Edit: updated with a fix for Sequel Ace connection issues too.

Suddenly unable to ssh into servers that you used to? Did you recently knowingly or unknowingly upgrade to MacOS Ventura?

You’ll need to add this to the top of your Mac’s ~/.ssh/config file:

PubkeyAcceptedKeyTypes +ssh-rsa

Without it, you’ll just get a Permission denied (publickey) error.

The underlying problem is that Ventura ships with OpenSSH_9 which disables RSA/SHA1 keys, and the real issue is that the server being ssh-ed into, doesn’t support RSA/SHA256. Upgrading the ssh server itself to one that supports RSA/SHA256 would fix the issue.

More detail in this Stackoverflow question.

Sequel Ace connection issues

You might find that even with that change, Sequel Ace refuses to connect, and you get a giant dialog with debug ssh output:

sequel ace can't connect ssh

That’s because Sequel Ace ships with its own default ssh config file which you can edit /Applications/Sequel Ace.app/Contents/Resources/ssh_config, add PubkeyAcceptedKeyTypes +ssh-rsa to the top of the file, save and then restart Ace. Or, more correctly, you can point Sequel Ace at your own ~/.ssh/config using Sequel Ace → Preferences → Network → SSH config

sequel ace use own ssh config

as this issue on github suggests.