NAME | SYNOPSIS | DESCRIPTION | PLAIN DM-CRYPT OR LUKS? | WARNINGS | BASIC COMMANDS | PLAIN MODE | LUKS EXTENSION | loop-AES EXTENSION | TCRYPT (TrueCrypt-compatible and VeraCrypt) EXTENSION | MISCELLANEOUS | OPTIONS | RETURN CODES | NOTES ON PASSPHRASE PROCESSING FOR PLAIN MODE | NOTES ON PASSPHRASE PROCESSING FOR LUKS | INCOHERENT BEHAVIOR FOR INVALID PASSPHRASES/KEYS | NOTES ON SUPPORTED CIPHERS, MODES, HASHES AND KEY SIZES | NOTES ON PASSPHRASES | NOTES ON RANDOM NUMBER GENERATORS | NOTES ON LOOPBACK DEVICE USE | DEPRECATED ACTIONS | REPORTING BUGS | AUTHORS | COPYRIGHT | SEE ALSO | COLOPHON

CRYPTSETUP(8)               Maintenance Commands               CRYPTSETUP(8)

NAME         top

       cryptsetup - manage plain dm-crypt and LUKS encrypted volumes

SYNOPSIS         top

       cryptsetup <options> <action> <action args>

DESCRIPTION         top

       cryptsetup is used to conveniently setup dm-crypt managed device-
       mapper mappings. These include plain dm-crypt volumes and LUKS
       volumes. The difference is that LUKS uses a metadata header and can
       hence offer more features than plain dm-crypt. On the other hand, the
       header is visible and vulnerable to damage.

       In addition, cryptsetup provides limited support for the use of
       historic loopaes volumes and for TrueCrypt compatible volumes.

PLAIN DM-CRYPT OR LUKS?         top

       Unless you understand the cryptographic background well, use LUKS.
       With plain dm-crypt there are a number of possible user errors that
       massively decrease security. While LUKS cannot fix them all, it can
       lessen the impact for many of them.

WARNINGS         top

       A lot of good information on the risks of using encrypted storage, on
       handling problems and on security aspects can be found in the
       Cryptsetup FAQ. Read it. Nonetheless, some risks deserve to be
       mentioned here.

       Backup: Storage media die. Encryption has no influence on that.
       Backup is mandatory for encrypted data as well, if the data has any
       worth. See the Cryptsetup FAQ for advice on how to do backup of an
       encrypted volume.

       Character encoding: If you enter a passphrase with special symbols,
       the passphrase can change depending character encoding. Keyboard
       settings can also change, which can make blind input hard or
       impossible. For example, switching from some ASCII 8-bit variant to
       UTF-8 can lead to a different binary encoding and hence different
       passphrase seen by cryptsetup, even if what you see on the terminal
       is exactly the same. It is therefore highly recommended to select
       passphrase characters only from 7-bit ASCII, as the encoding for
       7-bit ASCII stays the same for all ASCII variants and UTF-8.

       LUKS header: If the header of a LUKS volume gets damaged, all data is
       permanently lost unless you have a header-backup.  If a key-slot is
       damaged, it can only be restored from a header-backup or if another
       active key-slot with known passphrase is undamaged.  Damaging the
       LUKS header is something people manage to do with surprising
       frequency. This risk is the result of a trade-off between security
       and safety, as LUKS is designed for fast and secure wiping by just
       overwriting header and key-slot area.

       Previously used partitions: If a partition was previously used, it is
       a very good idea to wipe filesystem signatures, data, etc. before
       creating a LUKS or plain dm-crypt container on it.  For a quick
       removal of filesystem signatures, use "wipefs". Take care though that
       this may not remove everything. In particular md (RAID) signatures at
       the end of a device may survive. It also does not remove data. For a
       full wipe, overwrite the whole partition before container creation.
       If you do not know how to to that, the cryptsetup FAQ describes
       several options.

BASIC COMMANDS         top

       The following are valid actions for all supported device types.

       open <device> <name> --type <device_type>

              Opens (creates a mapping with) <name> backed by device
              <device>.

              Device type can be plain, luks (default), loopaes or tcrypt.

              For backward compatibility there are open command aliases:

              create (argument-order <name> <device>): open --type plain
              plainOpen: open --type plain
              luksOpen: open --type luks
              loopaesOpen: open --type loopaes
              tcryptOpen: open --type tcrypt

              <options> are type specific and are described below for
              individual device types. For create, the order of the <name>
              and <device> options is inverted for historical reasons, all
              other aliases use the standard <device> <name> order.

       close <name>

              Removes the existing mapping <name> and wipes the key from
              kernel memory.

              For backward compatibility there are close command aliases:
              remove, plainClose, luksClose, loopaesClose, tcryptClose (all
              behaves exactly the same, device type is determined
              automatically from active device).

       status <name>

              Reports the status for the mapping <name>.

       resize <name>

              Resizes an active mapping <name>.

              If --size (in sectors) is not specified, the size is computed
              from the underlying device. For LUKS it is the size of the
              underlying device without the area reserved for LUKS header
              (see data payload offset in luksDump command).  For plain
              crypt device the whole device size is used.

