SSH (Secure SHell) is a generic term for a software package or command which implements the SSH communications protocol to enable secure system administration and file transfers over insecure networks. It is used in nearly every data center, in every larger enterprise.

An SSH key is an access credential that fulfils a similar function to that of user names and passwords. The keys are primarily used for automated processes and for implementing single sign-on by system administrators and power users. A key comes as a pair of files: a Public key (also known as an Authorized key) and a private key (also know as an Identity key) .

Public keys are analogous to locks that the corresponding private key can open. Private keys are used by an SSH client to authenticate itself when logging into an SSH server and are analogous to physical keys that can open one or more locks (Public keys).

Many components of MettleCI are integrated using SSH to avoid the need for various software components to repeatedly prompt users for authentication credentials.

Instructions - Windows

The easiest way to generate an SSH key on Window is to use the de facto Windows SSH client called PuTTY. When you use the PuTTY MSI package installer you can also install the PuTTYgen utility which is what you will use to generate your SSH key for Windows. You can also just download and install the PuTTYgen executable separately if you prefer.

Instructions - Unix

Here’s an example of creating and deploying an SSH key to avoid a username/password prompt when connecting from one host ('localhost', in this example) to another ('remotehost').

1. If you already have an SSH key, you can skip this step. You can just hit Enter for the key and both passphrases (less secure):

   Code Block
   localhost:~$ ssh-keygen -t rsa -b 2048 Generating public/private rsa key pair. Enter file in which to save the key (/home/username/.ssh/id_rsa): .ssh/mykey Enter passphrase (empty for no passphrase): Enter same passphrase again: Your identification has been saved in /home/username/.ssh/mykey. Your public key has been saved in /home/username/.ssh/mykey.pub.

2. Copy the public key of your computer to the trusted keys of the target server:

   Code Block
   language bash
   localhost:~$ ssh-copy-id -i .ssh/mykey user@remotehost user@remotehost's password: ••••••••

3. Now try logging into the machine, with ssh 'user@remotehost' to verify the keys we’ve added:

   Code Block
   localhost:~$ # Create the .ssh directory: localhost:~$ mkdir ~/.ssh localhost:~$ # Set the right permissions: localhost:~$ chmod 700 ~/.ssh localhost:~$ # Create the authorized_keys file: touch ~/.ssh/authorized_keys localhost:~$ # Set the right permissions: chmod 600 ~/.ssh/authorized_keys localhost:~$ # verify localhost:~$ ls ~/.ssh/authorized_keys

4. Finally check you can log in using your new key…

   Code Block
   localhost:~$ ssh id@server user@remotehost:~$

   You may also want to look into using ssh-agent if you want to try keeping your keys protected with a passphrase (more secure).

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