x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
SYSTEMD-CRYPTENROLL(1) systemd-cryptenroll SYSTEMD-CRYPTENROLL(1)
NAME
systemd-cryptenroll - Enroll PKCS#11, FIDO2, TPM2 token/devices to
LUKS2 encrypted volumes
SYNOPSIS
systemd-cryptenroll [OPTIONS...] [DEVICE]
DESCRIPTION
systemd-cryptenroll is a tool for enrolling hardware security tokens
and devices into a LUKS2 encrypted volume, which may then be used to
unlock the volume during boot. Specifically, it supports tokens and
credentials of the following kind to be enrolled:
1. PKCS#11 security tokens and smartcards that may carry an RSA key
pair (e.g. various YubiKeys)
2. FIDO2 security tokens that implement the "hmac-secret" extension
(most FIDO2 keys, including YubiKeys)
3. TPM2 security devices
4. Regular passphrases
5. Recovery keys. These are similar to regular passphrases, however
are randomly generated on the computer and thus generally have
higher entropy than user-chosen passphrases. Their character set
has been designed to ensure they are easy to type in, while having
high entropy. They may also be scanned off screen using QR codes.
Recovery keys may be used for unlocking LUKS2 volumes wherever
passphrases are accepted. They are intended to be used in
combination with an enrolled hardware security token, as a recovery
option when the token is lost.
In addition, the tool may be used to enumerate currently enrolled
security tokens and wipe a subset of them. The latter may be combined
with the enrollment operation of a new security token, in order to
update or replace enrollments.
The tool supports only LUKS2 volumes, as it stores token
meta-information in the LUKS2 JSON token area, which is not available
in other encryption formats.
TPM2 PCRs and policies
PCRs allow binding of the encryption of secrets to specific software
versions and system state, so that the enrolled key is only accessible
(may be "unsealed") if specific trusted software and/or configuration
is used. Such bindings may be created with the option --tpm2-pcrs=
described below.
Secrets may also be bound indirectly: a signed policy for a state of
some combination of PCR values is provided, and the secret is bound to
the public part of the key used to sign this policy. This means that
the owner of a key can generate a sequence of signed policies, for
specific software versions and system states, and the secret can be
decrypted as long as the machine state matches one of those policies.
For example, a vendor may provide such a policy for each kernel+initrd
update, allowing users to encrypt secrets so that they can be decrypted
when running any kernel+initrd signed by the vendor. Such bindings may
be created with the options --tpm2-public-key=,
--tpm2-public-key-pcrs=, --tpm2-signature= described below.
See Linux TPM PCR Registry[1] for an authoritative list of PCRs and how
they are updated. The table below contains a quick reference,
describing in particular the PCRs modified by systemd.
Table 1. Well-known PCR Definitions
+----+---------------------+-----------------------+
|PCR | name | Explanation |
+----+---------------------+-----------------------+
|0 | platform-code | Core system |
| | | firmware executable |
| | | code; changes on |
| | | firmware updates |
+----+---------------------+-----------------------+
|1 | platform-config | Core system |
| | | firmware data/host |
| | | platform |
| | | configuration; |
| | | typically contains |
| | | serial and model |
| | | numbers, changes on |
| | | basic |
| | | hardware/CPU/RAM |
| | | replacements |
+----+---------------------+-----------------------+
|2 | external-code | Extended or |
| | | pluggable |
| | | executable code; |
| | | includes option |
| | | ROMs on pluggable |
| | | hardware |
+----+---------------------+-----------------------+
|3 | external-config | Extended or |
| | | pluggable firmware |
| | | data; includes |
| | | information about |
| | | pluggable hardware |
+----+---------------------+-----------------------+
|4 | boot-loader-code | Boot loader and |
| | | additional drivers, |
| | | PE binaries invoked |
