You can secure your SSH keys and configure an authentication agent so that you won't have to reenter your passphrase every time you use your SSH keys.

With SSH keys, if someone gains access to your computer, they also gain access to every system that uses that key. To add an extra layer of security, you can add a passphrase to your SSH key. You can use ssh-agent to securely save your passphrase so you don't have to reenter it.

Adding or changing a passphrase

You can change the passphrase for an existing private key without regenerating the keypair by typing the following command:

ssh-keygen -p
# Start the SSH key creation process
Enter file in which the key is (/Users/you/.ssh/id_rsa): [Hit enter]
Key has comment '/Users/you/.ssh/id_rsa'
Enter new passphrase (empty for no passphrase): [Type new passphrase]
Enter same passphrase again: [One more time for luck]
Your identification has been saved with the new passphrase.

If your key already has a passphrase, you will be prompted to enter it before you can change to a new passphrase.

Auto-launching ssh-agent on Git for Windows

If you're using Git Shell that's installed with GitHub Desktop, you don't need to follow these steps. GitHub Desktop automatically launches ssh-agent for you.

Otherwise, follow these steps to run ssh-agent automatically when you open bash or Git shell. Copy the following lines and paste them into your ~/.profile or ~/.bashrc file in Git shell:

env=~/.ssh/agent.env

agent_load_env () { test -f "$env" && . "$env" >| /dev/null ; }

agent_start () {
    (umask 077; ssh-agent >| "$env")
    . "$env" >| /dev/null ; }

agent_load_env

# agent_run_state: 0=agent running w/ key; 1=agent w/o key; 2= agent not running
agent_run_state=$(ssh-add -l >| /dev/null 2>&1; echo $?)

if [ ! "$SSH_AUTH_SOCK" ] || [ $agent_run_state = 2 ]; then
    agent_start
    ssh-add
elif [ "$SSH_AUTH_SOCK" ] && [ $agent_run_state = 1 ]; then
    ssh-add
fi

unset env

If your private key is not stored in one of the default locations (~/.ssh/id_rsa or ~/.ssh/id_dsa), you'll need to tell your SSH authentication agent where to find it. To add your key to ssh-agent, type ssh-add ~/path/to/my_key. For more information, see "Generating a new SSH key and adding it to the ssh-agent"

Tip: If you want ssh-agent to forget your key after some time, you can configure it to do so by running ssh-add -t <seconds>.

Now, when you first run Git Bash, you are prompted for your passphrase:

Initializing new SSH agent...
succeeded
Enter passphrase for /c/Users/you/.ssh/id_rsa:
Identity added: /c/Users/you/.ssh/id_rsa (/c/Users/you/.ssh/id_rsa)
Welcome to Git (version 1.6.0.2-preview20080923)
>
Run 'git help git' to display the help index.
Run 'git help ' to display help for specific commands.

The ssh-agent process will continue to run until you log out, shut down your computer, or kill the process.

Saving your passphrase in the keychain

On OS X Leopard through OS X El Capitan, these default private key files are handled automatically:

  • .ssh/id_rsa
  • .ssh/id_dsa
  • .ssh/identity

The first time you use your key, you will be prompted to enter your passphrase. If you choose to save the passphrase with your keychain, you won't have to enter it again.

Otherwise, you can store your passphrase in the keychain when you add your key to the ssh-agent. For more information, see "Adding your SSH key to the ssh-agent."

Further reading