| <?xml version="1.0"?> |
| <!--*-nxml-*--> |
| <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
| "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
| <!-- |
| SPDX-License-Identifier: LGPL-2.1-or-later |
| |
| This is based on crypttab(5) from Fedora's initscripts package, which in |
| turn is based on Debian's version. |
| |
| The Red Hat version has been written by Miloslav Trmac <mitr@redhat.com>. |
| --> |
| <refentry id="crypttab" conditional='HAVE_LIBCRYPTSETUP' xmlns:xi="http://www.w3.org/2001/XInclude"> |
| |
| <refentryinfo> |
| <title>crypttab</title> |
| <productname>systemd</productname> |
| </refentryinfo> |
| |
| <refmeta> |
| <refentrytitle>crypttab</refentrytitle> |
| <manvolnum>5</manvolnum> |
| </refmeta> |
| |
| <refnamediv> |
| <refname>crypttab</refname> |
| <refpurpose>Configuration for encrypted block devices</refpurpose> |
| </refnamediv> |
| |
| <refsynopsisdiv> |
| <para><filename>/etc/crypttab</filename></para> |
| </refsynopsisdiv> |
| |
| <refsect1> |
| <title>Description</title> |
| |
| <para>The <filename>/etc/crypttab</filename> file describes |
| encrypted block devices that are set up during system boot.</para> |
| |
| <para>Empty lines and lines starting with the <literal>#</literal> |
| character are ignored. Each of the remaining lines describes one |
| encrypted block device. Fields are delimited by white space.</para> |
| |
| <para>Each line is in the form<programlisting><replaceable>volume-name</replaceable> <replaceable>encrypted-device</replaceable> <replaceable>key-file</replaceable> <replaceable>options</replaceable></programlisting> |
| The first two fields are mandatory, the remaining two are |
| optional.</para> |
| |
| <para>Setting up encrypted block devices using this file supports four encryption modes: LUKS, TrueCrypt, |
| BitLocker and plain. See <citerefentry |
| project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry> for |
| more information about each mode. When no mode is specified in the options field and the block device |
| contains a LUKS signature, it is opened as a LUKS device; otherwise, it is assumed to be in raw dm-crypt |
| (plain mode) format.</para> |
| |
| <para>The four fields of <filename>/etc/crypttab</filename> are defined as follows:</para> |
| |
| <orderedlist> |
| |
| <listitem><para>The first field contains the name of the resulting volume with decrypted data; its |
| block device is set up below <filename>/dev/mapper/</filename>.</para></listitem> |
| |
| <listitem><para>The second field contains a path to the underlying block |
| device or file, or a specification of a block device via |
| <literal>UUID=</literal> followed by the UUID.</para></listitem> |
| |
| <listitem><para>The third field specifies an absolute path to a file with the encryption |
| key. Optionally, the path may be followed by <literal>:</literal> and an |
| <filename>/etc/fstab</filename> style device specification (e.g. starting with |
| <literal>LABEL=</literal> or similar); in which case the path is taken relative to the specified |
| device's file system root. If the field is not present or is <literal>none</literal> or |
| <literal>-</literal>, a key file named after the volume to unlock (i.e. the first column of the line), |
| suffixed with <filename>.key</filename> is automatically loaded from the |
| <filename>/etc/cryptsetup-keys.d/</filename> and <filename>/run/cryptsetup-keys.d/</filename> |
| directories, if present. Otherwise, the password has to be manually entered during system boot. For |
| swap encryption, <filename>/dev/urandom</filename> may be used as key file, resulting in a randomized |
| key.</para> |
| |
| <para>If the specified key file path refers to an <constant>AF_UNIX</constant> stream socket in the |
| file system, the key is acquired by connecting to the socket and reading it from the connection. This |
| allows the implementation of a service to provide key information dynamically, at the moment when it is |
| needed. For details see below.</para></listitem> |
| |
| <listitem><para>The fourth field, if present, is a comma-delimited list of options. The supported |
| options are listed below.</para></listitem> |
| </orderedlist> |
| </refsect1> |
| |
| <refsect1> |
| <title>Key Acquisition</title> |
| |
| <para>Six different mechanisms for acquiring the decryption key or passphrase unlocking the encrypted |
| volume are supported. Specifically:</para> |
| |
| <orderedlist> |
| |
| <listitem><para>Most prominently, the user may be queried interactively during volume activation |
| (i.e. typically at boot), asking them to type in the necessary passphrases.</para></listitem> |
| |
| <listitem><para>The (unencrypted) key may be read from a file on disk, possibly on removable media. The third field |
| of each line encodes the location, for details see above.</para></listitem> |
| |
| <listitem><para>The (unencrypted) key may be requested from another service, by specifying an |
| <constant>AF_UNIX</constant> file system socket in place of a key file in the third field. For details |
| see above and below.</para></listitem> |
| |
| <listitem><para>The key may be acquired via a PKCS#11 compatible hardware security token or |
| smartcard. In this case an encrypted key is stored on disk/removable media, acquired via |
| <constant>AF_UNIX</constant>, or stored in the LUKS2 JSON token metadata header. The encrypted key is |
