dm-crypt/Encrypting an entire system
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.
If you want to encrypt an existing unencrypted file system, see dm-crypt/Device encryption#Encrypt an existing unencrypted file system.
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 |
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#LUKS on a partition
shows a basic and straightforward set-up for a fully LUKS encrypted root. |
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#LVM on LUKS
achieves partitioning flexibility by using LVM inside a single LUKS encrypted partition. |
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#LUKS on LVM
uses dm-crypt only after the LVM is setup. |
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#LUKS on software RAID
uses dm-crypt only after RAID is setup. |
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#Plain dm-crypt
uses dm-crypt plain mode, i.e. without a LUKS header and its options for multiple keys. |
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#Encrypted boot partition (GRUB)
shows how to encrypt the boot partition using the GRUB bootloader. |
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#Btrfs subvolumes with swap
shows how to encrypt a Btrfs system, including the |
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| #Root on ZFS |
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 Data-at-rest 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.
For solid state drives you might want to consider enabling TRIM support, but be warned, there are potential security implications. See dm-crypt/Specialties#Discard/TRIM support for solid state drives (SSD) for more information.
- 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.
- For the LUKS2 format:
- GRUB's support for LUKS2 is limited; see GRUB#Encrypted /boot for details. Use LUKS1 (
cryptsetup luksFormat --type luks1) for partitions that GRUB will need to unlock. - The LUKS2 format has a high RAM usage per design, defaulting to 1GB per encrypted mapper. Machines with low RAM and/or multiple LUKS2 partitions unlocked in parallel may error on boot. See the
--pbkdf-memoryoption to control memory usage.[1]
- GRUB's support for LUKS2 is limited; see GRUB#Encrypted /boot for details. Use LUKS1 (
LUKS on a partition
This example covers a full system encryption with dm-crypt + LUKS in a simple partition layout:
+-----------------------+------------------------+-----------------------+ | Boot partition | LUKS2 encrypted system | Optional free space | | | partition | for additional | | | | partitions to be set | | /boot | / | up later | | | | | | | /dev/mapper/root | | | |------------------------| | | /dev/sda1 | /dev/sda2 | | +-----------------------+------------------------+-----------------------+
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/sda2) and /boot (/dev/sda1). 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. For information on changing the default sector size, see dm-crypt/Device encryption#Sector size.
# cryptsetup -y -v luksFormat /dev/sda2 # cryptsetup open /dev/sda2 root # mkfs.ext4 /dev/mapper/root # mount /dev/mapper/root /mnt
Check the mapping works as intended:
# umount /mnt # cryptsetup close root # cryptsetup open /dev/sda2 root # mount /dev/mapper/root /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 an encrypted root. For an ordinary boot partition on BIOS systems, for example, execute:
# mkfs.ext4 /dev/sda1
or for an EFI system partition on UEFI systems:
# mkfs.fat -F32 /dev/sda1
Afterwards create the directory for the mountpoint and mount the partition:
# mount --mkdir /dev/sda1 /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.
Configuring mkinitcpio
Add the keyboard, keymap and encrypt hooks to mkinitcpio.conf. If the default US keymap is fine for you, you can omit the keymap hook.
HOOKS=(base udev autodetect keyboard keymap consolefont modconf block encrypt filesystems fsck)
If using the sd-encrypt hook with the systemd-based initramfs, the following needs to be set instead:
HOOKS=(base systemd autodetect keyboard sd-vconsole modconf block sd-encrypt filesystems fsck)
Regenerate the initramfs after saving the changes. 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:root root=/dev/mapper/root
If using the sd-encrypt hook, the following need to be set instead:
rd.luks.name=device-UUID=root root=/dev/mapper/root
See dm-crypt/System configuration#Boot loader for details.
The device-UUID refers to the UUID of /dev/sda2. See Persistent block device naming for details.
