x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
CRYPTTAB(5) crypttab CRYPTTAB(5)
NAME
crypttab - Configuration for encrypted block devices
SYNOPSIS
/etc/crypttab
DESCRIPTION
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
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 passphrases.
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. 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 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. 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 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 be 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
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 header
containing the master key(s) is stored. This option is only
relevant for LUKS and TrueCrypt/VeraCrypt 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
or the device used as the key file, and falls back to a password if
it could not be accessed. 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.
veracrypt-pim=
Specifies a custom Personal Iteration Multiplier (PIM) value, which
can range from 0..2147468 for standard veracrypt volumes and
0..65535 for veracrypt system volumes. A value of 0 will imply the
VeraCrypt default. This option is only effective when
tcrypt-veracrypt is set.
Note that VeraCrypt enforces a minimal allowed PIM value depending
on the password strength and the hash algorithm used for key
derivation, however veracrypt-pim= is not checked against these
bounds. See documentation[1] for more information.
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[2]
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 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.
tpm2-pin=
Takes a boolean argument, defaults to "false". 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.
tpm2-signature=
Takes an absolute path to a TPM2 PCR JSON signature file, as
produced by the systemd-measure(1) 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
systemd-cryptenroll(1) 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 tpm2-pcr-signature.json is searched for in
/etc/systemd/, /run/systemd/, /usr/lib/systemd/ (in this order).
tpm2-measure-pcr=
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.
tpm2-measure-bank=
Selects one or more TPM2 PCR banks to measure the volume key into,
as configured with tpm2-measure-pcr= 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. "sha1", "sha256", ...) as argument, to
identify the bank.
token-timeout=
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
systemd.time(7) 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.
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 block 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 initrd, 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 initrd 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
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 to 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. For
example, for the volume "myvol":
\0d7067f78d9827418/cryptsetup/myvol
Services listening on the AF_UNIX stream socket may query the source
socket name with getpeername(2), 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
"/cryptsetup-pkcs11/" is used. And similarly for FIDO2
("/cryptsetup-fido2/") and TPM2 ("/cryptsetup-tpm2/"). 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.
EXAMPLES
Example 1. /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 2. 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:
# SPDX-License-Identifier: MIT-0
# 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:
o We use RSA2048, which is the longest key size current Yubikeys
support
o We use Yubikey key slot 9d, since that's apparently the keyslot to
use for decryption purposes, see documentation[3].
Example 3. 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):
# SPDX-License-Identifier: MIT-0
# 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 4. 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):
# SPDX-License-Identifier: MIT-0
# 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
systemd(1), systemd-cryptsetup@.service(8), systemd-cryptsetup-
generator(8), systemd-cryptenroll(1), fstab(5), cryptsetup(8),
mkswap(8), mke2fs(8)
NOTES
1. See documentation
https://www.veracrypt.fr/en/Personal%20Iterations%20Multiplier%20%28PIM%29.html
2. RFC7512 PKCS#11 URI
https://tools.ietf.org/html/rfc7512
3. see documentation
https://developers.yubico.com/PIV/Introduction/Certificate_slots.html
systemd 254 CRYPTTAB(5)
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