dm-crypt/Encrypting an entire system - ArchWiki

# dm-crypt/Encrypting an entire system

< Dm-crypt

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
#LUKS on software RAID uses dm-crypt only after RAID is setup. | Analogous to LUKS on LVM | Analogous to LUKS on LVM
#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. | Data resilience for cases where a LUKS header may be damaged Allows Full Disk Encryption Helps addressing problems with SSDs | 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. | Similar advantages as #Encrypted boot partition (GRUB) Availability of Btrfs' features | Similar disadvantages as #Encrypted boot partition (GRUB)

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.

Warning: In any scenario, never use file system repair software such as fsck directly on an encrypted volume, or it will destroy any means to recover the key used to decrypt your files. Such tools must be used on the decrypted (opened) device instead.

## 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.ext4 /dev/mapper/cryptroot
    # mount /dev/mapper/cryptroot /mnt

Check the mapping works as intended:

    # umount /mnt
    # cryptsetup close cryptroot
    # cryptsetup open /dev/sdaX cryptroot
    # mount /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.ext4 /dev/sdaY
    # mkdir /mnt/boot
    # mount /dev/sdaY /mnt/boot

### Mounting the devices

At Installation guide#Mount the file systems 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 `keyboard` and `encrypt` hooks to mkinitcpio.conf:

    etc/mkinitcpio.conf

    HOOKS="... keyboard block 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      |
    +-----------------------------------------------------------------------+ +----------------+

Warning: This method does not allow you to span the logical volumes over multiple disks easily; see Dm-crypt/Specialties#Modifying the encrypt hook for multiple partitions.
Tip: Two variants of this setup:

- Instructions at Dm-crypt/Specialties#Encrypted system using a remote LUKS header use this setup with a remote LUKS header on a USB device to achieve a two factor authentication with it.
- Instructions at Pavel Kogan's blog show how to encrypt the `/boot` partition while keeping it on the main LUKS partition when using GRUB.

### 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 /dev/sdaX cryptolvm

The decrypted container is now available at `/dev/mapper/cryptolvm`.

### Preparing the logical volumes

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

    # pvcreate /dev/mapper/cryptolvm

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

    # vgcreate MyVol /dev/mapper/cryptolvm

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 `keyboard`, `encrypt` and `lvm2` hooks to mkinitcpio.conf:

    /etc/mkinitcpio.conf

    HOOKS="... keyboard 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 parameter needs to be set by the boot loader:

    cryptdevice=UUID=device-UUID:cryptolvm

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.

Tip: 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.

This article or section needs expansion.

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:

    +----------------+-----------------------------------------------------------------------+
    |                | LUKS encrypted volume | LUKS encrypted volume | LUKS encrypted volume |
    |                | /dev/mapper/swap      | /dev/mapper/root      | /dev/mapper/home      |
    |                |_ _ _ _ _ _ _ _ _ _ _ _|_ _ _ _ _ _ _ _ _ _ _ _|_ _ _ _ _ _ _ _ _ _ _ _|
    |                | Logical volume1       | Logical volume2       | Logical volume3       |
    |                |/dev/mapper/MyVol-swap |/dev/mapper/MyVol-root |/dev/mapper/MyVol-home |
    |                |_ _ _ _ _ _ _ _ _ _ _ _|_ _ _ _ _ _ _ _ _ _ _ _|_ _ _ _ _ _ _ _ _ _ _ _|
    | Boot partition |                                                                       |
    |   /dev/sda1    |                               /dev/sda2                               |
    +----------------+-----------------------------------------------------------------------+

Randomise `/dev/sda2` according to Dm-crypt/Drive preparation#dm-crypt wipe on an empty disk or partition.