LVM on LUKS
The straightforward 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 volume 1 | Logical volume 2 | Logical volume 3 | | Boot partition | | | | | | | | [SWAP] | / | /home | | /boot | | | | | | | | /dev/MyVolGroup/swap | /dev/MyVolGroup/root | /dev/MyVolGroup/home | | | |_ _ _ _ _ _ _ _ _ _ _ _|_ _ _ _ _ _ _ _ _ _ _ _|_ _ _ _ _ _ _ _ _ _ _ _| | (may be on | | | | other device) | | LUKS2 encrypted partition | | | | /dev/sda1 | | /dev/sdb1 | +-----------------------------------------------------------------------+ +----------------+
encrypt hook this method does not allow you to span the logical volumes over multiple disks; either use the sd-encrypt or see dm-crypt/Specialties#Modifying the encrypt hook for multiple partitions.- Instructions at dm-crypt/Specialties#Encrypted system using a detached LUKS header use this setup with a detached LUKS header on a USB device to achieve a two factor authentication with it.
- Instructions at dm-crypt/Specialties#Encrypted /boot and a detached LUKS header on USB use this setup with a detached LUKS header, encrypted
/bootpartition, and encrypted keyfile all on a USB device.
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 a partition to be mounted at /boot with a size of 200 MiB or more.
/boot.Create a partition which will later contain the encrypted container.
Create the LUKS encrypted container at the "system" partition. Enter the chosen password twice.
# cryptsetup luksFormat /dev/sda1
For more information about the available cryptsetup options see the LUKS encryption options prior to above command.
Open the container:
# cryptsetup open /dev/sda1 cryptlvm
The decrypted container is now available at /dev/mapper/cryptlvm.
Preparing the logical volumes
Create a physical volume on top of the opened LUKS container:
# pvcreate /dev/mapper/cryptlvm
Create a volume group (in this example named MyVolGroup, but it can be whatever you want) and add the previously created physical volume to it:
# vgcreate MyVolGroup /dev/mapper/cryptlvm
Create all your logical volumes on the volume group:
# lvcreate -L 8G MyVolGroup -n swap # lvcreate -L 32G MyVolGroup -n root # lvcreate -l 100%FREE MyVolGroup -n home
Format your filesystems on each logical volume:
# mkfs.ext4 /dev/MyVolGroup/root # mkfs.ext4 /dev/MyVolGroup/home # mkswap /dev/MyVolGroup/swap
Mount your filesystems:
# mount /dev/MyVolGroup/root /mnt # mount --mkdir /dev/MyVolGroup/home /mnt/home # swapon /dev/MyVolGroup/swap
Preparing the boot partition
The bootloader loads the kernel, initramfs, and its own configuration files from the /boot directory. Any filesystem on a disk that can be read by the bootloader is eligible.
Create a filesystem on the partition intended for /boot:
# mkfs.ext4 /dev/sdb1
/boot on an EFI system partition the recommended formatting is
# mkfs.fat -F32 /dev/sdb1
Mount the partition to /mnt/boot:
# mount --mkdir /dev/sdb1 /mnt/boot
Configuring mkinitcpio
Make sure the lvm2 package is installed and add the keyboard, keymap, encrypt and lvm2 hooks to mkinitcpio.conf:
HOOKS=(base udev autodetect keyboard keymap consolefont modconf block encrypt lvm2 filesystems fsck)
If using the sd-encrypt hook with the systemd-based initramfs, the following needs to be set instead:
HOOKS=(base systemd autodetect keyboard sd-vconsole modconf block sd-encrypt lvm2 filesystems fsck)
Regenerate the initramfs after saving the changes. 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:cryptlvm root=/dev/MyVolGroup/root
If using the sd-encrypt hook, the following needs to be set instead:
rd.luks.name=device-UUID=cryptlvm root=/dev/MyVolGroup/root
The device-UUID refers to the UUID of /dev/sda1. See Persistent block device naming for details.
If using dracut, you may need a more extensive list of parameters, try:
kernel_cmdline="rd.luks.uuid=luks-deviceUUID rd.lvm.lv=MyVolGroup/root rd.lvm.lv=MyVolGroup/swap root=/dev/mapper/MyVolGroup-root rootfstype=ext4 rootflags=rw,relatime"
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.
