Don't manage SSH ciphers on bullseye

[mweinelt]

The OpenSSH daemon comes with reasonable defaults these days, so don't
try to manage that, by copying the same cipher list from release to
release.

Between Debian releases there is usually a large overlap over compatible
ciphers, so there shouldn't be any fear of breaking compatibility
between Proxmox VE releases either.

---

It might be reasonable to do the same on buster, but since I'm starting
a 7.0 cluster right now and I don't know the entire reasoning behind this
setting, I'm erring on the conservative side.

[lae]

pvecm add (when you go to manually stand up a cluster) iirc does this to disable weak ciphers, so this task emulates that behaviour.

Is it erring out somehow?

[mweinelt]

No, it is not erroring out, but it is also just pinning the current (openssh 7.9) default cipher list and therefore provides no added value.

From the man 5 sshd_config

The default is:

chacha20-poly1305@openssh.com,
aes128-ctr,aes192-ctr,aes256-ctr,
aes128-gcm@openssh.com,aes256-gcm@openssh.com

Ideally one would manage acceptable ciphers, as well as MACs and KexAlgorithms in an sshd_config using Mozillas recommendations, but that is probably out of scope for this role.

https://infosec.mozilla.org/guidelines/openssh

[lae]

I guess there was another reason - from: https://git.proxmox.com/?p=pve-cluster.git;a=blob;f=data/PVE/Cluster/Setup.pm;h=1f064775af3cc4b2ac12a59d7d8abb7283f4b998;hb=HEAD#l162

# changed order to put AES before Chacha20 (most hardware has AESNI)

I'm not sure if making something that's hardcoded in PVE itself optional has any effect on support (this role is meant to mimic PVE tooling wherever it can't use them directly), but this seems like a relatively harmless thing to change in the first place. I'll wait to see if anyone else has any thoughts.

[mweinelt]

Pretty sure that we should prefer chacha20-poly1305 these days, in spite of AES-NI support in hardware, I trust the OpenSSH upstream alot more to make good decisions.

I feel we as sysadmins are in a good position to make better choices that don't break any compatibility.

[lae]

Some further research:

https://lists.proxmox.com/pipermail/pve-devel/2017-August/028157.html Discussion behind the change to the ordering of ciphers
https://old.reddit.com/r/sysadmin/comments/c62owo/10_gbits_connection_but_only_1_gbits_via_scp/ Real world example of performance degradation with chacha20 on 10gbit vs AES

I vote that we keep the behaviour PVE imposes by default on both distributions. I'm fine with converting the pve_ssh_ciphers variable into a role variable so that administrators can override it, however. If you could, can you rebase this on the develop branch/force push a new commit that does this?

[mweinelt]

Putting it on my todo list.

[lae]

Rebased against develop to at least cleanup the unrelated/unmerged commits from the old pve7 branch.