### Preparing the logical volumes

    # pvcreate /dev/sda2
    # vgcreate MyVol /dev/sda2
    # lvcreate -L 10G -n lvroot MyVol
    # lvcreate -L 500M -n swap MyVol
    # lvcreate -L 500M -n tmp MyVol
    # lvcreate -l 100%FREE -n home MyVol

    # cryptsetup luksFormat -c aes-xts-plain64 -s 512 /dev/mapper/MyVol-lvroot
    # cryptsetup open /dev/mapper/MyVol-lvroot root
    # mkfs.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 status=progress
    # mkfs.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 `keyboard`, `lvm2` and `encrypt` hooks to mkinitcpio.conf:

    /etc/mkinitcpio.conf

    HOOKS="... keyboard block lvm2 encrypt ... 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/mapper/MyVol-lvroot:root root=/dev/mapper/root

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/mapper/MyVol-swap	/dev/urandom	swap,cipher=aes-xts-plain64,size=256
    tmp	/dev/mapper/MyVol-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 status=progress

The logical volume is encrypted with it:

    # cryptsetup luksFormat -v -s 512 /dev/mapper/MyVol-home /etc/luks-keys/home
    # cryptsetup -d /etc/luks-keys/home open /dev/mapper/MyVol-home home
    # mkfs.ext4 /dev/mapper/home
    # mount /dev/mapper/home /home

The encrypted mount is configured in crypttab:

    /etc/crypttab

    home	/dev/mapper/MyVol-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

This example is based on a real-world setup for a workstation class laptop equipped with two SSDs of equal size, and an additional HDD for bulk storage. The end result is LUKS based full disk encryption (including `/boot`) for all drives, with the SSDs in a RAID0 array, and keyfiles used to unlock all encryption after GRUB is given a correct passphrase at boot. TRIM support is enabled on the SSDs, but you may wish to review the security implications detailed at Dm-crypt/Specialties#Discard/TRIM support for solid state drives (SSD) before considering using this.

This setup utilizes a very simplistic partitioning scheme, with all the available RAID storage being mounted at `/` (no separate `/boot` partition), and the decrypted HDD being mounted at `/mnt/data`. It is also worth mentioning that the system in this example boots in BIOS mode and the drives are partitioned with GPT partitions.

Please note that regular backups are very important in this setup. If either of the SSDs fail, the data contained in the RAID array will be practically impossible to recover. You may wish to select a different RAID level if fault tolerance is important to you.

The encryption is not deniable in this setup.

For the sake of the instructions below, the following block devices are used:

    /dev/sda = first SSD
    /dev/sdb = second SSD
    /dev/sdc = HDD

Be sure to substitue them with the appropriate device designations for your setup, as they may be different.

### Preparing the disks

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. For this setup, this includes a 1M partition for "BIOS boot" at `/dev/sda1` and the remaining space on the drive being partitioned for "Linux RAID" at `/dev/sda2`.

Once partitions have been created on `/dev/sda`, the following commands can be used to clone them to `/dev/sdb`.

    # sfdisk -d /dev/sda > sda.dump
    # sfdisk /dev/sdb < sda.dump

The HDD is prepared with a single Linux partition covering the whole drive at `/dev/sdc1`.

### Building the RAID array

Create the RAID array for the SSDs. This example utilizes RAID0, you may wish to substitute a different level based on your preferences or requirements.

    # mdadm --create --verbose --level=0 --metadata=1.2 --raid-devices=2 /dev/md0 /dev/sda2 /dev/sdb2

### Preparing the block devices

As explained in Dm-crypt/Drive preparation, the devices are wiped with random data utilizing `/dev/zero` and a crypt device with a random key. Alternatively, you could use `dd` with `/dev/random` or `/dev/urandom`, though it will be much slower.

    # cryptsetup open --type plain /dev/md0 container --key-file /dev/random
    # dd if=/dev/zero of=/dev/mapper/container bs=1M status=progress
    # cryptsetup close container

And repeat above for the HDD (`/dev/sdc1` in this example).

Set up encryption for `/dev/md0`:

    # cryptsetup -y -v luksFormat -c aes-xts-plain64 -s 512 /dev/md0
    # cryptsetup open /dev/md0 cryptroot
    # mkfs.ext4 /dev/mapper/cryptroot
    # mount /dev/mapper/cryptroot /mnt

And repeat for the HDD:

    # cryptsetup -y -v luksFormat -c aes-xts-plain64 -s 512 /dev/sdc1
    # cryptsetup open /dev/sdc1 cryptdata
    # mkfs.ext4 /dev/mapper/cryptdata
    # mkdir -p /mnt/mnt/data
    # mount /dev/mapper/cryptdata /mnt/mnt/data

### Configuring the boot loader

Configure GRUB for the encrypted system by editing `/etc/defaults/grub` with the following. Note that the `:allow-discards` option enables TRIM support on the SSDs, if you do not wish to use it you should omit this.

