Difference between revisions of "Dm-crypt"

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(Encrypting the Swap partition: moved to Dm-crypt with LUKS/Swap encryption)
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[[fr:LUKS]]
 
[[fr:LUKS]]
 
[[ru:System Encryption with LUKS]]
 
[[ru:System Encryption with LUKS]]
[[zh-CN:System Encryption with LUKS]]
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[[zh-CN:Dm-crypt]]
{{Stub|1=This article is currently under heavy restructuring: for its latest stable revision see [[Dm-crypt with LUKS]]}}
 
{{Merge|Plain dm-crypt without LUKS|Assess the possibility of merging the common content between the two articles in order to avoid duplication.|Talk:Plain dm-crypt without LUKS#Merge}}
 
 
{{Related articles start}}
 
{{Related articles start}}
 
{{Related|Disk Encryption}}
 
{{Related|Disk Encryption}}
 
{{Related|Removing System Encryption}}
 
{{Related|Removing System Encryption}}
{{Related|Plain dm-crypt without LUKS}}
 
 
{{Related articles end}}
 
{{Related articles end}}
 +
This article focuses on how to set up encryption on Arch Linux using ''dm-crypt'', which is the standard device-mapper encryption functionality provided by the Linux kernel.
  
This article focuses on how to set up full system encryption on Arch Linux, using dm-crypt with LUKS.
+
==Common scenarios==
 +
This section introduces common scenarios to employ ''dm-crypt'' to encrypt a system or individual filesystem mount points. The scenarios cross-link to the other subpages where needed. It is meant as starting point to familiarize with different practical encryption procedures.
  
'''dm-crypt''' is the standard device-mapper encryption functionality provided by the Linux kernel. It can be used directly by those who like to have full control over all aspects of partition and key management.
+
See [[Dm-crypt/Encrypting a Non-Root File System]] if you need to encrypt a device that is not used for booting a system, like a [[Dm-crypt/Encrypting a Non-Root File System#Partition|partition]] or a [[Dm-crypt/Encrypting a Non-Root File System#Loop device|loop device]].
  
'''LUKS''' is an additional convenience layer which stores all of the needed setup information for dm-crypt on the disk itself and abstracts partition and key management in an attempt to improve ease of use.
+
See [[Dm-crypt/Encrypting an Entire System]] if you want to encrypt an entire system, in particular a root partition. Several scenarios are covered, including the use of ''dm-crypt'' with the ''LUKS'' extension, ''plain'' mode encryption and encryption and ''LVM''.
  
For more details on how dm-crypt+LUKS compares to other disk encryption solution, see [[Disk Encryption#Comparison table]].
+
==Drive preparation==
 +
This step will deal with operations like [[Dm-crypt/Drive Preparation#Secure erasure of the hard disk drive|securely erasing the drive]] and [[Dm-crypt/Drive Preparation#Partitioning|partitioning it]].  
  
== Caveats ==
+
See [[Dm-crypt/Drive Preparation]].
{{Warning|Encrypting a disk or partition will erase everything currently on that disk or partition:
 
* Please make appropriate data backups prior to starting
 
Also be aware that encrypting a system might not only make the life of laptop thieves more miserable, but also yours if you don't plan ahead on
 
* how to make secure backups of the encrypted system/-setup/data and
 
* how to access the encrypted system manually for maintenance.
 
Keeping those points in mind while deciding on how to use encryption may help to decide on method and tools as well.}}
 
  
== Initial Setup ==
+
==Device encryption==
=== Overview and Preparation ===
+
This section covers how to manually utilize dm-crypt to encrypt a system through the [[dm-crypt/Device Encryption#Cryptsetup usage|cryptsetup]] command, also dealing with the usage of [[dm-crypt/Device Encryption#Cryptsetup actions specific for LUKS|LUKS]] and [[dm-crypt/Device Encryption#Cryptsetup and keyfiles|keyfiles]].
The installation of a LUKS-encrypted system is largely the same as installing an unencrypted system. Routine creation of an encrypted system follows these general steps:
 
  
::* Secure erasure of the hard disk drive(s)
+
See [[Dm-crypt/Device Encryption]].
::* Partitioning and setup of encryption ([[LVM]] optional)
 
::* Routine package selection and installation
 
::* System configuration to handle the encryption
 
  
This page covers the first two points in a general way for different configuration options available with LUKS.  
+
==System configuration==
 +
This page illustrates how to configure [[Dm-crypt/System Configuration#mkinitcpio|mkinitcpio]], the [[Dm-crypt/System Configuration#Boot loader|boot loader]] and the [[Dm-crypt/System Configuration#crypttab|crypttab]] file when encrypting a system.
  
The third and fourth point are covered in the later sections. Since the Arch installation media comes with all the tools required for system encryption, you can follow the [[Installation Guide]] or the [[Beginners' Guide]] after the encrypted partitions are set up. You will have to adjust the system configuration to be able to boot from your LUKS-volumes though, which is also covered in setup examples in the later sections.
+
See [[Dm-crypt/System Configuration]].
  
