dm-crypt/Encrypting an entire system

From ArchWiki
(Redirected from Encrypted LVM)
Jump to: navigation, search

Back to dm-crypt.

The following are examples of common scenarios of full system encryption with dm-crypt. They explain all the adaptations that need to be done to the normal installation procedure. All the necessary tools are on the installation image.

Overview

Securing a root filesystem is where dm-crypt excels, feature and performance-wise. Unlike selectively encrypting non-root filesystems, an encrypted root filesystem can conceal information such as which programs are installed, the usernames of all user accounts, and common data-leakage vectors such as mlocate and /var/log/. Furthermore, an encrypted root filesystem makes tampering with the system far more difficult, as everything except the boot loader and (usually) the kernel is encrypted.

All scenarios illustrated in the following share these advantages, other pros and cons differentiating them are summarized below:

Scenarios Advantages Disadvantages
#Simple partition layout with LUKS

shows a basic and straight-forward set-up for a fully LUKS encrypted root.

  • Simple partitioning and setup
  • Inflexible; disk-space to be encrypted has to be pre-allocated
#LVM on LUKS

achieves partitioning flexiblity by using LVM inside a single LUKS encrypted partition.

  • Simple partitioning with knowledge of LVM
  • Only one key required to unlock all volumes (e.g. easy resume-from-disk setup)
  • Volume layout not transparent when locked
  • Easiest method to allow suspension to disk
  • LVM adds an additional mapping layer and hook
  • Less useful, if a singular volume should receive a separate key
#LUKS on LVM

uses dm-crypt only after the LVM is setup.

  • LVM can be used to have encrypted volumes span multiple disks
  • Easy mix of un-/encrypted volume groups
  • Complex; changing volumes requires changing encryption mappers too
  • Volumes require individual keys
  • LVM layout is transparent when locked
#Plain dm-crypt

uses dm-crypt plain mode, i.e. without a LUKS header and its options for multiple keys.
This scenario also employs USB devices for /boot and key storage, which may be applied to the other scenarios.

  • High care to all encryption parameters is required
  • Single encryption key and no option to change it
#Encrypted boot partition (GRUB)

shows how to encrypt the boot partition using the GRUB bootloader.
This scenario also employs an ESP partition, which may be applied to the other scenarios.

  • Same advantages as the scenario the installation is based on (LVM on LUKS for this particular example)
  • Less data is left unencrypted, i.e. the boot loader and the ESP partition, if present
  • Same disadvantages as the scenario the installation is based on (LVM on LUKS for this particular example)
  • More complicated configuration
  • Not supported by other boot loaders
#Btrfs subvolumes with swap

shows how to encrypt a Btrfs system, including the /boot directory, also adding a partition for swap, on UEFI hardware.

While all above scenarios provide much greater protection from outside threats than encrypted secondary filesystems, they also share a common disadvantage: any user in possession of the encryption key is able to decrypt the entire drive, and therefore can access other users' data. If that is of concern, it is possible to use a combination of blockdevice and stacked filesystem encryption and reap the advantages of both. See Disk encryption to plan ahead.

See Dm-crypt/Drive preparation#Partitioning for a general overview of the partitioning strategies used in the scenarios.

Another area to consider is whether to set up an encrypted swap partition and what kind. See Dm-crypt/Swap encryption for alternatives.

If you anticipate to protect the system's data not only against physical theft, but also have a requirement of precautions against logical tampering, see Dm-crypt/Specialties#Securing the unencrypted boot partition for further possibilities after following one of the scenarios.

Simple partition layout with LUKS

This example covers a full system encryption with dmcrypt + LUKS in a simple partition layout:

+--------------------+--------------------------+--------------------------+
|Boot partition      |LUKS encrypted system     |Optional free space       |
|                    |partition                 |for additional partitions |
|/dev/sdaY           |/dev/sdaX                 |or swap to be setup later |
+--------------------+--------------------------+--------------------------+

The first steps can be performed directly after booting the Arch Linux install image.

Preparing the disk

Prior to creating any partitions, you should inform yourself about the importance and methods to securely erase the disk, described in Dm-crypt/Drive preparation.

Then create the needed partitions, at least one for / (e.g. /dev/sdaX) and /boot (/dev/sdaY), see Partitioning.

