Generating SSH Keys and Linking with Github

Learning Objectives

• Explain how SSH serves as extra layer of security
• Define and Differentiate between HTTPS and SSH
• List the advantages of an SSH connection

Opening

Secure Shell (SSH) is a command interface and protocol for securely getting access to a remote computer. SSH uses public-key cryptography to authenticate the remote computer and allow it to authenticate the user, if necessary. Both ends of the client/server connection are authenticated using a digital certificate, and passwords are protected by being encrypted.

Today, we will be learning about SSH keys and how we can use them in a way to identify trusted computers, without involving passwords.

As you may recall, we have been using https:// clone URLs when we first started using Git because this allows us to access all repositories, public and private, and these URLs work everywhere.

However, as you might have noticed, whenever you git pull, or git push to the remote repository using HTTPS, you'll be asked for your GitHub username and password.

Now, not only is this disruptive in our workflow, especially in the scope of this class where we are just developing in an educational environment, but sometimes we might require an extra layer of security rather just our user name and password.

Enter SSH clone URLs. These allow us to use the SSH protocol and require a two step authentication process via an encrypted keypair, which will not only speed up development but also give us extra control over the computers that can connect to our repositories.

If your are interested in learning more we recommend you checkout this chapter of the Pro Git book.

Step 0: Checking for existing Keys

First, we need to check for existing SSH keys on your computer. Open Terminal and enter:

$ ls -al ~/.ssh
# Lists the files in your .ssh directory, if they exist

If you see two files: id_rsa and id_rsa.pub, skip to step 2. Otherwise proceed to step 1.

Step 1: Generate a new SSH Key

1. With Terminal still open, copy and paste the text below. Make sure you substitute in your GitHub email address.

$ ssh-keygen -t rsa -b 4096 -C "[email protected]"
# Creates a new ssh key, using the provided email as a label
# Generating public/private rsa key pair.

2. We strongly suggest keeping the default settings as they are, so when you're prompted to "Enter a file in which to save the key", just press Enter to continue.

Enter file in which to save the key (/Users/you/.ssh/id_rsa): [Press enter]

3. You'll be asked to enter a passphrase. We recommend no passphrase, just press Enter twice to continue.

Enter passphrase (empty for no passphrase): [Type a passphrase]
# Enter same passphrase again: [Type passphrase again]

4. After you enter a passphrase, you'll be given the fingerprint, or id, of your SSH key. It will look something like this:

Your identification has been saved in /Users/you/.ssh/id_rsa.
# Your public key has been saved in /Users/you/.ssh/id_rsa.pub.
# The key fingerprint is:
# 01:0f:f4:3b:ca:85:d6:17:a1:7d:f0:68:9d:f0:a2:db [email protected]

As well as generate some neat ASCII art too:

The key's randomart image is:
+--[ RSA 2048]----+
|        .o..o..=+|
|       ..  ..o= +|
|        + + o+ + |
|         X o .o o|
|        E =    . |
|                 |
|                 |
|                 |
|                 |
+-----------------+

Great now that we have created a new key, we need to add it to the ssh-agent so we can easily access it.

Step 2: Add Your Key to the SSH-Agent

To configure the ssh-agent program to use your SSH key:

1. Ensure ssh-agent is enabled:

# start the ssh-agent in the background
$ eval "$(ssh-agent -s)"
# Agent pid 59566

2. Add your SSH key to the ssh-agent:

$ ssh-add ~/.ssh/id_rsa
# Identity added: ...

Note: If you didn't generate a new SSH key in Step 1, and used an existing SSH key instead, you will need to replace id_rsa in the above command with the name of your existing private key file.

Step 3: Add Your SSH Key to your Github Account

To configure your GitHub account to use your SSH key:

Copy the SSH key to your clipboard with:

$ pbcopy < ~/.ssh/id_rsa.pub
# Copies the contents of the id_rsa.pub file to your clipboard

Note:

pbcopy is a Mac only command.

If you are using Linux, type: cat ~/.ssh/id_rsa.pub and manually copy the output. It's important to copy the key exactly without adding newlines or whitespace.

Keep in mind that your key may also be named id_dsa.pub, id_ecdsa.pub or id_ed25519.pub, in which case you must change the filename in the above command

Then in Github:

1. In the top right corner of any page, click your profile photo, then click Settings.
2. In the user settings sidebar, click SSH keys.
3. Click Add SSH key.
4. In the Title field, add a descriptive label that uniquely identifies the computer you're currently using, e.g. Nick's MacBook Air.
5. Paste your key into the "Key" field
6. Click Add key
7. Confirm the action by entering your GitHub password

Step 4: Checking your Connection

To make sure everything is working, you'll now try to SSH into GitHub. When you do this, you may be asked to authenticate this action using your password, which is the SSH key passphrase you created earlier.

To do this let's:

1. Open Terminal and enter:

$ ssh -T [email protected]
# Attempts to ssh to GitHub

2. You may see this warning:

The authenticity of host 'github.com (207.97.227.239)' can't be established.
# RSA key fingerprint is 16:27:ac:a5:76:28:2d:36:63:1b:56:4d:eb:df:a6:48.
# Are you sure you want to continue connecting (yes/no)?

It is now our responsibility to ensure that we are connecting to GitHub. We do this by verify the fingerprint displayed in the message against keys provided by github:

• RSA: 16:27:ac:a5:76:28:2d:36:63:1b:56:4d:eb:df:a6:48
• DSA: ad:1c:08:a4:40:e3:6f:9c:f5:66:26:5d:4b:33:5d:8c
• RAS SHA256: SHA256:nThbg6kXUpJWGl7E1IGOCspRomTxdCARLviKw6E5SY8
• DSA SHA256: SHA256:br9IjFspm1vxR3iA35FWE+4VTyz1hYVLIE2t1/CeyWQ

3. You should then see output similar to this:

Hi <username>! You've successfully authenticated, but GitHub does not
# provide shell access.

If the username in the message is yours, you've successfully set up your SSH key!

Note: If you receive a message about "access denied," please notify an instructor or you can read these instructions for diagnosing the issue

Note: If you're switching from HTTPS to SSH, you'll now need to update your remote repository URLs. For more information, see Changing a remote's URL.

Upstream on a Cloned Repo

Since we have all already forked and cloned the GA-DC/Curriculum repository onto our local machine - we need a way to be able to update our local copy with any changes being made to the master repository.

One of the ways we can do this is by establishing a link to this remote repository so that we can get all the changes anytime we want.

The convention is to add an upstream remote.

This remote is where we can pull from at any time, but do not have permission to push our changes.

Please go back into Github and make sure your profile has your accurate FULL NAME, and a relevant Photo of you. Your presence on github is important! Potential employers will visit your profile!

Closing

Go over learning objectives, and make sure everyone's profiles are up to date.

Resources

• Github guide to configure SSH keys
• Changing a remote's URL
• Configuring a remote for a fork