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Generating a new SSH key and adding it to the ssh-agent

After you've checked for existing SSH keys, you can generate a new SSH key to use for authentication, then add it to the ssh-agent.

About SSH key passphrases

You can access and write data in repositories on your GitHub Enterprise Server instance using SSH (Secure Shell Protocol). When you connect via SSH, you authenticate using a private key file on your local machine. For more information, see "About SSH."

When you generate an SSH key, you can add a passphrase to further secure the key. Whenever you use the key, you must enter the passphrase. If your key has a passphrase and you don't want to enter the passphrase every time you use the key, you can add your key to the SSH agent. The SSH agent manages your SSH keys and remembers your passphrase.

If you don't already have an SSH key, you must generate a new SSH key to use for authentication. If you're unsure whether you already have an SSH key, you can check for existing keys. For more information, see "Checking for existing SSH keys."

If you want to use a hardware security key to authenticate to GitHub Enterprise Server, you must generate a new SSH key for your hardware security key. You must connect your hardware security key to your computer when you authenticate with the key pair. For more information, see the OpenSSH 8.2 release notes.

Generating a new SSH key

You can generate a new SSH key on your local machine. After you generate the key, you can add the key to your account on your GitHub Enterprise Server instance to enable authentication for Git operations over SSH.

If you are a site administrator for your GitHub Enterprise Server instance, you can use the same key to grant yourself administrative SSH access to the instance. For more information, see "Accessing the administrative shell (SSH)."

Note: By default with GitHub Enterprise Server 3.6 and later, as of the cutoff date of midnight UTC on August 1, 2022, SSH connections that satisfy both of the following conditions will fail.


  • The RSA key was added to a user account on your GitHub Enterprise Server instance after the cutoff date of midnight UTC on August 1, 2022.
  • The SSH client signs the connection attempt with the SHA-1 hash function.

GitHub Enterprise Server 3.6 and later also does not support SSH connections that use DSA, HMAC-SHA-1, or CBC ciphers. RSA SSH keys uploaded before the cutoff date can continue to authenticate using the SHA-1 hash function as long as the key remains valid. For more information about finding the version of GitHub Enterprise Server that you use, see "About versions of GitHub Docs."

Your site administrator can adjust the cutoff date for connections using RSA-SHA-1, and may block all connections using RSA-SHA-1. For more information, contact your site administrator or see "Configuring SSH connections to your instance."

  1. Open TerminalTerminalGit Bash.

  2. Paste the text below, substituting in your GitHub Enterprise Server email address.

    $ ssh-keygen -t ed25519 -C "your_email@example.com"

    Note: If you are using a legacy system that doesn't support the Ed25519 algorithm, use:

    $ ssh-keygen -t rsa -b 4096 -C "your_email@example.com"

    This creates a new SSH key, using the provided email as a label.

    > Generating public/private ALGORITHM key pair.

    When you're prompted to "Enter a file in which to save the key", you can press Enter to accept the default file location. Please note that if you created SSH keys previously, ssh-keygen may ask you to rewrite another key, in which case we recommend creating a custom-named SSH key. To do so, type the default file location and replace id_ssh_keyname with your custom key name.

    > Enter a file in which to save the key (/Users/YOU/.ssh/id_ALGORITHM: [Press enter]
    > Enter a file in which to save the key (/c/Users/YOU/.ssh/id_ALGORITHM):[Press enter]
    > Enter a file in which to save the key (/home/YOU/.ssh/ALGORITHM):[Press enter]
  3. At the prompt, type a secure passphrase. For more information, see "Working with SSH key passphrases."

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

Adding your SSH key to the ssh-agent

Before adding a new SSH key to the ssh-agent to manage your keys, you should have checked for existing SSH keys and generated a new SSH key. When adding your SSH key to the agent, use the default macOS ssh-add command, and not an application installed by macports, homebrew, or some other external source.

  1. Start the ssh-agent in the background.

    $ eval "$(ssh-agent -s)"
    > Agent pid 59566

    Depending on your environment, you may need to use a different command. For example, you may need to use root access by running sudo -s -H before starting the ssh-agent, or you may need to use exec ssh-agent bash or exec ssh-agent zsh to run the ssh-agent.

  2. If you're using macOS Sierra 10.12.2 or later, you will need to modify your ~/.ssh/config file to automatically load keys into the ssh-agent and store passphrases in your keychain.

    • First, check to see if your ~/.ssh/config file exists in the default location.

      $ open ~/.ssh/config
      > The file /Users/YOU/.ssh/config does not exist.
    • If the file doesn't exist, create the file.

