser's CA roots or actively acquiring and misusing an illegally obtained valid TLS cert for ubuntu.com". Sure, most nation states can craft whatever TLS cert they want, with only some risk of bad press if they get caught signing a ubuntu.com TLS cert fraudulently via a CA they control/coerce. If those people are my adversary I'm screwed. "YOU'RE STILL GONNA GET MOSSAD'D UPON!" A TLS connection for the download (and the gpg signature) protects against people like the disgruntled hotel IT guy, the kid futzing with the cafe wifi, an evil housemate, some crappy rooted IoT shit somebody hooked up to the wifi, an overly curious coworker or corporate IT drone, the red team in a company pen test. I've heard the arguments here - that it's a difficult problem for all the mirror operators to add ssl certs, that it'll stop downloads being cacheable, etc. But I didn't really buy those arguments 5 years ago, and these days, with LetsEncrypt and HSTS - I think those arguments are even more bogus than they were in 2015...
- selfhoster11 6y agoSide-channel verification with the distro developers. Contact them over a channel that's unlikely to be compromised, get them to confirm that the keys in the system signature keyrings belong to them. Repeat for many channels until you get enough confidence.
- prutschman 6y agoFortunately, the ISOs themselves are served over https: https://ubuntu.com/download/desktop https://ubuntu.com/download/desktop links to https://ubuntu.com/download/desktop/thank-you/?version=20.10&architecture=amd64 https://ubuntu.com/download/desktop/thank-you/?version=20.10...