volume_key man page

volume_key — work with volume encryption secrets and escrow packets


volume_key [OPTION]... OPERAND...


volume_key extracts "secrets" used for volume encryption (for example keys or passphrases) and stores them into separate encrypted "escrow packets", uses a previously created escrow packet to restore access to a volume (e.g. if the user forgets a passphrase), or manipulates the information in escrow packets.

The mode of operation and operands of volume_key are determined by specifying one of the --save, --restore, --setup-volume, --reencrypt, --dump or --secrets options. See the Options sections for details.


In all options described below, VOLUME is a LUKS device, not the plaintext device containted within:

blkid -s TYPE VOLUME

should report TYPE="crypto_LUKS".

The following options determine the mode of operation and expected operands of volume_key:

Expects operands VOLUME [PACKET]. Open VOLUME. If PACKET is provided, load the secrets from it. Otherwise, extract secrets from VOLUME, prompting the user if necessary. In any case, store secrets in one or more output packets.
Expects operands VOLUME PACKET. Open VOLUME and use the secrets in PACKET to make VOLUME accessible again, prompting the user if necessary (e.g. by letting the user enter a new passphrase).

Expects operands VOLUME PACKET NAME. Open VOLUME and use the secrets in PACKET to set up VOLUME for use of the decrypted data as NAME.

Currently NAME is a name of a dm-crypt volume, and this operation makes the decrypted volume available as /dev/mapper/NAME.

This operation should not permanently alter VOLUME (e.g. by adding a new passphrase); the user can of course access and modify the decrypted volume, modifying VOLUME in the process.

Expects operand PACKET. Open PACKET, decrypting it if necessary, and store the information in one or more new output packets.
Expects operand PACKET. Open PACKET, decrypting it if necessary, and output the contents of PACKET. The secrets are not output by default.
Expects operand PACKET. Open PACKET, decrypting it if necessary, and output secrets contained in PACKET.
Show usage information.
Show version of volume_key.

The following options alter the behavior of the specified operation:

-b, --batch
Run in batch mode. Read passwords and passphrases from standard input, each terminated by a NUL character. If a packet does not match a volume exactly, fail instead of prompting the user.
-d, --nss-dir DIR
Use private keys in NSS database in DIR to decrypt public key-encrypted packets.
-o, --output PACKET

Write the default secret to PACKET.

Which secret is the default depends on volume format: it should not be likely to expire, and it should allow restoring access to the volume using --restore.

--output-data-encryption-key PACKET
Write the data encryption key (the key directly used to encrypt the actual volume data) to PACKET.
--output-passphrase PACKET
Write a passphrase that can be used to access the volume to PACKET.
--create-random-passphrase PACKET
Generate a random alphanumeric passphrase, add it to VOLUME (without affecting other passphrases) and store the random passphrase into PACKET.
-c, --certificate CERT

Load a certificate from the file specified by CERT and encrypt all output packets using the public key contained in the certificate. If this option is not specified, all output packets are encrypted using a passphrase.

Note that CERT is a certificate file name, not a NSS certificate nickname.

--output-format FORMAT
Use FORMAT for all output packets. FORMAT can currently be one of asymmetric (use CMS to encrypt the whole packet, requires a certificate), asymmetric_wrap_secret_only (wrap only the secret, requires a certificate), passphrase (use GPG to encrypt the whole packet, requires a passphrase).
Only dump the unencrypted parts of the packet, if any, with --dump. Do not require any passphrase or private key access.
Include secrets in the output of --dump

Exit Status

volume_key returns with exit status 0 on success, 1 on error.


The only currently supported volume format is LUKS.


Typical usage of volume_key proceeds as follows. During system installation or soon after, back up the default secret of a volume, and add a system-specific random passphrase. Encrypt both using a certificate:

volume_key --save VOLUME -c CERT -o PACKET_DEFAULT --create-random-passphrase PACKET_PASSPHRASE

Store PACKET_DEFAULT and PACKET_PASSPHRASE outside of the computer.

If the user forgets a passphrase, and you can access the computer, decrypt PACKET_DEFAULT using the certificate private key (which should never leave a secure machine):

volume_key --reencrypt -d NSS_DB PACKET_DEFAULT -o PACKET_DEFAULT_PW

Then boot the computer (e.g. using a "rescue mode"), copy PACKET_DEFAULT_PW to it, and restore access to the volume:

volume_key --restore VOLUME PACKET_DEFAULT_PW

If the user forgets the passphrase, and you cannot access the computer, decrypt the backup passphrase:

volume_key --secrets PACKET_PASSPHRASE

and tell the backup passphrase to the user. (You can later generate a new backup passphrase.)


volume_key Jun 2011