      $ touch ~/.ssh/config
    • Open your ~/.ssh/config file, then modify the file to contain the following lines. If your SSH key file has a different name or path than the example code, modify the filename or path to match your current setup.

      Host *.HOSTNAME
        AddKeysToAgent yes
        UseKeychain yes
        IdentityFile ~/.ssh/id_ed25519
      

      Notes:

      • If you chose not to add a passphrase to your key, you should omit the UseKeychain line.

      • If you see a Bad configuration option: usekeychain error, add an additional line to the configuration's' Host *.HOSTNAME section.

        Host *.HOSTNAME
          IgnoreUnknown UseKeychain
        
  3. Add your SSH private key to the ssh-agent and store your passphrase in the keychain. If you created your key with a different name, or if you are adding an existing key that has a different name, replace id_ed25519 in the command with the name of your private key file.

    $ ssh-add --apple-use-keychain ~/.ssh/id_ed25519

    Note: The --apple-use-keychain option stores the passphrase in your keychain for you when you add an SSH key to the ssh-agent. If you chose not to add a passphrase to your key, run the command without the --apple-use-keychain option.

    The --apple-use-keychain option is in Apple's standard version of ssh-add. In MacOS versions prior to Monterey (12.0), the --apple-use-keychain and --apple-load-keychain flags used the syntax -K and -A, respectively.

    If you don't have Apple's standard version of ssh-add installed, you may receive an error. For more information, see "Error: ssh-add: illegal option -- K."

  4. Add the SSH key to your account on GitHub Enterprise Server. For more information, see "Adding a new SSH key to your GitHub account."

If you have GitHub Desktop installed, you can use it to clone repositories and not deal with SSH keys.

  1. Ensure the ssh-agent is running. You can use the "Auto-launching the ssh-agent" instructions in "Working with SSH key passphrases", or start it manually:

    # start the ssh-agent in the background
    $ eval "$(ssh-agent -s)"
    > Agent pid 59566
  2. Add your SSH private key to the ssh-agent. If you created your key with a different name, or if you are adding an existing key that has a different name, replace id_ed25519 in the command with the name of your private key file.

    $ ssh-add ~/.ssh/id_ed25519
  3. Add the SSH key to your account on GitHub Enterprise Server. For more information, see "Adding a new SSH key to your GitHub account."

  1. Start the ssh-agent in the background.

    $ eval "$(ssh-agent -s)"
    > Agent pid 59566

    Depending on your environment, you may need to use a different command. For example, you may need to use root access by running sudo -s -H before starting the ssh-agent, or you may need to use exec ssh-agent bash or exec ssh-agent zsh to run the ssh-agent.

  2. Add your SSH private key to the ssh-agent. If you created your key with a different name, or if you are adding an existing key that has a different name, replace id_ed25519 in the command with the name of your private key file.

    $ ssh-add ~/.ssh/id_ed25519
  3. Add the SSH key to your account on GitHub Enterprise Server. For more information, see "Adding a new SSH key to your GitHub account."

Generating a new SSH key for a hardware security key

If you are using macOS or Linux, you may need to update your SSH client or install a new SSH client prior to generating a new SSH key. For more information, see "Error: Unknown key type."

  1. Insert your hardware security key into your computer.

  2. Open TerminalTerminalGit Bash.

  3. Paste the text below, substituting in the email address for your account on GitHub Enterprise Server.

    $ ssh-keygen -t ed25519-sk -C "YOUR_EMAIL"

    Note: If the command fails and you receive the error invalid format or feature not supported, you may be using a hardware security key that does not support the Ed25519 algorithm. Enter the following command instead.

    $ ssh-keygen -t ecdsa-sk -C "your_email@example.com"
  4. When you are prompted, touch the button on your hardware security key.

  5. When you are prompted to "Enter a file in which to save the key," press Enter to accept the default file location.

    > Enter a file in which to save the key (/Users/YOU/.ssh/id_ed25519_sk): [Press enter]
    > Enter a file in which to save the key (/c/Users/YOU/.ssh/id_ed25519_sk):[Press enter]
    > Enter a file in which to save the key (/home/YOU/.ssh/id_ed25519_sk):[Press enter]
  6. When you are prompted to type a passphrase, press Enter.

    > Enter passphrase (empty for no passphrase): [Type a passphrase]
    > Enter same passphrase again: [Type passphrase again]
  7. Add the SSH key to your account on GitHub. For more information, see "Adding a new SSH key to your GitHub account."