1 .TH CRYPTSETUP "8" "March 2005" "cryptsetup" "Maintenance Commands"
3 cryptsetup - setup cryptographic volumes for dm-crypt (including LUKS extension)
6 .B cryptsetup <options> <action> <action args>
9 .\" Add any additional description here
11 cryptsetup is used to conveniently setup dm-crypt managed device-mapper mappings. For basic dm-crypt mappings, there are five operations.
13 These strings are valid for \fB<action>\fR, followed by their \fB<action args>\fR:
15 \fIcreate\fR <name> <device>
17 creates a mapping with <name> backed by device <device>.
18 <options> can be [\-\-hash, \-\-cipher, \-\-verify-passphrase, \-\-key-file, \-\-key-size, \-\-offset, \-\-skip, \-\-readonly]
22 removes an existing mapping <name>. No options.
26 reports the status for the mapping <name>. No options.
30 resizes an active mapping <name>.
32 If \-\-size (in sectors) is not specified, the size of the underlying block device is used.
37 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 effectively and that are protected against dictionary attacks with PBKDF2.
39 These are valid LUKS actions:
41 \fIluksFormat\fR <device> [<key file>]
43 initializes a LUKS partition and sets the initial key, either via prompting or via <key file>.
44 <options> can be [\-\-cipher, \-\-verify-passphrase, \-\-key-size, \-\-key-slot].
46 \fIluksOpen\fR <device> <name>
48 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).
49 <options> can be [\-\-key-file, \-\-readonly].
51 \fIluksClose\fR <name>
53 identical to \fIremove\fR.
55 \fIluksSuspend\fR <name>
57 suspends active device (all IO operations are frozen) and wipes encryption key from kernel. Kernel version 2.6.19 or later is required.
59 After that operation you have to use \fIluksResume\fR to reinstate encryption key (and resume device) or \fIluksClose\fR to remove mapped device.
61 \fBWARNING:\fR never try to suspend device where is the cryptsetup binary itself.
63 \fIluksResume\fR <name>
65 Resumes suspended device and reinstates encryption key. You will need provide passphrase identical to \fIluksOpen\fR command (using prompting or key file).
67 \fIluksAddKey\fR <device> [<new key file>]
69 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 a positional argument. <options> can be [\-\-key-file, \-\-key-slot].
71 \fIluksRemoveKey\fR <device> [<key file>]
73 remove supplied key or key file from LUKS device
75 \fIluksKillSlot\fR <device> <key slot number>
77 wipe key with number <key slot> from LUKS device. A remaining passphrase or key file (via \-\-key-file) must be supplied. <options> can be [\-\-key-file].
79 \fIluksDelKey\fR <device> <key slot number>
81 identical to luksKillSlot, but deprecated action name.
83 \fIluksUUID\fR <device>
85 print UUID, if <device> has a LUKS header. No options.
89 returns true, if <device> is a LUKS partition. Otherwise, false. No options.
91 \fIluksDump\fR <device>
93 dumps the header information of a LUKS partition. No options.
95 \fIluksHeaderBackup\fR <device> --header-backup-file <file>
97 Stores binary backup of LUKS header and keyslot areas.
99 \fBWARNING:\fR Please note that with this backup file (and old passphrase knowledge) you can decrypt data even if old passphrase was wiped from real device.
101 Also note that anti-forensic splitter is not used during manipulation with backup file.
103 \fIluksHeaderRestore\fR <device> --header-backup-file <file>
106 Restores binary backup of LUKS header and keyslot areas from specified file.
108 \fBWARNING:\fR All the keyslot areas are overwritten, only active keyslots form backup file are available after issuing this command.
110 This command allows restoring header if device do not contain LUKS header or if the master key size and data offset in LUKS header on device match the backup file.
113 For more information about LUKS, see \fBhttp://code.google.com/p/cryptsetup/wiki/Specification\fR
118 For \fIcreate\fR action specifies hash to use for password hashing.
120 For \fIluksFormat\fR action specifies hash used in LUKS key setup scheme and volume key digest.
122 \fBWARNING:\fR setting hash other than \fBsha1\fR causes LUKS device incompatible with older version of cryptsetup.
