For me, it's not enough to verify the integrity of an ISO – I also have to verify its authenticity (or at least verify the checksum file) with GPG. I don't know why, but just need to see that "Good signature" message before I feel safe installing Linux.
I notice, though, that the download pages of some prominent distros (Pop_OS!, openSUSE, etc) just give you a checksum, probably because they feel that anything else is unnecessary. This makes me shy away from installing them, which is a shame because I'd like to give some of those distros a try on bare metal.
Am I being paranoid when it comes to installing Linux?
What is the benefit of a gpg signature over a checksum? In either case you have to trust someone.
Signature = authentication: signed (presumably) by the private key of the project owner(s).
Checksum = integrity: confirms the file hasn't been corrupted or tampered with in transit.
If the checksum file is signed by the project owners, that's the highest guarantee available that the file on your local is identical to the one compiled by the project owner(s).
Where do you get the public key to verify the signature from? My point being, that you have to trust someone. I don't really see the benefit of trusting a key server, that the public key really belongs to the owner over a checksum file being published on the website of the owner.
You mean trusting a key published on a different site (and replicated between all GPG key registries), Vs a checksum published on the same website that's serving you the suspect ISO?
Which do you think is more likely to also be compromised?
Oh you are absolutely right about it being much harder to compromise the distro website as well as a key server. And as much as I am aware of the concept of the web of trust, I still do not get how you securely draw a relation between a key on a third party website and the publisher of a distro?
I just checked for OpenSuse and Fedora. Both link to their keys on their own website, which both target files on their own domain. And even if they linked to a third party, what is stopping an attacker, who already managed to swap the iso and checksum file to also change the link to the key server?
You are right about already imported keys. But why would someone, who does not already have distro xyz installed, have the keys of the publisher of distro xyz imported?
Thanks in advance for the discussion!
You publish the master GPG key in a DNS record for the website you download from, and you sign the DNS records with DNSSEC. (Yes I know, ironically the TLS cert for the page with the explanation has expired last month…) You can also use DNS records to enable autodiscovery of the GPG keyserver hosting the relevant master key.
Once you have one GPG key you can trust you can use it to verify downloads as well as other GPG keys.
Unfortunately most Linux distros don't use DNS records. Most of them publish the GPG key on the same page as the checksum, which can be compromised just the same, you are correct. Some of them publish their key on a separate keyserver, but to find that key you need to know its fingerprint or its associated email address… and if those are provided via the download page then you're back to square one. 😆
TIL about GPG keys in DNS records. Thanks, that is indeed a real benefit!
Thank you. I think the issue here is most people (unlike you) have no clue what I'm talking about, which explains the immaturity in the comments section.
GPG keys are hosted on separate websites not on the distro's website, and also replicated (there are multiple GPG key registries) and if you have previously used a GPG key you already have it.
So now let's see. With just checksum, the attacker that wants you to download their malware-riddled ISO just has to break into the distro's website and change the checksum in one place. If they managed to break in and change the ISO there's a good chance they can break in to change the checksum too.
On the other hand, if the distro publishes a GPG signature, the attacker would have to compromise all the GPG registries and may still fail if you already had the good key.
Even if they managed to do that, if the key is used to sign other downloads, that the attacker hasn't changed, now the signature check will start failing for those, alerting other people.
It's just a lot harder to falsify downloads signed with GPG than just checksums.