Preparing non-boot partitions

The following commands create and mount the encrypted root partition. They correspond to the procedure described in detail in Dm-crypt/Encrypting a non-root file system#Partition (which, despite the title, can be applied to root partitions, as long as mkinitcpio and the boot loader are correctly configured). If you want to use particular non-default encryption options (e.g. cipher, key length), see the encryption options before executing the first command:

# cryptsetup -y -v luksFormat /dev/sdaX
# cryptsetup open /dev/sdaX cryptroot
# mkfs -t ext4 /dev/mapper/cryptroot
# mount -t ext4 /dev/mapper/cryptroot /mnt

Check the mapping works as intended:

# umount /mnt
# cryptsetup close cryptroot
# cryptsetup open /dev/sdaX cryptroot
# mount -t ext4 /dev/mapper/cryptroot /mnt

If you created separate partitions (e.g. /home), these steps have to be adapted and repeated for all of them, except for /boot. See Dm-crypt/Encrypting a non-root file system#Automated unlocking and mounting on how to handle additional partitions at boot.

Note that each blockdevice requires its own passphrase. This may be inconvenient, because it results in a separate passphrase to be input during boot. An alternative is to use a keyfile stored in the system partition to unlock the separate partition via crypttab. See Dm-crypt/Device encryption#Using LUKS to Format Partitions with a Keyfile for instructions.

Preparing the boot partition

What you do have to setup is a non-encrypted /boot partition, which is needed for a crypted root. For a standard MBR/non-EFI /boot partition, for example, execute:

# mkfs -t ext4 /dev/sdaY
# mkdir /mnt/boot
# mount -t ext4 /dev/sdaY /mnt/boot

Mounting the devices

At Installation guide#Mount the partitions you will have to mount the mapped devices, not the actual partitions. Of course /boot, which is not encrypted, will still have to be mounted directly.

Afterwards continue with the installation procedure up to the mkinitcpio step.

Configuring mkinitcpio

Add the encrypt hook to mkinitcpio.conf:

etc/mkinitcpio.conf
HOOKS="... encrypt ... filesystems ..."

Depending on which other hooks are used, the order may be relevant. See dm-crypt/System configuration#mkinitcpio for details and other hooks that you may need.

Configuring the boot loader

In order to unlock the encrypted root partition at boot, the following kernel parameters need to be set by the boot loader:

cryptdevice=UUID=<device-UUID>:cryptroot root=/dev/mapper/cryptroot

See Dm-crypt/System configuration#Boot loader for details.

The <device-UUID> refers to the UUID of /dev/sdaX, see Persistent block device naming for details.

LVM on LUKS

The straight-forward method is to set up LVM on top of the encrypted partition instead of the other way round. Technically the LVM is setup inside one big encrypted blockdevice. Hence, the LVM is not transparent until the blockdevice is unlocked and the underlying volume structure is scanned and mounted during boot.

The disk layout in this example is:

+-----------------------------------------------------------------------+ +----------------+
| Logical volume1       | Logical volume2       | Logical volume3       | |                |
|/dev/mapper/MyVol-swap |/dev/mapper/MyVol-root |/dev/mapper/MyVol-home | | Boot partition |
|_ _ _ _ _ _ _ _ _ _ _ _|_ _ _ _ _ _ _ _ _ _ _ _|_ _ _ _ _ _ _ _ _ _ _ _| | (may be on     |
|                                                                       | | other device)  |
|                        LUKS encrypted partition                       | |                |
|                          /dev/sdaX                                    | | /dev/sdbY      |
+-----------------------------------------------------------------------+ +----------------+

This method does not allow you to span the logical volumes over multiple disks, even in the future. The #LUKS on LVM method does not have this limitation.

Tip: Two variants of this setup:

Preparing the disk

Prior to creating any partitions, you should inform yourself about the importance and methods to securely erase the disk, described in Dm-crypt/Drive preparation.

When using the GRUB bootloader together with GPT, create a BIOS Boot Partition as explained in GRUB#BIOS systems.

Create a partition to be mounted at /boot of type 8300 with a size of 100 MB or more.

Create a partition of type 8E00, which will later contain the encrypted container.

Create the LUKS encrypted container at the "system" partition. Enter the chosen password twice.

# cryptsetup luksFormat /dev/sdaX

For more information about the available cryptsetup options see the LUKS encryption options prior to above command.

Open the container:

# cryptsetup open --type luks /dev/sdaX lvm

The decrypted container is now available at /dev/mapper/lvm.

