- 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.
systemd-cryptenroll allows enrolling smartcards, FIDO2 tokens and Trusted Platform Module security chips into LUKS devices, as well as regular passphrases. These devices are later unlocked by , using the enrolled tokens.
systemd-cryptenroll is part of and packaged with. However, extra packages are required to use hardware devices as keys:
- To use PKCS#11 tokens, install .
- To use FIDO2 tokens, install .
- To use TPM2 devices, install .
systemd-cryptenroll can list the keyslots in a LUKS device, similar to
cryptsetup luksDump, but in a more user-friendly format.
# systemd-cryptenroll /dev/disk
SLOT TYPE 0 password 1 tpm2
# systemd-cryptenroll /dev/disk --wipe-slot=SLOT
Where SLOT can be:
- A single keyslot index, as represented in #List keyslots
- A type of keyslot, which will erase all keyslots of that type. Valid types are
- A combination of all of the above, separated by commas
- The string
all, which erases all keyslots on the device. This option can only be used when enrolling another device or passphrase at the same time.
--wipe-slot operation can be used in combination with all enrollment options, which is useful to update existing device enrollments:
# systemd-cryptenroll /dev/disk --wipe-slot=fido2 --fido2-device=auto
This is equivalent to
# systemd-cryptenroll /dev/disk --password
- 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.
A recovery key is designed to be used as a fallback if the hardware tokens are unavailable, and can be used in place of regular passphrases whenever they are required.
# systemd-cryptenroll /dev/disk --recovery-key
Enrolling hardware devices
--type-device options must point to a valid device path of their respective type. A list of available devices can be obtained by passing the
list argument to this option. Alternatively, if you only have a single device of the desired type connected, the
auto option can be used to automatically select it.
PKCS#11 tokens or smartcards
The token or smartcard must contain a RSA key pair, which will be used to encrypt the generated key that will be used to unlock the volume.
# systemd-cryptenroll /dev/disk --pkcs11-token-uri=device
Any FIDO2 token that supports the "hmac-secret" extension can be used with systemd-cryptenroll. The following example would enroll a FIDO2 token to an encrypted LUKS2 block device, requiring only user presence as authentication.
# systemd-cryptenroll /dev/disk --fido2-device=device --fido2-with-client-pin=no
In addition, systemd-cryptenroll supports using the token's built-in user verification methods:
--fido2-with-user-presencedefines whether to verify the user presence (i.e. by tapping the token) before unlocking, defaults to yes
--fido2-with-user-verificationdefines whether to require user verification before unlocking, defaults to no
- These options will have no effect if the token does not support these features.
- See User Presence vs User Verification for more information on the difference between the two.
By default, the cryptographic algorithm used when generating a FIDO2 credential is es256 which denotes Elliptic Curve Digital Signature Algorithm (ECDSA) over NIST P-256 with SHA-256. If desired and provided by the FIDO2 token, a different cryptographic algorithm can be specified during enrollment.
Suppose that a previous FIDO2 token has already been enrolled and the user wishes to enroll another, the following generates an eddsa credential which denotes EdDSA over Curve25519 with SHA-512 and authenticates the device with a previous enrolled token instead of a password.
# systemd-cryptenroll /dev/disk --fido2-device=device --fido2-credential-algorithm=eddsa --unlock-fido2-device=auto
Trusted Platform Module
systemd-cryptenroll has native support for enrolling LUKS keys in TPMs. It requires the following:
- installed, must be
- A LUKS2 device (currently the default type used by cryptsetup),
- If you intend to use this method on your root partition, some tweaks need to be made to the initramfs (see dm-crypt/System configuration#Using systemd-cryptsetup-generator for advanced configuration) :
To begin, run the following command to list your installed TPMs and the driver in use:
$ systemd-cryptenroll --tpm2-device=list
--tpm2-device=/path/to/tpm2_devicein the following steps.
A key may be enrolled in both the TPM and the LUKS volume using only one command. The following example generates a new random key, adds it to the volume so it can be used to unlock it in addition to the existing keys, and binds this new key to PCR 7 (Secure Boot state):
# systemd-cryptenroll --tpm2-device=auto /dev/sdX
/dev/sdX is the full path to the encrypted LUKS volume. Use
--unlock-key-file=/path/to/keyfile if the LUKS volume is unlocked by a keyfile instead of a passphrase.
Refer to Trusted Platform Module#Accessing PCR registers for common PCR measurements in Linux. Adjust the
--tpm2-pcrs=7 default as necessary (parameters are separated by the
- Make sure Secure Boot is active and in user mode when binding to PCR 7, otherwise, unauthorized boot devices could unlock the encrypted volume.
- The state of PCR 7 can change if firmware certificates change, which can risk locking the user out. This can be implicitly done by fwupd or explicitly by rotating Secure Boot keys.
The combination of PCRs to bind to depends on the individual case to balance usability and lock-down. For example, you may require UEFI firmware updates without manual intervention to the Secure Boot state, or different boot devices. As another example, Microsoft's Bitlocker prefers PCR
7+11, but may also use other PCR combinations.
- It is possible to require a PIN to be entered in addition to the TPM state being correct. Simply add the option
--tpm2-with-pin=yesto the command above and enter the PIN when prompted.
- systemd-cryptenroll does not check the TPM measurement before asking for the PIN, therefore consider using a unique PIN since the environment may be untrustworthy.
To check that the new key was enrolled, dump the LUKS configuration and look for a
systemd-tpm2 token entry, as well as an additional entry in the Keyslots section:
# cryptsetup luksDump /dev/sdX
To test that the key works, run the following command while the LUKS volume is closed:
# systemd-cryptsetup attach mapping_name /dev/sdX - tpm2-device=auto
mapping_name is your chosen name for the volume once opened.
See dm-crypt/System configuration#crypttab and dm-crypt/System configuration#Trusted Platform Module and FIDO2 keys in order to unlock the volume at boot time.
/etc/crypttab, the systemd-cryptenroll command itself currently only supports path names.
To remove a key enrolled using this method, run:
# systemd-cryptenroll /dev/sdX --wipe-slot=slot_number
slot_number is the numeric LUKS slot number in which your TPM key is stored.
# systemd-cryptenroll /dev/sdX --wipe-slot=tpm2
to remove all TPM-associated keys from your LUKS volume.
Seeand for more information and examples.