124 The hash string is passed to libgcrypt, so all hashes accepted by gcrypt are supported.
125 Default is \fB"ripemd160"\fR for \fIcreate\fR action and \fB"sha1"\fR for \fIluksFormat\fR.
128 set cipher specification string. For plain dm-crypt mappings, the default is "aes-cbc-plain", for LUKS mappings it's "aes-cbc-essiv:sha256". 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".
130 For XTS mode, kernel version 2.6.24 or more recent is required. Use "aes-xts-plain" cipher specification and set key size to 256 (or 512) bits (see \-s option).
132 .B "\-\-verify-passphrase, \-y"
133 query for passwords twice. Useful when creating a (regular) mapping for the first time, or when running \fIluksFormat\fR.
135 .B "\-\-key-file, \-d"
136 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 \fIluksFormat\fR or \fIluksAddKey\fR.
138 If the key file is "-", stdin will be used. This is different from how cryptsetup usually reads from stdin. See section \fBNOTES ON PASSWORD PROCESSING\fR for more information.
140 .B "\-\-master-key-file"
141 Use pre-generated master key stored in file. For \fIluksFormat\fR it allows LUKS header reformatting with the same master key (if all other parameters are the same existing encrypted data remains intact).
143 For \fIluksAddKey\fR it allows adding new passphrase with only master key knowledge.
145 .B "\-\-key-slot, \-S"
146 For LUKS operations that add key material, this options allows to you specify which key slot is selected for the new key. This option can be used for \fIluksFormat\fR and \fIluksAddKey\fR.
148 .B "\-\-key-size, \-s"
149 set key size in bits. Has to be a multiple of 8 bits. The key size is limited by the used cipher. See output of /proc/crypto for more information. Can be used for \fIcreate\fR or \fIluksFormat\fR, all other LUKS actions will use key-size specified by the LUKS header. Default is 128 for \fIluksFormat\fR and 256 for \fIcreate\fR.
151 For \fIluksOpen\fR this option specifies number of bits read from the key-file (default is exhaustive read from key-file).
154 force the size of the underlying device in sectors.
155 This option is only relevant for \fIcreate\fR and \fIresize\fR action.
158 start offset in the backend device.
159 This option is only relevant for \fIcreate\fR action.
162 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 calculation by the same negative amount. Hence, if \-\-offset \fIn\fR, sector \fIn\fR will be the first sector on the mapping with IV \fI0\fR. Using \-\-skip would have resulted in sector \fIn\fR being the first sector also, but with IV \fIn\fR.
163 This option is only relevant for \fIcreate\fR action.
166 set up a read-only mapping.
168 .B "\-\-iter-time, \-i"
169 The number of milliseconds to spend with PBKDF2 password processing. This option is only relevant to the LUKS operations as \fIluksFormat\fR or \fIluksAddKey\fR.
171 .B "\-\-batch-mode, \-q"
172 Do not ask for confirmation. Use with care! This option is only relevant for \fIluksFormat\fR, \fIluksAddKey\fR, \fIluksRemoveKey\fR or \fIluksKillSlot\fR.
174 .B "\-\-timeout, \-t"
175 The number of seconds to wait before timeout. This option is relevant every time a password is asked, like \fIcreate\fR, \fIluksOpen\fR, \fIluksFormat\fR or \fIluksAddKey\fR. It has no effect if used in conjunction with \-\-key-file.
178 How often the input of the passphrase shall be retried. This option is relevant every time a password is asked, like \fIcreate\fR, \fIluksOpen\fR, \fIluksFormat\fR or \fIluksAddKey\fR. The default is 3 tries.
180 .B "\-\-align-payload=\fIvalue\fR"
181 Align payload at a boundary of \fIvalue\fR 512-byte sectors. This option is relevant for \fIluksFormat\fR. If your block device lives on a RAID, it is
182 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
183 in the mkfs.xfs manual page. By default, the payload is aligned at an 8 sector (4096 byte) boundary.
