Add a new SSH Key to a server digital ocean

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your machine: ssh-keygen in ~/.ssh -> all the defaults
your machine: pbcopy < thenewkey.pub
On server: append to ~/.ssh/authorized_keys the new public key - either via gui or another machine
your machine: ssh-add the thenewkey ( this is the private key )

// another thing to try
your machine: sudo nano /etc/ssh/sshd_config
alter -> PasswordAuthentication yes 

sudo service sshd reload