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 that have already been set up, or expand the logical volume for /home (or any other volume), a procedure to do so is described in dm-crypt/Specialties#Expanding LVM on multiple disks. It is important to note that the LUKS encrypted container has to be resized as well.
Preparing the disk
Partitioning scheme:
+----------------+-------------------------------------------------------------------------------------------------+ | Boot partition | dm-crypt plain encrypted volume | LUKS2 encrypted volume | LUKS2 encrypted volume | | | | | | | /boot | [SWAP] | / | /home | | | | | | | | /dev/mapper/swap | /dev/mapper/root | /dev/mapper/home | | |_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _|_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _|_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _| | | Logical volume 1 | Logical volume 2 | Logical volume 3 | | | /dev/MyVolGroup/cryptswap | /dev/MyVolGroup/cryptroot | /dev/MyVolGroup/crypthome | | |_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _|_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _|_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _| | | | | /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 MyVolGroup /dev/sda2 # lvcreate -L 32G -n cryptroot MyVolGroup # lvcreate -L 500M -n cryptswap MyVolGroup # lvcreate -L 500M -n crypttmp MyVolGroup # lvcreate -l 100%FREE -n crypthome MyVolGroup
# cryptsetup luksFormat /dev/MyVolGroup/cryptroot # cryptsetup open /dev/MyVolGroup/cryptroot 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.
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 # mount --mkdir /dev/sda1 /mnt/boot
Configuring mkinitcpio
Make sure the lvm2 package is installed and add the keyboard, lvm2 and encrypt hooks to mkinitcpio.conf:
HOOKS=(base udev autodetect keyboard keymap consolefont modconf block lvm2 encrypt filesystems fsck)
If using the sd-encrypt hook with the systemd-based initramfs, the following needs to be set instead:
HOOKS=(base systemd autodetect keyboard sd-vconsole modconf block sd-encrypt lvm2 filesystems fsck)
Regenerate the initramfs after saving the changes. 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:root root=/dev/mapper/root
If using the sd-encrypt hook, the following need to be set instead:
rd.luks.name=device-UUID=root root=/dev/mapper/root
The device-UUID refers to the UUID of /dev/MyVolGroup/cryptroot. See Persistent block device naming for details.
See dm-crypt/System configuration#Boot loader for details.
Configuring fstab and crypttab
Both crypttab and fstab entries are required to both unlock the device and mount the filesystems, respectively. The following lines will re-encrypt the temporary filesystems on each reboot:
/etc/crypttab
swap /dev/MyVolGroup/cryptswap /dev/urandom swap,cipher=aes-xts-plain64,size=256 tmp /dev/MyVolGroup/crypttmp /dev/urandom tmp,cipher=aes-xts-plain64,size=256
/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
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 of course be persistent. The following assumes you have rebooted into the installed system, otherwise you have to adjust paths.
To save on entering a second passphrase at boot, 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 /dev/MyVolGroup/crypthome /etc/luks-keys/home # cryptsetup -d /etc/luks-keys/home open /dev/MyVolGroup/crypthome home # mkfs.ext4 /dev/mapper/home # mount /dev/mapper/home /home
The encrypted mount is configured in both crypttab and fstab:
/etc/crypttab
home /dev/MyVolGroup/crypthome /etc/luks-keys/home
/etc/fstab
/dev/mapper/home /home ext4 defaults 0 2
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 LUKS1 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.
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 /data.
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
+---------------------+---------------------------+---------------------------+ +---------------------+---------------------------+---------------------------+ +---------------------------+ | BIOS boot partition | EFI system partition | LUKS1 encrypted volume | | BIOS boot partition | EFI system partition | LUKS1 encrypted volume | | LUKS2 encrypted volume | | | | | | | | | | | | | /efi | / | | | /efi | / | | /data | | | | | | | | | | | | | | /dev/mapper/root | | | | /dev/mapper/root | | | | +---------------------------+---------------------------+ | +---------------------------+---------------------------+ | | | | RAID1 array (part 1 of 2) | RAID0 array (part 1 of 2) | | | RAID1 array (part 2 of 2) | RAID0 array (part 2 of 2) | | | | | | | | | | | | | | | /dev/md/ESP | /dev/md/root | | | /dev/md/ESP | /dev/md/root | | /dev/mapper/data | | +---------------------------+---------------------------+ | +---------------------------+---------------------------+ +---------------------------+ | /dev/sda1 | /dev/sda2 | /dev/sda3 | | /dev/sdb1 | /dev/sdb2 | /dev/sdb3 | | /dev/sdc1 | +---------------------+---------------------------+---------------------------+ +---------------------+---------------------------+---------------------------+ +---------------------------+
Be sure to substitute 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.