| | | by the boot loader; |
| | | changes on boot |
| | | loader updates. sd- |
| | | stub(7) measures |
| | | system extension |
| | | images read from |
| | | the ESP here too |
| | | (see systemd- |
| | | sysext(8)). |
+----+---------------------+-----------------------+
|5 | boot-loader-config | GPT/Partition |
| | | table; changes when |
| | | the partitions are |
| | | added, modified, or |
| | | removed |
+----+---------------------+-----------------------+
|7 | secure-boot-policy | Secure Boot state; |
| | | changes when UEFI |
| | | SecureBoot mode is |
| | | enabled/disabled, |
| | | or firmware |
| | | certificates (PK, |
| | | KEK, db, dbx, ...) |
| | | changes. |
+----+---------------------+-----------------------+
|9 | kernel-initrd | The Linux kernel |
| | | measures all |
| | | initrds it receives |
| | | into this PCR. |
+----+---------------------+-----------------------+
|10 | ima | The IMA project |
| | | measures its |
| | | runtime state into |
| | | this PCR. |
+----+---------------------+-----------------------+
|11 | kernel-boot | systemd-stub(7) |
| | | measures the ELF |
| | | kernel image, |
| | | embedded initrd and |
| | | other payload of |
| | | the PE image it is |
| | | placed in into this |
| | | PCR. systemd- |
| | | pcrphase.service(8) |
| | | measures boot phase |
| | | strings into this |
| | | PCR at various |
| | | milestones of the |
| | | boot process. |
+----+---------------------+-----------------------+
|12 | kernel-config | systemd-boot(7) |
| | | measures the kernel |
| | | command line into |
| | | this PCR. systemd- |
| | | stub(7) measures |
| | | any manually |
| | | specified kernel |
| | | command line (i.e. |
| | | a kernel command |
| | | line that overrides |
| | | the one embedded in |
| | | the unified PE |
| | | image) and loaded |
| | | credentials into |
| | | this PCR. |
+----+---------------------+-----------------------+
|13 | sysexts | systemd-stub(7) |
| | | measures any |
| | | systemd-sysext(8) |
| | | images it passes to |
| | | the booted kernel |
| | | into this PCR. |
+----+---------------------+-----------------------+
|14 | shim-policy | The shim project |
| | | measures its "MOK" |
| | | certificates and |
| | | hashes into this |
| | | PCR. |
+----+---------------------+-----------------------+
|15 | system-identity | systemd- |
| | | cryptsetup(8) |
| | | optionally measures |
| | | the volume key of |
| | | activated LUKS |
| | | volumes into this |
| | | PCR. systemd- |
| | | pcrmachine.service(8) |
| | | measures the |
| | | machine-id(5) into |
| | | this PCR. systemd- |
| | | pcrfs@.service(8) |
| | | measures mount |
| | | points, file system |
| | | UUIDs, labels, |
| | | partition UUIDs of |
| | | the root and /var/ |
| | | filesystems into |
| | | this PCR. |
+----+---------------------+-----------------------+
|16 | debug | Debug |
+----+---------------------+-----------------------+
|23 | application-support | Application Support |
+----+---------------------+-----------------------+
In general, encrypted volumes would be bound to some combination of
PCRs 7, 11, and 14 (if shim/MOK is used). In order to allow firmware
and OS version updates, it is typically not advisable to use PCRs such
as 0 and 2, since the program code they cover should already be covered
indirectly through the certificates measured into PCR 7. Validation
through certificates hashes is typically preferable over validation
through direct measurements as it is less brittle in context of
OS/firmware updates: the measurements will change on every update, but
signatures should remain unchanged. See the Linux TPM PCR Registry[1]
for more discussion.
LIMITATIONS
Note that currently when enrolling a new key of one of the five
supported types listed above, it is required to first provide a
passphrase, a recovery key or a FIDO2 token. It's currently not
supported to unlock a device with a TPM2/PKCS#11 key in order to enroll
a new TPM2/PKCS#11 key. Thus, if in future key roll-over is desired
it's generally recommended to ensure a passphrase, a recovery key or a
FIDO2 token is always enrolled.