| then decrypted by the PKCS#11 token with an RSA key stored on it, and then used to unlock the encrypted |
| volume. Use the <option>pkcs11-uri=</option> option described below to use this mechanism.</para></listitem> |
| |
| <listitem><para>Similarly, the key may be acquired via a FIDO2 compatible hardware security token |
| (which must implement the "hmac-secret" extension). In this case a key generated randomly during |
| enrollment is stored on disk/removable media, acquired via <constant>AF_UNIX</constant>, or stored in |
| the LUKS2 JSON token metadata header. The random key is hashed via a keyed hash function (HMAC) on the |
| FIDO2 token, using a secret key stored on the token that never leaves it. The resulting hash value is |
| then used as key to unlock the encrypted volume. Use the <option>fido2-device=</option> option |
| described below to use this mechanism.</para></listitem> |
| |
| <listitem><para>Similarly, the key may be acquired via a TPM2 security chip. In this case a (during |
| enrollment) randomly generated key — encrypted by an asymmetric key derived from the TPM2 chip's seed |
| key — is stored on disk/removable media, acquired via <constant>AF_UNIX</constant>, or stored in the |
| LUKS2 JSON token metadata header. Use the <option>tpm2-device=</option> option described below to use |
| this mechanism.</para></listitem> |
| </orderedlist> |
| |
| <para>For the latter five mechanisms the source for the key material used for unlocking the volume is |
| primarily configured in the third field of each <filename>/etc/crypttab</filename> line, but may also |
| configured in <filename>/etc/cryptsetup-keys.d/</filename> and |
| <filename>/run/cryptsetup-keys.d/</filename> (see above) or in the LUKS2 JSON token header (in case of |
| the latter three). Use the |
| <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry> |
| tool to enroll PKCS#11, FIDO2 and TPM2 devices in LUKS2 volumes.</para> |
| </refsect1> |
| |
| <refsect1> |
| <title>Supported Options</title> |
| |
| <para>The following options may be used in the fourth field of each line:</para> |
| |
| <variablelist class='fstab-options'> |
| |
| <varlistentry> |
| <term><option>cipher=</option></term> |
| |
| <listitem><para>Specifies the cipher to use. See <citerefentry |
| project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry> |
| for possible values and the default value of this option. A cipher with unpredictable IV values, such |
| as <literal>aes-cbc-essiv:sha256</literal>, is recommended. Embedded commas in the cipher |
| specification need to be escaped by preceding them with a backslash, see example below.</para> |
| </listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>discard</option></term> |
| |
| <listitem><para>Allow discard requests to be passed through the encrypted block |
| device. This improves performance on SSD storage but has security implications. |
| </para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>hash=</option></term> |
| |
| <listitem><para>Specifies the hash to use for password |
| hashing. See |
| <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry> |
| for possible values and the default value of this |
| option.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>header=</option></term> |
| |
| <listitem><para>Use a detached (separated) metadata device or |
| file where the LUKS header is stored. This option is only |
| relevant for LUKS devices. See |
| <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry> |
| for possible values and the default value of this |
| option.</para> |
| |
| <para>Optionally, the path may be followed by <literal>:</literal> and an |
| <filename>/etc/fstab</filename> device specification (e.g. starting with <literal>UUID=</literal> or |
| similar); in which case, the path is relative to the device file system root. The device gets mounted |
| automatically for LUKS device activation duration only.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>keyfile-offset=</option></term> |
| |
| <listitem><para>Specifies the number of bytes to skip at the |
| start of the key file. See |
| <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry> |
| for possible values and the default value of this |
| option.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>keyfile-size=</option></term> |
| |
| <listitem><para>Specifies the maximum number of bytes to read |
| from the key file. See |
| <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry> |
| for possible values and the default value of this option. This |
| option is ignored in plain encryption mode, as the key file |
| size is then given by the key size.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>keyfile-erase</option></term> |
| |
| <listitem><para>If enabled, the specified key file is erased after the volume is activated or when |
| activation fails. This is in particular useful when the key file is only acquired transiently before |
| activation (e.g. via a file in <filename>/run/</filename>, generated by a service running before |
| activation), and shall be removed after use. Defaults to off.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>key-slot=</option></term> |
| |
| <listitem><para>Specifies the key slot to compare the |
| passphrase or key against. If the key slot does not match the |
| given passphrase or key, but another would, the setup of the |
| device will fail regardless. This option implies |