For BIOS systems with GPT, create a BIOS boot partition with size of 1 MiB for GRUB to store the second stage of BIOS bootloader. Do not mount the partition.
For UEFI systems create an EFI system partition with an appropriate size, it will later be mounted at /efi.
In the remaining space on the drive create a partition (/dev/sda3 in this example) for "Linux RAID". Choose partition type ID fd for MBR or partition type GUID A19D880F-05FC-4D3B-A006-743F0F84911E for GPT.
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.
- All parts of an EFI system partition RAID array must be individually usable, that means that ESP can only placed in a RAID1 array.
- The RAID superblock must be placed at the end of the EFI system partition using
--metadata=1.0, otherwise the firmware will not be able to access the partition.
# mdadm --create --verbose --level=1 --metadata=1.0 --raid-devices=2 /dev/md/ESP /dev/sda2 /dev/sdb2
This example utilizes RAID0 for root, 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/md/root /dev/sda3 /dev/sdb3
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/md/root 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/md/root:
cryptsetup luksFormat --type luks1) for partitions that GRUB will need to unlock.# cryptsetup -y -v luksFormat --type luks1 /dev/md/root # cryptsetup open /dev/md/root root # mkfs.ext4 /dev/mapper/root # mount /dev/mapper/root /mnt
And repeat for the HDD:
# cryptsetup -y -v luksFormat /dev/sdc1 # cryptsetup open /dev/sdc1 data # mkfs.ext4 /dev/mapper/data # mount --mkdir /dev/mapper/data /mnt/data
For UEFI systems, set up the EFI system partition:
# mkfs.fat -F32 /dev/md/ESP # mount --mkdir /dev/md/ESP /mnt/efi
Configuring GRUB
Configure GRUB for the LUKS1 encrypted system by editing /etc/default/grub with the following:
GRUB_CMDLINE_LINUX="cryptdevice=/dev/md/root:root" GRUB_ENABLE_CRYPTODISK=y
If you have a USB keyboard on a newer system either enable legacy USB support in firmware or add the following to /etc/default/grub:
GRUB_TERMINAL_INPUT="usb_keyboard" GRUB_PRELOAD_MODULES="usb usb_keyboard ohci uhci ehci"
Otherwise you may not be able to use your keyboard at the LUKS prompt.
See dm-crypt/System configuration#Boot loader and GRUB#Encrypted /boot 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-install --target=x86_64-efi --efi-directory=/efi --bootloader-id=GRUB # grub-mkconfig -o /boot/grub/grub.cfg
Creating the keyfiles
The next steps save you from entering your passphrase twice when you boot the system (once so GRUB can unlock the LUKS1 device, 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 details.
- Create the keyfile and add the key to
/dev/md/root. - Create another keyfile for the HDD (
/dev/sdc1) 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. Edit/etc/crypttabto decrypt the HDD at boot. See Dm-crypt/System configuration#Unlocking with a keyfile.
Configuring the system
Edit fstab to mount the root and data block devices and the ESP:
/dev/mapper/root / ext4 rw,noatime 0 1 /dev/mapper/data /data ext4 defaults 0 2 /dev/md/ESP /efi vfat rw,relatime,codepage=437,iocharset=iso8859-1,shortname=mixed,utf8,tz=UTC,errors=remount-ro 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=(base udev autodetect keyboard keymap consolefont modconf block mdadm_udev encrypt filesystems fsck)
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 Data-at-rest 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).
