crypttab(5) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | KEY ACQUISITION | SUPPORTED OPTIONS | AF_UNIX KEY FILES | EXAMPLES | SEE ALSO | NOTES | COLOPHON

CRYPTTAB(5)                     crypttab                     CRYPTTAB(5)

NAME         top

       crypttab - Configuration for encrypted block devices

SYNOPSIS         top

       /etc/crypttab

DESCRIPTION         top

       The /etc/crypttab file describes encrypted block devices that are
       set up during system boot.

       Empty lines and lines starting with the "#" character are
       ignored. Each of the remaining lines describes one encrypted
       block device. Fields are delimited by white space.

       Each line is in the form

           volume-name encrypted-device key-file options

       The first two fields are mandatory, the remaining two are
       optional.

       Setting up encrypted block devices using this file supports four
       encryption modes: LUKS, TrueCrypt, BitLocker and plain. See
       cryptsetup(8) 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.

       The four fields of /etc/crypttab are defined as follows:

        1. The first field contains the name of the resulting volume
           with decrypted data; its block device is set up below
           /dev/mapper/.

        2. The second field contains a path to the underlying block
           device or file, or a specification of a block device via
           "UUID=" followed by the UUID.

        3. The third field specifies an absolute path to a file with the
           encryption key. Optionally, the path may be followed by ":"
           and an /etc/fstab style device specification (e.g. starting
           with "LABEL=" 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 "none" or "-", a key file named
           after the volume to unlock (i.e. the first column of the
           line), suffixed with .key is automatically loaded from the
           /etc/cryptsetup-keys.d/ and /run/cryptsetup-keys.d/
           directories, if present. Otherwise, the password has to be
           manually entered during system boot. For swap encryption,
           /dev/urandom may be used as key file, resulting in a
           randomized key.

           If the specified key file path refers to an AF_UNIX 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.

        4. The fourth field, if present, is a comma-delimited list of
           options. The supported options are listed below.

KEY ACQUISITION         top

       Six different mechanisms for acquiring the decryption key or
       passphrase unlocking the encrypted volume are supported.
       Specifically:

        1. Most prominently, the user may be queried interactively
           during volume activation (i.e. typically at boot), asking
           them to type in the necessary passphrase(s).

        2. 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.

        3. The (unencrypted) key may be requested from another service,
           by specifying an AF_UNIX file system socket in place of a key
           file in the third field. For details see above and below.

        4. 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 AF_UNIX, 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 pkcs11-uri= option described below to use this
           mechanism.

        5. Similar, the key may be acquired via a FIDO2 compatible
           hardware security token (which must implement the
           "hmac-secret" extension). In this case a (during enrollment)
           randomly generated key is stored on disk/removable media,
           acquired via AF_UNIX, 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
           fido2-device= option described below to use this mechanism.

        6. Similar, 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
           AF_UNIX, or stored in the LUKS2 JSON token metadata header.
           Use the tpm2-device= option described below to use this
           mechanism.

       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 /etc/crypttab line, but may also configured
       in /etc/cryptsetup-keys.d/ and /run/cryptsetup-keys.d/ (see
       above) or in the LUKS2 JSON token header (in case of the latter
       three). Use the systemd-cryptenroll(1) tool to enroll PKCS#11,
       FIDO2 and TPM2 devices in LUKS2 volumes.

SUPPORTED OPTIONS         top

       The following options may be used in the fourth field of each
       line:

       cipher=
           Specifies the cipher to use. See cryptsetup(8) for possible
           values and the default value of this option. A cipher with
           unpredictable IV values, such as "aes-cbc-essiv:sha256", is
           recommended. Embedded commas in the cipher specification need
           to be escaped by preceding them with a backslash, see example
           below.

       discard
           Allow discard requests to be passed through the encrypted
           block device. This improves performance on SSD storage but
           has security implications.

       hash=
           Specifies the hash to use for password hashing. See
           cryptsetup(8) for possible values and the default value of
           this option.

       header=
           Use a detached (separated) metadata device or file where the
           LUKS header is stored. This option is only relevant for LUKS
           devices. See cryptsetup(8) for possible values and the
           default value of this option.

           Optionally, the path may be followed by ":" and an /etc/fstab
           device specification (e.g. starting with "UUID=" 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.

       keyfile-offset=
           Specifies the number of bytes to skip at the start of the key
           file. See cryptsetup(8) for possible values and the default
           value of this option.

       keyfile-size=
           Specifies the maximum number of bytes to read from the key
           file. See cryptsetup(8) 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.

       keyfile-erase
           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 /run/, generated by a service
           running before activation), and shall be removed after use.
           Defaults to off.

       key-slot=
           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 luks. See cryptsetup(8) for
           possible values. The default is to try all key slots in
           sequential order.

       keyfile-timeout=
           Specifies the timeout for the device on which the key file
           resides and falls back to a password if it could not be
           mounted. See systemd-cryptsetup-generator(8) for key files on
           external devices.

       luks
           Force LUKS mode. When this mode is used, the following
           options are ignored since they are provided by the LUKS
           header on the device: cipher=, hash=, size=.

       bitlk
           Decrypt BitLocker drive. Encryption parameters are deduced by
           cryptsetup from BitLocker header.