Preparing the logical volumes

Create a physical volume on top of the opened LUKS container:

# pvcreate /dev/mapper/lvm

Create the volume group named MyVol (or whatever you want), adding the previously created physical volume to it:

# vgcreate MyVol /dev/mapper/lvm

Create all your logical volumes on the volume group:

# lvcreate -L 8G MyVol -n swap
# lvcreate -L 15G MyVol -n root
# lvcreate -l 100%FREE MyVol -n home

Format your filesystems on each logical volume:

# mkfs.ext4 /dev/mapper/MyVol-root
# mkfs.ext4 /dev/mapper/MyVol-home
# mkswap /dev/mapper/MyVol-swap

Mount your filesystems:

# mount /dev/mapper/MyVol-root /mnt
# mkdir /mnt/home
# mount /dev/mapper/MyVol-home /mnt/home
# swapon /dev/mapper/MyVol-swap

Preparing the boot partition

The bootloader loads the kernel, initramfs, and its own configuration files from the /boot directory. This directory must be located on a separate unencrypted filesystem.

Create an Ext2 filesystem on the partition intended for /boot. Any filesystem that can be read by the bootloader is eligible.

# mkfs.ext2 /dev/sdbY

Create the directory /mnt/boot:

# mkdir /mnt/boot

Mount the partition to /mnt/boot:

# mount /dev/sdbY /mnt/boot

Afterwards continue with the installation procedure up to the mkinitcpio step.

Configuring mkinitcpio

Add the encrypt and lvm2 hooks to mkinitcpio.conf:

/etc/mkinitcpio.conf
HOOKS="... encrypt lvm2 ... filesystems ..."
Note: The order of both hooks no longer matters with the current implementation of lvm2.

See dm-crypt/System configuration#mkinitcpio for details and other hooks that you may need.

Configuring the boot loader

In order to unlock the encrypted root partition at boot, the following kernel parameters need to be set by the boot loader:

cryptdevice=UUID=device-UUID:lvm root=/dev/mapper/MyVol-root

The <device-UUID> refers to the UUID of /dev/sdaX, see Persistent block device naming for details.

See Dm-crypt/System configuration#Boot loader for details.

LUKS on LVM

To use encryption on top of LVM, the LVM volumes are set up first and then used as the base for the encrypted partitions. This way, a mixture of encrypted and non-encrypted volumes/partitions is possible as well. Unlike #LVM on LUKS, this method allows normally spanning the logical volumes over multiple disks.

The following short example creates a LUKS on LVM setup and mixes in the use of a key-file for the /home partition and temporary crypt volumes for /tmp and /swap. The latter is considered desirable from a security perspective, because no potentially sensitive temporary data survives the reboot, when the encryption is re-initialised. If you are experienced with LVM, you will be able to ignore/replace LVM and other specifics according to your plan. If you want to span a logical volume over multiple disks during setup already, a procedure to do so is described in Dm-crypt/Specialties#Expanding LVM on multiple disks.

Tango-view-fullscreen.pngThis article or section needs expansion.Tango-view-fullscreen.png

Reason: The intro of this scenario needs some adjustment now that a comparison has been added to #Overview. A suggested structure is to make it similar to the #Simple partition layout with LUKS intro. (Discuss in Talk:Dm-crypt/Encrypting an entire system#)

Preparing the disk

Partitioning scheme:

  • /dev/sda1 -> /boot
  • /dev/sda2 -> LVM

Randomise /dev/sda2 according to Dm-crypt/Drive preparation#dm-crypt wipe before installation.

Preparing the logical volumes

# lvm pvcreate /dev/sda2
# lvm vgcreate lvm /dev/sda2
# lvm lvcreate -L 10G -n lvroot lvm
# lvm lvcreate -L 500M -n swap lvm
# lvm lvcreate -L 500M -n tmp lvm
# lvm lvcreate -l 100%FREE -n home lvm
# cryptsetup luksFormat -c aes-xts-plain64 -s 512 /dev/lvm/lvroot
# cryptsetup open --type luks /dev/lvm/lvroot root
# mkfs -t ext4 /dev/mapper/root
# mount /dev/mapper/root /mnt

More information about the encryption options can be found in Dm-crypt/Device encryption#Encryption options for LUKS mode. Note that /home will be encrypted in #Encrypting logical volume /home. Further, note that if you ever have to access the encrypted root from the Arch-ISO, the above open action will allow you to after the LVM shows up.

Preparing the boot partition

# dd if=/dev/zero of=/dev/sda1 bs=1M
# mkfs -t ext4 /dev/sda1
# mkdir /mnt/boot
# mount /dev/sda1 /mnt/boot

Now after setup of the encrypted LVM partitioning, it would be time to install: Arch Install Scripts.

Configuring mkinitcpio

Add the lvm2 and encrypt hooks to mkinitcpio.conf:

etc/mkinitcpio.conf
HOOKS="... block ''encrypt lvm2 ... filesystems ..."