              Note that this does not change the raw device geometry, it
              just changes how many sectors of the raw device are
              represented in the mapped device.

PLAIN MODE         top

       Plain dm-crypt encrypts the device sector-by-sector with a single,
       non-salted hash of the passphrase. No checks are performed, no
       metadata is used. There is no formatting operation.  When the raw
       device is mapped (opened), the usual device operations can be used on
       the mapped device, including filesystem creation.  Mapped devices
       usually reside in /dev/mapper/<name>.

       The following are valid plain device type actions:

       open --type plain <device> <name>
       create <name> <device> (OBSOLETE syntax)

              Opens (creates a mapping with) <name> backed by device
              <device>.

              <options> can be [--hash, --cipher, --verify-passphrase,
              --key-file, --keyfile-offset, --key-size, --offset, --skip,
              --size, --readonly, --shared, --allow-discards]

              Example: 'cryptsetup open --type plain /dev/sda10 e1' maps the
              raw encrypted device /dev/sda10 to the mapped (decrypted)
              device /dev/mapper/e1, which can then be mounted, fsck-ed or
              have a filesystem created on it.

LUKS EXTENSION         top

       LUKS, the Linux Unified Key Setup, is a standard for disk encryption.
       It adds a standardized header at the start of the device, a key-slot
       area directly behind the header and the bulk data area behind that.
       The whole set is called a 'LUKS container'.  The device that a LUKS
       container resides on is called a 'LUKS device'.  For most purposes
       both terms can be used interchangeably. But note that when the LUKS
       header is at a nonzero offset in a device, then the device is not a
       LUKS device anymore, but has a LUKS container stored in it at an
       offset.

       LUKS can manage multiple passphrases that can be individually revoked
       or changed and that can be securely scrubbed from persistent media
       due to the use of anti-forensic stripes. Passphrases are protected
       against brute-force and dictionary attacks by PBKDF2, which
       implements hash iteration and salting in one function.

       Each passphrase, also called a key in this document, is associated
       with one of 8 key-slots.  Key operations that do not specify a slot
       affect the first slot that matches the supplied passphrase or the
       first empty slot if a new passphrase is added.

       The <device> parameter can be also specified by a LUKS UUID in the
       format UUID=<uuid>. Translation to real device name uses symlinks in
       /dev/disk/by-uuid directory.

       To specify a detached header, the --header parameter can be used in
       all LUKS commands and always takes precedence over positional
       <device> parameter.

       The following are valid LUKS actions:

       luksFormat <device> [<key file>]

              Initializes a LUKS partition and sets the initial passphrase
              (for key-slot 0), either via prompting or via <key file>. Note
              that if the second argument is present, then the passphrase is
              taken from the file given there, without the need to use the
              --key-file option. Also note that for both forms of reading
              the passphrase from file you can give '-' as file name, which
              results in the passphrase being read from stdin and the
              safety-question being skipped.

              You can only call luksFormat on a LUKS device that is not
              mapped.

              <options> can be [--hash, --cipher, --verify-passphrase,
              --key-size, --key-slot, --key-file (takes precedence over
              optional second argument), --keyfile-offset, --keyfile-size,
              --use-random | --use-urandom, --uuid, --master-key-file,
              --iter-time, --header, --force-password].

              WARNING: Doing a luksFormat on an existing LUKS container will
              make all data the old container permanently irretrievable,
              unless you have a header backup.

       open --type luks <device> <name>
       luksOpen <device> <name> (old syntax)

              Opens the LUKS device <device> and sets up a mapping <name>
              after successful verification of the supplied passphrase.  If
              the passphrase is not supplied via --key-file, the command
              prompts for it interactively.

              <options> can be [--key-file, --keyfile-offset,
              --keyfile-size, --readonly, --test-passphrase,
              --allow-discards, --header, --key-slot, --master-key-file].

       luksSuspend <name>

              Suspends an active device (all IO operations will blocked and
              accesses to the device will wait indefinitely) and wipes the
              encryption key from kernel memory. Needs kernel 2.6.19 or
              later.

              After this operation you have to use luksResume to reinstate
              the encryption key and unblock the device or close to remove
              the mapped device.

              WARNING: never suspend the device on which the cryptsetup
              binary resides.

              <options> can be [--header].

       luksResume <name>

              Resumes a suspended device and reinstates the encryption key.
              Prompts interactively for a passphrase if --key-file is not
              given.

              <options> can be [--key-file, --keyfile-size, --header]

       luksAddKey <device> [<key file with new key>]

              adds a new passphrase. An existing passphrase must be supplied
              interactively or via --key-file.  The new passphrase to be
              added can be specified interactively or read from the file
              given as positional argument.

              <options> can be [--key-file, --keyfile-offset,
              --keyfile-size, --new-keyfile-offset, --new-keyfile-size,
              --key-slot, --master-key-file, --iter-time, --force-password,
              --header].

       luksRemoveKey <device> [<key file with passphrase to be removed>]

              Removes the supplied passphrase from the LUKS device. The
              passphrase to be removed can be specified interactively, as
              positional argument or via --key-file.

