SSH Connection with No Password

Useful if you frequently connect to a remote machine using ssh.

Prerequisites:

• SSH server running on remote machine (Obvious)
• ssh client on you local machine

Step 0: Trust the remote machine

Before you connect to a remote machine using ssh you should verify its public key. If it is different than what you expected, it is possible that someone is attempting a man-in-the-middle attack on you. If already know the remote server's public key fingerprint, then you can use it.

When you setup a server, you can run the following command to obtain the fingerprint of its public key:

$ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key.pub

You should see something like the following as output:

2048 f9:a0:eb:0a:61:e7:9b:43:4a:ec:1e:40:01:6b:17:e3  root@vagrant-ubuntu-trusty-64 (RSA)

The first number is its keysize. The second element is the server's public key fingerprint. It is this fingerprint that you should use to verify the server with.

Step 1: Generate a ssh key pair on the local machine

You might want to check your .ssh directory (in your home directory) before generating a ssh key pair (you might have an existing key pair (which you could utilize).

$ ssh-keygen -t rsa -b 4096

The -t option allows you to specify the key type. The -b option allows you to specify the key size.

You will be prompted to enter a filename and password (both can be left default/blank).

Step 2: Copy the public key to the remote account/machine

 $ ssh-copy-id user@remote_machine

You will be prompted to enter the password for the account on the remote_machine.

Note: ssh-copy-id is a available on most Linux distributions. If you are in a Mac OS X environment, then you can add this command using this Github repository.

Step 3: Attempt a SSH connection using the installed keys

 $ ssh user@remote_machine