== Encrypting a system partition ==
+
==Swap device encryption==
 +
A swap partition may be added to an encrypted system, if required. The swap partition must be encrypted as well to protect any data swapped out by the system. This part details methods [[Dm-crypt_with_LUKS/Swap_Encryption#Without_suspend-to-disk_support|without]] and [[Dm-crypt_with_LUKS/Swap_Encryption#With_suspend-to-disk_support|with]] suspend-to-disk support.
  
{{Note | This install example covers the a full system encryption with dmcrypt+LUKS in a simple partition layout. For other partition layouts, e.g. LVM, please see the other examples.}}
+
See [[Dm-crypt/Swap Encryption]].
 
 
Most of the installation of an encrypted system partition can be carried out normally. However, there are a few areas where it is important to make certain selections. These are marked below.
 
 
 
=== Prepare hard drive for Arch Install Scripts ===
 
 
 
This assumes you want to install an encrypted system with the Arch Install Scripts, have created partitions for {{ic|/}} (e.g. {{ic|/dev/sdaX}}) and {{ic|/boot}} ({{ic|/dev/sdaY}}) at least, following the [[Installation_Guide|Installation Guide]] and deciding against [[LUKS#Encrypting a LVM setup|using LVM]]. Prior to creating the partitions you have done a [[LUKS#Secure_erasure_of_the_hard_disk_drive|preparation]] of the disk for encryption according to your necessities (the necessary tools are on the installation-ISO).
 
 
 
First check, if the blockdevice mapper {{ic|dm_mod}} is loaded with
 
# lsmod | grep mod
 
If one wants to use the default LUKS-cipher algorithm, there is no need to specify one for the luksFormat. You may want to check the [[LUKS#Using_LUKS_to_Format_Partitions_with_a_Passphrase|defaults]] used by the cryptsetup version at time of installation and decide yourself. With defaults a dm-crypt/LUKS blockdevice for the crypted root can be created 
 
# cryptsetup -y -v luksFormat /dev/sdaX
 
opened
 
# cryptsetup open /dev/sdaX cryptroot
 
formatted with your desired filesystem
 
# mkfs -t ext4 /dev/mapper/cryptroot
 
and mounted
 
# mount -t ext4 /dev/mapper/cryptroot /mnt
 
 
 
At this point, just before installing the base system, it might be useful to check the mapping works as intended:
 
# umount /mnt
 
# cryptsetup close cryptroot
 
and mount it again to check.
 
 
 
If you created a separate {{ic|/home}} partition, the steps have to be adapted and repeated for that. In [[LUKS#Encrypting_the_home_partition]] the creation is described and in [[LUKS#Crypttab]] how to activate the automount during 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 key-file stored in the system partition to unlock the separate partition via {{ic|crypttab}}. How that is done may be derived from the [[Dm-crypt_with_LUKS#Encrypting_.2Fhome_after_reboot|LVM example]] below. If you leave unpartitioned disk space, the necessary configuration for the {{ic|/home}} partition may be done later too along with migrating data.
 
 
What you do have to setup is a non-encrypted {{ic|/boot}} partition, which is needed for a crypted root. For a standard [[EFI|MBR/non-EFI]] {{ic|/boot}} partition that may be achieved by formatting
 
# mkfs -t ext2 /dev/sdaY
 
creating a mount-point for installation
 
# mkdir /mnt/boot
 
and mounting it
 
# mount -t ext2 /dev/sdaY /mnt/boot
 
 
 
That is basically what is necessary at this point before installing the base system with the [[Installation_Guide#Mount_the_partitions|Arch Install Scripts]]. Take care to install the bootloader to {{ic|/mnt/boot}} with the {{ic|pacstrap}} script. Additional configuration steps must be followed before booting the installed system.
 
 
 
=== Configure initramfs ===
 
One important point is to add the hooks relevant for your particular install in the correct order to {{ic|/etc/mkinitcpio.conf}}. The one you ''have'' to add when encrypting the root filesystem is {{ic|encrypt}}. A recommended hook for LUKS encrypted blockdevices is {{ic|shutdown}} to ensure controlled unmounting during system shutdown. Others needed, e.g. {{ic|keymap}}, should be clear from other manual steps you follow during the installation and further details in the following. For detailed information about initramfs configuration and available Hooks refer to [[Mkinitcpio#HOOKS]].
 
 
 
{{Note|The {{ic|encrypt}} hook is only needed if your '''root''' partition is a ''LUKS'' partition (or a LUKS partition that needs to be mounted ''before'' root). The {{ic|encrypt}} hook is not needed for any other encrypted partitions (swap, for example). System initialization scripts ({{ic|/etc/rc.sysinit}} and {{ic|/etc/crypttab}} among others) take care of those.}}
 
 
 
It is important that the {{ic|encrypt}} hook comes ''before'' the {{ic|filesystems}} hook (in case you are using '''LVM on LUKS''', the order should be: {{ic|encrypt lvm2 filesystems}}), so make sure that your {{ic|HOOKS}} array looks something like this:
 
{{hc|etc/mkinitcpio.conf|HOOKS<nowiki>=</nowiki>"(base udev) ... '''encrypt''' ... filesystems ..."}}
 
 
 
If you need support for foreign keymaps for your encryption password, you have to specify the hook {{ic|keymap}} as well before {{ic|encrypt}}.
 
