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Create SSH keys for Fuchsia devices

To make an SSH connection to a Fuchsia device, some ffx commands (such as ffx target show and ffx log) require Fuchsia-specific SSH keys to be present on the host machine.

Concepts

During development, one or more public SSH keys (listed in fuchsia_authorized_keys) are loaded to a Fuchsia device, typically when a new Fuchsia image is flashed to the device. Once the device is loaded with these public SSH keys, the ffx commands (running from the host machine where a matching private SSH key is stored) can establish an SSH connection to the device.

By default, Fuchsia-specific SSH keys are stored in the $HOME/.ssh directory of the host machine, as shown below:

$HOME/.ssh/fuchsia_ed25519
$HOME/.ssh/fuchsia_authorized_keys

These files contain the following:

  • fuchsia_ed25519: A private SSH key. The content of this file must not be revealed or shared.
  • fuchsia_authorized_keys: A list of one or more authorized public SSH keys.

The fuchsia_authorized_keys file must include the public SSH key for fuchsia_ed25519. During the flashing process, the fuchsia_authorized_keys file gets uploaded from the host machine to the Fuchsia device.

If you have multiple development machines, it's recommended that the Fuchsia SSH keys are synchronized across your development machines. This may require you to copy the existing Fuchsia SSH keys files from one machine to another.

Generate SSH keys manually

To manually generate Fuchsia-specific SSH keys on your host machine, do the following;

  1. Generate a new private and public SSH key pair:

    ssh-keygen -P "" -t ed25519 -f "${HOME}/.ssh/fuchsia_ed25519" -C "${USER}@$(hostname -f) Shared SSH Key for Fuchsia"
    
  2. Generate a fuchsia_authorized_keys file:

    ssh-keygen -y -f "${HOME}/.ssh/fuchsia_ed25519" > "${HOME}/.ssh/fuchsia_authorized_keys"
    
  3. Verify that Fuchsia-specific SSH keys are generated:

    ls ~/.ssh | grep fuchsia
    

    This command prints output similar to the following:

    $ ls ~/.ssh | grep fuchsia
    fuchsia_authorized_keys
    fuchsia_ed25519
    fuchsia_ed25519.pub
    

After creating new SSH keys, you'd need to flash your Fuchsia device again so that the device is loaded with the new fuchsia_authorized_keys file.