    GRUB_CMDLINE_LINUX="cryptdevice=/dev/md0:cryptroot:allow-discards root=/dev/mapper/cryptroot"
    GRUB_ENABLE_CRYPTODISK=y

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

Complete the GRUB install to both SSDs (in reality, installing only to `/dev/sda` will work).

    # grub-install --target=i386-pc /dev/sda
    # grub-install --target=i386-pc /dev/sdb
    # grub-mkconfig -o /boot/grub/grub.cfg

### Creating the keyfiles

This article or section needs language, wiki syntax or style improvements.

Reason: Reduce duplication with Dm-crypt/Device_encryption#Keyfiles, see #Create keyfile under #Btrfs subvolumes with swap for example. (Discuss in Talk:Dm-crypt/Encrypting an entire system#)

The next steps save you from entering your passphrase twice when you boot the system (once so GRUB can unlock the encryption, and second time once the initramfs assumes control of the system). This is done by creating a keyfile for the encryption and adding it to the initramfs image to allow the encrypt hook to unlock the root device. See dm-crypt/Device encryption#With a keyfile embedded in the initramfs for additional details.

Create the keyfile.

    # dd bs=512 count=4 if=/dev/random of=/crypto_keyfile.bin

Make sure only root can read it. If on a multi-user system, you may want to apply similar permissions to `/boot` as well, as someone could dump the keyfile from the initramfs image.

    # chmod 600 /crypto_keyfile.bin
    # chmod -R g-rwx,o-rwx /boot

Add the key to `/dev/md0`.

    # cryptsetup luksAddKey /dev/md0 /crypto_keyfile.bin

Create another keyfile for the HDD so it can also be unlocked at boot. For convenience, leave the passphrase created above in place as this can make recovery easier if you ever need it.

    # mkdir -m 700 /etc/luks-keys
    # dd bs=512 count=4 if=/dev/random of=/etc/luks-keys/data
    # cryptsetup luksAddKey /dev/sdc1 /etc/luks-keys/data

Find the UUID for `/dev/sdc1`, to be used in `/etc/crypttab` for persistent naming.

    # ls -al /dev/disk/by-uuid | grep sdc1

Edit `/etc/crypttab` to decrypt the HDD at boot, substituting in the UUID found in the previous step.

    cryptdata    UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx   /etc/luks-keys/data

### Configuring the system

Edit /etc/fstab to mount the cryptroot and cryptdata block devices; if you are not enabling TRIM support, delete the `discard` mount option:

    /dev/mapper/cryptroot  /           ext4    rw,noatime,discard  0   1
    /dev/mapper/cryptdata  /mnt/data   ext4    defaults            0   2

Save the RAID configuration:

    # mdadm --detail --scan > /etc/mdadm.conf

Edit mkinitcpio.conf to include your keyfile and add the proper hooks:

    FILES="/crypto_keyfile.bin"
    HOOKS=" ... mdadm_udev encrypt ... " (insert right before "filesystems")

See dm-crypt/System configuration#mkinitcpio for details.

## 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#Create a file system 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 `keyboard`, `encrypt` and `lvm2` hooks to mkinitcpio.conf:

    etc/mkinitcpio.conf

    HOOKS="... keyboard 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 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:

Note: If using sd-encrypt instead of encrypt, use `luks.uuid` instead of cryptdevice, see systemd-cryptsetup-generator(8).

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.
Note: You can use `cryptboot` script from cryptbootAUR package for simplified encrypted boot management (mounting, unmounting, upgrading packages) and as a defense against Evil Maid attacks with UEFI Secure Boot. For more informations and limitations see cryptboot project page.

