cryptsetup-reencrypt man page on ElementaryOS
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CRYPTSETUP-REENCRYPT(8) Maintenance Commands CRYPTSETUP-REENCRYPT(8)
NAME
cryptsetup-reencrypt - tool for offline LUKS device re-encryption
SYNOPSIS
cryptsetup-reencrypt <options> <device>
DESCRIPTION
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).
ALWAYS BE SURE YOU HAVE RELIABLE BACKUP BEFORE USING THIS TOOL.
THIS TOOL IS EXPERIMENTAL.
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 reencryp‐
tion 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).
OPTIONS
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 crypt‐
setup(8) man page.
--verbose, -v
Print more information on command execution.
--debug
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 performed.
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.
--iter-time, -i <milliseconds>
The number of milliseconds to spend with PBKDF2 passphrase pro‐
cessing for the new LUKS header.
--use-random
--use-urandom
Define which kernel random number generator will be used to cre‐
ate 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 passphrases.
--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.
--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 usefull 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 unre‐
coverable.
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-directio
Use direct-io (O_DIRECT) for all read/write data operations.
Usefull if direct-io operations perform better than normal
buffered operations (e.g. in virtual environments).
--use-fsync
Use fsync call after every written block.
--write-log
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.
--version
Show the program version.
RETURN CODES
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.
EXAMPLES
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
cryptsetup-reencrypt /dev/sdb1 --new --reduce-device-size 4096
REPORTING BUGS
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
Cryptsetup-reencrypt was written by Milan Broz <gmazyland@gmail.com>.
COPYRIGHT
Copyright © 2012 Milan Broz
Copyright © 2012 Red Hat, Inc.
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 project website at http://code.google.com/p/cryptsetup/
cryptsetup-reencrypt June 2012 CRYPTSETUP-REENCRYPT(8)
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