1CRYPTSETUP(8) Maintainance Commands CRYPTSETUP(8)
2
6 cryptsetup - setup cryptographic volumes for dm-crypt (including LUKS
7 extension)
8
10 cryptsetup <options> <action> <action args>
11
14 cryptsetup is used to conveniently setup up dm-crypt managed device-
15 mapper mappings. For basic dm-crypt mappings, there are five opera‐
16 tions.
17
19 These strings are valid for <action>, followed by their <action args>:
20 create <name> <device>
22 creates a mapping with <name> backed by device <device>.
24 <options> can be [--hash, --cipher, --verify-passphrase, --key-
25 file, --key-size, --offset, --skip, --readonly]
26 remove <name>
28 removes an existing mapping <name>. No options.
30 status <name>
32 reports the status for the mapping <name>. No options.
34 reload <name>
36 modifies an active mapping <name>. Same options as for create.
38 resize <name>
40 resizes an active mapping <name>. <options> must include --size
42
44 LUKS, Linux Unified Key Setup, is a standard for hard disk encryption.
45 It standardizes a partition header, as well as the format of the bulk
46 data. LUKS can manage multiple passwords, that can be revoked effec‐
47 tively and that are protected against dictionary attacks with PBKDF2.
48 These are valid LUKS actions:
50 luksFormat <device> [<key file>]
52 initializes a LUKS partition and set the initial key, either via
54 prompting or via <key file>. <options> can be [--cipher, --ver‐
55 ify-passphrase, --key-size]
56 luksOpen <device> <name>
58 opens the LUKS partition <device> and sets up a mapping <name>
60 after successful verification of the supplied key material
61 (either via key file by --key-file, or via prompting).
62 <options> can be [--key-file, --readonly].
63 luksClose <name>
65 identical to remove.
67 luksAddKey <device> [<new key file>]
69 add a new key file/passphrase. An existing passphrase or key
71 file (via --key-file) must be supplied. The key file with the
72 new material is supplied as after luksAddKey as positional argu‐
73 ment. <options> can be [--key-file].
74 luksDelKey <device> <key slot number>
76 remove key from key slot. A remaining passphrase or key file
78 (via --key-file) must be supplied. <options> can be [--key-
79 file].
80 luksUUID <device>
82 print UUID, if <device> has a LUKS header. No options.
84 isLuks <device>
86 returns true, if <device> is a LUKS partition. Otherwise, false.
88 No options.
89 luksDump <device>
91 dumps the header information of a LUKS partition. No options.
93 For more information about LUKS, see http://luks.endorphin.org
95
97 --hash, -h
98 specifies hash to use for password hashing. This option is only
99 relevant for the "create" action. The hash string is passed to
100 libgcrypt, so all hashes accepted by gcrypt are supported.
101 Default is "ripemd160".
102 --cipher, -c
104 set cipher specification string. Usually, this is "aes-cbc-
105 plain". For pre-2.6.10 kernels, use "aes-plain" as they don't
106 understand the new cipher spec strings. To use ESSIV, use "aes-
107 cbc-essiv:sha256".
108 --verify-passphrase, -y
110 query for passwords twice. Useful, when creating a (regular)
111 mapping for the first time, or when running luksFormat.
112 --key-file, -d
114 use file as key material. With LUKS, key material supplied in
115 key files via -d are always used for existing passphrases. If
116 you want to set a new key via a key file, you have to use a
117 positional arg to luksFormat or luksAddKey. If the key file is
118 "-", stdin will be used.
119 --key-size, -s
121 set key size in bits. Has to be a multiple of 8 bits. The key
122 size is limited by the used cipher. See output of /proc/crypto
123 for more information. Can be used for create or luksFormat, all
124 other LUKS actions will ignore this flag, as the key-size is
125 specified by the partition header. Default is 128.
126 --size, -b
128 force the size of the underlaying device in sectors.
129 --offset, -o
131 start offset in the backend device.
132 --skip, -p
134 how many sectors of the encrypted data to skip at the beginning.
135 This is different from the --offset options with respect to IV
136 calculations. Using --offset will shift the IV calculcation by
137 the same negative amount. Hence, if --offset n, sector n will be
138 the first sector on the mapping with IV 0. Using --skip would
139 have resulted in sector n being the first sector also, but with
140 IV n.
141 --readonly
143 setup a read-only mapping.
