cryptsetup man page on YellowDog
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CRYPTSETUP(8) Maintainance 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 up dm-crypt managed device-
mapper mappings. For basic dm-crypt mappings, there are five opera‐
tions.
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>. No options.
status <name>
reports the status for the mapping <name>. No options.
reload <name>
modifies an active mapping <name>. Same options as for create.
resize <name>
resizes an active mapping <name>. <options> must include --size
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 effec‐
tively and that are protected against dictionary attacks with PBKDF2.
These are valid LUKS actions:
luksFormat <device> [<key file>]
initializes a LUKS partition and set the initial key, either via
prompting or via <key file>. <options> can be [--cipher, --ver‐
ify-passphrase, --key-size]
luksOpen <device> <name>
opens the LUKS partition <device> and sets up a mapping <name>
after successful verification of the supplied key material
(either via key file by --key-file, or via prompting).
<options> can be [--key-file, --readonly].
luksClose <name>
identical to remove.
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 after luksAddKey as positional argu‐
ment. <options> can be [--key-file].
luksDelKey <key slot number>
remove key from key slot. No options.
luksUUID <device>
print UUID, if <device> has a LUKS header. No options.
isLuks <device>
returns true, if <device> is a LUKS partition. Otherwise, false.
No options.
luksDump <device>
dumps the header information of a LUKS partition. No options.
For more information about LUKS, see http://luks.endorphin.org
OPTIONS
--hash, -h
specifies hash to use for password hashing. This option is only
relevant for the "create" action. The hash string is passed to
libgcrypt, so all hashes accepted by gcrypt are supported.
--cipher, -c
set cipher specification string. Usually, this is "aes-cbc-
plain". 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".
--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. If
you want to set a new key via a key file, you have to use a
positional arg to luksFormat or luksAddKey.
--key-size, -s
set key size in bits. Usually, this is 128, 192 or 256. Can be
used for create or luksFormat, all other LUKS actions will
ignore this flag, as the key-size is specified by the partition
header.
--size, -b
force the size of the underlaying device in sectors.
--offset, -o
start offset in the backend device.
--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 calculcation by
the same negative 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.
--readonly
setup a read-only mapping.
--iter-time, -i
The number of microseconds to spend with PBKDF2 password pro‐
cessing. This options is only relevant to LUKS key setting oper‐
ations as luksFormat or luksAddKey.
--batch-mode, -q
Do not ask for confirmation. This option is only relevant for
luksFormat.
--timeout, -t
The number of seconds to wait before timeout. This option is
relevant evertime a password is asked, like create, luksOpen,
luksFormat or luksAddKey.
--align-payload=value
Align payload at a boundary of value 512-byte sectors. This
option is relevant for luksFormat. If your block device lives
on a RAID it is useful to align the filesystem at full stripe
boundaries so it can take advantage of the RAID's geometry. See
for instance the sunit and swidth options in the mkfs.xfs manual
page. By default the payload is aligned at an 8 sector (4096
byte) boundary.
--version
Show the version.
NOTES ON PASSWORD PROCESSING FOR REGULAR MAPPINGS
From a file descriptor or a terminal: Password processing is new-line
sensitive, meaning the reading will stop after encountering \n. It will
processed the read material with the default hash or the hash given by
--hash. After hashing it will be cropped to the key size given by -s
(or default 256bit).
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.
NOTES ON PASSWORD PROCESSING FOR LUKS
Password processing is totally different for LUKS. LUKS uses PBKDF2 to
protect against dictionary attacks (see RFC 2898). LUKS will always
use SHA1 in HMAC mode, and no other mode is supported at the moment.
Hence, -h is ignored.
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.
LUKS saves the processing options when a password is set to the respec‐
tive key slot. Therefore, no options can be given to luksOpen. For
any password creation action (luksAddKey, or luksFormat), the user
specify, how much the time the password 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.
NOTES ON PASSWORDS
Mathematic can't be bribed. Make sure you keep your passwords save.
There are a few nice tricks for constructing a fallback, when suddely
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.
AUTHORS
cryptsetup is written by Christophe Saout <christophe@saout.de>
LUKS extensions, and man page by Clemens Fruhwirth <clemens@endor‐
phin.org>
REPORTING BUGS
Report bugs to <dm-crypt@saout.de>.
COPYRIGHT
Copyright © 2004 Christophe Saout
Copyright © 2004-2006 Clemens Fruhwirth
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
dm-crypt website, http://www.saout.de/misc/dm-crypt/
LUKS website, http://luks.endorphin.org
dm-crypt TWiki, http://www.saout.de/tikiwiki/tiki-index.php
cryptsetup 1.0.3 March 2005 CRYPTSETUP(8)
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