              <options> can be [--key-file, --keyfile-offset,
              --keyfile-size, --header]

              WARNING: If you read the passphrase from stdin (without
              further argument or with '-' as argument to --key-file),
              batch-mode (-q) will be implicitly switched on and no warning
              will be given when you remove the last remaining passphrase
              from a LUKS container. Removing the last passphrase makes the
              LUKS container permanently inaccessible.

       luksChangeKey <device> [<new key file>]

              Changes an existing passphrase. The passphrase to be changed
              must be supplied interactively or via --key-file.  The new
              passphrase can be supplied interactively or in a file given as
              positional argument.

              If a key-slot is specified (via --key-slot), the passphrase
              for that key-slot must be given and the new passphrase will
              overwrite the specified key-slot. If no key-slot is specified
              and there is still a free key-slot, then the new passphrase
              will be put into a free key-slot before the key-slot
              containing the old passphrase is purged. If there is no free
              key-slot, then the key-slot with the old passphrase is
              overwritten directly.

              WARNING: If a key-slot is overwritten, a media failure during
              this operation can cause the overwrite to fail after the old
              passphrase has been wiped and make the LUKS container
              inaccessible.

              <options> can be [--key-file, --keyfile-offset,
              --keyfile-size, --new-keyfile-offset, --new-keyfile-size,
              --key-slot, --force-password, --header].

       luksKillSlot <device> <key slot number>

              Wipe the key-slot number <key slot> from the LUKS device.
              Except running in batch-mode (-q) a remaining passphrase must
              be supplied, either interactively or via --key-file.  This
              command can remove the last remaining key-slot, but requires
              an interactive confirmation when doing so. Removing the last
              passphrase makes a LUKS container permanently inaccessible.

              <options> can be [--key-file, --keyfile-offset,
              --keyfile-size, --header].

              WARNING: If you read the passphrase from stdin (without
              further argument or with '-' as argument to --key-file),
              batch-mode (-q) will be implicitly switched on and no warning
              will be given when you remove the last remaining passphrase
              from a LUKS container. Removing the last passphrase makes the
              LUKS container permanently inaccessible.

              NOTE: If there is no passphrase provided (on stdin or through
              --key-file argument) and batch-mode (-q) is active, the key-
              slot is removed without any other warning.

       erase <device>
       luksErase <device>

              Erase all keyslots and make the LUKS container permanently
              inaccessible.  You do not need to provide any password for
              this operation.

              WARNING: This operation is irreversible.

       luksUUID <device>

              Print the UUID of a LUKS device.
              Set new UUID if --uuid option is specified.

       isLuks <device>

              Returns true, if <device> is a LUKS device, false otherwise.
              Use option -v to get human-readable feedback. 'Command
              successful.'  means the device is a LUKS device.

       luksDump <device>

              Dump the header information of a LUKS device.

              If the --dump-master-key option is used, the LUKS device
              master key is dumped instead of the keyslot info. Beware that
              the master key cannot be changed and can be used to decrypt
              the data stored in the LUKS container without a passphrase and
              even without the LUKS header. This means that if the master
              key is compromised, the whole device has to be erased to
              prevent further access. Use this option carefully.

              In order to dump the master key, a passphrase has to be
              supplied, either interactively or via --key-file.

              <options> can be [--dump-master-key, --key-file,
              --keyfile-offset, --keyfile-size, --header].

              WARNING: If --dump-master-key is used with --key-file and the
              argument to --key-file is '-', no validation question will be
              asked and no warning given.

       luksHeaderBackup <device> --header-backup-file <file>

              Stores a binary backup of the LUKS header and keyslot area.
              Note: Using '-' as filename writes the header backup to a file
              named '-'.

              WARNING: This backup file and a passphrase valid at the time
              of backup allows decryption of the LUKS data area, even if the
              passphrase was later changed or removed from the LUKS device.
              Also note that with a header backup you lose the ability to
              securely wipe the LUKS device by just overwriting the header
              and key-slots. You either need to securely erase all header
              backups in addition or overwrite the encrypted data area as
              well.  The second option is less secure, as some sectors can
              survive, e.g. due to defect management.

       luksHeaderRestore <device> --header-backup-file <file>

              Restores a binary backup of the LUKS header and keyslot area
              from the specified file.
              Note: Using '-' as filename reads the header backup from a
              file named '-'.

              WARNING: Header and keyslots will be replaced, only the
              passphrases from the backup will work afterwards.

              This command requires that the master key size and data offset
              of the LUKS header already on the device and of the header
              backup match. Alternatively, if there is no LUKS header on the
              device, the backup will also be written to it.

loop-AES EXTENSION         top

       cryptsetup supports mapping loop-AES encrypted partition using a
       compatibility mode.

       open --type loopaes <device> <name> --key-file <keyfile>
       loopaesOpen <device> <name> --key-file <keyfile>  (old syntax)

              Opens the loop-AES <device> and sets up a mapping <name>.

              If the key file is encrypted with GnuPG, then you have to use
              --key-file=- and decrypt it before use, e.g. like this:
              gpg --decrypt <keyfile> | cryptsetup loopaesOpen --key-file=-
              <device> <name>

              WARNING: The loop-AES extension cannot use direct input of key
              file on real terminal because the keys are separated by end-
              of-line and only part of the multi-key file would be read.
              If you need it in script, just use the pipe redirection:
              echo $keyfile | cryptsetup loopaesOpen --key-file=- <device>
              <name>

              Use --keyfile-size to specify the proper key length if needed.