       _netdev
           Marks this cryptsetup device as requiring network. It will be
           started after the network is available, similarly to
           systemd.mount(5) units marked with _netdev. The service unit
           to set up this device will be ordered between
           remote-fs-pre.target and remote-cryptsetup.target, instead of
           cryptsetup-pre.target and cryptsetup.target.

           Hint: if this device is used for a mount point that is
           specified in fstab(5), the _netdev 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
           local-fs.target, while the service to configure the network
           is usually only started after the local file system has been
           mounted.

       noauto
           This device will not be added to cryptsetup.target. 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 noauto.

       nofail
           This device will not be a hard dependency of
           cryptsetup.target. 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 nofail
           option, or the boot will fail if the device is not unlocked
           successfully.

       offset=
           Start offset in the backend device, in 512-byte sectors. This
           option is only relevant for plain devices.

       plain
           Force plain encryption mode.

       read-only, readonly
           Set up the encrypted block device in read-only mode.

       same-cpu-crypt
           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.

           This requires kernel 4.0 or newer.

       submit-from-crypt-cpus
           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.

           This requires kernel 4.0 or newer.

       no-read-workqueue
           Bypass dm-crypt internal workqueue and process read requests
           synchronously. The default is to queue these requests and
           process them asynchronously.

           This requires kernel 5.9 or newer.

       no-write-workqueue
           Bypass dm-crypt internal workqueue and process write requests
           synchronously. The default is to queue these requests and
           process them asynchronously.

           This requires kernel 5.9 or newer.

       skip=
           How many 512-byte sectors of the encrypted data to skip at
           the beginning. This is different from the offset= option with
           respect to the sector numbers used in initialization vector
           (IV) calculation. Using offset= will shift the IV calculation
           by the same negative amount. Hence, if offset=n is given,
           sector n will get a sector number of 0 for the IV
           calculation. Using skip= causes sector n to also be the first
           sector of the mapped device, but with its number for IV
           generation being n.

           This option is only relevant for plain devices.

       size=
           Specifies the key size in bits. See cryptsetup(8) for
           possible values and the default value of this option.

       sector-size=
           Specifies the sector size in bytes. See cryptsetup(8) for
           possible values and the default value of this option.

       swap
           The encrypted block device will be used as a swap device, and
           will be formatted accordingly after setting up the encrypted
           block device, with mkswap(8). This option implies plain.

           WARNING: Using the swap option will destroy the contents of
           the named partition during every boot, so make sure the
           underlying block device is specified correctly.

       tcrypt
           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: cipher=,
           hash=, keyfile-offset=, keyfile-size=, size=.

           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.

           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
           tcrypt-keyfile= to provide the absolute path to all key
           files. When using an empty passphrase in combination with one
           or more key files, use "/dev/null" as the password file in
           the third field.

       tcrypt-hidden
           Use the hidden TrueCrypt volume. This option implies tcrypt.

           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 cryptsetup(8) for more information on
           this limitation.

       tcrypt-keyfile=
           Specifies the absolute path to a key file to use for a
           TrueCrypt volume. This implies tcrypt and can be used more
           than once to provide several key files.

           See the entry for tcrypt on the behavior of the passphrase
           and key files when using TrueCrypt encryption mode.

       tcrypt-system
           Use TrueCrypt in system encryption mode. This option implies
           tcrypt.

       tcrypt-veracrypt
           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 tcrypt.

       timeout=
           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).

       tmp=
           The encrypted block device will be prepared for using it as
           /tmp/; it will be formatted using mkfs(8). Takes a file
           system type as argument, such as "ext4", "xfs" or "btrfs". If
           no argument is specified defaults to "ext4". This option
           implies plain.

           WARNING: Using the tmp option will destroy the contents of
           the named partition during every boot, so make sure the
           underlying block device is specified correctly.

       tries=
           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.

       headless=
           Takes a boolean argument, defaults to false. If true, never
           query interactively for the password/PIN. Useful for headless
           systems.

       verify
           If the encryption password is read from console, it has to be
           entered twice to prevent typos.

       password-echo=yes|no|masked
           Controls whether to echo passwords or security token PINs
           that are read from console. Takes a boolean or the special
           string "masked". The default is password-echo=masked.