See dm-crypt/System configuration#mkinitcpio for details and other hooks that you may need.

Configuring the boot loader

In order to unlock the encrypted root partition at boot, the following kernel parameters need to be set by the boot loader:

cryptdevice=/dev/lvm/lvroot:cryptoroot root=/dev/mapper/cryptoroot

See Dm-crypt/System configuration#Boot loader for details.

Configuring fstab and crypttab

/etc/fstab
 /dev/mapper/root        /       ext4            defaults        0       1
 /dev/sda1               /boot   ext4            defaults        0       2
 /dev/mapper/tmp         /tmp    tmpfs           defaults        0       0
 /dev/mapper/swap        none    swap            sw              0       0

The following crypttab options will re-encrypt the temporary filesystems each reboot:

/etc/crypttab
 swap	/dev/lvm/swap	/dev/urandom	swap,cipher=aes-xts-plain64,size=256
 tmp	/dev/lvm/tmp	/dev/urandom	tmp,cipher=aes-xts-plain64,size=256

Encrypting logical volume /home

Since this scenario uses LVM as the primary and dm-crypt as secondary mapper, each encrypted logical volume requires its own encryption. Yet, unlike the temporary filesystems configured with volatile encryption above, the logical volume for /home should be persistent, of course. The following assumes you have rebooted into the installed system, otherwise you have to adjust paths. To safe on entering a second passphrase at boot for it, a keyfile is created:

mkdir -m 700 /etc/luks-keys
dd if=/dev/random of=/etc/luks-keys/home bs=1 count=256

The logical volume is encrypted with it:

cryptsetup luksFormat -v -s 512 /dev/lvm/home /etc/luks-keys/home
cryptsetup -d /etc/luks-keys/home open --type luks /dev/lvm/home home
mkfs -t ext4 /dev/mapper/home
mount /dev/mapper/home /home

The encrypted mount is configured in crypttab:

/etc/crypttab
home	/dev/lvm/home   /etc/luks-keys/home
/etc/fstab
/dev/mapper/home        /home   ext4        defaults        0       2

and setup is done.

If you want to expand the logical volume for /home (or any other volume) at a later point, it is important to note that the LUKS encrypted part has to be resized as well. For a procedure see Dm-crypt/Specialties#Expanding LVM on multiple disks.

LUKS on software RAID

Tango-view-fullscreen.pngThis article or section needs expansion.Tango-view-fullscreen.png

Reason: Some references: RAID, Software RAID and LVM, http://wiki.drewhess.com/wiki/Creating_an_encrypted_filesystem_on_a_partition , http://jasonwryan.com/blog/2012/02/11/lvm/ . Note that full-disk encryption is not deniable with this configuration (consider RAID on LUKS instead?). (Discuss in Talk:Dm-crypt/Encrypting an entire system#)

Plain dm-crypt

Contrary to LUKS, dm-crypt plain mode does not require a header on the encrypted device: this scenario exploits this feature to set up a system on an unpartitioned, encrypted disk that will be indistinguishable from a disk filled with random data, which could allow deniable encryption. See also wikipedia:Disk encryption#Full disk encryption.

Note that if full-disk encryption is not required, the methods using LUKS described in the sections above are better options for both system encryption and encrypted partitions. LUKS features like key management with multiple passphrases/key-files or re-encrypting a device in-place are unavailable with plain mode.

Plain dm-crypt encryption can be more resilient to damage than LUKS, because it does not rely on an encryption master-key which can be a single-point of failure if damaged. However, using plain mode also requires more manual configuration of encryption options to achieve the same cryptographic strength. See also Disk encryption#Cryptographic metadata. Using plain mode could also be considered if concerned with the problems explained in Dm-crypt/Specialties#Discard/TRIM support for solid state drives (SSD).

Tip: If headerless encryption is your goal but you are unsure about the lack of key-derivation with plain mode, then two alternatives are:
  • tcplay which offers headerless encryption but with the PBKDF2 function, or
  • dm-crypt LUKS mode by using the cryptsetup --header option. It cannot be used with the standard encrypt hook, but the hook may be modified.

The scenario uses two USB sticks:

  • one for the boot device, which also allows storing the options required to open/unlock the plain encrypted device in the boot loader configuration, since typing them on each boot would be error prone;
  • another for the encryption key file, assuming it stored as raw bits so that to the eyes of an unaware attacker who might get the usbkey the encryption key will appear as random data instead of being visible as a normal file. See also Wikipedia:Security through obscurity, follow Dm-crypt/Device encryption#Keyfiles to prepare the keyfile.