              Use --offset to specify device offset. Note that the units
              need to be specified in number of 512 byte sectors.

              Use --skip to specify the IV offset. If the original device
              used an offset and but did not use it in IV sector
              calculations, you have to explicitly use --skip 0 in addition
              to the offset parameter.

              Use --hash to override the default hash function for
              passphrase hashing (otherwise it is detected according to key
              size).

              <options> can be [--key-file, --key-size, --offset, --skip,
              --hash, --readonly, --allow-discards].

       See also section 7 of the FAQ and http://loop-aes.sourceforge.net for
       more information regarding loop-AES.

TCRYPT (TrueCrypt-compatible and VeraCrypt) EXTENSION         top

       cryptsetup supports mapping of TrueCrypt, tcplay or VeraCrypt (with
       --veracrypt option) encrypted partition using a native Linux kernel
       API.  Header formatting and TCRYPT header change is not supported,
       cryptsetup never changes TCRYPT header on-device.

       TCRYPT extension requires kernel userspace crypto API to be available
       (introduced in Linux kernel 2.6.38).  If you are configuring kernel
       yourself, enable "User-space interface for symmetric key cipher
       algorithms" in "Cryptographic API" section (CRYPTO_USER_API_SKCIPHER
       .config option).

       Because TCRYPT header is encrypted, you have to always provide valid
       passphrase and keyfiles.

       Cryptsetup should recognize all header variants, except legacy cipher
       chains using LRW encryption mode with 64 bits encryption block
       (namely Blowfish in LRW mode is not recognized, this is limitation of
       kernel crypto API).

       To recognize a VeraCrypt device use the --veracrypt option.
       VeraCrypt is just extension of TrueCrypt header with increased
       iteration count so unlocking can take quite a lot of time (in
       comparison with TCRYPT device).

       To open a VeraCrypt device with a custom Personal Iteration
       Multiplier (PIM) value, additionally to --veracrypt  use either the
       --veracrypt-pim=<PIM> option to directly specify the PIM on the
       command- line or use --veracrypt-query-pim to be prompted for the
       PIM.

       The PIM value affects the number of iterations applied during key
       derivation. Please refer to
       https://veracrypt.codeplex.com/wikipage?title=Personal%20Iterations%20Multiplier%20(PIM) 
       for more detailed information.

       NOTE: Activation with tcryptOpen is supported only for cipher chains
       using LRW or XTS encryption modes.

       The tcryptDump command should work for all recognized TCRYPT devices
       and doesn't require superuser privilege.

       To map system device (device with boot loader where the whole
       encrypted system resides) use --tcrypt-system option.  You can use
       partition device as the parameter (parameter must be real partition
       device, not image in file), then only this partition is mapped.

       If you have whole TCRYPT device as a file image and you want to map
       multiple partition encrypted with system encryption, please create
       loopback mapping with partitions first (losetup -P, see losetup(8)
       man page for more info), and use loop partition as the device
       parameter.

       If you use whole base device as parameter, one device for the whole
       system encryption is mapped. This mode is available only for backward
       compatibility with older cryptsetup versions which mapped TCRYPT
       system encryption using whole device.

       To use hidden header (and map hidden device, if available), use
       --tcrypt-hidden option.

       To explicitly use backup (secondary) header, use --tcrypt-backup
       option.

       NOTE: There is no protection for a hidden volume if the outer volume
       is mounted. The reason is that if there were any protection, it would
       require some metadata describing what to protect in the outer volume
       and the hidden volume would become detectable.

       open --type tcrypt <device> <name>
       tcryptOpen <device> <name>  (old syntax)

              Opens the TCRYPT (a TrueCrypt-compatible) <device> and sets up
              a mapping <name>.

              <options> can be [--key-file, --tcrypt-hidden,
              --tcrypt-system, --tcrypt-backup, --readonly,
              --test-passphrase, --allow-discards].

              The keyfile parameter allows combination of file content with
              the passphrase and can be repeated. Note that using keyfiles
              is compatible with TCRYPT and is different from LUKS keyfile
              logic.

              WARNING: Option --allow-discards cannot be combined with
              option --tcrypt-hidden. For normal mapping it can cause
              destruction of hidden volume (hidden volume appears as unused
              space for outer volume so this space can be discarded).

       tcryptDump <device>

              Dump the header information of a TCRYPT device.

              If the --dump-master-key option is used, the TCRYPT device
              master key is dumped instead of TCRYPT header info. Beware
              that the master key (or concatenated master keys if cipher
              chain is used) can be used to decrypt the data stored in the
              TCRYPT container without a passphrase.  This means that if the
              master key is compromised, the whole device has to be erased
              to prevent further access. Use this option carefully.

              <options> can be [--dump-master-key, --key-file,
              --tcrypt-hidden, --tcrypt-system, --tcrypt-backup].

              The keyfile parameter allows combination of file content with
              the passphrase and can be repeated.

