From systemd-cryptenroll(1):
- 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 systemd-cryptsetup@.service(8), using the enrolled tokens.
Installation
systemd-cryptenroll is part of and packaged with systemd. However, extra packages are required to use hardware devices as keys:
- To use PKCS#11 tokens, install libp11-kit.
- To use FIDO2 tokens, install libfido2.
- To use TPM2 devices, install tpm2-tss.
List keyslots
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
Erasing keyslots
# 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
empty
,password
,recovery
,pkcs11
,fido2
,tpm2
- 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.
The --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
Enrolling passphrases
Regular password
This is equivalent to cryptsetup luksAddKey
.
# systemd-cryptenroll /dev/disk --password
Recovery key
From systemd-cryptenroll(1):
- 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
The --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
FIDO2 tokens
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-presence
defines whether to verify the user presence (i.e. by tapping the token) before unlocking, defaults to yes -
--fido2-with-user-verification
defines 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.
Furthermore, 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 /dev/disk --tpm2-device=device
By default, enrolling a TPM will bind the key to PCR7, which measures the Secure Boot state. It is possible to change which PCRs the key will be bound to by using the --tpm2-pcrs
option. Multiple PCRs can be used at once by separating them with +
symbol. A full list of PCRs and what they measure is available in Trusted Platform Module#Accessing PCR registers.
Using TPM with a PIN
It is possible to require a PIN to be entered in addition to the TPM measurement check. Add the option --tpm2-with-pin=yes
while enrolling a TPM device, then enter the PIN when asked. Although systemd-cryptenroll calls this a PIN, any characters may be used.