Github SSH Keys

Adding a public ssh key to Github allow us to perform git commands without having to type in our password to authenticate. For this to work we need to make sure that our repo is set to use ssh and that Github has our public key.

jmlopez-rod.github.io $ cat .git/config 
[core]
	repositoryformatversion = 0
	filemode = true
	bare = false
	logallrefupdates = true
[remote "origin"]
	url = git@github.com:jmlopez-rod/jmlopez-rod.github.io.git
	fetch = +refs/heads/*:refs/remotes/origin/*
[branch "master"]
	remote = origin
	merge = refs/heads/master

Notice that the url under [remote "origin"] starts with git@github.com and not with https://github.com. Some reasons as to why it would use the https protocol may be due to using Github Desktop or because we manually issued the command git clone https://github.com/....

ssh

If you do not have any ssh keys in your machine then attempting to ssh to github.com as the git user yields the following

$ ssh git@github.com
git@github.com: Permission denied (publickey).

Create a key

Start by navigating to your .ssh directory

$ mkdir -p ~/.ssh && chmod 700 ~/.ssh && cd .ssh

The command to generate an ssh key is of the following form.

$ ssh-keygen -m PEM -f [file-name] -C [key-comment] -N '' -t rsa -q

Its helpful to add a comment on the key to help you remember what the key is used for. Here is one way for instance

$ githubUser=[your-github-username]
$ ssh-keygen -m PEM -f "github_${githubUser}" -C "${githubUser}@github" -N '' -t rsa -q

Print the key with

cat "github_${githubUser}.pub"

Copy the string and add it to Github.

Using the key

To use the newly created key after the public key is added to Github we need to tell ssh to use it. Here is one way

$ ssh -i "~/.ssh/github_${githubUser}" git@github.com
PTY allocation request failed on channel 0
Hi jmlopez-rod! You've successfully authenticated, but GitHub does not provide shell access.
Connection to github.com closed.

The -i option specifies the identity file and it is useful whenever we are testing connections via ssh keys without modifying the ssh configuration file. Which brings us to the next step. Do the following command

$ touch ~/.ssh/config && chmod 600 ~/.ssh/config

Open it with your favorite editor and add the following

Host github.com
  User git
  HostName github.com
  IdentityFile ~/.ssh/github_[your-github-username]

Now ssh will know how to connect to host.

$ ssh github.com
PTY allocation request failed on channel 0
Hi jmlopez-rod! You've successfully authenticated, but GitHub does not provide shell access.
Connection to github.com closed.

Note that we did not have to specify the user, that is ssh git@github.com. This is because the configuration specifies it in the User field. Now you should be able to do

git clone git@github.com:owner/repo.git

as long as you have permissions to said repo.