 
 
If you have a USB keyboard, you will need the {{ic|keyboard}} hook. Without it, no USB keyboard will work in early userspace. If you still have this problem after adding {{ic|keyboard}}, try {{ic|usbinput}}, though this is deprecated.
 
 
 
In the same file, you may want to add to "MODULES" '''dm_mod''' and the filesystem types used, e.g: {{ic|MODULES<nowiki>=</nowiki>"dm_mod ext4"}}
 
 
 
After you are done don't forget:
 
mkinitcpio -p linux
 
 
 
=== Kernel parameter configuration of the bootloader ===
 
In order to enable booting an encrypted root partition, it is passed to the {{ic|encrypt}} hook with [[kernel parameters]] to be set up in the bootloader.
 
The main parameter is '''cryptdevice''', with the following syntax:
 
cryptdevice=<device>:<dmname>
 
; <device>: The path to the raw encrypted device. Usage of [[Persistent block device naming]] is advisable.
 
; <dmname>: The name given to the device after decryption, will be available as {{ic|/dev/mapper/<dmname>}}. (<dmname> '''MUST NOT''' be set to a name already used for LVM partitions!)
 
 
 
So if the encrypted root device in the example is {{ic|/dev/sda2}} and the decrypted one should be mapped to {{ic|/dev/mapper/cryptroot}}, the kernel parameter would be:
 
cryptdevice=/dev/sda2:cryptroot
 
This will make the system prompt for the passphrase to unlock the root device on a cold boot.
 
 
 
Depending on the setup other parameters are required as well:
 
cryptdevice=<device>:<dmname> root=<device> resume=<device> cryptkey=<device>:<fstype>:<path>
 
 
 
; root=<device>: The device file of the actual (decrypted) root filesystem. If the filesystem is formatted directly on the decrypted device file this will be {{ic|/dev/mapper/<dmname>}}. If LVM is used, the device must be addressed like {{ic|/dev/mapper/<volgroup>-<pvol>}} or {{ic|/dev/<volgroup>/<pvol>}}.
 
; resume=<device>: The device file of the decrypted (swap) filesystem used for suspend2disk.
 
; cryptkey=<nowiki><device>:<fstype>:<path></nowiki>: Required for reading a [[#Storing_the_Key_File|keyfile]] from a filesystem.
 
 
 
The syntax for the optional '''cryptkey''' parameter is:
 
 
 
cryptkey=<device>:<fstype>:<path>
 
 
 
; <device>: The raw block device where the key exists.
 
; <fstype>: The filesystem type of <device> (or auto).
 
; <path>: The absolute path of the keyfile within the device.
 
 
 
Examples on configuration for [[GRUB#Root encryption|GRUB]] and [[Syslinux#Basic Config|Syslinux]] are available on the respective pages.
 
 
 
=== Fstab ===
 
Further, double-check the {{ic|gen[[fstab]]}} scripts result for your {{ic|/dev/mapper/cryptroot}} and other mounts.
 
== Encrypting the home partition ==
 
This example covers encryption of a home partition or comparable other partition containing user data. For full system encryption see [[LUKS#Encrypting a system partition|Encrypting a system partition]].
 
You can either have a single user's home directory on a partition, or create a common partition for all user's home partitions.
 
 
 
Prepare the hard disk drive by performing a [[LUKS#Secure_erasure_of_the_hard_disk_drive|secure erasure]]. Create at least one partition, that will be used as home partition, with a [[Partitioning|partitioning tool]] of your choice. Note that the secure erasure can also be done to that single partition only.
 
Setup the LUKS and dm-crypt magic with
 
# cryptsetup  [OPTION...] luksFormat <device>
 
as described in the section [[LUKS#Mapping_Physical_Partitions_to_LUKS|Mapping Physical Partitions to LUKS]].
 
In the above command replace {{ic|<device>}} with the previously created home partition.
 
 
 
To gain access to the encrypted partition, unlock it with the device mapper, using
 
# cryptsetup open <device> <name>
 
It is recommended to read the full explanation about this command [[LUKS#Using_LUKS_to_Format_Partitions_with_a_Passphrase|here]].
 
 
 
After unlocking the partition, it will be available at {{ic|/dev/mapper/<name>}}. Now create a [[File_Systems|filesystem]] of your choice with
 
# mkfs.fstype /dev/mapper/<name>
 
Mount the filesystem to {{ic|/home}}, or if it should be accessible to only one user to {{ic|/home/username}}.
 
Before shutting down the filesystem needs to unmounted and, in this order, the LUKS partition needs to be closed with
 
# cryptsetup close <name>
 
 
 
=== Automated unlocking and mounting ===
 
There are two different solutions for automating the process of unlocking the home partition and mounting its filesystem. Using crypttab, unlocking happens at boot time, and with Pam mount it happens on user login.
 