           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
           "masked", an asterisk ("*") is echoed for each character
           typed. Regardless of which mode is chosen, if the user hits
           the tabulator key ("↹") at any time, or the backspace key
           ("⌫") before any other data has been entered, then echo is
           turned off.

       pkcs11-uri=
           Takes either the special value "auto" or an RFC7512 PKCS#11
           URI[1] 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.

           If specified as "auto" 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
           systemd-cryptenroll(1) as simple tool for enrolling PKCS#11
           security tokens or smartcards in a way compatible with
           "auto". In this mode the third column of the line should
           remain empty (that is, specified as "-").

           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.

           Use systemd-cryptenroll --pkcs11-token-uri=list to list all
           suitable PKCS#11 security tokens currently plugged in, along
           with their URIs.

           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 fido2-device=
           (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.

       fido2-device=
           Takes either the special value "auto" or the path to a
           "hidraw" device node (e.g.  /dev/hidraw1) referring to a
           FIDO2 security token that implements the "hmac-secret"
           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.

           If specified as "auto" the FIDO2 token device is
           automatically discovered, as it is plugged in.

           FIDO2 volume unlocking requires a client ID hash (CID) to be
           configured via fido2-cid= (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 systemd-cryptenroll(1)
           as simple tool for enrolling FIDO2 security tokens,
           compatible with this automatic mode, which is only available
           for LUKS2 volumes.

           Use systemd-cryptenroll --fido2-device=list to list all
           suitable FIDO2 security tokens currently plugged in, along
           with their device nodes.

           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.

           Note that many security tokens that implement FIDO2 also
           implement PKCS#11, suitable for unlocking volumes via the
           pkcs11-uri= option described above. Typically the newer,
           simpler FIDO2 standard is preferable.

       fido2-cid=
           Takes a Base64 encoded FIDO2 client ID to use for the FIDO2
           unlock operation. If specified, but fido2-device= is not,
           fido2-device=auto is implied. If fido2-device= is used but
           fido2-cid= is not, the volume must be of LUKS2 type, and the
           CID is read from the LUKS2 JSON token header. Use
           systemd-cryptenroll(1) for enrolling a FIDO2 token in the
           LUKS2 header compatible with this automatic mode.

       fido2-rp=
           Takes a string, configuring the FIDO2 Relying Party (rp) for
           the FIDO2 unlock operation. If not specified
           "io.systemd.cryptsetup" is used, except if the the LUKS2 JSON
           token header contains a different value. It should normally
           not be necessary to override this.

       tpm2-device=
           Takes either the special value "auto" or the path to a device
           node (e.g.  /dev/tpmrm0) 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.

           Use tpm2-pcrs= (see below) to configure the set of TPM2 PCRs
           to bind the volume unlocking to. Use systemd-cryptenroll(1)
           as simple tool for enrolling TPM2 security chips in LUKS2
           volumes.

           If specified as "auto" the TPM2 device is automatically
           discovered. Use systemd-cryptenroll --tpm2-device=list to
           list all suitable TPM2 devices currently available, along
           with their device nodes.

           This option implements the following mechanism: when
           enrolling a TPM2 device via systemd-cryptenroll 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.

       tpm2-pcrs=
           Takes a "+" 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 systemd-cryptenroll 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.

       try-empty-password=
           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.

       x-systemd.device-timeout=
           Specifies how long systemd should wait for a device to show
           up before giving up on the entry. The argument is a time in
           seconds or explicitly specified units of "s", "min", "h",
           "ms".

       x-initrd.attach
           Setup this encrypted block device in the initramfs, similarly
           to systemd.mount(5) units marked with x-initrd.mount.

           Although it's not necessary to mark the mount entry for the
           root file system with x-initrd.mount, x-initrd.attach 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.

           All other encrypted block devices that contain file systems
           mounted in the initramfs should use this option.

       At early boot and when the system manager configuration is
       reloaded, this file is translated into native systemd units by
       systemd-cryptsetup-generator(8).

AF_UNIX KEY FILES         top

       If the key file path (as specified in the third column of
       /etc/crypttab entries, see above) refers to an AF_UNIX 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 AF_UNIX socket name in the abstract
       namespace, see unix(7) for details. The source socket name is
       chosen according the following format:

           NUL RANDOM "/cryptsetup/" VOLUME

       In other words: a NUL byte (as required for abstract namespace
       sockets), followed by a random string (consisting of alphanumeric
       characters only), followed by the literal string "/cryptsetup/",
       followed by the name of the volume to acquire they key for.
       Example (for a volume "myvol"):

       Example 1.

           \0d7067f78d9827418/cryptsetup/myvol

       Services listening on the AF_UNIX stream socket may query the
       source socket name with getpeername(2), and use it to determine
       which key to send, allowing a single listening socket to serve
       keys for a multitude of volumes. If the PKCS#11 logic is used
       (see above) the socket source name is picked in identical
       fashion, except that the literal string "/cryptsetup-pkcs11/" is
       used (similar for FIDO2: "/cryptsetup-fido2/" and TPM2:
       "/cryptsetup-tpm2/"). This is done so that services providing key
       material know that not a secret key is requested but an encrypted
       key that will be decrypted via the PKCS#11/FIDO2/TPM2 logic to
       acquire the final secret key.

