Provided by: cryptsetup-bin_1.6.6-5ubuntu2_amd64 bug


       cryptsetup-reencrypt - tool for offline LUKS device re-encryption


       cryptsetup-reencrypt <options> <device>


       Cryptsetup-reencrypt can be used to change reencryption parameters which otherwise require
       full on-disk data change (re-encryption).

       You can regenerate volume key (the real  key  used  in  on-disk  encryption  unclocked  by
       passphrase), cipher, cipher mode.

       Cryptsetup-reencrypt  reencrypts data on LUKS device in-place. During reencryption process
       the LUKS device is marked unavailable.

       WARNING: The cryptsetup-reencrypt program is not resistant to hardware or kernel  failures
       during reencryption (you can lose you data in this case).


       The  reencryption can be temporarily suspended (by TERM signal or by using ctrl+c) but you
       need  to  retain  temporary  files  named  LUKS-<uuid>.[log|org|new].   LUKS   device   is
       unavailable until reencryption is finished though.

       Current working directory must by writable and temporary files created during reencryption
       must be present.

       For more info about LUKS see cryptsetup(8).


       To start (or continue) re-encryption for <device> use:

       cryptsetup-reencrypt <device>

       <options> can be [--block-size,  --cipher,  --hash,  --iter-time,  --use-random  |  --use-
       urandom,   --key-file,   --key-slot,  --keyfile-offset,  --keyfile-size,  --tries,  --use-
       directio, --use-fsync, --write-log]

       For detailed description of encryption and key file options see cryptsetup(8) man page.

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

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

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

       --key-size, -s <bits>
              Set 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.

              If  you  are increasing key size, there must be enough space in the LUKS header for
              enlarged keyslots (data offset must be large  enough)  or  reencryption  cannot  be

              If  there is not enough space for keyslots with new key size, you can destructively
              shrink device with --reduce-device-size option.

       --hash, -h <hash-spec>
              Specifies the hash used in the LUKS key setup scheme and volume key digest.

              NOTE: if this parameter is not specified, default hash algorithm is always used for
              new device header.

       --iter-time, -i <milliseconds>
              The  number  of milliseconds to spend with PBKDF2 passphrase processing for the new
              LUKS header.


              Define which kernel random number generator will be used to create the volume key.

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

              WARNING: --key-file option can be used only if there only one  active  keyslot,  or
              alternatively, also if --key-slot option is specified (then all other keyslots will
              be disabled in new LUKS device).

              If this option is not used, cryptsetup-reencrypt will ask for  all  active  keyslot

       --key-slot, -S <0-7>
              Specify which key slot is used.

              WARNING: All other keyslots will be disabled if this option is used.

       --keyfile-offset value
              Skip value bytes at the beginning of the key file.

       --keyfile-size, -l
              Read a maximum of value bytes from the key file.  Default is to read the whole file
              up to the compiled-in maximum.

              Do not change encryption key, just reencrypt the LUKS header and keyslots.

              This option can be combined only with --hash or --iter-time options.

       --tries, -T
              Number of retries for invalid passphrase entry.

       --block-size, -B value
              Use re-encryption block size of <value> in MiB.

              Values can be between 1 and 64 MiB.

       --device-size size[units]
              Instead of real device size, use specified value.

              It means that only specified area (from the start of the device  to  the  specified
              size) will be reencrypted.

              WARNING: This is destructive operation.

              If no unit suffix is specified, the size is in bytes.

              Unit  suffix  can be S for 512 byte sectors, K/M/G/T (or KiB,MiB,GiB,TiB) for units
              with 1024 base or KB/MB/GB/TB for 1000 base (SI scale).

              WARNING: This is destructive operation.

       --reduce-device-size size[units]
              Enlarge data offset to specified value by shrinking device size.

              This means that last sectors on the original device will be lost,  ciphertext  data
              will be effectively shifted by specified number of sectors.

              It  can  be  useful  if  you e.g. added some space to underlying partition (so last
              sectors contains no data).

              For units suffix see --device-size parameter description.

              WARNING: This is destructive operation and cannot be reverted.   Use  with  extreme
              care - shrinked filesystems are usually unrecoverable.

              You cannot shrink device more than by 64 MiB (131072 sectors).

       --new, N
              Create new header (encrypt not yet encrypted device).

              This option must be used together with --reduce-device-size.

              WARNING: This is destructive operation and cannot be reverted.

              Use direct-io (O_DIRECT) for all read/write data operations.

              Useful if direct-io operations perform better than normal buffered operations (e.g.
              in virtual environments).

              Use fsync call after every written block.

              Update log file after every block write. This can slow down reencryption  but  will
              minimize data loss in the case of system crash.

       --batch-mode, -q
              Suppresses all warnings and reencryption progress output.

              Show the program version.


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

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


       Reencrypt /dev/sdb1 (change volume key)
              cryptsetup-reencrypt /dev/sdb1

       Reencrypt and also change cipher and cipher mode
              cryptsetup-reencrypt /dev/sdb1 -c aes-xts-plain64

       Add LUKS encryption to not yet encrypted device

              First, be sure you have space added to disk.

              Or alternatively shrink filesystem in advance.
              Here we need 4096 512-bytes sectors (enough for 2x128 bit key).

              fdisk -u /dev/sdb # move sdb1 partition end + 4096 sectors  (or  use  resize2fs  or
              tool for your filesystem and shrink it)

              cryptsetup-reencrypt /dev/sdb1 --new --reduce-device-size 4096S


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


       Cryptsetup-reencrypt was written by Milan Broz <>.


       Copyright © 2012-2014 Milan Broz
       Copyright © 2012-2013 Red Hat, Inc.

       This  is  free software; see the source for copying conditions.  There is NO warranty; not


       The project website at