The disk layout is:

+--------------------+------------------+--------------------+ +---------------+ +---------------+
|Volume 1:           |Volume 2:         |Volume 3:           | |Boot device    | |Encryption key |
|                    |                  |                    | |               | |file storage   |
|root                |swap              |home                | |/boot          | |(unpartitioned |
|                    |                  |                    | |               | |in example)    |
|/dev/store/root     |/dev/store/swap   |/dev/store/home     | |/dev/sdY1      | |/dev/sdZ       |
|--------------------+------------------+--------------------| |---------------| |---------------|
|disk drive /dev/sdaX encrypted using plain mode and LVM     | |USB stick 1    | |USB stick 2    |
+------------------------------------------------------------+ +---------------+ +---------------+
Tip:
  • It is also possible to use a single usb key by copying the keyfile to the initram directly. An example keyfile /etc/keyfile gets copied to the initram image by setting FILES="/etc/keyfile" in /etc/mkinitcpio.conf. The way to instruct the encrypt hook to read the keyfile in the initram image is using rootfs: prefix before the filename, e.g. cryptkey=rootfs:/etc/keyfile.
  • Another option is using a passphrase with good entropy.

Preparing the disk

It is vital that the mapped device is filled with data. In particular this applies to the scenario usecase we apply here.

See Dm-crypt/Drive preparation and Dm-crypt/Drive preparation#dm-crypt specific methods

Preparing the non-boot partitions

See Dm-crypt/Device encryption#Encryption options for plain mode for details.

Using the device /dev/sdX, with the twofish-xts cipher with a 512 bit key size and using a keyfile we have the following options for this scenario:

# cryptsetup --hash=sha512 --cipher=twofish-xts-plain64 --offset=0 --key-file=/dev/sdZ --key-size=512 open --type=plain /dev/sdX enc

Unlike encrypting with LUKS, the above command must be executed in full whenever the mapping needs to be re-established, so it is important to remember the cipher, hash and key file details.

We can now check a mapping entry has been made for /dev/mapper/enc:

# fdisk -l

Next, we setup LVM logical volumes on the mapped device, see LVM#Installing Arch Linux on LVM for further details:

# pvcreate /dev/mapper/enc
# vgcreate store /dev/mapper/enc
# lvcreate -L 20G store -n root
# lvcreate -L 10G store -n swap
# lvcreate -l 100%FREE store -n home

We format and mount them and activate swap, see File systems#Format a device for further details:

# mkfs.ext4 /dev/store/root
# mkfs.ext4 /dev/store/home
# mount /dev/store/root /mnt
# mkdir /mnt/home
# mount /dev/store/home /mnt/home
# mkswap /dev/store/swap
# swapon /dev/store/swap

Preparing the boot partition

The /boot partition can be installed on the standard vfat partition of a USB stick, if required. But if manual partitioning is needed, then a small 200MB partition is all that is required. Create the partition using a partitioning tool of your choice.

We choose a non-journalling file system to preserve the flash memory of the /boot partition, if not already formatted as vfat:

# mkfs.ext2 /dev/sdY1
# mkdir /mnt/boot
# mount /dev/sdY1 /mnt/boot

Configuring mkinitcpio

Add the encrypt and lvm2 hooks to mkinitcpio.conf:

etc/mkinitcpio.conf
HOOKS="... encrypt lvm2 ... filesystems ..."

See dm-crypt/System configuration#mkinitcpio for details and other hooks that you may need.

Configuring the boot loader

In order to boot the encrypted root partition, the following kernel parameters need to be set by the boot loader:

cryptdevice=/dev/sdX:enc cryptkey=/dev/sdZ:0:512 crypto=sha512:twofish-xts-plain64:512:0:

See Dm-crypt/System configuration#Boot loader for details and other parameters that you may need.

Tip: If using GRUB, you can install it on the same USB as the /boot partition with:
# grub-install --recheck /dev/sdY

Post-installation

You may wish to remove the USB sticks after booting. Since the /boot partition is not usually needed, the noauto option can be added to the relevant line in /etc/fstab:

/etc/fstab
# /dev/sdYn
/dev/sdYn /boot ext2 noauto,rw,noatime 0 2

However, when an update to the kernel or bootloader is required, the /boot partition must be present and mounted. As the entry in fstab already exists, it can be mounted simply with:

# mount /boot

Encrypted boot partition (GRUB)

This setup utilizes the same partition layout and configuration for the system's root partition as the previous #LVM on LUKS section, with two distinct differences:

  1. The setup is performed for an UEFI system and
  2. A special feature of the GRUB bootloader is used to additionally encrypt the boot partition /boot. See also GRUB#Boot partition.