EXAMPLES         top

       Example 2. /etc/crypttab example

       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 "cipher=xchacha12,aes-adiantum-plain64",
       "keyfile-timeout=10s".

           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

       Example 3. Yubikey-based PKCS#11 Volume Unlocking Example

       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 ykmap(1)
       from the yubikey-manager project to initialize the token and
       systemd-cryptenroll(1) to add it in the LUKS2 volume:

           # Destroy any old key on the Yubikey (careful!)
           ykman piv reset

           # Generate a new private/public key pair on the device, store the public key in
           # 'pubkey.pem'.
           ykman piv generate-key -a RSA2048 9d pubkey.pem

           # Create a self-signed certificate from this public key, and store it on the
           # device. The "subject" should be an arbitrary user-chosen string to identify
           # the token with.
           ykman piv generate-certificate --subject "Knobelei" 9d pubkey.pem

           # We don't need the public key anymore, let's remove it. Since it is not
           # security sensitive we just do a regular "rm" here.
           rm pubkey.pem

           # Enroll the freshly initialized security token in the LUKS2 volume. Replace
           # /dev/sdXn by the partition to use (e.g. /dev/sda1).
           sudo systemd-cryptenroll --pkcs11-token-uri=auto /dev/sdXn

           # Test: Let's run systemd-cryptsetup to test if this all worked.
           sudo /usr/lib/systemd/systemd-cryptsetup attach mytest /dev/sdXn - pkcs11-uri=auto

           # If that worked, let's now add the same line persistently to /etc/crypttab,
           # for the future.
           sudo bash -c 'echo "mytest /dev/sdXn - pkcs11-uri=auto" >> /etc/crypttab'

       A few notes on the above:

       •   We use RSA2048, which is the longest key size current
           Yubikeys support

       •   We use Yubikey key slot 9d, since that's apparently the
           keyslot to use for decryption purposes, see documentation[2].

       Example 4. FIDO2 Volume Unlocking Example

       The FIDO2 logic allows using any compatible FIDO2 security token
       that implements the "hmac-secret" 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
       systemd-cryptenroll(1):

           # Enroll the security token in the LUKS2 volume. Replace /dev/sdXn by the
           # partition to use (e.g. /dev/sda1).
           sudo systemd-cryptenroll --fido2-device=auto /dev/sdXn

           # Test: Let's run systemd-cryptsetup to test if this worked.
           sudo /usr/lib/systemd/systemd-cryptsetup attach mytest /dev/sdXn - fido2-device=auto

           # If that worked, let's now add the same line persistently to /etc/crypttab,
           # for the future.
           sudo bash -c 'echo "mytest /dev/sdXn - fido2-device=auto" >> /etc/crypttab'

       Example 5. TPM2 Volume Unlocking Example

       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
       systemd-cryptenroll(1):

           # Enroll the TPM2 security chip in the LUKS2 volume, and bind it to PCR 7
           # only. Replace /dev/sdXn by the partition to use (e.g. /dev/sda1).
           sudo systemd-cryptenroll --tpm2-device=auto --tpm2-pcrs=7 /dev/sdXn

           # Test: Let's run systemd-cryptsetup to test if this worked.
           sudo /usr/lib/systemd/systemd-cryptsetup attach mytest /dev/sdXn - tpm2-device=auto

           # If that worked, let's now add the same line persistently to /etc/crypttab,
           # for the future.
           sudo bash -c 'echo "mytest /dev/sdXn - tpm2-device=auto" >> /etc/crypttab'

SEE ALSO         top

       systemd(1), systemd-cryptsetup@.service(8),
       systemd-cryptsetup-generator(8), systemd-cryptenroll(1),
       fstab(5), cryptsetup(8), mkswap(8), mke2fs(8)

NOTES         top

        1. RFC7512 PKCS#11 URI
           https://tools.ietf.org/html/rfc7512

        2. see documentation
           https://developers.yubico.com/PIV/Introduction/Certificate_slots.html

COLOPHON         top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨http://www.freedesktop.org/wiki/Software/systemd⟩.  If you have
       a bug report for this manual page, see
       ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
       This page was obtained from the project's upstream Git repository
       ⟨https://github.com/systemd/systemd.git⟩ on 2021-06-20.  (At that
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       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

systemd 249                                                  CRYPTTAB(5)

Pages that refer to this page: systemd-cryptenroll(1)systemd.directives(7)systemd.index(7)systemd-cryptsetup-generator(8)systemd-cryptsetup@.service(8)