1CRYPTSETUP(8) Maintenance Commands CRYPTSETUP(8)
2
6 cryptsetup - manage plain dm-crypt and LUKS encrypted volumes
7
9 cryptsetup <options> <action> <action args>
10
12 cryptsetup is used to conveniently setup dm-crypt managed device-mapper
13 mappings. These include plain dm-crypt volumes and LUKS volumes. The
14 difference is that LUKS uses a metadata header and can hence offer more
15 features than plain dm-crypt. On the other hand, the header is visible
16 and vulnerable to damage.
17 In addition, cryptsetup provides limited support for the use of loop-
19 AES volumes and for TrueCrypt compatible volumes.
20
23 Unless you understand the cryptographic background well, use LUKS.
24 With plain dm-crypt there are a number of possible user errors that
25 massively decrease security. While LUKS cannot fix them all, it can
26 lessen the impact for many of them.
27
29 A lot of good information on the risks of using encrypted storage, on
30 handling problems and on security aspects can be found in the Crypt‐
31 setup FAQ. Read it. Nonetheless, some risks deserve to be mentioned
32 here.
33 Backup: Storage media die. Encryption has no influence on that. Backup
35 is mandatory for encrypted data as well, if the data has any worth. See
36 the Cryptsetup FAQ for advice on how to do a backup of an encrypted
37 volume.
38 Character encoding: If you enter a passphrase with special symbols, the
40 passphrase can change depending on character encoding. Keyboard set‐
41 tings can also change, which can make blind input hard or impossible.
42 For example, switching from some ASCII 8-bit variant to UTF-8 can lead
43 to a different binary encoding and hence different passphrase seen by
44 cryptsetup, even if what you see on the terminal is exactly the same.
45 It is therefore highly recommended to select passphrase characters only
46 from 7-bit ASCII, as the encoding for 7-bit ASCII stays the same for
47 all ASCII variants and UTF-8.
48 LUKS header: If the header of a LUKS volume gets damaged, all data is
50 permanently lost unless you have a header-backup. If a key-slot is
51 damaged, it can only be restored from a header-backup or if another
52 active key-slot with known passphrase is undamaged. Damaging the LUKS
53 header is something people manage to do with surprising frequency. This
54 risk is the result of a trade-off between security and safety, as LUKS
55 is designed for fast and secure wiping by just overwriting header and
56 key-slot area.
57 Previously used partitions: If a partition was previously used, it is a
59 very good idea to wipe filesystem signatures, data, etc. before creat‐
60 ing a LUKS or plain dm-crypt container on it. For a quick removal of
61 filesystem signatures, use "wipefs". Take care though that this may not
62 remove everything. In particular, MD RAID signatures at the end of a
63 device may survive. It also does not remove data. For a full wipe,
64 overwrite the whole partition before container creation. If you do not
65 know how to do that, the cryptsetup FAQ describes several options.
66
69 The following are valid actions for all supported device types.
70 open <device> <name> --type <device_type>
72 Opens (creates a mapping with) <name> backed by device <device>.
74 Device type can be plain, luks (default), luks1, luks2, loopaes
76 or tcrypt.
77 For backward compatibility there are open command aliases:
79 create (argument-order <name> <device>): open --type plain
81 plainOpen: open --type plain
82 luksOpen: open --type luks
83 loopaesOpen: open --type loopaes
84 tcryptOpen: open --type tcrypt
85 <options> are type specific and are described below for individ‐
87 ual device types. For create, the order of the <name> and
88 <device> options is inverted for historical reasons, all other
89 aliases use the standard <device> <name> order.
90 close <name>
92 Removes the existing mapping <name> and wipes the key from ker‐
94 nel memory.
95 For backward compatibility there are close command aliases:
97 remove, plainClose, luksClose, loopaesClose, tcryptClose (all
98 behaves exactly the same, device type is determined automati‐
99 cally from active device).
100 <options> can be [--deferred]
102 status <name>
105 Reports the status for the mapping <name>.
107 resize <name>
109 Resizes an active mapping <name>.
111 If --size (in 512-bytes sectors) is not specified, the size is
113 computed from the underlying device. For LUKS it is the size of
114 the underlying device without the area reserved for LUKS header
115 (see data payload offset in luksDump command). For plain crypt
116 device, the whole device size is used.
117 Note that this does not change the raw device geometry, it just
119 changes how many sectors of the raw device are represented in
120 the mapped device.