       See also https://en.wikipedia.org/wiki/TrueCrypt for more information
       regarding TrueCrypt.

       Please note that cryptsetup does not use TrueCrypt code, please
       report all problems related to this compatibility extension to
       cryptsetup project.

MISCELLANEOUS         top

       repair <device>

              Tries to repair the device metadata if possible. Currently
              supported only for LUKS device type.

              This command is useful to fix some known benign LUKS metadata
              header corruptions. Only basic corruptions of unused keyslot
              are fixable. This command will only change the LUKS header,
              not any key-slot data.

              WARNING: Always create a binary backup of the original header
              before calling this command.

       benchmark <options>

              Benchmarks ciphers and KDF (key derivation function).  Without
              parameters it tries to measure few common configurations.

              To benchmark other ciphers or modes, you need to specify
              --cipher and --key-size options or --hash for KDF test.

              NOTE: This benchmark is using memory only and is only
              informative.  You cannot directly predict real storage
              encryption speed from it.

              For testing block ciphers, this benchmark requires kernel
              userspace crypto API to be available (introduced in Linux
              kernel 2.6.38).  If you are configuring kernel yourself,
              enable "User-space interface for symmetric key cipher
              algorithms" in "Cryptographic API" section
              (CRYPTO_USER_API_SKCIPHER .config option).

              <options> can be [--cipher, --key-size, --hash].

OPTIONS         top

       --verbose, -v
              Print more information on command execution.

       --debug
              Run in debug mode with full diagnostic logs. Debug output
              lines are always prefixed by '#'.

       --hash, -h <hash-spec>
              Specifies the passphrase hash for open (for plain and loopaes
              device types).

              Specifies the hash used in the LUKS key setup scheme and
              volume key digest for luksFormat. The specified hash is used
              as hash-parameter for PBKDF2 and for the AF splitter.

              The specified hash name is passed to the compiled-in crypto
              backend.  Different backends may support different hashes.
              For luksFormat, the hash algorithm must provide at least 160
              bits of output, which excludes, e.g., MD5. Do not use a non-
              crypto hash like "crc32" as this breaks security.

              Values compatible with old version of cryptsetup are
              "ripemd160" for open --type plain and "sha1" for luksFormat.

              Use cryptsetup --help to show the defaults.

       --cipher, -c <cipher-spec>
              Set the cipher specification string.

              cryptsetup --help shows the compiled-in defaults.  The current
              default in the distributed sources is "aes-cbc-essiv:sha256"
              for plain dm-crypt and "aes-xts-plain64" for LUKS.

              If a hash is part of the cipher specification, then it is used
              as part of the IV generation. For example, ESSIV needs a hash
              function, while "plain64" does not and hence none is
              specified.

              For XTS mode you can optionally set a key size of 512 bits
              with the -s option. Key size for XTS mode is twice that for
              other modes for the same security level.

              XTS mode requires kernel 2.6.24 or later and plain64 requires
              kernel 2.6.33 or later. More information can be found in the
              FAQ.

       --verify-passphrase, -y
              When interactively asking for a passphrase, ask for it twice
              and complain if both inputs do not match. Advised when
              creating a regular mapping for the first time, or when running
              luksFormat. Ignored on input from file or stdin.

       --key-file, -d name
              Read the passphrase from file.

              If the name given is "-", then the passphrase will be read
              from stdin.  In this case, reading will not stop at newline
              characters.

              With LUKS, passphrases supplied via --key-file are always the
              existing passphrases requested by a command, except in the
              case of luksFormat where --key-file is equivalent to the
              positional key file argument.

              If you want to set a new passphrase via key file, you have to
              use a positional argument to luksAddKey.

              See section NOTES ON PASSPHRASE PROCESSING for more
              information.

       --keyfile-offset value
              Skip value bytes at the beginning of the key file.  Works with
              all commands that accepts key files.

       --keyfile-size, -l value
              Read a maximum of value bytes from the key file.  Default is
              to read the whole file up to the compiled-in maximum that can
              be queried with --help. Supplying more data than the compiled-
              in maximum aborts the operation.

              This option is useful to cut trailing newlines, for example.
              If --keyfile-offset is also given, the size count starts after
              the offset.  Works with all commands that accepts key files.

       --new-keyfile-offset value
              Skip value bytes at the start when adding a new passphrase
              from key file with luksAddKey.

       --new-keyfile-size  value
              Read a maximum of value bytes when adding a new passphrase
              from key file with luksAddKey.  Default is to read the whole
              file up to the compiled-in maximum length that can be queried
              with --help.  Supplying more than the compiled in maximum
              aborts the operation.  When --new-keyfile-offset is also
              given, reading starts after the offset.

       --master-key-file
              Use a master key stored in a file.

              For luksFormat this allows creating a LUKS header with this
              specific master key. If the master key was taken from an
              existing LUKS header and all other parameters are the same,
              then the new header decrypts the data encrypted with the
              header the master key was taken from.

              WARNING: If you create your own master key, you need to make
              sure to do it right. Otherwise you can end up with a low-
              entropy or otherwise partially predictable master key which
              will compromise security.

