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CRYPTSETUP(8)                Maintenance Commands                CRYPTSETUP(8)



NAME
       cryptsetup - setup cryptographic volumes for dm-crypt (including LUKS extension)

SYNOPSIS
       cryptsetup <options> <action> <action args>

DESCRIPTION
       cryptsetup  is  used to conveniently setup dm-crypt managed device-mapper mappings.  For basic (plain) dm-crypt
       mappings, there are four operations.

ACTIONS
       These strings are valid for <action>, followed by their <action args>:

       create <name> <device>

              creates a mapping with <name> backed by device <device>.

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

       remove <name>

              removes an existing mapping <name>.

       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 of the underlying block device is used.


LUKS EXTENSION
       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>]

              initializes a LUKS partition and sets the initial key, either via prompting or via <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>

              opens the LUKS partition <device> and sets up a mapping <name> after successful verification of the sup-
              plied key material (either via key file by --key-file, or via prompting).

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

       luksClose <name>

              identical to remove.

       luksSuspend <name>

              suspends  active device (all IO operations are frozen) and wipes encryption key from kernel. Kernel ver-
              sion 2.6.19 or later is required.

              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>

              Resumes  suspended  device  and reinstates encryption key. You will need provide passphrase identical to
              luksOpen command (using prompting or key file).

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

       luksAddKey <device> [<new key file>]

              add a new key file/passphrase. An existing passphrase or key file (via  --key-file)  must  be  supplied.
              The key file with the new material is supplied as a positional argument.

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

       luksRemoveKey <device> [<key file>]

              remove supplied key or key file from LUKS device

       luksKillSlot <device> <key slot number>

              wipe  key  with  number <key slot> from LUKS device. A remaining passphrase or key file (via --key-file)
              must be supplied.

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

       luksUUID <device>

              print UUID, if <device> has a LUKS header.

              set new UUID if --uuid option is specified.

       isLuks <device>

              returns true, if <device> is a LUKS partition. Otherwise, false.

       luksDump <device>

              dumps the header information of a LUKS partition.

              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>

              Stores binary backup of LUKS header and keyslot areas.

              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


OPTIONS
       --verbose, -v
              Print more verbose messages.

       --debug
              Run in debug mode with full diagnostic logs.

       --hash, -h
              For create action specifies hash to use for password hashing.

              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.

       --cipher, -c
              set cipher specification string.

              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 specifica-
              tion and set key size to 256 (or 512) bits (see -s option).

       --verify-passphrase, -y
              query for passwords twice. Useful when creating a (regular) mapping for the first time, or when  running
              luksFormat.

       --key-file, -d
              use file as key material.

              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.

       --keyfile-size, -d value
              Limits read from keyfile to value bytes.  Usable together with all comands using key file.

       --new-keyfile-size  value
              Limits read from new keyfile to value bytes in luksAddKey when adding new key file.  Default is  exhaus-
              tive read from key file.

       --master-key-file
              Use  pre-generated master key stored in file. For luksFormat it allows LUKS header reformatting with the
              same master key (if all other parameters are the same existing encrypted data remains intact).

              For luksAddKey it allows adding new passphrase with only master key knowledge.

       --dump-master-key
              For luksDump it allows LUKS header dump including volume (master) key.  Use with care (this  information
              allows access to device without passphrase knowledge).

              See luksDump for more info.

       --use-random

       --use-urandom
              For  luksFormat  it  defines which kernel random number generator will be used for long-term key (volume
              key).

              See NOTES ON RNG for more information. Use cryptsetup --help to show default RNG.

       --key-slot, -S
              For LUKS operations that add key material, this options allows to you specify which key slot is selected
              for the new key. This option can be used for luksFormat and luksAddKey.

       --key-size, -s
              set key size in bits.

              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.

       --size, -b
              force  the size of the underlying device in sectors.  This option is only relevant for create and resize
              action.

       --offset, -o
              start offset in the backend device (in 512-byte sectors).  This  option  is  only  relevant  for  create
              action.

