December 01, 2015

Creating and Using SSH Keys

Generate an SSH key and use it to log into a user on a new server.

Generate an SSH key and use it to log into a user on a new server.On your local computer, create an ssh key:

cd ~/.ssh
ssh-keygen -t rsa -b 4096 -C "" -f id_whatever

# On Mac, copy the public key to clipboard
cat | pbcopy

What's that command doing:

  • -t rsa - picking the RSA key type. This is the most-used, but see the resources link below to read on other types.
  • -b 4096 - Key size (bits). "Larger is better", sort of.
  • -C - A comment, typically used to identity who the key belongs to (an email address or username)
  • -f id_whatever - The filename of the SSH key created. In this example, we'll get id_whatever private key and public key.

New User

On our new server in the video, we make a new user, and then add the SSH key to that user's authorized_keys file, so that we can use our new SSH key to log in as that user.

On the new server:

# Create a new user, give it a password
# set any additional values you'd like
sudo adduser fideloper

# Log in as new user, create
# and go into a ~/.ssh directory
sudo su fideloper
mkdir ~/.ssh
cd ~/.ssh

# Create/edit ~/.ssh/authorized_keys dir
# and paste in the public key we put into
# our clipboard when we first created it
vim authorized_keys

Then you can log in as that user from your local computer!

# If you only have a few SSH keys, you won't hit the
# max attempts limit and can just do this:
ssh fideloper@server-ip

# If you want to explicitly say which ssh key to use, or
# have enough keys (like me!) to hit the max attempt limit:
ssh -o "IdentitiesOnly yes" -i ~/.ssh/id_whatever fideloper@server-ip


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