==== Crypttab ====
 
This is the recommended solution if you want to use one common partition for all user's home partitions.
 
To make systemd open and mount the encrypted partition on boot, two files need to be edited, {{ic|/etc/crypttab}} and {{ic|/etc/fstab}}. The {{ic|/etc/crypttab}} file describes encrypted block devices that are set up during system boot by {{ic|systemd-cryptsetup-generator}} automatically.
 
 
 
For example, to open the encrypted LUKS partition on the device {{ic|/dev/sdx1}} with the name {{ic|home}}, add this line:
 
 
 
{{hc|/etc/crypttab|home /dev/sdx1 none luks}}
 
The option {{ic|none}} will trigger a prompt during boot to type the passphrase for unlocking the partition. A keyfile can also be set up and referenced instead. This results in an automatic unlocking, if the keyfile is accessible during boot. Since LUKS offers the option to have multiple keys, the chosen option can also be changed later.
 
 
 
See {{ic|man crypttab (5)}} and read the file {{ic|/etc/crypttab}} for more information.
 
 
 
Edit {{ic|/etc/fstab}} and add an entry for the previously created path in {{ic|/dev/mapper}}. Following above example the fstab entry looks like this:
 
 
 
{{hc|/etc/fstab|/dev/mapper/home /home <filesystem> defaults 0 2}}
 
 
 
==== Pam mount ====
 
This is the recommended solution if you want to have a single user's home directory on a partition.
 
To automount user homes on login see [[Pam mount]].
 
 
 
== Encrypting a loopback filesystem ==
 
 
 
A loop device enables to map a blockdevice to a file with the standard util-linux tool {{ic|losetup}}. The file can then contain a filesystem, which can be used quite like any other filesystem. A lot of users know [[Truecrypt]] as a tool to create encrypted containers. Just about the same functionality can be achieved with a loopback filesystem encrypted with LUKS and is shown in the following example.
 
 
 
=== Preparation and mapping ===
 
First, start by creating an encrypted container!
 
 
 
dd if=/dev/urandom of=/bigsecret bs=1M count=10
 
 
 
This will create the file {{ic|bigsecret}} with a size of 10 megabytes.
 
 
 
losetup /dev/loop0 /bigsecret
 
 
 
This will create the device node {{ic|/dev/loop0}}, so that we can mount/use our container.
 
 
 
{{Note|If it gives you the error {{ic|/dev/loop0: No such file or directory}}, you need to first load the kernel module with {{ic|modprobe loop}}. These days (Kernel 3.2) loop devices are created on demand. Ask for a new loop device with {{ic|losetup -f}}.}}
 
 
 
cryptsetup luksFormat /dev/loop0
 
 
 
This will ask you for a password for your new container file.
 
 
 
{{Note|If you get an error like {{ic|Command failed: Failed to setup dm-crypt key mapping. Check kernel for support for the aes-cbc-essiv:sha256 cipher spec and verify that /dev/loop0 contains at least 133 sectors|}}, then run {{ic|modprobe dm-mod}}.}}
 
 
 
cryptsetup open --type luks /dev/loop0 secret
 
 
 
The encrypted container is now available through the device file {{ic|/dev/mapper/secret}}.
 
Now we are able to create a partition in the container:
 
 
 
mkfs.ext2 /dev/mapper/secret
 
 
 
and mount it...
 
 
 
mkdir /mnt/secret
 
mount -t ext2 /dev/mapper/secret /mnt/secret
 
 
 
We can now use the container as if it was a normal partition!
 
To unmount the container:
 
 
 
umount /mnt/secret
 
cryptsetup luksClose secret
 
losetup -d /dev/loop0 # free the loopdevice.
 
 
 
so, if you want to mount the container again, you just apply the following commands:
 
 
 
losetup /dev/loop0 /bigsecret
 
cryptsetup open --type luks /dev/loop0 secret
 
mount -t ext2 /dev/mapper/secret /mnt/secret
 
 
 
=== Encrypt using a key-file ===
 
Let us first generate a 2048 byte random keyfile:
 
 
dd if=/dev/urandom of=keyfile bs=1k count=2
 
 
 
We can now format our container using this key
 
 
 
cryptsetup luksFormat /dev/loop0 keyfile
 
 
 
or our partition :
 
 
 
cryptsetup luksFormat /dev/hda2 keyfile
 
 
 
Once formatted, we can now open the LUKS device using the key:
 
 
 
cryptsetup -d keyfile open --type luks /dev/loop0 container
 
 
 
You can now like before format the device {{ic|/dev/mapper/container}} with your favorite filesystem and then mount it just as easily.
 
 
 
The keyfile is now the only key to your file. I personally advise encrypting your keyfile using your private GPG key and storing an off-site secured copy of the file.
 
 
 
=== Resizing the loopback filesystem ===
 
First we should unmount the encrypted container:
 
umount /mnt/secret
 
cryptsetup luksClose secret
 
losetup -d /dev/loop0 # free the loopdevice.
 
