0. Installing SSH Key

If you have the latest Windows 10 update, you should already have the OpenSSH installed.

However if the ssh command doesn’t work or you’re using an older version of Windows, you can install OpenSSH manually by finding it on Google or from https://chocolatey.org/packages/openssh

1. Create a SSH Key

To create this key, you simply type the following command in cmd/terminal:
ssh-keygen -t rsa -b 4096
Follow the steps that the keygen provides, passphrase is optional. When you’re done with generating the key, you should have 2 new files in this directory:

Windows: C:\Users\USER\.ssh
Mac/Linux: ~/.ssh

id_rsa.pub = Public key
id_rsa = Private key (Do NOT share this one to anyone!)

2. Make a server only accept SSH [ Advanced ]

NOTE: Enforcing your server to only accept SSH can be risky if you do mistakes, however, to ensure nothing wrong happens, never close the current SSH window to your server and always test your key with a new SSH session.

2.1 Adding SSH keys

When you’ve logged in to your server, do the following commands inside the home directory of your user choice:

chmod 700 ~/.ssh
touch ~/.ssh/authorized_keys
chmod 600 ~/.ssh/authorized_keys

When that’s done, edit ~/.ssh/authorized_keys file with nano/vim and add your Public key inside it. If you’re going to add more than one, be sure to split between keys, example:

LONG_KEY_1 LONG_KEY_1 LONG_KEY_1 LONG_KEY_1 LONG_KEY_1
LONG_KEY_2 LONG_KEY_2 LONG_KEY_2
LONG_KEY_3 LONG_KEY_3 LONG_KEY_3 LONG_KEY_3

2.2 Enforcing SSH Key only

Edit /etc/ssh/sshd_config with nano/vim and ensure that the following settings are set to these:

- PermitRootLogin without-password
- RSAAuthentication yes
- PubkeyAuthentication yes
- PermitEmptyPasswords no
- PasswordAuthentication no

After such, reload sshd (Example: systemctl reload sshd) and test with a new session if the SSH key works. If you can get in to your server without password, you’ve successfully completed it and ready to go.
If it didn’t work, then check what you did wrong above.

Commands

Command to login with SSH Key:
ssh [email protected]

If you’re on Windows and it doesn’t work, try this:
ssh -m hmac-sha2-256 [email protected]