| <option>luks</option>. See |
| <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry> |
| for possible values. The default is to try all key slots in |
| sequential order.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>keyfile-timeout=</option></term> |
| |
| <listitem><para> Specifies the timeout for the device on |
| which the key file resides or the device used as the key file, |
| and falls back to a password if it could not be accessed. See |
| <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry> |
| for key files on external devices. |
| </para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>luks</option></term> |
| |
| <listitem><para>Force LUKS mode. When this mode is used, the |
| following options are ignored since they are provided by the |
| LUKS header on the device: <option>cipher=</option>, |
| <option>hash=</option>, |
| <option>size=</option>.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>bitlk</option></term> |
| |
| <listitem><para>Decrypt BitLocker drive. Encryption parameters |
| are deduced by cryptsetup from BitLocker header.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>_netdev</option></term> |
| |
| <listitem><para>Marks this cryptsetup device as requiring network. It will be |
| started after the network is available, similarly to |
| <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry> |
| units marked with <option>_netdev</option>. The service unit to set up this device |
| will be ordered between <filename>remote-fs-pre.target</filename> and |
| <filename>remote-cryptsetup.target</filename>, instead of |
| <filename>cryptsetup-pre.target</filename> and |
| <filename>cryptsetup.target</filename>.</para> |
| |
| <para>Hint: if this device is used for a mount point that is specified in |
| <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>, |
| the <option>_netdev</option> option should also be used for the mount |
| point. Otherwise, a dependency loop might be created where the mount point |
| will be pulled in by <filename>local-fs.target</filename>, while the |
| service to configure the network is usually only started <emphasis>after</emphasis> |
| the local file system has been mounted.</para> |
| </listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>noauto</option></term> |
| |
| <listitem><para>This device will not be added to <filename>cryptsetup.target</filename>. |
| This means that it will not be automatically unlocked on boot, unless something else pulls |
| it in. In particular, if the device is used for a mount point, it'll be unlocked |
| automatically during boot, unless the mount point itself is also disabled with |
| <option>noauto</option>.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>nofail</option></term> |
| |
| <listitem><para>This device will not be a hard dependency of |
| <filename>cryptsetup.target</filename>. It'll still be pulled in and started, but the system |
| will not wait for the device to show up and be unlocked, and boot will not fail if this is |
| unsuccessful. Note that other units that depend on the unlocked device may still fail. In |
| particular, if the device is used for a mount point, the mount point itself also needs to |
| have the <option>nofail</option> option, or the boot will fail if the device is not unlocked |
| successfully.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>offset=</option></term> |
| |
| <listitem><para>Start offset in the backend device, in 512-byte sectors. This |
| option is only relevant for plain devices.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>plain</option></term> |
| |
| <listitem><para>Force plain encryption mode.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>read-only</option></term><term><option>readonly</option></term> |
| |
| <listitem><para>Set up the encrypted block device in read-only |
| mode.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>same-cpu-crypt</option></term> |
| |
| <listitem><para>Perform encryption using the same CPU that IO was submitted on. The default is to use |
| an unbound workqueue so that encryption work is automatically balanced between available CPUs.</para> |
| |
| <para>This requires kernel 4.0 or newer.</para> |
| </listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>submit-from-crypt-cpus</option></term> |
| |
| <listitem><para>Disable offloading writes to a separate thread after encryption. There are some |
| situations where offloading write requests from the encryption threads to a dedicated thread degrades |
| performance significantly. The default is to offload write requests to a dedicated thread because it |
| benefits the CFQ scheduler to have writes submitted using the same context.</para> |
| |
| <para>This requires kernel 4.0 or newer.</para> |
| </listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>no-read-workqueue</option></term> |
| |
| <listitem><para>Bypass dm-crypt internal workqueue and process read requests synchronously. The |
| default is to queue these requests and process them asynchronously.</para> |
| |
| <para>This requires kernel 5.9 or newer.</para> |
| </listitem> |
| </varlistentry> |
| <varlistentry> |
| <term><option>no-write-workqueue</option></term> |
| |
| <listitem><para>Bypass dm-crypt internal workqueue and process write requests synchronously. The |
| default is to queue these requests and process them asynchronously.</para> |
| |
| <para>This requires kernel 5.9 or newer.</para> |