-
dm-crypt LUKS mode with a detached header by using the cryptsetup
--headeroption. It cannot be used with the standard encrypt hook, but the hook may be modified. - tcplay which offers headerless encryption but with the PBKDF2 function.
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:
+----------------------+----------------------+----------------------+ +----------------+ +----------------+ | Logical volume 1 | Logical volume 2 | Logical volume 3 | | Boot device | | Encryption key | | | | | | | | file storage | | / | [SWAP] | /home | | /boot | | (unpartitioned | | | | | | | | in example) | | /dev/MyVolGroup/root | /dev/MyVolGroup/swap | /dev/MyVolGroup/home | | /dev/sdb1 | | /dev/sdc | |----------------------+----------------------+----------------------| |----------------| |----------------| | disk drive /dev/sda encrypted using plain mode and LVM | | USB stick 1 | | USB stick 2 | +--------------------------------------------------------------------+ +----------------+ +----------------+
- It is also possible to use a single USB key physical device:
- By putting the key on another partition (/dev/sdb2) of the USB storage device (/dev/sdb).
- By copying the keyfile to the initramfs directly. An example keyfile
/etc/keyfilegets copied to the initramfs image by settingFILES=(/etc/keyfile)in/etc/mkinitcpio.conf. The way to instruct theencrypthook to read the keyfile in the initramfs image is usingrootfs: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 random data. In particular this applies to the scenario use case 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/sda, with the aes-xts cipher with a 512 bit key size and using a keyfile we have the following options for this scenario:
# cryptsetup --cipher=aes-xts-plain64 --offset=0 --key-file=/dev/sdc --key-size=512 open --type plain /dev/sda cryptlvm
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, and key file details.
We can now check a mapping entry has been made for /dev/mapper/cryptlvm:
# fdisk -l
Next, we setup LVM logical volumes on the mapped device. See Install Arch Linux on LVM for further details:
# pvcreate /dev/mapper/cryptlvm # vgcreate MyVolGroup /dev/mapper/cryptlvm # lvcreate -L 32G MyVolGroup -n root # lvcreate -L 10G MyVolGroup -n swap # lvcreate -l 100%FREE MyVolGroup -n home
We format and mount them and activate swap. See File systems#Create a file system for further details:
# mkfs.ext4 /dev/MyVolGroup/root # mkfs.ext4 /dev/MyVolGroup/home # mount /dev/MyVolGroup/root /mnt # mount --mkdir /dev/MyVolGroup/home /mnt/home # mkswap /dev/MyVolGroup/swap # swapon /dev/MyVolGroup/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 200 MiB partition is all that is required. Create the partition using a partitioning tool of your choice.
Create a filesystem on the partition intended for /boot:
# mkfs.fat -F32 /dev/sdb1 # mount --mkdir /dev/sdb1 /mnt/boot
Configuring mkinitcpio
Make sure the lvm2 package is installed and add the keyboard, keymap, encrypt and lvm2 hooks to mkinitcpio.conf:
HOOKS=(base udev autodetect keyboard keymap consolefont modconf block encrypt lvm2 filesystems fsck)
Regenerate the initramfs after saving the changes. 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 (note that 64 is the number of bytes in 512 bits):
cryptdevice=/dev/disk/by-id/disk-ID-of-sda:cryptlvm cryptkey=/dev/disk/by-id/disk-ID-of-sdc:0:64 crypto=:aes-xts-plain64:512:0:
The disk-ID-of-disk refers to the id of the referenced disk. See Persistent block device naming for details.
See dm-crypt/System configuration#Boot loader for details and other parameters that you may need.
/boot partition with:
# grub-install --recheck /dev/sdb
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/sdb1 /dev/sdb1 /boot vfat noauto,rw,noatime 0 2
However, when an update to anything used in the initramfs, or a kernel, or the 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 as the previous #LVM on LUKS section, with the difference that the GRUB boot loader is used since it is capable of booting from an LVM logical volume and a LUKS1-encrypted /boot. See also GRUB#Encrypted /boot.