121 If cryptsetup detected volume key for active device loaded in
123 kernel keyring service, resize action would first try to
124 retrieve the key using a token and only if it failed it'd ask
125 for a passphrase to unlock a keyslot (LUKS) or to derive a vol‐
126 ume key again (plain mode). The kernel keyring is used by
127 default for LUKS2 devices.
128 With LUKS2 device additional <options> can be [--token-id,
130 --token-only, --key-slot, --key-file, --keyfile-size, --key‐
131 file-offset, --timeout, --disable-locks, --disable-keyring].
132
135 Plain dm-crypt encrypts the device sector-by-sector with a single, non-
136 salted hash of the passphrase. No checks are performed, no metadata is
137 used. There is no formatting operation. When the raw device is mapped
138 (opened), the usual device operations can be used on the mapped device,
139 including filesystem creation. Mapped devices usually reside in
140 /dev/mapper/<name>.
141 The following are valid plain device type actions:
143 open --type plain <device> <name>
145 create <name> <device> (OBSOLETE syntax)
146 Opens (creates a mapping with) <name> backed by device <device>.
148 <options> can be [--hash, --cipher, --verify-passphrase, --sec‐
150 tor-size, --key-file, --keyfile-offset, --key-size, --offset,
151 --skip, --size, --readonly, --shared, --allow-discards]
152 Example: 'cryptsetup open --type plain /dev/sda10 e1' maps the
154 raw encrypted device /dev/sda10 to the mapped (decrypted) device
155 /dev/mapper/e1, which can then be mounted, fsck-ed or have a
156 filesystem created on it.
157
159 LUKS, the Linux Unified Key Setup, is a standard for disk encryption.
160 It adds a standardized header at the start of the device, a key-slot
161 area directly behind the header and the bulk data area behind that. The
162 whole set is called a 'LUKS container'. The device that a LUKS con‐
163 tainer resides on is called a 'LUKS device'. For most purposes, both
164 terms can be used interchangeably. But note that when the LUKS header
165 is at a nonzero offset in a device, then the device is not a LUKS
166 device anymore, but has a LUKS container stored in it at an offset.
167 LUKS can manage multiple passphrases that can be individually revoked
169 or changed and that can be securely scrubbed from persistent media due
170 to the use of anti-forensic stripes. Passphrases are protected against
171 brute-force and dictionary attacks by PBKDF2, which implements hash
172 iteration and salting in one function.
173 LUKS2 is a new version of header format that allows additional exten‐
175 sions like different PBKDF algorithm or authenticated encryption. You
176 can format device with LUKS2 header if you specify --type luks2 in
177 luksFormat command. For activation, the format is already recognized
178 automatically.
179 Each passphrase, also called a key in this document, is associated with
181 one of 8 key-slots. Key operations that do not specify a slot affect
182 the first slot that matches the supplied passphrase or the first empty
183 slot if a new passphrase is added.
184 The <device> parameter can also be specified by a LUKS UUID in the for‐
186 mat UUID=<uuid>. Translation to real device name uses symlinks in
187 /dev/disk/by-uuid directory.
188 To specify a detached header, the --header parameter can be used in all
190 LUKS commands and always takes precedence over the positional <device>
191 parameter.
192 The following are valid LUKS actions:
194 luksFormat <device> [<key file>]
196 Initializes a LUKS partition and sets the initial passphrase
198 (for key-slot 0), either via prompting or via <key file>. Note
199 that if the second argument is present, then the passphrase is
200 taken from the file given there, without the need to use the
201 --key-file option. Also note that for both forms of reading the
202 passphrase from a file you can give '-' as file name, which
203 results in the passphrase being read from stdin and the safety-
204 question being skipped.
205 You can only call luksFormat on a LUKS device that is not
207 mapped.
208 To use LUKS2, specify --type luks2.
210 <options> can be [--hash, --cipher, --verify-passphrase,
212 --key-size, --key-slot, --key-file (takes precedence over
213 optional second argument), --keyfile-offset, --keyfile-size,
214 --use-random | --use-urandom, --uuid, --master-key-file,
215 --iter-time, --header, --pbkdf-force-iterations, --force-pass‐
216 word, --disable-locks].
217 For LUKS2, additional <options> can be [--integrity,
219 --integrity-no-wipe, --sector-size, --label, --subsystem,
220 --pbkdf, --pbkdf-memory, --pbkdf-parallel, --disable-locks,
221 --disable-keyring].
222 WARNING: Doing a luksFormat on an existing LUKS container will
224 make all data the old container permanently irretrievable unless
225 you have a header backup.
