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dm-crypt/filesystems: automatic mounting
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# DM-Crypt
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`dm-crypt` can create and manage encrypted devices.
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DM-Crypt can create and manage encrypted devices.
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## Creating an encrypted devices
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## Usage
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### Creating an Encrypted Devices
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To create a encrypted device simply run:
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`cryptsetup -y -v luksFormat /dev/sda2`.
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Where `/dev/sda2` is the device you want to create.
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Where `/dev/sda2` is the device to be created.
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## Open/Close an encrypted device
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### Create/Add a Key File to an encrypted volume
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To open and map a device run `cryptsetup luksOpen /dev/sda1 crypt0` where
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`/dev/sda1` is your encrypted device and `crypt0` is where it will be mapped to
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with `dev/mapper/crypt0`.
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Afterwards it can be closed by running `cryptsetup close /dev/mapper/crypt0`.
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First a key file has to be created.
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With the following lines a random file will be created that will later be used
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as the key file.
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If a key file already exists this part can be skipped.
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The following command needs to be adapted.
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It will create a key of bitlength 2048 (512 x 4).
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## Resize a LUKS encrypted volume
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```txt
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dd bs=512 count=4 if=/dev/random of=<path to destination>
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```
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If you have volume groups on the encrypted volume make sure to close them
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with the following command modified to your needs:
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It is possible to increase the length to get a stronger key file.
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Alternatively strong LUKS keys can be created using [OpenSSL](./openssl.md)
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using a bitlength of 4096:
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`openssl genrsa -out <path to destination> 4096`.
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The key file will then be saved to `<path to destination>`.
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Finally the key file can be added to an opened LUKS encrypted volume by running
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the following command:
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`cryptsetup luksAddKey <path to LUKS volume> <path to key file>`.
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`<path to LUKS device>` is the encrypted device (for example `/dev/sda2`) and
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`<path to key file>` is the location of the key file.
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### Resize a LUKS Encrypted Volume
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If volume groups on the encrypted volume are opened make sure to close them
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with the following command modified to the present needs:
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`vgchange -a n <volume group>`
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Open the encrypted volume (assuming its stored at `/dev/sda2` and you map it
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to `crypt-volume`):
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`cryptsetup luksOpen /dev/sda2 crypt-volume`
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Open the encrypted volume:
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`cryptsetup luksOpen <path to LUKS volume> <mapper location>`.
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`<path to LUKS device>` is the encrypted device (for example `/dev/sda2`) and
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`<mapper location>` is where it will be mapped to with `dev/mapper/` prepended.
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Now resize the encrypted volume to all available space of the partition.
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If you don't want to extend the encrypted volume to the whole partition
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or the partition is to small for your purposes, make sure to resize the
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If the encrypted volume should not be extended to the whole partition
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or the partition is too small for its intended purposes, make sure to resize the
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partition first accordingly (see [disk management](./disk-management.md)).
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`cryptsetup resize crypt-volume`
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## Creating an automatic decryption key with an USB stick
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### Open/Close an Encrypted Volume
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This guide assumes you to have an Arch Linux System, as installed in
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To open and map a device using a set password run
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`cryptsetup luksOpen <path to LUKS device> <mapper location>` where
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`<path to LUKS device>` is the encrypted device (for example `/dev/sda2`) and
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`<mapper location>` is where it will be mapped to with `dev/mapper/` prepended.
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Using `secret` as a `<map location>` the opened drive is available at
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`/dev/mapper/secret`.
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Alternatively an encrypted volume can be decrypted using
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[a key file](#createadd-a-key-file-to-an-encrypted-volume) if set up for it.
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This can be achieved by running:
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`cryptsetup luksOpen <path to LUKS volume> crypt-volume --key-file=<key file location>`.
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`<path to LUKS device>` is the encrypted device (for example `/dev/sda2`).
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Afterwards it can be closed by running `cryptsetup close /dev/mapper/crypt0`.
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### Creating/Add a USB Decryption Key
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This guide assumes an Arch Linux System, as installed in
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[this wikis arch linux installation](./arch-linux/installation.md).
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This section is based on entries from the
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[arch linux forum](https://forum.archlinux.de/d/28886-systementschluesselung-per-usb-stick).
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It uses a similar technique to the decryption of the encrypted volume via
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[a key file](#createadd-a-key-file-to-an-encrypted-volume).
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Insert your USB stick.
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Insert the USB stick.
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This guide will assume its address is `/dev/sde`.