       --skip, -p
              how  many  sectors  of  the encrypted data to skip at the beginning. This is different from the --offset
              options with respect to IV calculations. Using --offset will shift the IV calculation by the same  nega-
              tive  amount.  Hence,  if  --offset n, sector n will be the first sector on the mapping with IV 0. Using
              --skip would have resulted in sector n being the first sector also, but with IV n.  This option is  only
              relevant for create action.

       --readonly
              set up a read-only mapping.

       --iter-time, -i
              The number of milliseconds to spend with PBKDF2 password processing. This option is only relevant to the
              LUKS operations as luksFormat or luksAddKey.

       --batch-mode, -q
              Do not ask for confirmation. Use with care! This option is only  relevant  for  luksFormat,  luksAddKey,
              luksRemoveKey or luksKillSlot.

       --timeout, -t
              The  number  of  seconds to wait before timeout. This option is relevant every time a password is asked,
              like create, luksOpen, luksFormat or luksAddKey. It has no effect if used  in  conjunction  with  --key-
              file.

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

       --align-payload=value
              Align payload at a boundary of value 512-byte sectors. This option is relevant for luksFormat.   If  not
              specified, cryptsetup tries to use topology info provided by kernel for underlying device to get optimal
              alignment.  If not available (or calculated value is multiple of default) data is by default aligned  to
              1 MiB boundary (2048 512-byte sectors).

       --uuid=UUID
              Use  provided UUID in luksFormat command instead of generating new one or change existing UUID in luksU-
              UID command.

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

       --version
              Show the version.


NOTES ON PASSWORD PROCESSING
       From a terminal: Password processing is new-line sensitive, meaning the reading will  stop  after  encountering
       \n.  It  will  process  the  read material (without newline) with the default hash or the hash given by --hash.
       After hashing, it will be cropped to the key size given by -s.

       From stdin: Reading will continue until EOF (so using e.g. /dev/random as stdin will not work), with the trail-
       ing 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.

NOTES ON PASSWORD PROCESSING FOR LUKS
       LUKS uses PBKDF2 to protect against dictionary attacks (see RFC 2898).

       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  pass-
       word  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.

INCOHERENT BEHAVIOUR FOR INVALID PASSWORDS/KEYS
       LUKS checks for a valid password or key when an encrypted partition is unlocked. Thus the luksOpen action fails
       with invalid password or key, contrary to the plain dm-crypt create action.

       Please also be sure that you are using the same keyboard and language setting as during device format.

NOTES ON SUPPORTED CIPHERS, MODES, HASHES AND KEY SIZES
       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 --hash option all algorithms supported by gcrypt library are available.

NOTES ON PASSWORDS
       Mathematics can't be bribed. Make sure you keep your passwords safe. There are a few nice tricks for construct-
       ing a fallback, when suddenly out of (or after being) blue, your brain refuses to  cooperate.  These  fallbacks
       are possible with LUKS, as it's only possible with LUKS to have multiple passwords.

NOTES ON RNG
       Random  Number Generator (RNG) used in cryptsetup always uses kernel RNG without any modifications or additions
       to data stream procudes by kernel (like internal random  pool  operations  or  mixing  with  the  other  random
       sources).

       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.

AUTHORS
       cryptsetup is written by Christophe Saout <christopheATsaout.de>
       LUKS extensions, and man page by Clemens Fruhwirth <clemensATendorphin.org>

DEPRECATED ACTIONS
       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
       Report bugs to <dm-cryptATsaout.de> or Issues section on LUKS website.  Please attach output of  failed  command
       with added --debug option.

COPYRIGHT
       Copyright (C) 2004 Christophe Saout
       Copyright (C) 2004-2006 Clemens Fruhwirth
       Copyright (C) 2009-2010 Red Hat, Inc.

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

SEE ALSO
       LUKS website, http://code.google.com/p/cryptsetup/



cryptsetup                                                       CRYPTSETUP(8)