188 .SH NOTES ON PASSWORD PROCESSING
189 \fIFrom a file descriptor or a terminal\fR: Password processing is new-line sensitive, meaning the reading will stop after encountering \\n. It will process the read material (without newline) with the default hash or the hash given by \-\-hash. After hashing, it will be cropped to the key size given by \-s.
191 \fIFrom stdin\fR: Reading will continue until EOF (so using e.g. /dev/random as stdin will not work), with the trailing newline stripped. After that the read data will be hashed with the default hash or the hash given by \-\-hash and the result will be cropped to the keysize given by \-s. If "plain" is used as an argument to the hash option, the input data will not be hashed.
192 Instead, it will be zero padded (if shorter than the keysize) or truncated (if longer than the keysize) and used directly as the key. No warning will be given if the amount of data read from stdin is less than the keysize.
194 \fIFrom a key file\fR: 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.
196 If \-\-key-file=- is used for reading the key from stdin, no trailing newline is stripped from the input. Without that option, cryptsetup strips trailing newlines from stdin input.
197 .SH NOTES ON PASSWORD PROCESSING FOR LUKS
198 LUKS uses PBKDF2 to protect against dictionary attacks (see RFC 2898).
200 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.
202 LUKS saves the processing options when a password is set to the respective key slot.
203 Therefore, no options can be given to luksOpen.
204 For any password creation action (luksAddKey, or luksFormat), the user may specify how much the time the password processing should consume.
205 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.
206 .SH INCOHERENT BEHAVIOUR FOR INVALID PASSWORDS/KEYS
207 LUKS checks for a valid password or key when an encrypted partition is unlocked. Thus the luksOpen action fails with invalid password or key, contrary to the plain dm-crypt create action.
208 .SH NOTES ON SUPPORTED CIPHERS, MODES, HASHES AND KEY SIZES
209 The available combinations of ciphers, modes, hashes and key sizes depend on kernel support. See /proc/crypto for a list of available options. You might need to load additional kernel crypto modules in order to get more options.
211 For --hash option all algorithms supported by gcrypt library are available.
212 .SH NOTES ON PASSWORDS
213 Mathematics can't be bribed. Make sure you keep your passwords safe. There are a few nice tricks for constructing a fallback, when suddenly 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.
215 cryptsetup is written by Christophe Saout <christophe@saout.de>
217 LUKS extensions, and man page by Clemens Fruhwirth <clemens@endorphin.org>
218 .SH "COMPATABILITY WITH OLD SUSE TWOFISH PARTITIONS"
219 To read images created with SuSE Linux 9.2's loop_fish2 use \-\-cipher
220 twofish-cbc-null \-s 256 \-h sha512, for images created with even
221 older SuSE Linux use \-\-cipher twofish-cbc-null \-s 192 \-h
224 .SH DEPRECATED ACTIONS
226 \fIreload\fR <name> <device>
228 modifies an active mapping <name>. Same options as for
231 Do not use this for LUKS devices, as the semantics
232 are identical to the create action, which are totally incompatible
233 with the LUKS key setup.
235 This action is deprected because it proved to be rarely useful. It is
236 uncommon to change the underlying device, key, or offset on the
237 fly. In case, you really want to do this, you certainly know what you
238 are doing and then you are probably better off with the swiss knive
239 tool for device mapper, namely dmsetup. It provides you with the same
240 functionality, see dmsetup reload.
242 \fIluksDelKey\fR <device> <key slot number>
244 identical to luksKillSlot, but deprecated action name. This option was
245 renamed, as we introduced luksRemoveKey, a softer method for disabling
246 password slots. To make a clear distinction that luksDelKey was more brutal than luksRemoveKey
250 Report bugs to <dm-crypt@saout.de>.
252 Copyright \(co 2004 Christophe Saout
254 Copyright \(co 2004-2006 Clemens Fruhwirth
256 This is free software; see the source for copying conditions. There is NO
257 warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
260 dm-crypt website, \fBhttp://www.saout.de/misc/dm-crypt/\fR
262 LUKS website, \fBhttp://code.google.com/p/cryptsetup/\fR
264 dm-crypt TWiki, \fBhttp://www.saout.de/tikiwiki/tiki-index.php\fR