 
 
After this we need to expand our container file with the size of the data we want to add:
 
 
 
dd if=/dev/urandom bs=1M count=1024 | cat - >> /bigsecret
 
 
 
Be careful to really use TWO {{ic|>}}, or you will override your current container!
 
 
 
You could use {{ic|/dev/zero}} instead of {{ic|/dev/urandom}} to significantly speed up the process, but with {{ic|/dev/zero}} your encrypted filesystems will ''not be as secure''. (A better option to create random data quicker than {{ic|/dev/urandom}} is {{ic|frandom}} [https://aur.archlinux.org/packages.php?ID=9869], available from the [[AUR]]).
 
A faster (almost instant) method than dd is {{ic|truncate}} , but its use has the same security implications as using /dev/zero. The size passed to truncate is the final size to make the file, so don't use a value less than that of the current file or you will lose data. e.g. to increase a 20G file by 10G: truncate -s 30G filename.
 
 
 
Now we have to map the container to the loop device:
 
losetup /dev/loop0 /bigsecret
 
cryptsetup open --type luks /dev/loop0 secret
 
After this we will resize the encrypted part of the container to the maximum size of the container file:
 
cryptsetup resize secret
 
Finally, we can resize the filesystem. Here is an example for ext2/3/4:
 
e2fsck -f /dev/mapper/secret # Just doing a filesystem check, because it's a bad idea to resize a broken fs
 
resize2fs /dev/mapper/secret
 
You can now mount your container again:
 
mount /dev/mapper/secret /mnt/secret
 
 
 
== Encrypting a LVM setup ==
 
 
 
It is easy to use encryption with [[LVM]]. This section describes specific aspects of setting up an encrypted LVM setup and has a mini-howto for users with experiences of using both, cryptsetup and LVM. If you are looking for verbose installation instructions of such a setup, you might want to read [[Encrypted_LVM]] first.
 
 
 
If you do not know how to set up LVM, then read [[Installing with Software RAID or LVM]]. Using LVM is particularly helpful when a system with multiple partitions is planned. While there are a number of alternatives for unlocking multiple partitions with the same passphrase/key, the default Arch {{ic|mkinitcpio}} hooks do not implement non-standard ways. A combination of the {{ic|encrypt}} and {{ic|lvm2}} hooks, however, enables to setup a system with numerous logical volumes as partitions while using one passphrase/key to unlock them.
 
 
 
'''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 most important thing in setting LVM on '''top''' of encryption is to [[#Configure initramfs|configure the initramfs]] for running '''both''' the {{ic|encrypt}} hook '''and''' the {{ic|lvm2}} hook (and those two before the {{ic|filesystems}} hook). In the past, it was necessary to ensure the correct ordering of these hooks in {{ic|/etc/mkinitcpio.conf}} but the order no longer matters with the current implementation of {{ic|lvm2}}.
 
 
 
'''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 around a mixture of encrypted and non-encrypted volumes/partitions is possible as well.
 
 
 
For encrypted partitions inside an LVM, the LVM-hook has to run first, before the respective encrypted logical volumes can be unlocked. So for this add the {{ic|encrypt}} hook in {{ic|/etc/mkinitcpio.conf}} '''after''' the {{ic|lvm2}} hook, if you chose to set up encrypted partitions on '''top''' of LVM.
 
 
 
Both these options are described in more detail in [[Encrypted_LVM]]. The following represents the historic guide from before the verbose page.
 
 
 
=== LVM and dm-crypt manually (short version) ===
 
 
 
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. For {{ic|cryptsetup}} options, please see [[Dm-crypt_with_LUKS#Configuring_LUKS|above]].
 
 
 
==== Partitioning scheme ====
 
{{ic|/dev/sda1}} -> {{ic|/boot}}
 
{{ic|/dev/sda2}} -> LVM
 
 
 
==== Setting up the encrypted system ====
 
cryptsetup -d /dev/random -c aes-xts-plain -s 512 create lvm /dev/sda2
 
dd if=/dev/urandom of=/dev/mapper/lvm
 
cryptsetup remove lvm
 
lvm pvcreate /dev/sda2
 
lvm vgcreate lvm /dev/sda2
 
lvm lvcreate -L 10G -n root lvm
 
lvm lvcreate -L 500M -n swap lvm
 
lvm lvcreate -L 500M -n tmp lvm
 
lvm lvcreate -l 100%FREE -n home lvm
 
cryptsetup luksFormat -c aes-xts-plain -s 512 /dev/lvm/root
 
cryptsetup open --type luks /dev/lvm/root root
 
mkreiserfs /dev/mapper/root
 
mount /dev/mapper/root /mnt
 
dd if=/dev/zero of=/dev/sda1 bs=1M
 
mkreiserfs /dev/sda1
 
mkdir /mnt/boot
 
mount /dev/sda1 /mnt/boot
 
mkdir -p -m 700 /mnt/etc/luks-keys
 
dd if=/dev/random of=/mnt/etc/luks-keys/home bs=1 count=256
 
 
 
==== Install Arch Linux ====
 
Now after setup of the encrypted LVM partitioning, it would be time to install: [[Installation_Guide#Mount_the_partitions|Arch Install Scripts]].
 