Also note that support for enrolling multiple FIDO2 tokens is currently
limited. When multiple FIDO2 tokens are enrolled, systemd-cryptseup
will perform pre-flight requests to attempt to identify which of the
enrolled tokens are currently plugged in. However, this is not possible
for FIDO2 tokens with user verification (UV, usually via biometrics),
in which case it will fall back to attempting each enrolled token one
by one. This will result in multiple prompts for PIN and user
verification. This limitation does not apply to PKCS#11 tokens.
COMPATIBILITY
Security technology both in systemd and in the general industry
constantly evolves. In order to provide best security guarantees, the
way TPM2, FIDO2, PKCS#11 devices are enrolled is regularly updated in
newer versions of systemd. Whenever this happens the following
compatibility guarantees are given:
o Old enrollments continue to be supported and may be unlocked with
newer versions of systemd-cryptsetup@.service(8).
o The opposite is not guaranteed however: it might not be possible to
unlock volumes with enrollments done with a newer version of
systemd-cryptenroll with an older version of systemd-cryptsetup.
That said, it is generally recommended to use matching versions of
systemd-cryptenroll and systemd-cryptsetup, since this is best tested
and supported.
It might be advisable to re-enroll existing enrollments to take benefit
of newer security features, as they are added to systemd.
OPTIONS
The following options are understood:
--password
Enroll a regular password/passphrase. This command is mostly
equivalent to cryptsetup luksAddKey, however may be combined with
--wipe-slot= in one call, see below.
--recovery-key
Enroll a recovery key. Recovery keys are mostly identical to
passphrases, but are computer-generated instead of being chosen by
a human, and thus have a guaranteed high entropy. The key uses a
character set that is easy to type in, and may be scanned off
screen via a QR code.
--unlock-key-file=PATH
Use a file instead of a password/passphrase read from stdin to
unlock the volume. Expects the PATH to the file containing your key
to unlock the volume. Currently there is nothing like
--key-file-offset= or --key-file-size= so this file has to only
contain the full key.
--unlock-fido2-device=PATH
Use a FIDO2 device instead of a password/passphrase read from stdin
to unlock the volume. Expects a hidraw device referring to the
FIDO2 device (e.g. /dev/hidraw1). Alternatively the special value
"auto" may be specified, in order to automatically determine the
device node of a currently plugged in security token (of which
there must be exactly one). This automatic discovery is unsupported
if --fido2-device= option is also specified.
--pkcs11-token-uri=URI
Enroll a PKCS#11 security token or smartcard (e.g. a YubiKey).
Expects a PKCS#11 smartcard URI referring to the token.
Alternatively the special value "auto" may be specified, in order
to automatically determine the URI of a currently plugged in
security token (of which there must be exactly one). The special
value "list" may be used to enumerate all suitable PKCS#11 tokens
currently plugged in. The security token must contain an RSA key
pair which is used to encrypt the randomly generated key that is
used to unlock the LUKS2 volume. The encrypted key is then stored
in the LUKS2 JSON token header area.
In order to unlock a LUKS2 volume with an enrolled PKCS#11 security
token, specify the pkcs11-uri= option in the respective
/etc/crypttab line:
myvolume /dev/sda1 - pkcs11-uri=auto
See crypttab(5) for a more comprehensive example of a
systemd-cryptenroll invocation and its matching /etc/crypttab line.
--fido2-credential-algorithm=STRING
Specify COSE algorithm used in credential generation. The default
value is "es256". Supported values are "es256", "rs256" and
"eddsa".
"es256" denotes ECDSA over NIST P-256 with SHA-256. "rs256"
denotes 2048-bit RSA with PKCS#1.5 padding and SHA-256. "eddsa"
denotes EDDSA over Curve25519 with SHA-512.
Note that your authenticator may not support some algorithms.
--fido2-device=PATH
Enroll a FIDO2 security token that implements the "hmac-secret"
extension (e.g. a YubiKey). Expects a hidraw device referring to
the FIDO2 device (e.g. /dev/hidraw1). Alternatively the special
value "auto" may be specified, in order to automatically determine
the device node of a currently plugged in security token (of which
there must be exactly one). This automatic discovery is unsupported
if --unlock-fido2-device= option is also specified. The special
value "list" may be used to enumerate all suitable FIDO2 tokens
currently plugged in. Note that many hardware security tokens that
implement FIDO2 also implement the older PKCS#11 standard.
