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CRYPTSETUP(8)                          Maintenance Commands                         CRYPTSETUP(8)

NAME
       cryptsetup - manage plain dm-crypt and LUKS encrypted volumes

SYNOPSIS
       cryptsetup   

DESCRIPTION
       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  meta‐
       data  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 TruerCrypt compatible volumes.

PLAIN DM-CRYPT OR LUKS?
       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
       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
       The following are valid actions for all supported device types.

       open   --type 

              Opens (creates a mapping with)  backed by device .

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

              For backward compatibility there are open command aliases:

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

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

       close 

              Removes the existing mapping  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 

              Reports the status for the mapping .

       resize 

              Resizes an active mapping .

              If --size (in sectors) is not specified, the size of the underlying block device 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
       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 opera‐
       tion.  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/.

       The following are valid plain device type actions:

       open --type plain  
       create   (OBSOLETE syntax)

              Opens (creates a mapping with)  backed by device .

               can be [--hash, --cipher, --verify-passphrase, --key-file, --keyfile-off‐
              set, --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
       LUKS, the Linux Unified Key Setup, is a standard for disk encryption.  It adds a standard‐
       ized 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 following are valid LUKS actions:

       luksFormat  []

              Initializes a LUKS partition and sets the  initial  passphrase  (for  key-slot  0),
              either  via  prompting  or  via  .  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.

                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  
       luksOpen   (old syntax)

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

              The    parameter  can  be  also  specified  by  LUKS  UUID  in  the  format
              UUID=, which uses the symlinks in /dev/disk/by-uuid.

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

       luksSuspend 

              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.

               can be [--header].

       luksResume 

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

               can be [--key-file, --keyfile-size, --header]

       luksAddKey  []

              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.

                can be [--key-file, --keyfile-offset, --keyfile-size, --new-keyfile-off‐
              set, --new-keyfile-size, --key-slot, --master-key-file, --iter-time,  --force-pass‐
              word].

       luksRemoveKey  []

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

               can be [--key-file, --keyfile-offset, --keyfile-size]

              WARNING: If you read the passphrase from stdin (without further  argument  or  with
              '-' as argument to --key-file), batch-mode (-q) will be implicitely 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 inac‐
              cessible.

       luksChangeKey  []

              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.

                can be [--key-file, --keyfile-offset, --keyfile-size, --new-keyfile-off‐
              set, --new-keyfile-size, --key-slot, --force-password].

       luksKillSlot  

              Wipe the key-slot number  from the LUKS device.  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.

               can be [--key-file, --keyfile-offset, --keyfile-size].

              WARNING:  If  you  read the passphrase from stdin (without further argument or with
              '-' as argument to --key-file), batch-mode (-q) will be implicitely 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  inac‐
              cessible.

       erase 
       luksErase 

              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 

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

       isLuks 

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

       luksDump 

              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 interac‐
              tively or via --key-file.

               can be [--dump-master-key, --key-file, --keyfile-offset, --keyfile-size].

              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  --header-backup-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 over‐
              write the encrypted data area as well.  The second option is less secure,  as  some
              sectors can survive, e.g. due to defect management.

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

       open --type loopaes   --key-file 
       loopaesOpen   --key-file   (old syntax)

              Opens the loop-AES  and sets up a mapping .

              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  | cryptsetup loopaesOpen --key-file=-  

              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).

               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) EXTENSION
       cryptsetup supports mapping of TrueCrypt or tcplay  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 key‐
       files.

       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 recog‐
       nized, this is limitation of kernel crypto API).

       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  ver‐
       sions 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 rea‐
       son 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  
       tcryptOpen    (old syntax)

              Opens the TCRYPT (a TrueCrypt-compatible)  and sets up a mapping .

                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 differ‐
              ent 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 

              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  care‐
              fully.

                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 http://www.truecrypt.org 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
       repair 

              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 

              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).

               can be [--cipher, --key-size, --hash].

OPTIONS
       --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 
              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 
              Set the cipher specification string.

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

              If  a  hash  is part of the cipher spefification, 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 equiv‐
              alent 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  luk‐
              sAddKey.

       --new-keyfile-size  value
              Read  a maximum of value bytes when adding a new passphrase from key file with luk‐
              sAddKey.  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 mas‐
              ter 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 mas‐
              ter key which will compromise security.

              For luksAddKey this allows adding a new passphrase without having to know an  exit‐
              ing 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 
              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 
              Force the size of the underlying device in sectors of 512 bytes.   This  option  is
              only relevant for the open and resize actions.

       --offset, -o 
              Start  offset in the backend device in 512-byte sectors.  This option is only rele‐
              vant for the open action with plain or loopaes device types.

       --skip, -p 
              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 
              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  luks‐
              Format 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 
              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 
              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  calcu‐
              lated  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, informa‐
              tion 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 no use it.

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

       --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 
              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).

       --version
              Show the program version.

       --usage
              Show short option help.

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

RETURN CODES
       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
       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
       has 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.  if the key file is shorter than the key, crypt‐
       setup will quit with an error.

NOTES ON PASSPHRASE PROCESSING FOR LUKS
       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, luks‐
       Format), 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  excep‐
       tion  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
       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 con‐
       tain encrypted data and will be unreadable.

NOTES ON SUPPORTED CIPHERS, MODES, HASHES AND KEY SIZES
       The  available  combinations of ciphers, modes, hashes and key sizes depend on kernel sup‐
       port. 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
       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
       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 sys‐
       tem),  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
       Cryptsetup is usually used directly on a block device (disk partition or LVM volume). How‐
       ever, 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  sup‐
       ports  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
       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,  including ones in the documentation, on the cryptsetup mailing list at  or in the 'Issues' section on LUKS website.  Please attach the  output  of
       the failed command with the --debug option added.

AUTHORS
       cryptsetup originally written by Jana Saout 
       The   LUKS   extensions   and   original  man  page  were  written  by  Clemens  Fruhwirth
       .
       Man page extensions by Milan Broz .
       Man page rewrite and extension by Arno Wagner .

COPYRIGHT
       Copyright © 2004 Jana Saout
       Copyright © 2004-2006 Clemens Fruhwirth
       Copyright © 2009-2012 Red Hat, Inc.
       Copyright © 2009-2014 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
       The LUKS website at http://code.google.com/p/cryptsetup/

       The   cryptsetup   FAQ,   contained   in   the   distribution   package   and   online  at
       http://code.google.com/p/cryptsetup/wiki/FrequentlyAskedQuestions

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

       The  LUKS  on-disk  format  specification  available  at   http://code.google.com/p/crypt‐
       setup/wiki/Specification

cryptsetup                                December 2013                             CRYPTSETUP(8)

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