              For luksAddKey this allows adding a new passphrase without
              having to know an exiting one.

              For open this allows one to open the LUKS device without
              giving a passphrase.

       --dump-master-key
              For luksDump this option includes the master key in the
              displayed information. Use with care, as the master key can be
              used to bypass the passphrases, see also option
              --master-key-file.

       --use-random

       --use-urandom
              For luksFormat these options define which kernel random number
              generator will be used to create the master key (which is a
              long-term key).

              See NOTES ON RANDOM NUMBER GENERATORS for more information.
              Use cryptsetup --help to show the compiled-in default random
              number generator.

              WARNING: In a low-entropy situation (e.g. in an embedded
              system), both selections are problematic.  Using /dev/urandom
              can lead to weak keys.  Using /dev/random can block a long
              time, potentially forever, if not enough entropy can be
              harvested by the kernel.

       --key-slot, -S <0-7>
              For LUKS operations that add key material, this options allows
              you to specify which key slot is selected for the new key.
              This option can be used for luksFormat, and luksAddKey.
              In addition, for open, this option selects a specific key-slot
              to compare the passphrase against.  If the given passphrase
              would only match a different key-slot, the operation fails.

       --key-size, -s <bits>
              Sets key size in bits. The argument has to be a multiple of 8.
              The possible key-sizes are limited by the cipher and mode
              used.

              See /proc/crypto for more information. Note that key-size in
              /proc/crypto is stated in bytes.

              This option can be used for open --type plain or luksFormat.
              All other LUKS actions will use the key-size specified in the
              LUKS header.  Use cryptsetup --help to show the compiled-in
              defaults.

       --size, -b <number of 512 byte sectors>
              Set the size of the device in sectors of 512 bytes.  This
              option is only relevant for the open and resize actions.

       --offset, -o <number of 512 byte sectors>
              Start offset in the backend device in 512-byte sectors.  This
              option is only relevant for the open action with plain or
              loopaes device types.

       --skip, -p <number of 512 byte sectors>
              Start offset used in IV calculation in 512-byte sectors (how
              many sectors of the encrypted data to skip at the beginning).
              This option is only relevant for the open action with plain or
              loopaes device types.

              Hence, if --offset n, and --skip s, sector n (the first sector
              of encrypted device) will get a sector number of s for the IV
              calculation.

       --readonly, -r
              set up a read-only mapping.

       --shared
              Creates an additional mapping for one common ciphertext
              device. Arbitrary mappings are supported.  This option is only
              relevant for the open --type plain action. Use --offset,
              --size and --skip to specify the mapped area.

       --iter-time, -i <number of milliseconds>
              The number of milliseconds to spend with PBKDF2 passphrase
              processing.  This option is only relevant for LUKS operations
              that set or change passphrases, such as luksFormat or
              luksAddKey.  Specifying 0 as parameter selects the compiled-in
              default.

       --batch-mode, -q
              Suppresses all confirmation questions. Use with care!

              If the -y option is not specified, this option also switches
              off the passphrase verification for luksFormat.

       --timeout, -t <number of seconds>
              The number of seconds to wait before timeout on passphrase
              input via terminal. It is relevant every time a passphrase is
              asked, for example for open, luksFormat or luksAddKey.  It has
              no effect if used in conjunction with --key-file.
              This option is useful when the system should not stall if the
              user does not input a passphrase, e.g. during boot. The
              default is a value of 0 seconds, which means to wait forever.

       --tries, -T
              How often the input of the passphrase shall be retried.  This
              option is relevant every time a passphrase is asked, for
              example for open, luksFormat or luksAddKey.  The default is 3
              tries.

       --align-payload <number of 512 byte sectors>
              Align payload at a boundary of value 512-byte sectors.  This
              option is relevant for luksFormat.

              If not specified, cryptsetup tries to use the topology info
              provided by kernel for the underlying device to get optimal
              alignment.  If not available (or the calculated value is a
              multiple of the default) data is by default aligned to a 1MiB
              boundary (i.e. 2048 512-byte sectors).

              For a detached LUKS header this option specifies the offset on
              the data device. See also the --header option.

       --uuid=UUID
              Use the provided UUID for the luksFormat command instead of
              generating new one. Changes the existing UUID when used with
              the luksUUID command.

              The UUID must be provided in the standard UUID format, e.g.
              12345678-1234-1234-1234-123456789abc.

       --allow-discards
              Allow the use of discard (TRIM) requests for device.  This
              option is only relevant for open action.

              WARNING: This command can have a negative security impact
              because it can make filesystem-level operations visible on the
              physical device. For example, information leaking filesystem
              type, used space, etc. may be extractable from the physical
              device if the discarded blocks can be located later. If in
              doubt, do not use it.

              A kernel version of 3.1 or later is needed. For earlier
              kernels this option is ignored.

       --perf-same_cpu_crypt
              Perform encryption using the same cpu that IO was submitted
              on.  The default is to use an unbound workqueue so that
              encryption work is automatically balanced between available
              CPUs.  This option is only relevant for open action.

              NOTE: This option is available only for low-level dm-crypt
              performance tuning, use only if you need a change to default
              dm-crypt behaviour. Needs kernel 4.0 or later.