The disk layout in this example is:
+---------------------+----------------------+----------------------+----------------------+----------------------+ | BIOS boot partition | EFI system partition | Logical volume 1 | Logical volume 2 | Logical volume 3 | | | | | | | | | /efi | / | [SWAP] | /home | | | | | | | | | | /dev/MyVolGroup/root | /dev/MyVolGroup/swap | /dev/MyVolGroup/home | | /dev/sda1 | /dev/sda2 |----------------------+----------------------+----------------------+ | unencrypted | unencrypted | /dev/sda3 encrypted using LVM on LUKS1 | +---------------------+----------------------+--------------------------------------------------------------------+
- 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.
- You can use
cryptbootscript 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 information 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.
For BIOS/GPT systems create a BIOS boot partition with size of 1 MiB for GRUB to store the second stage of BIOS bootloader. Do not mount the partition. For BIOS/MBR systems this is not necessary.
For UEFI systems create an EFI system partition with an appropriate size, it will later be mounted at /efi.
Create a partition of type 8309, which will later contain the encrypted container for the LVM.
Create the LUKS encrypted container:
cryptsetup luksFormat --type luks1) for partitions that GRUB will need to unlock.# cryptsetup luksFormat --type luks1 /dev/sda3
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 -l /dev/sda
... Number Start (sector) End (sector) Size Code Name 1 2048 4095 1024.0 KiB EF02 BIOS boot partition 2 4096 1130495 550.0 MiB EF00 EFI System 3 1130496 68239360 32.0 GiB 8309 Linux LUKS
Open the container:
# cryptsetup open /dev/sda3 cryptlvm
The decrypted container is now available at /dev/mapper/cryptlvm.
Preparing the logical volumes
The LVM logical volumes of this example follow the exact layout as the #LVM on LUKS scenario. Therefore, please follow #Preparing the logical volumes above and adjust as required.
If you plan to boot in UEFI mode, create a mountpoint for the EFI system partition at /efi for compatibility with grub-install and mount it:
# mount --mkdir /dev/sda2 /mnt/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 1M 0 part
├─sda2 8:2 0 550M 0 part /mnt/efi
└─sda3 8:3 0 100G 0 part
└─cryptlvm 254:0 0 100G 0 crypt
├─MyVolGroup-swap 254:1 0 8G 0 lvm [SWAP]
├─MyVolGroup-root 254:2 0 32G 0 lvm /mnt
└─MyVolGroup-home 254:3 0 60G 0 lvm /mnt/home
Configuring mkinitcpio
Make sure the lvm2 package is installed and add the keyboard, keymap, encrypt and lvm2 hooks to mkinitcpio.conf:
HOOKS=(base udev autodetect keyboard keymap consolefont modconf block encrypt lvm2 filesystems fsck)
If using the sd-encrypt hook with the systemd-based initramfs, the following needs to be set instead:
HOOKS=(base systemd autodetect keyboard sd-vconsole modconf block sd-encrypt lvm2 filesystems fsck)
Regenerate the initramfs after saving the changes. See dm-crypt/System configuration#mkinitcpio for details and other hooks that you may need.
Configuring GRUB
Configure GRUB to allow booting from /boot on a LUKS1 encrypted partition:
/etc/default/grub
GRUB_ENABLE_CRYPTODISK=y
Set the kernel parameters, so that the initramfs can unlock the encrypted root partition. Using the encrypt hook:
/etc/default/grub
GRUB_CMDLINE_LINUX="... cryptdevice=UUID=device-UUID:cryptlvm ..."
If using the sd-encrypt hook, the following need to be set instead:
/etc/default/grub
GRUB_CMDLINE_LINUX="... rd.luks.name=device-UUID=cryptlvm ..."
See dm-crypt/System configuration#Boot loader and GRUB#Encrypted /boot for details. The device-UUID refers to the UUID of /dev/sda3 (the partition which holds the lvm containing the root filesystem). See Persistent block device naming.
install GRUB to the mounted ESP for UEFI booting:
# grub-install --target=x86_64-efi --efi-directory=/efi --bootloader-id=GRUB --recheck
install GRUB to the disk for BIOS booting:
# grub-install --target=i386-pc --recheck /dev/sda
Generate GRUB's configuration file:
# grub-mkconfig -o /boot/grub/grub.cfg
If all commands finished without errors, GRUB should prompt for the passphrase to unlock the /dev/sda3 partition after the next reboot.
