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Full disk encryption with Yubikey (Yubico key) for mkinitcpio
=============================================================

This enables you to automatically unlock a LUKS encrypted filesystem from
a `systemd`-enabled initramfs.

Requirements
------------

To compile and use Yubikey full disk encryption you need:

* [yubikey-personalization](https://github.com/Yubico/yubikey-personalization)
* [iniparser](https://github.com/ndevilla/iniparser)
* [systemd](https://www.github.com/systemd/systemd)
* [cryptsetup](https://gitlab.com/cryptsetup/cryptsetup)
* keyutils and linux with `CONFIG_KEYS` enabled
* [mkinitcpio](https://projects.archlinux.org/mkinitcpio.git/)
* [markdown](https://daringfireball.net/projects/markdown/) (HTML documentation)
* [libarchive](https://www.libarchive.org/) (Update challenge on boot)

Additionally you will need to have `make` and `pkg-config` installed to
successfully compile.

Build and install
-----------------

Building and installing is very easy. Just run:

> make

followed by:

> make install-mkinitcpio

This will place the files in their desired places in the filesystem.
Keep in mind that you need `root` privileges for installation, so switch
user or prepend the last command with `sudo`.

Usage
-----

### config files `/etc/crypttab.initramfs` and `/etc/ykfde.conf`

Make sure systemd knows about your encrypted device by
adding a line to `/etc/crypttab.initramfs`. It should read like:

> `mapping-name` /dev/`LUKS-device` -

Usually there is already an entry for your device. If you do not already
have a `systemd`-enabled initramfs, you will need to create this file from
scratch.

Update `/etc/ykfde.conf` with correct settings. Add the value of
`mapping-name` from above to `device name` in the `general` section. Then
add a new section with your key's decimal serial number containing the key
slot setting. The minimal file should look like this:

    [general]
    device name = crypt

    [1234567]
    luks slot = 1

*Be warned*: Do not remove or overwrite your interactive (regular) key!
Keep that for backup and rescue - LUKS encrypted volumes have a total
of 8 slots (from 0 to 7).

### Key setup

`ykfde` will read its information from these files and understands some
additional options. Run `ykfde --help` for details. Then prepare
the key. Plug it in and make sure it is configured for `HMAC-SHA1`. This can
be done with `ykpersonalize` from terminal (package `yubikey-personalization`)
or with GUI application `YubiKey Personalization Tool` (package
`yubikey-personalization-gui`). After that, run:

> ykfde

This will store a challenge in `/etc/ykfde.d/` and add a new slot to
your LUKS device based on the `/etc/ykfde.conf` configuration. When
`ykfde` asks for a passphrase it requires a valid passphrase from a
previously available slot.

Alternatively, adding a key with second factor (`foo` in this example)
is as easy:

> ykfde --new-2nd-factor foo

To update the challenge run:

> ykfde --2nd-factor foo

And changing second factor (from `foo` to `bar` in this example) is
straight forward:

> ykfde --2nd-factor foo --new-2nd-factor bar

The current and new second factor can be read from terminal, increasing
security by not displaying on display and not writing to shell history.
Use switches `--ask-2nd-factor` and `--ask-new-2nd-factor` for that.

Make sure to enable second factor in `/etc/ykfde.conf`.

### cpio archive with challenges

Every time you update a challenge and/or a second factor run:

> ykfde-cpio

This will write a cpio archive to `/boot/ykfde-challenges.img` containing
your current challenges. Enable systemd service `ykfde` to do this
automatically on every boot:

> systemctl enable ykfde.service

### mkinitcpio hook `ykfde`

Lastly, add `ykfde` to your hook list in `/etc/mkinitcpio.conf`. You should
already have `systemd` and `sd-encrypt` there as a `systemd`-enabled
initramfs is prerequisite. A working example config is as follows:

> HOOKS="base systemd keyboard autodetect modconf block ykfde sd-encrypt sd-lvm2 filesystems fsck"

Now rebuild your initramfs with:

> mkinitcpio -p linux

### Boot loader

Make sure to load the cpio archive `/boot/ykfde-challenges.img`
as an additional initramfs.

With `grub` you need to list `ykfde-challenges.img` in configuration
variable `GRUB_EARLY_INITRD_LINUX_CUSTOM` in `/etc/default/grub`:

> GRUB_EARLY_INITRD_LINUX_CUSTOM="ykfde-challenges.img"

Then update your `grub` configuration by running:

> grub-mkconfig -o /boot/grub/grub.cfg

Reboot and have fun!