 
 
==== Configuration ====
 
 
 
===== /etc/mkinitcpio.conf =====
 
Put {{ic|lvm2}} and {{ic|encrypt}} (in that order) before {{ic|filesystems}} in the {{ic|HOOKS}} array. Again, note that this is setting encryption on '''top''' of LVM.
 
 
 
If you want install the system on a usb stick, you need to put {{ic|usb}} just after {{ic|udev}}.
 
 
 
===== Boot options for LUKS-LVM =====
 
For the above example, change the kernel options for the root-device auto-configured in the bootloader installation from {{ic|root<nowiki>=</nowiki>/dev/hda3}} to
 
cryptdevice=/dev/lvm/root:root root=/dev/mapper/root
 
 
 
More general, the kernel command line for LUKS <-> LVM is constructed like this:
 
root=/dev/mapper/<volume-group>-<logical-volume> cryptdevice=/dev/<luks-part>:<volume-group>
 
For example:
 
root=/dev/mapper/vg-arch cryptdevice=/dev/sda4:vg
 
 
 
Or like this:
 
cryptdevice=/dev/<volume-group>/<logical-volume>:root root=/dev/mapper/root
 
 
 
If you want install the system on a usb stick, you need to add {{ic|lvmdelay<nowiki>=</nowiki>/dev/mapper/lvm-root}}
 
 
 
===== Filesystem mounts system =====
 
{{hc|/etc/fstab|
 
/dev/mapper/root        /      reiserfs        defaults        0      1
 
/dev/sda1              /boot  reiserfs        defaults        0      2
 
/dev/mapper/tmp        /tmp    tmpfs          defaults        0      0
 
/dev/mapper/swap        none    swap            sw              0      0}}
 
 
 
{{hc|/etc/crypttab|
 
swap /dev/lvm/swap SWAP -c aes-xts-plain -h whirlpool -s 512
 
tmp /dev/lvm/tmp /dev/urandom -c aes-xts-plain -s 512}}
 
 
 
===== Encrypting /home after reboot =====
 
cryptsetup luksFormat -c aes-xts-plain -s 512 /dev/lvm/home /etc/luks-keys/home
 
cryptsetup open --type luks -d /etc/luks-keys/home /dev/lvm/home home
 
mkreiserfs /dev/mapper/home
 
mount /dev/mapper/home /home
 
 
 
===== Filesystem mounts home =====
 
{{hc|/etc/crypttab|
 
home /dev/lvm/home  /etc/luks-keys/home}}
 
 
 
{{hc|/etc/fstab|
 
/dev/mapper/home        /home  reiserfs        defaults        0      0}}
 
  
 
==Specialties==
 
==Specialties==
===Using GPG or OpenSSL Encrypted Keyfiles===
+
This part deals with special operations like [[Dm-crypt/Specialties#Securing the unencrypted boot partition|securing the unencrypted boot partition]], [[Dm-crypt/Specialties#Using GPG or OpenSSL Encrypted Keyfiles|using GPG or OpenSSL encrypted keyfiles]], a method to [[Dm-crypt/Specialties#Remote_unlocking_of_the_root_.28or_other.29_partition|boot and unlock via the network]], or [[Dm-crypt/Specialties#Discard.2FTRIM_support_for_solid_state_disks_.28SSD.29|setting up discard/TRIM for a SSD]].
The following forum posts give instructions to use two factor authentication, gpg or openssl encrypted keyfiles, instead of a plaintext keyfile described earlier in this wiki article [https://bbs.archlinux.org/viewtopic.php?id=120243 System Encryption using LUKS with GPG encrypted keys]:
 
* GnuPG: [https://bbs.archlinux.org/viewtopic.php?pid=943338#p943338 Post regarding GPG encrypted keys] This post has the generic instructions.
 
* OpenSSL: [https://bbs.archlinux.org/viewtopic.php?pid=947805#p947805 Post regarding OpenSSL encrypted keys] This post only has the {{ic|ssldec}} hooks.
 
* OpenSSL: [https://bbs.archlinux.org/viewtopic.php?id=155393 Post regarding OpenSSL salted bf-cbc encrypted keys] This post has the {{ic|bfkf}} initcpio hooks, install, and encrypted keyfile generator scripts.
 
 
 
Note that:
 
* You can follow the above instructions with only two primary partitions one boot partition  
 
(required because of LVM), and one primary LVM partition. Within the LVM partition you can have
 
as many partitions as you need, but most importantly it should contain at least root, swap, and
 
home logical volume partitions. This has the added benefit of having only one keyfile for all
 
your partitions, and having the ability to hibernate your computer (suspend to disk) where the
 
swap partition is encrypted. If you decide to do so your hooks in {{ic|/etc/mkinitcpio.conf}}
 
should look like
 
{{ic|HOOKS&#61;" ... usb usbinput (etwo or ssldec) encrypt(if using openssl) lvm2 resume ... "}}
 
and you should add {{ic|"resume&#61;/dev/mapper/<VolumeGroupName>-<LVNameOfSwap>"}} to your [[kernel parameters]].
 