| </listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>skip=</option></term> |
| |
| <listitem><para>How many 512-byte sectors of the encrypted data to skip at the |
| beginning. This is different from the <option>offset=</option> option with respect |
| to the sector numbers used in initialization vector (IV) calculation. Using |
| <option>offset=</option> will shift the IV calculation by the same negative |
| amount. Hence, if <option>offset=<replaceable>n</replaceable></option> is given, |
| sector <replaceable>n</replaceable> will get a sector number of 0 for the IV |
| calculation. Using <option>skip=</option> causes sector |
| <replaceable>n</replaceable> to also be the first sector of the mapped device, but |
| with its number for IV generation being <replaceable>n</replaceable>.</para> |
| |
| <para>This option is only relevant for plain devices.</para> |
| </listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>size=</option></term> |
| |
| <listitem><para>Specifies the key size in bits. See |
| <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry> |
| for possible values and the default value of this |
| option.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>sector-size=</option></term> |
| |
| <listitem><para>Specifies the sector size in bytes. See |
| <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry> |
| for possible values and the default value of this |
| option.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>swap</option></term> |
| |
| <listitem><para>The encrypted block device will be used as a |
| swap device, and will be formatted accordingly after setting |
| up the encrypted block device, with |
| <citerefentry project='man-pages'><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>. |
| This option implies <option>plain</option>.</para> |
| |
| <para>WARNING: Using the <option>swap</option> option will |
| destroy the contents of the named partition during every boot, |
| so make sure the underlying block device is specified |
| correctly.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>tcrypt</option></term> |
| |
| <listitem><para>Use TrueCrypt encryption mode. When this mode |
| is used, the following options are ignored since they are |
| provided by the TrueCrypt header on the device or do not |
| apply: |
| <option>cipher=</option>, |
| <option>hash=</option>, |
| <option>keyfile-offset=</option>, |
| <option>keyfile-size=</option>, |
| <option>size=</option>.</para> |
| |
| <para>When this mode is used, the passphrase is read from the |
| key file given in the third field. Only the first line of this |
| file is read, excluding the new line character.</para> |
| |
| <para>Note that the TrueCrypt format uses both passphrase and |
| key files to derive a password for the volume. Therefore, the |
| passphrase and all key files need to be provided. Use |
| <option>tcrypt-keyfile=</option> to provide the absolute path |
| to all key files. When using an empty passphrase in |
| combination with one or more key files, use |
| <literal>/dev/null</literal> as the password file in the third |
| field.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>tcrypt-hidden</option></term> |
| |
| <listitem><para>Use the hidden TrueCrypt volume. This option |
| implies <option>tcrypt</option>.</para> |
| |
| <para>This will map the hidden volume that is inside of the |
| volume provided in the second field. Please note that there is |
| no protection for the hidden volume if the outer volume is |
| mounted instead. See |
| <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry> |
| for more information on this limitation.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>tcrypt-keyfile=</option></term> |
| |
| <listitem><para>Specifies the absolute path to a key file to |
| use for a TrueCrypt volume. This implies |
| <option>tcrypt</option> and can be used more than once to |
| provide several key files.</para> |
| |
| <para>See the entry for <option>tcrypt</option> on the |
| behavior of the passphrase and key files when using TrueCrypt |
| encryption mode.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>tcrypt-system</option></term> |
| |
| <listitem><para>Use TrueCrypt in system encryption mode. This |
| option implies <option>tcrypt</option>.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>tcrypt-veracrypt</option></term> |
| |
| <listitem><para>Check for a VeraCrypt volume. VeraCrypt is a fork of |
| TrueCrypt that is mostly compatible, but uses different, stronger key |
| derivation algorithms that cannot be detected without this flag. |
| Enabling this option could substantially slow down unlocking, because |
| VeraCrypt's key derivation takes much longer than TrueCrypt's. This |
| option implies <option>tcrypt</option>.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>timeout=</option></term> |
| |
| <listitem><para>Specifies the timeout for querying for a |
| password. If no unit is specified, seconds is used. Supported |
| units are s, ms, us, min, h, d. A timeout of 0 waits |
| indefinitely (which is the default).</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>tmp=</option></term> |
| |
| <listitem><para>The encrypted block device will be prepared for using it as |
| <filename>/tmp/</filename>; it will be formatted using <citerefentry |
| project='man-pages'><refentrytitle>mkfs</refentrytitle><manvolnum>8</manvolnum></citerefentry>. Takes |
