No, Sierra will not "break" your old DSA keys. But recent versions of OpenSSH disable these by default, for good reason. You can (temporarily, I would suggest)

No, Sierra will not "break" your old DSA keys. But recent versions of OpenSSH disable these by default, for good reason. You can (temporarily, I would suggest) reenable these with a one-liner in ~/.ssh/config. See for example http://www.openssh.com/legacy.html http://www.openssh.com/legacy.html