12 Set up keys for SSH

If you plan to push/pull using SSH, you need to set up SSH keys. You want to do this (or cache your username and password, chapter 11), so you don’t have to authenticate yourself interactively with GitHub over and over again. You’ll need to set this up on each computer you want to connect to GitHub from.

12.1 SSH keys

SSH keys provide a more secure way of logging into a server than using a password alone. While a password can eventually be cracked with a brute force attack, SSH keys are nearly impossible to decipher by brute force alone. Generating a key pair provides you with two long strings of characters: a public and a private key. You can place the public key on any server, and then unlock it by connecting to it with a client that already has the private key. When the two match up, the system unlocks without the need for a password. You can increase security even more by protecting the private key with a passphrase.

Adapted from instructions provided by GitHub and Digital Ocean.

12.2 Check for existing keys

Go to the shell (appendix A).

List existing keys (at least, those in the default location):

ls -al ~/.ssh 

If you are told .ssh doesn’t exist, you don’t have SSH keys! Keep reading to create them.

If you see a pair of files like id_rsa.pub and id_rsa, you have a key pair already. You can skip to the section about adding a key to the ssh-agent.

12.3 Set up from RStudio

Instructions for setting up SSH keys from RStudio are given in the Git and GitHub chapter of Wickham’s R packages book. Look at the end of the section on initial set up:

12.4 Set up from the shell

12.4.1 Create SSH key pair

Create the key pair by entering this, but substitute the email address associated with your GitHub account:

$ ssh-keygen -t rsa -b 4096 -C "jenny@stat.ubc.ca"

Accept the proposal to save the key in the default location, i.e., just press Enter here:

Enter file in which to save the key (/Users/jenny/.ssh/id_rsa):

You have the option to protect the key with a passphrase. If you take it, you will want to configure something called the ssh-agent to manage this for you (more below).

So either enter a passphrase (and store in your favorite password manager!) or decline by leaving this empty.

Enter passphrase (empty for no passphrase):

The process should complete now and should have looked like this:

jenny@2015-mbp ~ $ ssh-keygen -t rsa -b 4096 -C "jenny@stat.ubc.ca"
Generating public/private rsa key pair.
Enter file in which to save the key (/Users/jenny/.ssh/id_rsa):     
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /Users/jenny/.ssh/id_rsa.
Your public key has been saved in /Users/jenny/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:ki0TNHm8qIvpH7/c0qQmdv2xxhYHCwlpn3+rVhKVeDo jenny@stat.ubc.ca
The key's randomart image is:
+---[RSA 4096]----+
|      o+   . .   |
|     .=.o . +    |
|     ..= + +     |
|      .+* E      |
|     .= So =     |
|    .  +. = +    |
|   o.. = ..* .   |
|  o ++=.o =o.    |
| ..o.++o.=+.     |

12.4.2 Add key to ssh-agent

Tell your ssh-agent about the key and, especially, set it up to manage the passphrase, if you chose to set one.

Make sure ssh-agent is enabled:

jenny@2015-mbp ~ $ eval "$(ssh-agent -s)"
Agent pid 95727

Add your key. If you set a passphrase, you’ll be challenged for it here. Give it.

jenny@2015-mbp ~ $ ssh-add ~/.ssh/id_rsa
Enter passphrase for /Users/jenny/.ssh/id_rsa: 
Identity added: /Users/jenny/.ssh/id_rsa (/Users/jenny/.ssh/id_rsa)

12.4.3 Provide public key to GitHub

Copy the public key onto your clipboard. Open ~/.ssh/id_rsa.pub in an editor and copy the contents to your clipboard or do one of the following at the command line:

  • Mac OS: pbcopy < ~/.ssh/id_rsa.pub
  • Windows: clip < ~/.ssh/id_rsa.pub
  • Linux: xclip -sel clip < ~/.ssh/id_rsa.pub

Linux: if needed, install via apt-get or yum. For example, sudo apt-get install xclip.

In the top right corner of any page on GitHub, click your profile photo, then click Settings.

In the user settings sidebar, click SSH and GPG keys.

Click New SSH key.

In the “Title” field, add a descriptive label for the new key. For example, if you’re using a personal Mac, you might call this key “Personal MacBook Air”.

Paste your key into the “Key” field.

Click Add SSH key.

Confirm the action by entering your GitHub password.