       --perf-submit_from_crypt_cpus
              Disable offloading writes to a separate thread after
              encryption.  There are some situations where offloading write
              bios from the encryption threads to a single thread degrades
              performance significantly.  The default is to offload write
              bios to the same thread.  This option is only relevant for
              open action.

              NOTE: This option is available only for low-level dm-crypt
              performance tuning, use only if you need a change to default
              dm-crypt behaviour. Needs kernel 4.0 or later.

       --test-passphrase
              Do not activate device, just verify passphrase.  This option
              is only relevant for open action (the device mapping name is
              not mandatory if this option is used).

       --header <device or file storing the LUKS header>
              Use a detached (separated) metadata device or file where the
              LUKS header is stored. This options allows one to store
              ciphertext and LUKS header on different devices.

              This option is only relevant for LUKS devices and can be used
              with the luksFormat, open, luksSuspend, luksResume, status and
              resize commands.

              For luksFormat with a file name as argument to --header, it
              has to exist and be large enough to contain the LUKS header.
              See the cryptsetup FAQ for header size calculation.

              For other commands that change the LUKS header (e.g.
              luksAddKey), specify the device or file with the LUKS header
              directly as the LUKS device.

              If used with luksFormat, the --align-payload option is taken
              as absolute sector alignment on ciphertext device and can be
              zero.

              WARNING: There is no check whether the ciphertext device
              specified actually belongs to the header given. In fact you
              can specify an arbitrary device as the ciphertext device for
              open with the --header option. Use with care.

       --force-password
              Do not use password quality checking for new LUKS passwords.

              This option applies only to luksFormat, luksAddKey and
              luksChangeKey and is ignored if cryptsetup is built without
              password quality checking support.

              For more info about password quality check, see manual page
              for pwquality.conf(5) and passwdqc.conf(5).

       --deferred
              Defers device removal in close command until the last user
              closes it.

       --version
              Show the program version.

       --usage
              Show short option help.

       --help, -?
              Show help text and default parameters.

RETURN CODES         top

       Cryptsetup returns 0 on success and a non-zero value on error.

       Error codes are: 1 wrong parameters, 2 no permission (bad
       passphrase), 3 out of memory, 4 wrong device specified, 5 device
       already exists or device is busy.

NOTES ON PASSPHRASE PROCESSING FOR PLAIN MODE         top

       Note that no iterated hashing or salting is done in plain mode.  If
       hashing is done, it is a single direct hash. This means that low-
       entropy passphrases are easy to attack in plain mode.

       From a terminal: The passphrase is read until the first newline, i.e.
       '\n'.  The input without the newline character is processed with the
       default hash or the hash specified with --hash.  The hash result will
       be truncated to the key size of the used cipher, or the size
       specified with -s.

       From stdin: Reading will continue until a newline (or until the
       maximum input size is reached), with the trailing newline stripped.
       The maximum input size is defined by the same compiled-in default as
       for the maximum key file size and can be overwritten using --keyfile-
       size option.

       The data read will be hashed with the default hash or the hash
       specified with --hash.  The hash result will be truncated to the key
       size of the used cipher, or the size specified with -s.

       Note that if --key-file=- is used for reading the key from stdin,
       trailing newlines are not stripped from the input.

       If "plain" is used as argument to --hash, the input data will not be
       hashed. Instead, it will be zero padded (if shorter than the key
       size) or truncated (if longer than the key size) and used directly as
       the binary key. This is useful for directly specifying a binary key.
       No warning will be given if the amount of data read from stdin is
       less than the key size.

       From a key file: It will be truncated to the key size of the used
       cipher or the size given by -s and directly used as binary key.

       WARNING: The --hash argument is being ignored.  The --hash option is
       usable only for stdin input in plain mode.

       If the key file is shorter than the key, cryptsetup will quit with an
       error.  The maximum input size is defined by the same compiled-in
       default as for the maximum key file size and can be overwritten using
       --keyfile-size option.

NOTES ON PASSPHRASE PROCESSING FOR LUKS         top

       LUKS uses PBKDF2 to protect against dictionary attacks and to give
       some protection to low-entropy passphrases (see RFC 2898 and the
       cryptsetup FAQ).

       From a terminal: The passphrase is read until the first newline and
       then processed by PBKDF2 without the newline character.

       From stdin: LUKS will read passphrases from stdin up to the first
       newline character or the compiled-in maximum key file length. If
       --keyfile-size is given, it is ignored.

       From key file: The complete keyfile is read up to the compiled-in
       maximum size. Newline characters do not terminate the input. The
       --keyfile-size option can be used to limit what is read.

       Passphrase processing: Whenever a passphrase is added to a LUKS
       header (luksAddKey, luksFormat), the user may specify how much the
       time the passphrase processing should consume. The time is used to
       determine the iteration count for PBKDF2 and higher times will offer
       better protection for low-entropy passphrases, but open will take
       longer to complete. For passphrases that have entropy higher than the
       used key length, higher iteration times will not increase security.

