Login over SSH using SSH key

I just set this up and it works like a charm. However I imagine that I won’t be doing this every day, so I am writing this note to my future self.

How logging in on a remote server using an SSH key works (intuition)

This is sort of my non-expert, but technically viable understanding of how all of this magic works.

  1. Create a pair of keys using the command ssh-keygen – one public key, and one private key.
  2. Upload the public key (that can be used to confirm the identity something generated using of the private key I believe), to the server (each user has a ~/.ssh/authorized_keys on the server).
  3. Make sure the .ssh directory on the server is only readable by your user.
  4. Make sure the directory where you store your key pair on your local computer is also only readable by you.
  5. When logging in, point ssh to use your private key, for the correct user on the remote server.

Commands

Create your ssh key pair using

ssh-keygen -t rsa -b 2048 -f ~/.ssh/id_rsa -C "Enter an optional comment about your key"

You can use another name than id_rsa. A public companion with the suffix .pub will also be created. You do not have to enter a passphrase, e.g. when using the key via a script.

Protect your local .ssh directory using the following:

chmod 700 ~/.ssh && chmod 600 ~/.ssh/* 

Upload the public key via ssh:

cat ~/.ssh/id_rsa.pub | ssh user@remote-server.com 'cat - >> ~/.ssh/authorized_keys'

Protect the .ssh directory on your remote server (remote shell) using:

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

Login using

ssh -i ~/.ssh/id_rsa user@remote-server.com

where id_rsa is your private key.

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One thought on “Login over SSH using SSH key”

  1. If you’re using a distro with SELinux, you may also have to set the contexts on the ~/.ssh folder.

    An easy way to do this is:
    restorecon -R ~/.ssh

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