I have two MacBooks. One that still has Mavericks OS X and one that I just upgrade to Sierra OS X.
Since the upgrade I can’t connect via SSH to one of my Linux servers using the RSA/DSA Keys any more.
It always asks for a password. After adding the ‘-v’ option to the ssh command line, to see the handshaking, I noticed the following line:
debug1: Skipping ssh-dss key /Users/michel/.ssh/id_dsa - not in PubkeyAcceptedKeyTypes
After doing some research in Google, it was said that the DSA keys are no more ‘secure’.
In order to make it work again against the same DSA keys it was suggested to do the following which worked:

Note: This solution is not recommended to be used because of the old DSA keys.
In MAC edit(or create if not existing) the file ~/.ssh/config and add the following line:
PubkeyAcceptedKeyTypes +ssh-dss