The disk layout in this example is:

+---------------+----------------+----------------+----------------+----------------+
|ESP partition: |Boot partition: |Volume 1:       |Volume 2:       |Volume 3:       |
|               |                |                |                |                |
|/boot/efi      |/boot           |root            |swap            |home            |
|               |                |                |                |                |
|               |                |/dev/store/root |/dev/store/swap |/dev/store/home |
|/dev/sdaX      |/dev/sdaY       +----------------+----------------+----------------+
|unencrypted    |LUKS encrypted  |/dev/sdaZ encrypted using LVM on LUKS             |
+---------------+----------------+--------------------------------------------------+
Tip: All scenarios are intended as examples. It is, of course, possible to apply both of the two above distinct installation steps with the other scenarios as well. See also the variants linked in #LVM on LUKS.

Preparing the disk

Prior to creating any partitions, you should inform yourself about the importance and methods to securely erase the disk, described in Dm-crypt/Drive preparation.

Create an EFI System Partition with an appropriate size, it will later be mounted at /boot/efi.

Create a partition to be mounted at /boot of type 8300 with a size of 100 MB or more.

Tip: When using the GRUB bootloader together with a BIOS/GPT, create a BIOS Boot Partition as explained in GRUB#BIOS systems instead of the ESP.

Create a partition of type 8E00, which will later contain the encrypted container.

Create the LUKS encrypted container at the "system" partition.

# cryptsetup luksFormat /dev/sdaZ

For more information about the available cryptsetup options see the LUKS encryption options prior to above command.

Your partition layout should look similar to this:

 gdisk /dev/sda 
Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048         1050623   512.0 MiB   EF00  EFI System
   2         1050624         1460223   200.0 MiB   8300  Linux filesystem
   3         1460224        41943006   19.3 GiB    8E00  Linux LVM

Open the container:

# cryptsetup open --type luks /dev/sdaZ lvm

The decrypted container is now available at /dev/mapper/lvm.

Preparing the logical volumes

The LVM logical volumes of this example follow the exact layout as the previous scenario. Therefore, please follow Preparing the logical volumes above or adjust as required.

Preparing the boot partition

The bootloader loads the kernel, initramfs, and its own configuration files from the /boot directory.

First, create the LUKS container where the files will be located and installed into:

# cryptsetup luksFormat /dev/sdaY 

Next, open it:

# cryptsetup open /dev/sdaY cryptboot 

Create a filesystem on the partition intended for /boot. Any filesystem that can be read by the bootloader is eligible:

# mkfs.ext2 /dev/mapper/cryptboot

Create the directory /mnt/boot:

# mkdir /mnt/boot

Mount the partition to /mnt/boot:

# mount /dev/mapper/cryptboot /mnt/boot

Create a mountpoint for the EFI System Partition at /boot/efi for compatibility with grub-install and mount it:

# mkdir /mnt/boot/efi
# mount /dev/sdaX /mnt/boot/efi

At this point, you should have the following partitions and logical volumes inside of /mnt:

lsblk
NAME              	  MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
sda                       8:0      0   200G  0 disk  
├─sda1                    8:1      0   512M  0 part  /boot/efi
├─sda2                    8:2      0   200M  0 part  
│ └─boot		  254:0    0   198M  0 crypt /boot
└─sda3                    8:3      0   100G  0 part  
  └─lvm                   254:1    0   100G  0 crypt 
    ├─MyStorage-swapvol   254:2    0     8G  0 lvm   [SWAP]
    ├─MyStorage-rootvol   254:3    0    15G  0 lvm   /
    └─MyStorage-homevol   254:4    0    77G  0 lvm   /home

Afterwards continue with the installation procedure up to the mkinitcpio step.

Configuring mkinitcpio

Add the encrypt and lvm2 hooks to mkinitcpio.conf:

/etc/mkinitcpio.conf
HOOKS="... encrypt lvm2 ... filesystems ..."

See dm-crypt/System configuration#mkinitcpio for details and other hooks that you may need.

Configuring the boot loader

Configure GRUB to recognize the LUKS encrypted /boot partition and unlock the encrypted root partition at boot:

/etc/default/grub
GRUB_CMDLINE_LINUX="... cryptdevice=UUID=<device-UUID>:lvm root=/dev/mapper/MyStorage-rootvol ..."
GRUB_ENABLE_CRYPTODISK=y

See Dm-crypt/System configuration#Boot loader and GRUB#Boot partition for details. The <device-UUID> refers to the UUID of /dev/sdaX, see Persistent block device naming.