       The default setting of one second is sufficient for most practical
       cases. The only exception is a low-entropy passphrase used on a
       device with a slow CPU, as this will result in a low iteration count.
       On a slow device it may be advisable to increase the iteration time
       using the --iter-time option in order to obtain a higher iteration
       count. This does slow down all later luksOpen operations accordingly.

INCOHERENT BEHAVIOR FOR INVALID PASSPHRASES/KEYS         top

       LUKS checks for a valid passphrase when an encrypted partition is
       unlocked. The behavior of plain dm-crypt is different.  It will
       always decrypt with the passphrase given. If the given passphrase is
       wrong, the device mapped by plain dm-crypt will essentially still
       contain encrypted data and will be unreadable.

NOTES ON SUPPORTED CIPHERS, MODES, HASHES AND KEY SIZES         top

       The available combinations of ciphers, modes, hashes and key sizes
       depend on kernel support. See /proc/crypto for a list of available
       options. You might need to load additional kernel crypto modules in
       order to get more options.

       For the --hash option, if the crypto backend is libgcrypt, then all
       algorithms supported by the gcrypt library are available.  For other
       crypto backends some algorithms may be missing.

NOTES ON PASSPHRASES         top

       Mathematics can't be bribed. Make sure you keep your passphrases
       safe.  There are a few nice tricks for constructing a fallback, when
       suddenly out of the blue, your brain refuses to cooperate.  These
       fallbacks need LUKS, as it's only possible with LUKS to have multiple
       passphrases. Still, if your attacker model does not prevent it,
       storing your passphrase in a sealed envelope somewhere may be a good
       idea as well.

NOTES ON RANDOM NUMBER GENERATORS         top

       Random Number Generators (RNG) used in cryptsetup are always the
       kernel RNGs without any modifications or additions to data stream
       produced.

       There are two types of randomness cryptsetup/LUKS needs. One type
       (which always uses /dev/urandom) is used for salts, the AF splitter
       and for wiping deleted keyslots.

       The second type is used for the 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 a system without
       enough entropy sources can cause luksFormat to block until the
       requested amount of random data is gathered. In a low-entropy
       situation (embedded system), this can take a very long time and
       potentially forever. At the same time, using /dev/urandom in a low-
       entropy situation will produce low-quality keys. This is a serious
       problem, but solving it is out of scope for a mere man-page.  See
       urandom(4) for more information.

NOTES ON LOOPBACK DEVICE USE         top

       Cryptsetup is usually used directly on a block device (disk partition
       or LVM volume). However, if the device argument is a file, cryptsetup
       tries to allocate a loopback device and map it into this file. This
       mode requires Linux kernel 2.6.25 or more recent which supports the
       loop autoclear flag (loop device is cleared on last close
       automatically). Of course, you can always map a file to a loop-device
       manually. See the cryptsetup FAQ for an example.

       When device mapping is active, you can see the loop backing file in
       the status command output. Also see losetup(8).

DEPRECATED ACTIONS         top

       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.

REPORTING BUGS         top

       Report bugs, including ones in the documentation, on the cryptsetup
       mailing list at <dm-crypt@saout.de> or in the 'Issues' section on
       LUKS website.  Please attach the output of the failed command with
       the --debug option added.

AUTHORS         top

       cryptsetup originally written by Jana Saout <jana@saout.de>
       The LUKS extensions and original man page were written by Clemens
       Fruhwirth <clemens@endorphin.org>.
       Man page extensions by Milan Broz <gmazyland@gmail.com>.
       Man page rewrite and extension by Arno Wagner <arno@wagner.name>.

COPYRIGHT         top

       Copyright © 2004 Jana Saout
       Copyright © 2004-2006 Clemens Fruhwirth
       Copyright © 2009-2017 Red Hat, Inc.
       Copyright © 2009-2017 Milan Broz
       Copyright © 2012-2014 Arno Wagner

       This is free software; see the source for copying conditions.  There
       is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
       PARTICULAR PURPOSE.

SEE ALSO         top

       The LUKS website at https://gitlab.com/cryptsetup/cryptsetup/ 

       The cryptsetup FAQ, contained in the distribution package and online
       at
       https://gitlab.com/cryptsetup/cryptsetup/wikis/FrequentlyAskedQuestions 

       The cryptsetup mailing list and list archive, see FAQ entry 1.6.

       The LUKS on-disk format specification available at
       https://gitlab.com/cryptsetup/cryptsetup/wikis/Specification 

COLOPHON         top

       This page is part of the Cryptsetup ((open-source disk encryption))
       project.  Information about the project can be found at 
       ⟨https://gitlab.com/cryptsetup/cryptsetup⟩.  If you have a bug report
       for this manual page, send it to dm-crypt@saout.de.  This page was
       obtained from the project's upstream Git repository 
       ⟨https://gitlab.com/cryptsetup/cryptsetup.git⟩ on 2017-07-05.  If you
       discover any rendering problems in this HTML version of the page, or
       you believe there is a better or more up-to-date source for the page,
       or you have corrections or improvements to the information in this
       COLOPHON (which is not part of the original manual page), send a mail
       to man-pages@man7.org

cryptsetup                       March 2017                    CRYPTSETUP(8)

Pages that refer to this page: cryptsetup-reencrypt(8)systemd-gpt-auto-generator(8)