226 open --type luks <device> <name>
228 luksOpen <device> <name> (old syntax)
229 Opens the LUKS device <device> and sets up a mapping <name>
231 after successful verification of the supplied passphrase.
232 First, the passphrase is searched in LUKS tokens. If it's not
234 found in any token and also the passphrase is not supplied via
235 --key-file, the command prompts for it interactively.
236 <options> can be [--key-file, --keyfile-offset, --keyfile-size,
238 --readonly, --test-passphrase, --allow-discards, --header,
239 --key-slot, --master-key-file, --token-id, --token-only, --dis‐
240 able-keyring, --disable-locks, --type].
241 luksSuspend <name>
243 Suspends an active device (all IO operations will block and
245 accesses to the device will wait indefinitely) and wipes the
246 encryption key from kernel memory. Needs kernel 2.6.19 or later.
247 After this operation you have to use luksResume to reinstate the
249 encryption key and unblock the device or close to remove the
250 mapped device.
251 WARNING: never suspend the device on which the cryptsetup binary
253 resides.
254 <options> can be [--header, --disable-locks].
256 luksResume <name>
258 Resumes a suspended device and reinstates the encryption key.
260 Prompts interactively for a passphrase if --key-file is not
261 given.
262 <options> can be [--key-file, --keyfile-size, --header, --dis‐
264 able-keyring, --disable-locks, --type]
265 luksAddKey <device> [<key file with new key>]
267 Adds a new passphrase. An existing passphrase must be supplied
269 interactively or via --key-file. The new passphrase to be added
270 can be specified interactively or read from the file given as
271 positional argument.
272 NOTE: with --unbound option the action creates new unbound LUKS2
274 keyslot. The keyslot cannot be used for device activation. If
275 you don't pass new key via --master-key-file option, new random
276 key is generated. Existing passphrase for any active keyslot is
277 not required.
278 <options> can be [--key-file, --keyfile-offset, --keyfile-size,
280 --new-keyfile-offset, --new-keyfile-size, --key-slot, --mas‐
281 ter-key-file, --iter-time, --force-password, --header, --dis‐
282 able-locks, --unbound, --type].
283 luksRemoveKey <device> [<key file with passphrase to be removed>]
285 Removes the supplied passphrase from the LUKS device. The
287 passphrase to be removed can be specified interactively, as the
288 positional argument or via --key-file.
289 <options> can be [--key-file, --keyfile-offset, --keyfile-size,
291 --header, --disable-locks, --type]
292 WARNING: If you read the passphrase from stdin (without further
294 argument or with '-' as an argument to --key-file), batch-mode
295 (-q) will be implicitly switched on and no warning will be given
296 when you remove the last remaining passphrase from a LUKS con‐
297 tainer. Removing the last passphrase makes the LUKS container
298 permanently inaccessible.
299 luksChangeKey <device> [<new key file>]
301 Changes an existing passphrase. The passphrase to be changed
303 must be supplied interactively or via --key-file. The new
304 passphrase can be supplied interactively or in a file given as
305 positional argument.
306 If a key-slot is specified (via --key-slot), the passphrase for
308 that key-slot must be given and the new passphrase will over‐
309 write the specified key-slot. If no key-slot is specified and
310 there is still a free key-slot, then the new passphrase will be
311 put into a free key-slot before the key-slot containing the old
312 passphrase is purged. If there is no free key-slot, then the
313 key-slot with the old passphrase is overwritten directly.
314 WARNING: If a key-slot is overwritten, a media failure during
316 this operation can cause the overwrite to fail after the old
317 passphrase has been wiped and make the LUKS container inaccessi‐
318 ble.
319 <options> can be [--key-file, --keyfile-offset, --keyfile-size,
321 --new-keyfile-offset, --new-keyfile-size, --key-slot,
322 --force-password, --header, --disable-locks, --type].
323 luksConvertKey <device>
325 Converts an existing LUKS2 keyslot to new pbkdf parameters. The
327 passphrase for keyslot to be converted must be supplied interac‐
328 tively or via --key-file. If no --pbkdf parameters are specified
329 LUKS2 default pbkdf values will apply.
330 If a keyslot is specified (via --key-slot), the passphrase for
332 that keyslot must be given. If no keyslot is specified and there
333 is still a free keyslot, then the new parameters will be put
334 into a free keyslot before the keyslot containing the old param‐
335 eters is purged. If there is no free keyslot, then the keyslot
336 with the old parameters is overwritten directly.