| a file system type as argument, such as <literal>ext4</literal>, <literal>xfs</literal> or |
| <literal>btrfs</literal>. If no argument is specified defaults to <literal>ext4</literal>. This |
| option implies <option>plain</option>.</para> |
| |
| <para>WARNING: Using the <option>tmp</option> option will destroy the contents of the named partition |
| during every boot, so make sure the underlying block device is specified correctly.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>tries=</option></term> |
| |
| <listitem><para>Specifies the maximum number of times the user |
| is queried for a password. The default is 3. If set to 0, the |
| user is queried for a password indefinitely.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>headless=</option></term> |
| |
| <listitem><para>Takes a boolean argument, defaults to false. If true, never query interactively |
| for the password/PIN. Useful for headless systems.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>verify</option></term> |
| |
| <listitem><para>If the encryption password is read from console, it has to be entered twice to |
| prevent typos.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>password-echo=yes|no|masked</option></term> |
| |
| <listitem><para>Controls whether to echo passwords or security token PINs |
| that are read from console. Takes a boolean or the special string <literal>masked</literal>. |
| The default is <option>password-echo=masked</option>.</para> |
| |
| <para>If enabled, the typed characters are echoed literally. If disabled, |
| the typed characters are not echoed in any form, the user will not get |
| feedback on their input. If set to <literal>masked</literal>, an asterisk |
| (<literal>*</literal>) is echoed for each character typed. Regardless of |
| which mode is chosen, if the user hits the tabulator key (<literal>↹</literal>) |
| at any time, or the backspace key (<literal>⌫</literal>) before any other |
| data has been entered, then echo is turned off.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>pkcs11-uri=</option></term> |
| |
| <listitem><para>Takes either the special value <literal>auto</literal> or an <ulink |
| url="https://tools.ietf.org/html/rfc7512">RFC7512 PKCS#11 URI</ulink> pointing to a private RSA key |
| which is used to decrypt the encrypted key specified in the third column of the line. This is useful |
| for unlocking encrypted volumes through PKCS#11 compatible security tokens or smartcards. See below |
| for an example how to set up this mechanism for unlocking a LUKS2 volume with a YubiKey security |
| token.</para> |
| |
| <para>If specified as <literal>auto</literal> the volume must be of type LUKS2 and must carry PKCS#11 |
| security token metadata in its LUKS2 JSON token section. In this mode the URI and the encrypted key |
| are automatically read from the LUKS2 JSON token header. Use |
| <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry> |
| as simple tool for enrolling PKCS#11 security tokens or smartcards in a way compatible with |
| <literal>auto</literal>. In this mode the third column of the line should remain empty (that is, |
| specified as <literal>-</literal>).</para> |
| |
| <para>The specified URI can refer directly to a private RSA key stored on a token or alternatively |
| just to a slot or token, in which case a search for a suitable private RSA key will be performed. In |
| this case if multiple suitable objects are found the token is refused. The encrypted key configured |
| in the third column of the line is passed as is (i.e. in binary form, unprocessed) to RSA |
| decryption. The resulting decrypted key is then Base64 encoded before it is used to unlock the LUKS |
| volume.</para> |
| |
| <para>Use <command>systemd-cryptenroll --pkcs11-token-uri=list</command> to list all suitable PKCS#11 |
| security tokens currently plugged in, along with their URIs.</para> |
| |
| <para>Note that many newer security tokens that may be used as PKCS#11 security token typically also |
| implement the newer and simpler FIDO2 standard. Consider using <option>fido2-device=</option> |
| (described below) to enroll it via FIDO2 instead. Note that a security token enrolled via PKCS#11 |
| cannot be used to unlock the volume via FIDO2, unless also enrolled via FIDO2, and vice |
| versa.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>fido2-device=</option></term> |
| |
| <listitem><para>Takes either the special value <literal>auto</literal> or the path to a |
| <literal>hidraw</literal> device node (e.g. <filename>/dev/hidraw1</filename>) referring to a FIDO2 |
| security token that implements the <literal>hmac-secret</literal> extension (most current hardware |
| security tokens do). See below for an example how to set up this mechanism for unlocking an encrypted |
| volume with a FIDO2 security token.</para> |
| |
| <para>If specified as <literal>auto</literal> the FIDO2 token device is automatically discovered, as |
| it is plugged in.</para> |
| |
| <para>FIDO2 volume unlocking requires a client ID hash (CID) to be configured via |
| <option>fido2-cid=</option> (see below) and a key to pass to the security token's HMAC functionality |
| (configured in the line's third column) to operate. If not configured and the volume is of type |
| LUKS2, the CID and the key are read from LUKS2 JSON token metadata instead. Use |
| <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry> |