144 --iter-time, -i
146 The number of microseconds to spend with PBKDF2 password pro‐
147 cessing. This options is only relevant to LUKS key setting oper‐
148 ations as luksFormat or luksAddKey.
149 --batch-mode, -q
151 Do not ask for confirmation. This option is only relevant for
152 luksFormat.
153 --timeout, -t
155 The number of seconds to wait before timeout. This option is
156 relevant evertime a password is asked, like create, luksOpen,
157 luksFormat or luksAddKey.
158 --tries, -T
160 How often the input of the passphrase shall be retried. This
161 option is relevant evertime a password is asked, like create,
162 luksOpen, luksFormat or luksAddKey. The default is 3 tries.
163 --align-payload=value
165 Align payload at a boundary of value 512-byte sectors. This
166 option is relevant for luksFormat. If your block device lives
167 on a RAID it is useful to align the filesystem at full stripe
168 boundaries so it can take advantage of the RAID's geometry. See
169 for instance the sunit and swidth options in the mkfs.xfs manual
170 page. By default the payload is aligned at an 8 sector (4096
171 byte) boundary.
172 --version
174 Show the version.
175
178 From a file descriptor or a terminal: Password processing is new-line
179 sensitive, meaning the reading will stop after encountering \n. It will
180 processed the read material with the default hash or the hash given by
181 --hash. After hashing it will be cropped to the key size given by -s
182 (default 256 bits).
183 From stdin: Reading will continue until EOF (so using e.g. /dev/random
185 as stdin will not work). After that the read data will be hashed with
186 the default hash or the hash given by --hash and the result will be
187 cropped to the keysize given by -s (default 256 bits). If "plain" is
188 used as an argument to the hash option, the input data will not be
189 hashed. Instead it will be zero padded (if shorter than the keysize) or
190 truncated (if longer than the keysize) and used directly as the key. No
191 warning will be given if the amount of data read from stdin is less
192 than the keysize.
193 From a key file: It will be cropped to the size given by -s. If there
195 is insufficient key material in the key file, cryptsetup will quit with
196 an error.
197
199 Password processing is totally different for LUKS. LUKS uses PBKDF2 to
200 protect against dictionary attacks (see RFC 2898). LUKS will always
201 use SHA1 in HMAC mode, and no other mode is supported at the moment.
202 Hence, -h is ignored.
203 LUKS will always do an exhaustive password reading. Hence, password can
205 not be read from /dev/random, /dev/zero or any other stream, that does
206 not terminate.
207 LUKS saves the processing options when a password is set to the respec‐
209 tive key slot. Therefore, no options can be given to luksOpen. For
210 any password creation action (luksAddKey, or luksFormat), the user
211 specify, how much the time the password processing should consume.
212 Increasing the time will lead to a more secure password, but also will
213 take luksOpen longer to complete. The default setting of one second is
214 sufficient for good security.
215
217 Mathematic can't be bribed. Make sure you keep your passwords safe.
218 There are a few nice tricks for constructing a fallback, when suddely
219 out of (or after being) blue, your brain refuses to cooperate. These
220 fallbacks are possible with LUKS, as it's only possible with LUKS to
221 have multiple passwords.
222
224 cryptsetup is written by Christophe Saout <christophe@saout.de>
225 LUKS extensions, and man page by Clemens Fruhwirth <clemens@endor‐
226 phin.org>
227
229 To read images created with SuSE Linux 9.2's loop_fish2 use --cipher
230 twofish-cbc-null -s 256 -h sha512, for images created with even older
231 SuSE Linux use --cipher twofish-cbc-null -s 192 -h ripemd160:20
232
234 Report bugs to <dm-crypt@saout.de>.
235
237 Copyright © 2004 Christophe Saout
238 Copyright © 2004-2006 Clemens Fruhwirth
239 This is free software; see the source for copying conditions. There is
241 NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
242 PURPOSE.
243
245 dm-crypt website, http://www.saout.de/misc/dm-crypt/
246 LUKS website, http://luks.endorphin.org
248 dm-crypt TWiki, http://www.saout.de/tikiwiki/tiki-index.php
250cryptsetup 1.0.3 March 2005 CRYPTSETUP(8)