Typically FIDO2 is preferable, given it's simpler to use and more
modern.
In order to unlock a LUKS2 volume with an enrolled FIDO2 security
token, specify the fido2-device= option in the respective
/etc/crypttab line:
myvolume /dev/sda1 - fido2-device=auto
See crypttab(5) for a more comprehensive example of a
systemd-cryptenroll invocation and its matching /etc/crypttab line.
--fido2-with-client-pin=BOOL
When enrolling a FIDO2 security token, controls whether to require
the user to enter a PIN when unlocking the volume (the FIDO2
"clientPin" feature). Defaults to "yes". (Note: this setting is
without effect if the security token does not support the
"clientPin" feature at all, or does not allow enabling or disabling
it.)
--fido2-with-user-presence=BOOL
When enrolling a FIDO2 security token, controls whether to require
the user to verify presence (tap the token, the FIDO2 "up" feature)
when unlocking the volume. Defaults to "yes". (Note: this setting
is without effect if the security token does not support the "up"
feature at all, or does not allow enabling or disabling it.)
--fido2-with-user-verification=BOOL
When enrolling a FIDO2 security token, controls whether to require
user verification when unlocking the volume (the FIDO2 "uv"
feature). Defaults to "no". (Note: this setting is without effect
if the security token does not support the "uv" feature at all, or
does not allow enabling or disabling it.)
--tpm2-device=PATH
Enroll a TPM2 security chip. Expects a device node path referring
to the TPM2 chip (e.g. /dev/tpmrm0). Alternatively the special
value "auto" may be specified, in order to automatically determine
the device node of a currently discovered TPM2 device (of which
there must be exactly one). The special value "list" may be used to
enumerate all suitable TPM2 devices currently discovered.
In order to unlock a LUKS2 volume with an enrolled TPM2 security
chip, specify the tpm2-device= option in the respective
/etc/crypttab line:
myvolume /dev/sda1 - tpm2-device=auto
See crypttab(5) for a more comprehensive example of a
systemd-cryptenroll invocation and its matching /etc/crypttab line.
Use --tpm2-pcrs= (see below) to configure which TPM2 PCR indexes to
bind the enrollment to.
--tpm2-pcrs= [PCR...]
Configures the TPM2 PCRs (Platform Configuration Registers) to bind
to when enrollment is requested via --tpm2-device=. Takes a list of
PCR names or numeric indices in the range 0...23. Multiple PCR
indexes are separated by "+". If not specified, the default is to
use PCR 7 only. If an empty string is specified, binds the
enrollment to no PCRs at all. See the table above for a list of
available PCRs.
Example:
--tpm2-pcrs=boot-loader-code+platform-config+boot-loader-config
specifies that PCR registers 4, 1, and 5 should be used.
--tpm2-with-pin=BOOL
When enrolling a TPM2 device, controls whether to require the user
to enter a PIN when unlocking the volume in addition to PCR
binding, based on TPM2 policy authentication. Defaults to "no".
Despite being called PIN, any character can be used, not just
numbers.
Note that incorrect PIN entry when unlocking increments the TPM
dictionary attack lockout mechanism, and may lock out users for a
prolonged time, depending on its configuration. The lockout
mechanism is a global property of the TPM, systemd-cryptenroll does
not control or configure the lockout mechanism. You may use
tpm2-tss tools to inspect or configure the dictionary attack
lockout, with tpm2_getcap(1) and tpm2_dictionarylockout(1)
commands, respectively.
--tpm2-public-key= [PATH], --tpm2-public-key-pcrs= [PCR...],
--tpm2-signature= [PATH]
Configures a TPM2 signed PCR policy to bind encryption to. The
--tpm2-public-key= option accepts a path to a PEM encoded RSA
public key, to bind the encryption to. If this is not specified
explicitly, but a file tpm2-pcr-public-key.pem exists in one of the
directories /etc/systemd/, /run/systemd/, /usr/lib/systemd/
(searched in this order), it is automatically used. The
--tpm2-public-key-pcrs= option takes a list of TPM2 PCR indexes to
bind to (same syntax as --tpm2-pcrs= described above). If not
specified defaults to 11 (i.e. this binds the policy to any unified
kernel image for which a PCR signature can be provided).