### 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 /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 `keyboard`, `encrypt` and `lvm2` hooks to mkinitcpio.conf:

    /etc/mkinitcpio.conf

    HOOKS="... keyboard block 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 ..."
    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/sdaZ` (the partition which holds the lvm containing the root filesystem), 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.

If using UEFI, an EFI System Partition (ESP) is required. `/boot` itself may reside on `/` and be encrypted; however, the ESP itself cannot be encrypted. In this example layout, the ESP is `/dev/sdaY` and is mounted at `/boot/efi`. `/boot` itself is located on the system partition, `/dev/sdaX`.

Since `/boot` resides on the encrypted `/`, GRUB must be used as the bootloader because only GRUB can load modules necessary to decrypt `/boot` (e.g., crypto.mod, cryptodisk.mod and luks.mod) [1].

Additionally an optional plain-encrypted 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                 |
    |--------------------------+--------------------------+--------------------------+

### Preparing the disk

Note: It is not possible to use btrfs partitioning as described in Btrfs#Partitionless Btrfs disk 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 the Partitioning article.

### Preparing the system partition

#### Create LUKS container

Follow dm-crypt/Device encryption#Encrypting devices with LUKS mode to setup `/dev/sdaX` for LUKS. See the Dm-crypt/Device encryption#Encryption options for LUKS mode before doing so for a list of encryption options.

#### Unlock LUKS container

Now follow Dm-crypt/Device encryption#Unlocking/Mapping LUKS partitions with the device mapper to unlock the LUKS container and map it.

#### Format mapped device

Proceed to format the mapped device as described in Btrfs#File system on a single device, where `/dev/partition` is the name of the mapped device (i.e., `cryptroot`) and not `/dev/sdaX`.

#### Mount mapped device

Finally, mount the now-formatted mapped device (i.e., `/dev/mapper/cryptroot`) to `/mnt`.

Tip: You may want to use the `compress=lzo` mount option. See Btrfs#Compression for more information.

### Creating btrfs subvolumes

#### Layout

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.

#### Create top-level subvolumes

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 `/`.

Following the Btrfs#Creating a subvolume article, create subvolumes at `/mnt/@`, `/mnt/@snapshots`, and `/mnt/@home`.

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

#### Mount top-level subvolumes

Unmount the system partition at `/mnt`.

Now mount the newly created `@` subvolume which will serve as `/` to `/mnt` using the `subvol=` mount option. Assuming the mapped device is named `cryptroot`, the command would look like:

    # mount -o compress=lzo,subvol=@ /dev/mapper/cryptroot /mnt

See Btrfs#Mounting subvolumes for more details.

Also mount the other subvolumes to their respective mount points: `@home` to `/mnt/home` and `@snapshots` to `/mnt/.snapshots`.

#### Create nested subvolumes

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.

Since the `@` subvolume is mounted at `/mnt` you will need to create a subvolume at `/mnt/var/cache/pacman/pkg` for this example. You may have to create any parent directories first.

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

#### Mount ESP

If you prepared an EFI system partition earlier, create its mount point and mount it now.

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

#### Create keyfile

In order for GRUB to open the LUKS partition without having the user enter his passphrase twice, we will use a keyfile embedded in the initramfs. Follow Dm-crypt/Device encryption#With a keyfile embedded in the initramfs making sure to add the key to `/dev/sdaX` at the luksAddKey step.

#### Edit mkinitcpio.conf

After creating, adding, and embedding the key as described above, add the `encrypt` hook to mkinitcpio.conf as well as any other hooks you require. See Dm-crypt/System configuration#mkinitcpio for detailed information. Be sure to regenerate the initial ramdisk when finished.

Tip: You may want to add `BINARIES="/usr/bin/btrfs"` to your `mkinitcpio.conf`. See the Btrfs#Corruption recovery article.

### Configuring the boot loader

Install GRUB to `/dev/sda`. Then, edit `/etc/default/grub` as instructed in the GRUB#Encryption article, following both the instructions for an encrypted root and boot partition. Finally, generate the GRUB configuration file.

### 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.

Categories:

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- File systems
- Getting and installing Arch

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