Encrypted Alpine Linux

Jan 28, 2017 00:00 · 269 words · 2 minutes read

Setting up basic LUKS encrypted alpine install.

Create two partitions

One for Boot and one for the rest. Make the boot partition bootable.

/dev/sda1 - Boot
/dev/sda2 - LUKS

Setup Luks

Create the encrypted block.

cryptsetup -y -v luksFormat /dev/sda2
cryptsetup open /dev/sda2 cryptroot
mkfs.ext4 /dev/mapper/cryptroot
mount /dev/mapper/cryptroot /mnt

Confirm its working as expected.

umount /mnt
cryptsetup close cryptroot
cryptsetup open /dev/sda2 cryptroot
mount /dev/mapper/cryptroot /mnt

Setup Boot

Format the boot partition. This will be in plain text.

mkfs.ext4 /dev/sda1
mkdir /boot
mount /dev/sda1 /mnt/boot


Install the base system to the mounted and unlocked encrypted partition. Make sure that you’ve mounted the boot partition because it will also install the necessary files there.

setup-disk -m sys /mnt

Chroot into the new system

cd /mnt
mount --bind /dev dev
mount -t devpts devpts dev/pts
mount -t tmpfs tmpfs dev/shm
mount -t proc proc proc
mount -t sysfs sysfs sys
chroot /mnt /bin/ash 

Setup crypttab

Add information about the encrypted file system.

echo "cryptroot /dev/sda2 none luks" > /etc/crypttab 

We also need to make sure that root and boot are mounted automatically via /etc/fstab.

/dev/sda1 /boot ext4 defaults 0 2
/dev/mapper/cryptroot / ext4 errors=remount-ro 0 1

Setup initramfs

Make sure that kernel can be start by loading the drivers needed to deal with an encrypted device.

  • /etc/mkinitfs/mkinitfs.conf - Features should include cryptsetup
  • /etc/update-extlinux.conf - default_kernel_opts should include “cryptroot=/dev/sda2” and “cryptdm=cryptroot”

Rebuild initramfs with the new options.

apk fix linux-grsec

You can ignore the error from extlinux:

/boot is device /dev/sda1
extlinux: cannot open device /dev/sda1

Write the MBR

This is related to the bootloader.

dd bs=440 count=1 conv=notrunc if=/usr/share/syslinux/mbr.bin of=/dev/sda