| as simple tool for enrolling FIDO2 security tokens, compatible with this automatic mode, which is |
| only available for LUKS2 volumes.</para> |
| |
| <para>Use <command>systemd-cryptenroll --fido2-device=list</command> to list all suitable FIDO2 |
| security tokens currently plugged in, along with their device nodes.</para> |
| |
| <para>This option implements the following mechanism: the configured key is hashed via they HMAC |
| keyed hash function the FIDO2 device implements, keyed by a secret key embedded on the device. The |
| resulting hash value is Base64 encoded and used to unlock the LUKS2 volume. As it should not be |
| possible to extract the secret from the hardware token, it should not be possible to retrieve the |
| hashed key given the configured key — without possessing the hardware token.</para> |
| |
| <para>Note that many security tokens that implement FIDO2 also implement PKCS#11, suitable for |
| unlocking volumes via the <option>pkcs11-uri=</option> option described above. Typically the newer, |
| simpler FIDO2 standard is preferable.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>fido2-cid=</option></term> |
| |
| <listitem><para>Takes a Base64 encoded FIDO2 client ID to use for the FIDO2 unlock operation. If |
| specified, but <option>fido2-device=</option> is not, <option>fido2-device=auto</option> is |
| implied. If <option>fido2-device=</option> is used but <option>fido2-cid=</option> is not, the volume |
| must be of LUKS2 type, and the CID is read from the LUKS2 JSON token header. Use |
| <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry> |
| for enrolling a FIDO2 token in the LUKS2 header compatible with this automatic |
| mode.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>fido2-rp=</option></term> |
| |
| <listitem><para>Takes a string, configuring the FIDO2 Relying Party (rp) for the FIDO2 unlock |
| operation. If not specified <literal>io.systemd.cryptsetup</literal> is used, except if the LUKS2 |
| JSON token header contains a different value. It should normally not be necessary to override |
| this.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>tpm2-device=</option></term> |
| |
| <listitem><para>Takes either the special value <literal>auto</literal> or the path to a device node |
| (e.g. <filename>/dev/tpmrm0</filename>) referring to a TPM2 security chip. See below for an example |
| how to set up this mechanism for unlocking an encrypted volume with a TPM2 chip.</para> |
| |
| <para>Use <option>tpm2-pcrs=</option> (see below) to configure the set of TPM2 PCRs to bind the |
| volume unlocking to. Use |
| <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry> |
| as simple tool for enrolling TPM2 security chips in LUKS2 volumes.</para> |
| |
| <para>If specified as <literal>auto</literal> the TPM2 device is automatically discovered. Use |
| <command>systemd-cryptenroll --tpm2-device=list</command> to list all suitable TPM2 devices currently |
| available, along with their device nodes.</para> |
| |
| <para>This option implements the following mechanism: when enrolling a TPM2 device via |
| <command>systemd-cryptenroll</command> on a LUKS2 volume, a randomized key unlocking the volume is |
| generated on the host and loaded into the TPM2 chip where it is encrypted with an asymmetric |
| "primary" key pair derived from the TPM2's internal "seed" key. Neither the seed key nor the primary |
| key are permitted to ever leave the TPM2 chip — however, the now encrypted randomized key may. It is |
| saved in the LUKS2 volume JSON token header. When unlocking the encrypted volume, the primary key |
| pair is generated on the TPM2 chip again (which works as long as the chip's seed key is correctly |
| maintained by the TPM2 chip), which is then used to decrypt (on the TPM2 chip) the encrypted key from |
| the LUKS2 volume JSON token header saved there during enrollment. The resulting decrypted key is then |
| used to unlock the volume. When the randomized key is encrypted the current values of the selected |
| PCRs (see below) are included in the operation, so that different PCR state results in different |
| encrypted keys and the decrypted key can only be recovered if the same PCR state is |
| reproduced.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>tpm2-pcrs=</option></term> |
| |
| <listitem><para>Takes a <literal>+</literal> separated list of numeric TPM2 PCR (i.e. "Platform |
| Configuration Register") indexes to bind the TPM2 volume unlocking to. This option is only useful |
| when TPM2 enrollment metadata is not available in the LUKS2 JSON token header already, the way |
| <command>systemd-cryptenroll</command> writes it there. If not used (and no metadata in the LUKS2 |
| JSON token header defines it), defaults to a list of a single entry: PCR 7. Assign an empty string to |
| encode a policy that binds the key to no PCRs, making the key accessible to local programs regardless |
| of the current PCR state.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>tpm2-pin=</option></term> |
| |
| <listitem><para>Takes a boolean argument, defaults to <literal>false</literal>. Controls whether |
| TPM2 volume unlocking is bound to a PIN in addition to PCRs. Similarly, this option is only useful |
| when TPM2 enrollment metadata is not available.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>tpm2-signature=</option></term> |
| |