Generate GRUB's configuration file and install to the mounted ESP:

# grub-mkconfig -o /boot/grub/grub.cfg
# grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=grub --recheck

If this finished without errors, GRUB should prompt for the passphrase to unlock the /boot partition after the next reboot.

Configuring fstab and crypttab

This section deals with extra configuration to let the system mount the encrypted /boot.

While GRUB asks for a passphrase to unlock the encrypted /boot after above instructions, the partition unlock is not passed on to the initramfs. Hence, /boot will not be available after the system has re-/booted, because the encrypt hook only unlocks the system's root.

If you used the genfstab script during installation, it will have generated /etc/fstab entries for the /boot and /boot/efi mount points already, but the system will fail to find the generated device mapper for the boot partition. To make it available, add it to crypttab. For example:

/etc/crypttab
cryptboot  /dev/sdaY      none        luks

will make the system ask for the passphrase again (i.e. you have to enter it twice at boot: once for GRUB and once for systemd init). To avoid the double entry for unlocking /boot, follow the instructions at Dm-crypt/Device encryption#Keyfiles to:

  1. Create a randomtext keyfile,
  2. Add the keyfile to the (/dev/sdaY) boot partition's LUKS header and
  3. Check the /etc/fstab entry and add the /etc/crypttab line to unlock it automatically at boot.

If for some reason the keyfile fails to unlock the boot partition, systemd will fallback to ask for a passphrase to unlock and, in case that is correct, continue booting.

Tip: Optional post-installation steps:
  • It may be worth considering to add the GRUB bootloader to the ignore list of /etc/pacman.conf in order to take particular control of when the bootloader (which includes its own encryption modules) is updated.
  • If you want to encrypt the /boot partition to protect against offline tampering threats, the mkinitcpio-chkcryptoboot hook has been contributed to help.

Btrfs subvolumes with swap

The following example creates a full system encryption with LUKS using btrfs subvolumes to simulate partitions. NOTE: the EFI System Partition (ESP) cannot be encrypted. The layout shows an unencrypted EFI System Partition with an encrypted /. This is the setup that works with UEFI.

Additionally an optional swap partition is shown.

Warning: Do not use a swap file instead of a separate partition, because this may result in data loss. See Btrfs#Swap file.
+--------------------------+--------------------------+--------------------------+
|ESP                       |System partition          |Swap partition            |
|unencrypted               |LUKS-encrypted            |plain-encrypted           |
|                          |                          |                          |
|/boot/efi                 |/                         |                          |
|/dev/sdaY                 |/dev/sdaX                 |/dev/sdaZ                 |
|--------------------------+--------------------------+--------------------------+

If using BIOS instead of UEFI, a separate and unencrypted /boot is not absolutely necessary. /boot can reside on the encrypted /. However, in that case GRUB must be used as the bootloader because (at this time) only GRUB can load modules necessary to decrypt /boot (e.g., crypto.mod, cryptodisk.mod and luks.mod) [1].

Preparing the disk

Note: It is not possible to use btrfs partitioning as described in Btrfs#Partitioning when using LUKS. Traditional partitioning must be used, even if it is just to create one partition.

Prior to creating any partitions, you should inform yourself about the importance and methods to securely erase the disk, described in Dm-crypt/Drive preparation. If you are using UEFI create an EFI System Partition with an appropriate size. It will later be mounted at /boot/efi. If you are going to create an encrypted swap partition, create the partition for it, but do not mark it as swap, since plain dm-crypt will be used with the partition.

Create the needed partitions, at least one for / (e.g. /dev/sdaX). See Partitioning.

Preparing the system partition

The following commands create and mount the encrypted system partition (which includes /boot). If you want to use particular non-default encryption options (e.g. cipher, key length), see the encryption options before executing the first command:

# cryptsetup -y -v luksFormat /dev/sdaX
# cryptsetup open /dev/sdaX cryptroot
# mkfs -t btrfs -L mylabel /dev/mapper/cryptroot
# mount -t btrfs -o compress=lzo /dev/mapper/cryptroot /mnt

Check the mapping works as intended:

# umount /mnt
# cryptsetup close cryptroot
# cryptsetup open /dev/sdaX cryptroot
# mount -t btrfs -o compress=lzo /dev/mapper/cryptroot /mnt