* If you need to temporarily store the unecrypted keyfile somewhere, do not store them on an unencrypted disk. Even better make sure to store them to RAM such as {{ic|/dev/shm}}.
 
* If you want to use a GPG encrypted keyfile, you need to use a statically compiled GnuPG version 1.4 or you could edit the hooks and use this AUR package [https://aur.archlinux.org/packages.php?ID=58030 gnupg1]
 
* It is possible that an update to OpenSSL could break the custom {{ic|ssldec}} mentioned in the second forum post.
 
 
 
===Remote unlocking of the root (or other) partition===
 
If you want to be able to reboot a fully LUKS-encrypted system remotely, or start it with a Wake-on-LAN service, you will need a way to enter a passphrase for the root partition/volume at startup. This can be achieved by running the {{ic|net}} hook along with an [[SSH]] server in initrd. Install the {{AUR|dropbear_initrd_encrypt}} package from the [[Arch User Repository|AUR]] and follow the post-installation instructions. Replace the {{ic|encrypt}} hook with {{ic|dropbear encryptssh}} in {{ic|/etc/mkinitcpio.conf}}. Put the {{ic|net}} hook early in the HOOKS array if your DHCP server takes a long time to lease IP addresses.
 
 
 
If you would simply like a nice solution to mount other encrypted partitions (such as {{ic|/home}})remotely, you may want to look at [https://bbs.archlinux.org/viewtopic.php?pid=880484 this forum thread].
 
 
 
===Modifying the encrypt hook for a non-root partition===
 
Maybe you have a requirement for using the {{ic|encrypt}} hook on a non-root partition. Arch does not support this out of the box, however, you can easily change the cryptdev and cryptname values in {{ic|/lib/initcpio/hooks/encrypt}} (the first one to your {{ic|/dev/sd*}} partition, the second to the name you want to attribute). That should be enough.
 
 
 
The big advantage is you can have everything automated, while setting up {{ic|/etc/crypttab}} with an external key file (i.e. the keyfile is not on any internal hard drive partition) can be a pain - you need to make sure the USB/FireWire/... device gets mounted before the encrypted partition, which means you have to change the order of {{ic|/etc/fstab}} (at least).
 
 
 
Of course, if the {{pkg|cryptsetup}} package gets upgraded, you will have to change this script again. Unlike {{ic|/etc/crypttab}}, only one partition is supported, but with some further hacking one should be able to have multiple partitions unlocked.
 
 
 
If you want to do this on a software RAID partition, there is one more thing you need to do. Just setting the {{ic|/dev/mdX}} device in {{ic|/lib/initcpio/hooks/encrypt}} is not enough; the {{ic|encrypt}} hook will fail to find the key for some reason, and not prompt for a passphrase either. It looks like the RAID devices are not brought up until after the {{ic|encrypt}} hook is run. You can solve this by putting the RAID array in {{ic|/boot/grub/menu.lst}}, like
 
kernel /boot/vmlinuz-linux md=1,/dev/hda5,/dev/hdb5
 
 
 
If you set up your root partition as a RAID, you will notice the similarities with that setup ;-). [[GRUB]] can handle multiple array definitions just fine:
 
kernel /boot/vmlinuz-linux root=/dev/md0 ro md=0,/dev/sda1,/dev/sdb1 md=1,/dev/sda5,/dev/sdb5,/dev/sdc5
 
 
 
===Securing the unencrypted boot partition===
 
Referring to an article from the ct-magazine (Issue 3/12, page 146, 01.16.2012 http://www.heise.de/ct/inhalt/2012/03/6/) the following script checks files under {{ic|/boot}} for changes of SHA-1 hash, inode and occupied blocks on the hard drive. It also checks the MBR. The script cannot prevent certain type of attacks, but a lot are made harder. No configuration of the script itself is stored in unencrypted {{ic|/boot}}. With a locked/powered-off crypted system this makes it infeasible for an attacker to recognize that an automatic checksum comparison of the partition is done upon boot.
 
 
 
The script with installation instructions is available here: ftp://ftp.heise.de/pub/ct/listings/1203-146.zip (Author: Juergen Schmidt, ju at heisec.de; License: GPLv2). There is also an AUR package: {{AUR|chkboot}}
 
 
 
After installation:
 
* For classical sysvinit: add {{ic|/usr/local/bin/chkboot.sh &}} to your {{ic|/etc/rc.local}}
 
* For systemd: add a service file and enable the service: [[systemd]]. The service file might look like:
 
[Unit]
 
Description=Check that boot is what we want
 
Requires=basic.target
 
After=basic.target
 
 
[Service]
 
Type=oneshot
 
ExecStart=/usr/local/bin/chkboot.sh
 
 
[Install]
 
WantedBy=multi-user.target
 
 
 
There is a small caveat for systemd: At the time of writing the original {{ic|chkboot.sh}} script provided contains an empty space at the beginning of {{ic|<u> </u>#!/bin/bash}} which has to be removed for the service to start successfully.
 