| <listitem><para>Takes an absolute path to a TPM2 PCR JSON signature file, as produced by the |
| <citerefentry><refentrytitle>systemd-measure</refentrytitle><manvolnum>1</manvolnum></citerefentry> |
| tool. This permits locking LUKS2 volumes to any PCR values for which a valid signature matching a |
| public key specified at key enrollment time can be provided. See |
| <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry> |
| for details on enrolling TPM2 PCR public keys. If this option is not specified but it is attempted to |
| unlock a LUKS2 volume with a signed TPM2 PCR enrollment a suitable signature file |
| <filename>tpm2-pcr-signature.json</filename> is searched for in <filename>/etc/systemd/</filename>, |
| <filename>/run/systemd/</filename>, <filename>/usr/lib/systemd/</filename> (in this |
| order).</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>tpm2-measure-pcr=</option></term> |
| |
| <listitem><para>Controls whether to measure the volume key of the encrypted volume to a TPM2 PCR. If |
| set to "no" (which is the default) no PCR extension is done. If set to "yes" the volume key is |
| measured into PCR 15. If set to a decimal integer in the range 0…23 the volume key is measured into |
| the specified PCR. The volume key is measured along with the activated volume name and its UUID. This |
| functionality is particularly useful for the encrypted volume backing the root file system, as it |
| then allows later TPM objects to be securely bound to the root file system and hence the specific |
| installation.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>tpm2-measure-bank=</option></term> |
| |
| <listitem><para>Selects one or more TPM2 PCR banks to measure the volume key into, as configured with |
| <option>tpm2-measure-pcr=</option> above. Multiple banks may be specified, separated by a colon |
| character. If not specified automatically determines available and used banks. Expects a message |
| digest name (e.g. <literal>sha1</literal>, <literal>sha256</literal>, …) as argument, to identify the |
| bank.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>token-timeout=</option></term> |
| |
| <listitem><para>Specifies how long to wait at most for configured security devices (i.e. FIDO2, |
| PKCS#11, TPM2) to show up. Takes a time value in seconds (but other time units may be specified too, |
| see <citerefentry><refentrytitle>systemd.time</refentrytitle><manvolnum>7</manvolnum></citerefentry> |
| for supported formats). Defaults to 30s. Once the specified timeout elapsed authentication via |
| password is attempted. Note that this timeout applies to waiting for the security device to show up — |
| it does not apply to the PIN prompt for the device (should one be needed) or similar. Pass 0 to turn |
| off the time-out and wait forever.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>try-empty-password=</option></term> |
| |
| <listitem><para>Takes a boolean argument. If enabled, right before asking the user for a password it |
| is first attempted to unlock the volume with an empty password. This is useful for systems that are |
| initialized with an encrypted volume with only an empty password set, which shall be replaced with a |
| suitable password during first boot, but after activation.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>x-systemd.device-timeout=</option></term> |
| |
| <listitem><para>Specifies how long systemd should wait for a block device to show up before |
| giving up on the entry. The argument is a time in seconds or explicitly specified units of |
| <literal>s</literal>, <literal>min</literal>, <literal>h</literal>, <literal>ms</literal>. |
| </para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><option>x-initrd.attach</option></term> |
| |
| <listitem><para>Setup this encrypted block device in the initrd, similarly to |
| <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry> |
| units marked with <option>x-initrd.mount</option>.</para> |
| |
| <para>Although it's not necessary to mark the mount entry for the root file system with |
| <option>x-initrd.mount</option>, <option>x-initrd.attach</option> is still recommended with |
| the encrypted block device containing the root file system as otherwise systemd will |
| attempt to detach the device during the regular system shutdown while it's still in |
| use. With this option the device will still be detached but later after the root file |
| system is unmounted.</para> |
| |
| <para>All other encrypted block devices that contain file systems mounted in the initrd should use |
| this option.</para> |
| </listitem> |
| </varlistentry> |
| |
| </variablelist> |
| |
| <para>At early boot and when the system manager configuration is |
| reloaded, this file is translated into native systemd units by |
| <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para> |
| </refsect1> |
| |
| <refsect1> |
| <title><constant>AF_UNIX</constant> Key Files</title> |
| |
| <para>If the key file path (as specified in the third column of <filename>/etc/crypttab</filename> |
| entries, see above) refers to an <constant>AF_UNIX</constant> stream socket in the file system, the key |
| is acquired by connecting to the socket and reading the key from the connection. The connection is made |
| from an <constant>AF_UNIX</constant> socket name in the abstract namespace, see <citerefentry |
| project='man-pages'><refentrytitle>unix</refentrytitle><manvolnum>7</manvolnum></citerefentry> for |
