cryptsetup <options> <action> <action args>
cryptsetup is used to conveniently setup dm-crypt managed device-mapper mappings. For basic (plain) dm-crypt mappings, there are four operations.
create <name> <device>
<options> can be [--hash, --cipher, --verify-passphrase, --key-file, --key-size, --offset, --skip, --readonly]
remove <name>
status <name>
resize <name>
If --size (in sectors) is not specified, the size of the underlying block device is used.
LUKS, Linux Unified Key Setup, is a standard for hard disk encryption. It standardizes a partition header, as well as the format of the bulk data. LUKS can manage multiple passwords, that can be revoked effectively and that are protected against dictionary attacks with PBKDF2.
These are valid LUKS actions:
luksFormat <device> [<key file>]
<options> can be [--cipher, --verify-passphrase, --key-size, --key-slot, --key-file (takes precedence over optional second argument), --keyfile-size, --use-random | --use-urandom, --uuid].
luksOpen <device> <name>
<options> can be [--key-file, --keyfile-size, --readonly].
luksClose <name>
luksSuspend <name>
After that operation you have to use luksResume to reinstate encryption key (and resume device) or luksClose to remove mapped device.
WARNING: never try to suspend device where is the cryptsetup binary itself.
luksResume <name>
<options> can be [--key-file, --keyfile-size]
luksAddKey <device> [<new key file>]
<options> can be [--key-file, --keyfile-size, --new-keyfile-size, --key-slot].
luksRemoveKey <device> [<key file>]
luksKillSlot <device> <key slot number>
<options> can be [--key-file, --keyfile-size].
luksUUID <device>
set new UUID if --uuid option is specified.
isLuks <device>
luksDump <device>
If --dump-master-key option is used, the volume (master) key is dumped instead of keyslot info. Because this information can be used to access encrypted device without passphrase knowledge (even without LUKS header) use this option very carefully.
Dump with volume key (either printed or stored to file) should be always stored encrypted and on safe place.
LUKS passphrase or key file is required for volume key dump.
<options> can be [--dump-master-key, --key-file, --keyfile-size].
luksHeaderBackup <device> --header-backup-file <file>
WARNING: Please note that with this backup file (and old passphrase knowledge) you can decrypt data even if old passphrase was wiped from real device.
Also note that anti-forensic splitter is not used during manipulation with backup file.
luksHeaderRestore <device> --header-backup-file <file>
Restores binary backup of LUKS header and keyslot areas from specified file.
WARNING: All the keyslot areas are overwritten, only active keyslots form backup file are available after issuing this command.
This command allows restoring header if device do not contain LUKS header or if the master key size and data offset in LUKS header on device match the backup file.
For more information about LUKS, see http://code.google.com/p/cryptsetup/wiki/Specification
For luksFormat action specifies hash used in LUKS key setup scheme and volume key digest.
WARNING: setting hash other than sha1 causes LUKS device incompatible with older version of cryptsetup.
The hash string is passed to libgcrypt, so all hash algorithms are supported (for luksFormat algorithm must provide at least 20 byte long hash). Default is set during compilation, compatible values with old version of cryptsetup are "ripemd160" for create action and "sha1" for luksFormat.
Use cryptsetup --help to show defaults.
Default mode is configurable during compilation, you can see compiled-in default using cryptsetup --help. If not changed, the default is for plain dm-crypt and LUKS mappings "aes-cbc-essiv:sha256".
For pre-2.6.10 kernels, use "aes-plain" as they don't understand the new cipher spec strings. To use ESSIV, use "aes-cbc-essiv:sha256".
For XTS mode, kernel version 2.6.24 or more recent is required. Use "aes-xts-plain" cipher specification and set key size to 256 (or 512) bits (see -s option).
With LUKS, key material supplied in key files via -d are always used for existing passphrases, except in luksFormat action where -d is equivalent to positional key file argument. If you want to set a new key via a key file, you have to use a positional arg to luksAddKey.
If the key file is "-", stdin will be used. With the "-" key file reading will not stop when new line character is detected. See section NOTES ON PASSWORD PROCESSING for more information.
For luksAddKey it allows adding new passphrase with only master key knowledge.
See luksDump for more info.
See NOTES ON RNG for more information. Use cryptsetup --help to show default RNG.
Has to be a multiple of 8 bits. The key size is limited by the used cipher. See output of /proc/crypto for more information. Can be used for create or luksFormat, all other LUKS actions will use key-size specified by the LUKS header. Default is set during compilation, if not changed it is 256 bits.
Use cryptsetup --help to show defaults.
The UUID must be provided in standard UUID format (e.g. 12345678-1234-1234-1234-123456789abc).
From stdin: Reading will continue until EOF (so using e.g. /dev/random as stdin will not work), with the trailing newline stripped. After that the read data will be hashed with the default hash or the hash given by --hash and the result will be cropped to the keysize given by -s. If "plain" is used as an argument to the hash option, the input data will not be hashed. Instead, it will be zero padded (if shorter than the keysize) or truncated (if longer than the keysize) and used directly as the key. No warning will be given if the amount of data read from stdin is less than the keysize.
From a key file: It will be cropped to the size given by -s. If there is insufficient key material in the key file, cryptsetup will quit with an error.
If --key-file=- is used for reading the key from stdin, no trailing newline is stripped from the input. Without that option, cryptsetup strips trailing newlines from stdin input.
LUKS will always do an exhaustive password reading. Hence, password can not be read from /dev/random, /dev/zero or any other stream that does not terminate.
For any password creation action (luksAddKey, or luksFormat), the user may specify how much the time the password processing should consume. Increasing the time will lead to a more secure password, but also will take luksOpen longer to complete. The default setting of one second is sufficient for good security.
Please also be sure that you are using the same keyboard and language setting as during device format.
For --hash option all algorithms supported by gcrypt library are available.
There are two types of randomness cryptsetup/LUKS needs. One type (which always uses /dev/urandom) is used for salt, AF splitter and for wiping removed keyslot.
Second type is used for volume (master) key. You can switch between using /dev/random and /dev/urandom here, see --use-random and --use-urandom options. Using /dev/random on system without enough entropy sources can cause luksFormat to block until the requested amount of random data is gathered. See urandom(4) for more information.
The reload action is no longer supported. Please use dmsetup(8) if you need to directly manipulate with the device mapping table.
The luksDelKey was replaced with luksKillSlot.
This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
LUKS website, http://code.google.com/p/cryptsetup/