Please stop publishing md5sum and sha1sums

[Dimitri John Ledkov]

Please stop publishing md5sum and sha1sums

they are weak, and insecure. We already publish SHA256 and everyone should use that.

[Steve Langasek (vorlon)]

Don't we still have documentation directing users to check the md5sums to verify the integrity of their downloads? That needs to be fixed first.

Also if we're not asking users to do complete cryptographic verification with gpg, then checking a stronger hash instead of a weaker one doesn't add any real protection against an attacker because they can MITM both the image and the checksum downloads.

[Dimitri John Ledkov (xnox)]

1) no, we do not ask users to veryfiy md5sums, we only ask them to verify sha256.

2) the second concern is irrelevant to whether or not we publish 3 sets of checksums, or 2.

I will address point #2 anyway.

Note, that releases.ubuntu.com and ubuntu.com are both served with HTTPS. Our short form instructions tell people how to confirm sha256, which they have acquired over HTTPS. (see attachment)

The longer form tutorial instructions tell users how to use gpg as well. So that is documented as well.

https://ubuntu.com/tutorials/tutorial-how-to-verify-ubuntu#4-retrieve-the-correct-signature-key

All of the above is linked from the welcome page. Maybe releases.ubuntu.com / cdimage.ubuntu.com should link to the tutorial too.

[Steve Langasek (vorlon)]

https://help.ubuntu.com/community/HowToMD5SUM exists. Should it be deleted?

[Steve Langasek (vorlon)]

and the checksum verification page also still doesn't ask the user to use gpg, so it's still MITMable.

[Steve Langasek (vorlon)]

ok, you did address the gpg issue in your previous comment.

[Dimitri John Ledkov (xnox)]

and that page is a duplicate of https://help.ubuntu.com/community/VerifyIsoHowto which is the duplicate of the tutorial.

I'd rather make those pages redirect to the tutorial.

[Dimitri John Ledkov (xnox)]

I fail to login into help.ubuntu.com

[Erich Eickmeyer (eeickmeyer)]

Jumping in on this as anything affecting cdimage.ubuntu.com affects flavors as well.

Note that cdimage.ubuntu.com is not presented over https. In #ubuntustudio we've had people complain when the SHA256 they are presented with is not over https, so they assume the checksums could be compromised. I would be happy to direct them to that tutorial since we use cdimage.ubuntu.com for our iso links, except it's moot if the basic assumption is that everything on cdimage.ubuntu.com *could* be compromised if it's not https.

I understand the logistical issues with changing cdimage.ubuntu.com to https due to the various mirrors, but this seems to be coming up with more frequently since 20.04's release.

Basically, unless cdimage.ubuntu.com becomes https, in the eyes of a lot of people, verifying SHA256 is moot if they fear it's compromised due to lack of https, which means that entire tutorial doesn't really apply in their eyes.

[Steve Langasek (vorlon)]

Verifying SHA256SUMS without verifying gpg signatures is only useful for detecting corruption, not a malicious attack, with or without https.

[Erich Eickmeyer (eeickmeyer)]

Steve, I agree, but it's more of a public perception issue. There's nothing we can do to convince people otherwise.

[Steve Langasek (vorlon)]

It's a question of education. When someone claims they need checksums over https for security, it should be explained to them why this does not provide security.

[Adolfo Jayme Barrientos (fitojb)]

The Community Help wiki pages are now redirected to Discourse-maintained tutorial per rationale in comment 7