Setting up encrypted volumes with LUKS

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LUKS allows encrypting a partition and mapping it as a virtual block device, which can then be used as a normal partition. Guides for other Linux distributions should serve as a general references for installing Alpine onto a LUKS encrypted disk.

The following approaches are known to work:

The installer has built-in support for encryption, and will automatically enable LVM to encrypt swap partitions, but it will not encrypt the boot partition. The GRUB bootloader supports BIOS and EFI boot with an encrypted boot partition.

mkinitfs and LUKS

For those familiar with setting up FDE on other Linux distributions, this section contains only Alpine-specific knowledge required and understanding mkinitfs.

First of all, the cryptsetup feature needs to be added to /etc/mkinitfs/mkinitfs.conf. Additionally, the following kernel parameters are required:

  • cryptroot kernel parameter should point to the encrypted block device.
  • cryptdm: the name that will be given to the device.
  • root kernel parameter should point to the mapped block device: /dev/mapper/<name used in cryptdm>.
  • rootfstype: the filesystem type of the root partition (e.g.: btrfs).

For example, if you use grub with GPT partition table using ext4 without LVM the /etc/default/grub file will be as follows:

Contents of /etc/default/grub

GRUB_TIMEOUT=2 GRUB_DISABLE_SUBMENU=y GRUB_DISABLE_RECOVERY=true GRUB_CMDLINE_LINUX_DEFAULT="modules=sd-mod,usb-storage,ext4 quiet rootfstype=ext4 cryptroot=UUID=a7dc90c4-6746-417e-b25b-cb8769ee6334 cryptdm=alpine-rootfs root=/dev/mapper/alpine-rootfs" GRUB_PRELOAD_MODULES="luks cryptodisk part_gpt" GRUB_ENABLE_CRYPTODISK=y

Decrypting non-root volumes during boot

Main article: LVM on LUKS#Mounting additional encrypted filesystems at boot

To have an encrypted non-root volume be decrypted prior to automatically mounting it somewhere via /etc/fstab, configure dmcrypt in the /etc/conf.d/dmcrypt file. The comments inside that file should guide you, but as a simple example, here's what you should include in that file to decrypt and map a partition to some volume named, say, “myvolume”, given its UUID (here represented using a series of Xs), using a passphrase

Contents of /etc/conf.d/dmcrypt

... target=myvolume source=UUID=XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXX key=/etc/keys/myvolume.key #not needed as passphrase is used in this example ...

In /etc/fstab file, then, you would include the following line as follows:

Contents of /etc/fstab

... /dev/mapper/myvolume <path> <fstype> <options> ...

substituting in the proper parameters.

Do not forget to enable the localmount service:

rc-update add localmount

Otherwise they will not be mounted automatically.

See also

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