knowledge/technology/linux/systemd/systemd-cryptenroll.md

obj	arch-wiki	rev
application	https://wiki.archlinux.org/title/Systemd-cryptenroll	2024-12-16

systemd-cryptenroll

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, using the enrolled tokens.

Usage

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
• 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

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

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:

• tpm2-tss must be installed,
• 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

To begin, run the following command to list your installed TPMs and the driver in use:

systemd-cryptenroll --tpm2-device=list

Tip: If your computer has multiple TPMs installed, specify the one you wish to use with --tpm2-device=/path/to/tpm2_device in 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

where /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.

Note: 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=yes to the command above and enter the PIN when prompted.

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 none tpm2-device=auto

where mapping_name is your chosen name for the volume once opened.

Modules

If your TPM requires a kernel module, edit /etc/mkinitcpio.conf and edit the MODULES line to add the module used by your TPM. For instance:

MODULES=(tpm_tis)