Note the difference between --tpm2-pcrs= and
--tpm2-public-key-pcrs=: the former binds decryption to the
current, specific PCR values; the latter binds decryption to any
set of PCR values for which a signature by the specified public key
can be provided. The latter is hence more useful in scenarios where
software updates shell be possible without losing access to all
previously encrypted LUKS2 volumes. Like with --tpm2-pcrs=, names
defined in the table above can also be used to specify the
registers, for instance
--tpm2-public-key-pcrs=boot-loader-code+system-identity.
The --tpm2-signature= option takes a path to a TPM2 PCR signature
file as generated by the systemd-measure(1) tool. If this is not
specified explicitly, a suitable signature file
tpm2-pcr-signature.json is searched for in /etc/systemd/,
/run/systemd/, /usr/lib/systemd/ (in this order) and used. If a
signature file is specified or found it is used to verify if the
volume can be unlocked with it given the current PCR state, before
the new slot is written to disk. This is intended as safety net to
ensure that access to a volume is not lost if a public key is
enrolled for which no valid signature for the current PCR state is
available. If the supplied signature does not unlock the current
PCR state and public key combination, no slot is enrolled and the
operation will fail. If no signature file is specified or found no
such safety verification is done.
--wipe-slot= [SLOT...]
Wipes one or more LUKS2 key slots. Takes a comma separated list of
numeric slot indexes, or the special strings "all" (for wiping all
key slots), "empty" (for wiping all key slots that are unlocked by
an empty passphrase), "password" (for wiping all key slots that are
unlocked by a traditional passphrase), "recovery" (for wiping all
key slots that are unlocked by a recovery key), "pkcs11" (for
wiping all key slots that are unlocked by a PKCS#11 token), "fido2"
(for wiping all key slots that are unlocked by a FIDO2 token),
"tpm2" (for wiping all key slots that are unlocked by a TPM2 chip),
or any combination of these strings or numeric indexes, in which
case all slots matching either are wiped. As safety precaution an
operation that wipes all slots without exception (so that the
volume cannot be unlocked at all anymore, unless the volume key is
known) is refused.
This switch may be used alone, in which case only the requested
wipe operation is executed. It may also be used in combination with
any of the enrollment options listed above, in which case the
enrollment is completed first, and only when successful the wipe
operation executed -- and the newly added slot is always excluded
from the wiping. Combining enrollment and slot wiping may thus be
used to update existing enrollments:
systemd-cryptenroll /dev/sda1 --wipe-slot=tpm2 --tpm2-device=auto
The above command will enroll the TPM2 chip, and then wipe all
previously created TPM2 enrollments on the LUKS2 volume, leaving
only the newly created one. Combining wiping and enrollment may
also be used to replace enrollments of different types, for example
for changing from a PKCS#11 enrollment to a FIDO2 one:
systemd-cryptenroll /dev/sda1 --wipe-slot=pkcs11 --fido2-device=auto
Or for replacing an enrolled empty password by TPM2:
systemd-cryptenroll /dev/sda1 --wipe-slot=empty --tpm2-device=auto
-h, --help
Print a short help text and exit.
--version
Print a short version string and exit.
EXIT STATUS
On success, 0 is returned, a non-zero failure code otherwise.
EXAMPLES
crypttab(5) and systemd-measure(1) contain various examples employing
systemd-cryptenroll.
SEE ALSO
systemd(1), systemd-cryptsetup@.service(8), crypttab(5), cryptsetup(8),
systemd-measure(1)
NOTES
1. Linux TPM PCR Registry
https://uapi-group.org/specifications/specs/linux_tpm_pcr_registry/
systemd 254 SYSTEMD-CRYPTENROLL(1)
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