 
 
As {{ic|/usr/local/bin/chkboot_user.sh}} need to be excuted after login, add it to the autostart (e.g. under KDE -> System Settings -> Startup and Shutdown -> Autostart; Gnome3: gnome-session-properties).  
 
 
 
With Arch Linux changes to {{ic|/boot}} are pretty frequent, for example by new kernels rolling-in. Therefore it may be helpful to use the scripts with every full system update. One way to do so:
 
 
 
#!/bin/bash
 
#
 
# Note: Insert your <user>  and execute it with sudo for pacman & chkboot to work automagically
 
#
 
echo "Pacman update [1] Quickcheck before updating" &
 
sudo -u <user> /usr/local/bin/chkboot_user.sh # insert your logged on <user>
 
/usr/local/bin/chkboot.sh
 
sync # sync disks with any results
 
sudo -u <user> /usr/local/bin/chkboot_user.sh # insert your logged on <user>
 
echo "Pacman update [2] Syncing repos for pacman"
 
pacman -Syu
 
/usr/local/bin/chkboot.sh
 
sync
 
sudo -u <user> /usr/local/bin/chkboot_user.sh # insert your logged on <user>
 
echo "Pacman update [3] All done, let's roll on ..."
 
 
 
Alternatively to above scripts, a hash check can be set up with [[AIDE]] which can be customized via a very flexible configuration file.
 
 
 
While one of these methods should serve the purpose for most users, they do not address all security problems associated with the unencrypted {{ic|/boot}}. One approach which endeavours to provide a fully authenticated boot chain was published with POTTS as an academic thesis to implement the [http://www1.informatik.uni-erlangen.de/stark STARK] authentication framework.  
 
  
The POTTS proof-of-concept uses Arch Linux as a base distribution and implements a system boot chain with 
+
See [[Dm-crypt/Specialties]].
* POTTS - a bootmenu for a one-time authentication message prompt
 
* TrustedGrub - a grub-legacy implementation which authenticates the kernel and initramfs against TPM chip registers
 
* TRESOR - a kernel patch which implements AES but keeps the master-key not in RAM but in CPU registers during runtime.   
 
As part of the thesis [http://13.tc/p/potts/manual.html installation] instructions based on Arch Linux (iso 2013-01) have been published. If you want to try it, be aware these tools are not in standard repositories and the solution will be time consuming to maintain.
 
  
== Resources ==
+
== See also ==
 
* [http://code.google.com/p/cryptsetup/wiki/FrequentlyAskedQuestions cryptsetup FAQ] - The main and foremost help resource, directly from the developers.
 
* [http://code.google.com/p/cryptsetup/wiki/FrequentlyAskedQuestions cryptsetup FAQ] - The main and foremost help resource, directly from the developers.
 
* [http://www.freeotfe.org/ FreeOTFE] - Supports unlocking LUKS encrypted volumes in Microsoft Windows.
 
* [http://www.freeotfe.org/ FreeOTFE] - Supports unlocking LUKS encrypted volumes in Microsoft Windows.

Revision as of 12:57, 15 January 2014

zh-CN:Dm-crypt

This article focuses on how to set up encryption on Arch Linux using dm-crypt, which is the standard device-mapper encryption functionality provided by the Linux kernel.

Common scenarios

This section introduces common scenarios to employ dm-crypt to encrypt a system or individual filesystem mount points. The scenarios cross-link to the other subpages where needed. It is meant as starting point to familiarize with different practical encryption procedures.

See Dm-crypt/Encrypting a Non-Root File System if you need to encrypt a device that is not used for booting a system, like a partition or a loop device.

See Dm-crypt/Encrypting an Entire System if you want to encrypt an entire system, in particular a root partition. Several scenarios are covered, including the use of dm-crypt with the LUKS extension, plain mode encryption and encryption and LVM.

Drive preparation

This step will deal with operations like securely erasing the drive and partitioning it.

See Dm-crypt/Drive Preparation.

Device encryption

This section covers how to manually utilize dm-crypt to encrypt a system through the cryptsetup command, also dealing with the usage of LUKS and keyfiles.

See Dm-crypt/Device Encryption.

System configuration

This page illustrates how to configure mkinitcpio, the boot loader and the crypttab file when encrypting a system.

See Dm-crypt/System Configuration.

Swap device encryption

A swap partition may be added to an encrypted system, if required. The swap partition must be encrypted as well to protect any data swapped out by the system. This part details methods without and with suspend-to-disk support.

See Dm-crypt/Swap Encryption.

Specialties

This part deals with special operations like securing the unencrypted boot partition, using GPG or OpenSSL encrypted keyfiles, a method to boot and unlock via the network, or setting up discard/TRIM for a SSD.

See Dm-crypt/Specialties.

See also

  • cryptsetup FAQ - The main and foremost help resource, directly from the developers.
  • FreeOTFE - Supports unlocking LUKS encrypted volumes in Microsoft Windows.