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diff --git a/man/crypttab.xml b/man/crypttab.xml new file mode 100644 index 0000000..ef6cd2b --- /dev/null +++ b/man/crypttab.xml @@ -0,0 +1,867 @@ +<?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>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 diffent + 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> |