Creating btrfs subvolumes

Subvolumes will be used to simulate partitions, but other (nested) subvolumes will also be created. Here is a partial representation of what the following example will generate:

subvolid=5 (/dev/sdaX)
   |
   ├── @ (mounted as /)
   |       |
   |       ├── /bin (directory)
   |       |
   |       ├── /home (mounted @home subvolume)
   |       |
   |       ├── /usr (directory)
   |       |
   |       ├── /.snapshots (mounted @snapshots subvolume)
   |       |
   |       ├── /var/cache/pacman/pkg (nested subvolume)
   |       |
   |       ├── ... (other directories and nested subvolumes)
   |
   ├── @snapshots (mounted as /.snapshots)
   |
   ├── @home (mounted as /home)
   |
   └── @... (additional subvolumes you wish to use as mount points)

This section follows the Snapper#Suggested filesystem layout, which is most useful when used with Snapper. You should also consult Btrfs Wiki SysadminGuide#Layout.

Here we are using the convention of prefixing @ to subvolume names that will be used as mount points, and @ will be the subvolume that is mounted as /.

# btrfs subvolume create /mnt/@
# btrfs subvolume create /mnt/@snapshots
# btrfs subvolume create /mnt/@home

Create any additional subvolumes you wish to use as mount points now.

Unmount the system partition and mount the newly created @ subvolume which will serve as /. Also mount the other subvolumes to their respective mount points.

# umount /mnt
# mount -o compress=lzo,subvol=@ /dev/mapper/cryptroot /mnt
# mkdir -p /mnt/home
# mount -o compress=lzo,subvol=@home /dev/mapper/cryptroot /mnt/home
# mkdir -p /mnt/.snapshots
# mount -o compress=lzo,subvol=@snapshots /dev/mapper/cryptroot /mnt/.snapshots

Create any subvolumes you do not want to have snapshots of when taking a snapshot of /. For example, you probably do not want to take snapshots of /var/cache/pacman/pkg. These subvolumes will be nested under the @ subvolume, but just as easily could have been created earlier at the same level as @ according to your preference. For this example do:

# mkdir -p /mnt/var/cache/pacman
# btrfs subvolume create /mnt/var/cache/pacman/pkg

Other directories you may wish to do this with are /var/abs, /var/tmp, /tmp, and /srv.

If you prepared an EFI partition earlier, mount it now:

# mkdir -p /mnt/boot/efi
# mount /dev/sdaY /mnt/boot/efi
Note: Btrfs snapshots will exclude /boot/efi, since it is not a btrfs file system.

At the pacstrap installation step, the btrfs-progs must be installed in addition to the base group.

Configuring mkinitcpio

In order for GRUB to open the LUKS partition without having the user enter his passphrase twice, we will use a keyfile. The following generates a keyfile which uses GRUB's default name for cryptkey, so it does not need to be specified with a kernel parameter.

# dd bs=512 count=4 if=/dev/urandom of=/crypto_keyfile.bin
# chmod 000 /crypto_keyfile.bin
# cryptsetup luksAddKey /dev/sdaX /crypto_keyfile.bin

See dm-crypt/Device encryption#With a keyfile embedded in the initramfs for more details.

Add the encrypt hook to mkinitcpio.conf:

/etc/mkinitcpio.conf
HOOKS="... encrypt ... filesystems ..."

Add /usr/bin/btrfsck to BINARIES, so that it is available if there is a problem booting the system later:

/etc/mkinitcpio.conf
BINARIES="/usr/bin/btrfsck"

Add the previously generated keyfile to FILES. This will embed the keyfile into the RAM disk:

/etc/mkinitcpio.conf
FILES="/crypto_keyfile.bin"

Create a new initial RAM disk with:

# mkinitcpio -p linux

Configuring the boot loader

Add the following lines to /etc/default/grub:

/etc/default/grub
GRUB_CMDLINE_LINUX="...cryptdevice=/dev/disk/by-uuid/UUID:cryptroot..."
GRUB_ENABLE_CRYPTODISK=y

where UUID is the UUID of the system partition (the UUID of /dev/sdaX, not the UUID of /dev/mapper/cryptroot).

See GRUB#Encryption for more details and options.

BIOS. If you are using a traditional BIOS (not UEFI) do:

# grub-install /dev/sda
# grub-mkconfig -o /boot/grub/grub.cfg

See GRUB#Install to disk for more details and options.

UEFI. If you are using UEFI do:

# grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=grub --recheck
# grub-mkconfig -o /boot/grub/grub.cfg

See GRUB#Installation 2 for more details and options.

Configuring swap

If you created a partition to be used for encrypted swap, now is the time to configure it. Follow the instructions at Dm-crypt/Swap encryption.

After completing this step, continue configuring your system as normal according to the installation guide.