SSH log with key

Reference: 

https://www.digitalocean.com/community/tutorials/how-to-configure-ssh-key-based-authentication-on-a-linux-server 

Step 1 — Creating SSH Keys in Client

On your local computer, generate a SSH key pair by typing:

ssh-keygen

Output
Generating public/private rsa key pair.
Enter file in which to save the key (/home/username/.ssh/id_rsa):

The utility will prompt you to select a location for the keys that will be generated. By default, the keys will be stored in the ~/.ssh directory within your user’s home directory. The private key will be called id_rsa and the associated public key will be called id_rsa.pub.

Step 2 — Copying an SSH Public Key to Your Server

The full command will look like this:

cat ~/.ssh/id_rsa.pub | ssh username@remote_host "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys"

You may see a message like this:

Output
The authenticity of host '203.0.113.1 (203.0.113.1)' can't be established.
ECDSA key fingerprint is fd:fd:d4:f9:77:fe:73:84:e1:55:00:ad:d6:6d:22:fe.
Are you sure you want to continue connecting (yes/no)? yes

This means that your local computer does not recognize the remote host. This will happen the first time you connect to a new host. Type yes and press ENTER to continue.