Avoiding having to enter the passphrase twice
While GRUB asks for a passphrase to unlock the LUKS1 encrypted partition after above instructions, the partition unlock is not passed on to the initramfs. Hence, you have to enter the passphrase twice at boot: once for GRUB and once for the initramfs.
This section deals with extra configuration to let the system boot by only entering the passphrase once, in GRUB. This is accomplished by with a keyfile embedded in the initramfs.
First create a keyfile and add it as LUKS key:
# dd bs=512 count=4 if=/dev/random of=/root/cryptlvm.keyfile iflag=fullblock # chmod 000 /root/cryptlvm.keyfile # cryptsetup -v luksAddKey /dev/sda3 /root/cryptlvm.keyfile
Add the keyfile to the initramfs image:
/etc/mkinitcpio.conf
FILES=(/root/cryptlvm.keyfile)
Recreate the initramfs image and secure the embedded keyfile:
# chmod 600 /boot/initramfs-linux*
Set the following kernel parameters to unlock the LUKS partition with the keyfile. Using the encrypt hook:
GRUB_CMDLINE_LINUX="... cryptkey=rootfs:/root/cryptlvm.keyfile"
Or, using the sd-encrypt hook:
GRUB_CMDLINE_LINUX="... rd.luks.key=device-UUID=/root/cryptlvm.keyfile"
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.
/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 LUKS1 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/sda1 and is mounted at /efi. /boot itself is located on the system partition, /dev/sda2.
Since /boot resides on the LUKS1 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).
Additionally an optional plain-encrypted swap partition is shown.
+----------------------+----------------------+----------------------+ | EFI system partition | System partition | Swap partition | | unencrypted | LUKS1-encrypted | plain-encrypted | | | | | | /efi | / | [SWAP] | | /dev/sda1 | /dev/sda2 | /dev/sda3 | |----------------------+----------------------+----------------------+
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. If you are using UEFI create an EFI system partition with an appropriate size. It will later be mounted at /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/sda2). See the Partitioning article.
Preparing the system partition
Create LUKS container
cryptsetup luksFormat --type luks1) for partitions that GRUB will need to unlock.Follow dm-crypt/Device encryption#Encrypting devices with LUKS mode to setup /dev/sda2 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., /dev/mapper/root) and not /dev/sda2.
Mount mapped device
Finally, mount the now-formatted mapped device (i.e., /dev/mapper/root) to /mnt.
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 | ├── @ -| | contained directories: | ├── /usr | ├── /bin | ├── /.snapshots | ├── ... | ├── @home ├── @snapshots ├── @var_log └── @...
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 subvolumes for initial mount
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.
Create subvolumes for excludes
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 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 root, the command would look like:
# mount -o compress=zstd,subvol=@ /dev/mapper/root /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.
Mount ESP
If you prepared an EFI system partition earlier, create its mount point and mount it now.
/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 meta package.
Configuring mkinitcpio
Create keyfile
In order for GRUB to open the LUKS partition without having the user enter their 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/sda2 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.
Regenerate the initramfs after saving the changes. See dm-crypt/System configuration#mkinitcpio for details and other hooks that you may need.
BINARIES=(btrfs) to your /etc/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#Additional arguments, GRUB#Encrypted /boot and dm-crypt/System configuration#Using encrypt hook, following both the instructions for an encrypted root and boot partition. Finally, generate the GRUB configuration file. Note that you will need to pass kernel parameters for the root mount point as instructed in Btrfs#Mounting subvolume as root.
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.
Root on ZFS
Root on ZFS can be configured to encrypt everything except boot loader. See installation guide on OpenZFS page.
Boot loader can be verified with Secure Boot on UEFI-based systems.
See also ZFS#Encryption in ZFS using dm-crypt.