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Fill in the first sectors (in this case 94, make sure this number is bigger
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@ -55,7 +97,7 @@ called `/dev/sda2`):
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Next it has to be made sure that the decryption key, is available at the same
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position every time.
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For this check the `serial` and `product` of your USB stick with the following
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For this check the `serial` and `product` of the USB stick with the following
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commands.
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```sh
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@ -64,7 +106,7 @@ udevadm info -a -p `udevadm info -q path -n /dev/sde` | grep ATTRS{product}
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```
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The first line gives the `serial`, the second the `product`.
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The `product` should match your USB stick.
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The `product` should match the USB stick.
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After this create a file at `/etc/udev/rules.d/50-usbkey.rules` with the
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following content.
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@ -80,6 +122,17 @@ Then reload the udev rules by running:
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Unplug the stick and plug it back in.
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It should be available under `dev/usbkey`.
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With the following command an encrypted device can be decrypted with the usb
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stick.
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Use this to confirm the correct setup of the decryption key and the encrypted
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device.
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Make sure to edit `--key-file`, `--keyfile-offset` and `--keyfile-size` to
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match the settings used in the creation of the USB key.
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```sh
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cryptsetup luksOpen /dev/sda2 crypt-volume --key-file=/dev/usbkey --keyfile-offset=14848 --keyfile-size=2048
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```
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After that make sure in `/etc/mkinitcpio.conf` under the `HOOKS` section
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`keymap encrypt lvm2` are written before `filesystems`.
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Add `/etc/udev/rules.d/50-usbkey.rules` under the `FILES` section.
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@ -95,13 +148,30 @@ Reboot the system with `reboot`.
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Make sure the USB key for decryption is plugged in.
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If so the encrypted partition should be decrypted automatically.
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## Unlock an encrypted device with the USB key created in the previous section
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### Automatical Mounting of an Encrypted Volume
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With the following command an encrypted device can be decrypted with the usb
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stick created in the previous section.
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Make sure to edit `--key-file`, `--keyfile-offset` and `--keyfile-size` to
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match the settings used in the creation of the USB key.
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For automatic mounting of an encrypted volume a keyfile is needed.
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This will be achieved by entries in the file`/etc/fstab` aswell as the file
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`/etc/crypttab`.
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First adapt and insert the following lines into `/etc/fstab`:
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```sh
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cryptsetup luksOpen /dev/sda2 crypt-volume --key-file=/dev/usbkey --keyfile-offset=14848 --keyfile-size=2048
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```txt
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/dev/mapper/<mapping location> <mount location> ext4 defaults 0 0
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```
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`<mapping location>` is a freely choosable identificator and while the
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`<mount location>` is an existing directory for the volume to be mounted on.
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Additionally the following lines has to be adapted and added to the file
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`/etc/crypttab`:
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```txt
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<mapping location> UUID=<UUID of encrypted volume> <location of key file>
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```
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`<mapping location>` has to be the same as chosen in the step before.
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`<UUID of encrypted volume>` is the
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[universally unique identifier](/wiki/linux/filesystems.md#universally-unique-identifier)
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of the volume.
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`<location of key file>` describes the location where to find the key file
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created in the previous step.
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@ -6,6 +6,9 @@ File systems control how data on a drive is stored.
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additionally be encrypted with [Bitlocker](./dislocker.md).
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- [Samba](./samba.md) is free windows interoperability software that is not a
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classic file system can be mounted so it will be mentioned here
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- [DM-Crypt] is an encryption service. Volumes encrypted with it follow a
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special decryption process.
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## Mounting
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@ -27,11 +30,21 @@ its subfolders.
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For automatic mounting the following line has to be adapted and added to the
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file `/etc/fstab`
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`<specified partition> <path to mount point> <file system> <additional options> <dump flag> <fsck order>`
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The partition can be specified by UUID - which can be found at
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`/dev/disk/by-uuid` or other identifiers aswell as the simple path to it (for
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example `/dev/sda1`).
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The partition can be specified by [UUID](#universally-unique-identifier).
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The file system varies and a file system specific guide on how to mount them
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can be found in their respective entries.
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The dump flag signals if the file system should be dumped.
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The `fsck` order signals if a file system should be checked at boot.
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Boot partitions should be flagged with a `1` for this reason, otherwise `0`.
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## Universally Unique identifier
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Universally Unique identifier (UUID) are identifiers for informations on
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computer systems.
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Most notably they are used to identify file systems.
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This way the UUID of a file system can be used to identify and
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[mount it](#mounting) persistently and correctly.
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By listing the directory `/dev/disk/by-partuuid` all mappings of devices to a
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UUID are displayed.
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