| details. The source socket name is chosen according the following format:</para> |
| |
| <programlisting><constant>NUL</constant> <replaceable>RANDOM</replaceable> /cryptsetup/ <replaceable>VOLUME</replaceable></programlisting> |
| |
| <para>In other words: a <constant>NUL</constant> byte (as required for abstract namespace sockets), |
| followed by a random string (consisting of alphanumeric characters only), followed by the literal |
| string <literal>/cryptsetup/</literal>, followed by the name of the volume to acquire they key |
| for. For example, for the volume <literal>myvol</literal>:</para> |
| |
| <programlisting>\0d7067f78d9827418/cryptsetup/myvol</programlisting> |
| |
| <para>Services listening on the <constant>AF_UNIX</constant> stream socket may query the source socket |
| name with <citerefentry |
| project='man-pages'><refentrytitle>getpeername</refentrytitle><manvolnum>2</manvolnum></citerefentry>, |
| and use this to determine which key to send, allowing a single listening socket to serve keys for |
| multiple volumes. If the PKCS#11 logic is used (see above), the socket source name is picked in similar |
| fashion, except that the literal string <literal>/cryptsetup-pkcs11/</literal> is used. And similarly for |
| FIDO2 (<literal>/cryptsetup-fido2/</literal>) and TPM2 (<literal>/cryptsetup-tpm2/</literal>). A different |
| path component is used so that services providing key material know that the secret key was not requested |
| directly, but instead an encrypted key that will be decrypted via the PKCS#11/FIDO2/TPM2 logic to acquire |
| the final secret key.</para> |
| </refsect1> |
| |
| <refsect1> |
| <title>Examples</title> |
| <example> |
| <title>/etc/crypttab example</title> |
| <para>Set up four encrypted block devices. One using LUKS for normal storage, another one for usage as |
| a swap device and two TrueCrypt volumes. For the fourth device, the option string is interpreted as two |
| options <literal>cipher=xchacha12,aes-adiantum-plain64</literal>, |
| <literal>keyfile-timeout=10s</literal>.</para> |
| |
| <programlisting>luks UUID=2505567a-9e27-4efe-a4d5-15ad146c258b |
| swap /dev/sda7 /dev/urandom swap |
| truecrypt /dev/sda2 /etc/container_password tcrypt |
| hidden /mnt/tc_hidden /dev/null tcrypt-hidden,tcrypt-keyfile=/etc/keyfile |
| external /dev/sda3 keyfile:LABEL=keydev keyfile-timeout=10s,cipher=xchacha12\,aes-adiantum-plain64 |
| </programlisting> |
| </example> |
| |
| <example> |
| <title>Yubikey-based PKCS#11 Volume Unlocking Example</title> |
| |
| <para>The PKCS#11 logic allows hooking up any compatible security token that is capable of storing RSA |
| decryption keys for unlocking an encrypted volume. Here's an example how to set up a Yubikey security |
| token for this purpose on a LUKS2 volume, using <citerefentry |
| project='debian'><refentrytitle>ykmap</refentrytitle><manvolnum>1</manvolnum></citerefentry> from the |
| yubikey-manager project to initialize the token and |
| <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry> |
| to add it in the LUKS2 volume:</para> |
| |
| <programlisting><xi:include href="yubikey-crypttab.sh" parse="text" /></programlisting> |
| |
| <para>A few notes on the above:</para> |
| |
| <itemizedlist> |
| <listitem><para>We use RSA2048, which is the longest key size current Yubikeys support</para></listitem> |
| <listitem><para>We use Yubikey key slot 9d, since that's apparently the keyslot to use for decryption purposes, |
| <ulink url="https://developers.yubico.com/PIV/Introduction/Certificate_slots.html">see |
| documentation</ulink>.</para></listitem> |
| </itemizedlist> |
| </example> |
| |
| <example> |
| <title>FIDO2 Volume Unlocking Example</title> |
| |
| <para>The FIDO2 logic allows using any compatible FIDO2 security token that implements the |
| <literal>hmac-secret</literal> extension for unlocking an encrypted volume. Here's an example how to |
| set up a FIDO2 security token for this purpose for a LUKS2 volume, using |
| <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>:</para> |
| |
| <programlisting><xi:include href="fido2-crypttab.sh" parse="text" /></programlisting> |
| </example> |
| |
| <example> |
| <title>TPM2 Volume Unlocking Example</title> |
| |
| <para>The TPM2 logic allows using any TPM2 chip supported by the Linux kernel for unlocking an |
| encrypted volume. Here's an example how to set up a TPM2 chip for this purpose for a LUKS2 volume, |
| using |
| <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>:</para> |
| |
| <programlisting><xi:include href="tpm2-crypttab.sh" parse="text" /></programlisting> |
| </example> |
| </refsect1> |
| |
| <refsect1> |
| <title>See Also</title> |
| <para> |
| <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, |
| <citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>, |
| <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>, |
| <citerefentry><refentrytitle>systemd-cryptenroll</refentrytitle><manvolnum>1</manvolnum></citerefentry>, |
| <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>, |
| <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>, |
| <citerefentry project='man-pages'><refentrytitle>mkswap</refentrytitle><manvolnum>8</manvolnum></citerefentry>, |
| <citerefentry project='man-pages'><refentrytitle>mke2fs</refentrytitle><manvolnum>8</manvolnum></citerefentry> |
| </para> |
| </refsect1> |
| |
| </refentry> |