337 WARNING: If a keyslot is overwritten, a media failure during
339 this operation can cause the overwrite to fail after the old
340 parameters have been wiped and make the LUKS container inacces‐
341 sible.
342 <options> can be [--key-file, --keyfile-offset, --keyfile-size,
344 --key-slot, --header, --disable-locks, --iter-time, --pbkdf,
345 --pbkdf-force-iterations, --pbkdf-memory, --pbkdf-parallel].
346 luksKillSlot <device> <key slot number>
348 Wipe the key-slot number <key slot> from the LUKS device. Except
350 running in batch-mode (-q) a remaining passphrase must be sup‐
351 plied, either interactively or via --key-file. This command can
352 remove the last remaining key-slot, but requires an interactive
353 confirmation when doing so. Removing the last passphrase makes a
354 LUKS container permanently inaccessible.
355 <options> can be [--key-file, --keyfile-offset, --keyfile-size,
357 --header, --disable-locks, --type].
358 WARNING: If you read the passphrase from stdin (without further
360 argument or with '-' as an argument to --key-file), batch-mode
361 (-q) will be implicitly switched on and no warning will be given
362 when you remove the last remaining passphrase from a LUKS con‐
363 tainer. Removing the last passphrase makes the LUKS container
364 permanently inaccessible.
365 NOTE: If there is no passphrase provided (on stdin or through
367 --key-file argument) and batch-mode (-q) is active, the key-slot
368 is removed without any other warning.
369 erase <device>
372 luksErase <device>
373 Erase all keyslots and make the LUKS container permanently inac‐
375 cessible. You do not need to provide any password for this
376 operation.
377 WARNING: This operation is irreversible.
379 luksUUID <device>
381 Print the UUID of a LUKS device.
383 Set new UUID if --uuid option is specified.
384 isLuks <device>
386 Returns true, if <device> is a LUKS device, false otherwise.
388 Use option -v to get human-readable feedback. 'Command success‐
389 ful.' means the device is a LUKS device.
390 By specifying --type you may query for specific LUKS version.
392 luksDump <device>
394 Dump the header information of a LUKS device.
396 If the --dump-master-key option is used, the LUKS device master
398 key is dumped instead of the keyslot info. Together with --mas‐
399 ter-key-file option, master key is dumped to a file instead of
400 standard output. Beware that the master key cannot be changed
401 without reencryption and can be used to decrypt the data stored
402 in the LUKS container without a passphrase and even without the
403 LUKS header. This means that if the master key is compromised,
404 the whole device has to be erased to prevent further access. Use
405 this option carefully.
406 To dump the master key, a passphrase has to be supplied, either
408 interactively or via --key-file.
409 <options> can be [--dump-master-key, --key-file, --keyfile-off‐
411 set, --keyfile-size, --header, --disable-locks, --mas‐
412 ter-key-file, --type].
413 WARNING: If --dump-master-key is used with --key-file and the
415 argument to --key-file is '-', no validation question will be
416 asked and no warning given.
417 luksHeaderBackup <device> --header-backup-file <file>
419 Stores a binary backup of the LUKS header and keyslot area.
421 Note: Using '-' as filename writes the header backup to a file
422 named '-'.
423 WARNING: This backup file and a passphrase valid at the time of
425 backup allows decryption of the LUKS data area, even if the
426 passphrase was later changed or removed from the LUKS device.
427 Also note that with a header backup you lose the ability to
428 securely wipe the LUKS device by just overwriting the header and
429 key-slots. You either need to securely erase all header backups
430 in addition or overwrite the encrypted data area as well. The
431 second option is less secure, as some sectors can survive, e.g.
432 due to defect management.
433 luksHeaderRestore <device> --header-backup-file <file>
435 Restores a binary backup of the LUKS header and keyslot area
437 from the specified file.
438 Note: Using '-' as filename reads the header backup from a file
439 named '-'.
440 WARNING: Header and keyslots will be replaced, only the
442 passphrases from the backup will work afterward.
443 This command requires that the master key size and data offset
445 of the LUKS header already on the device and of the header
446 backup match. Alternatively, if there is no LUKS header on the
447 device, the backup will also be written to it.
448 token <add|remove|import|export> <device>
450 Action add creates new keyring token to enable auto-activation
452 of the device. For the auto-activation, the passphrase must be
453 stored in keyring with the specified description. Usually, the
454 passphrase should be stored in user or user-session keyring.
455 The token command is supported only for LUKS2.
456 For adding new keyring token, option --key-description is manda‐
458 tory. Also, new token is assigned to key slot specified with
459 --key-slot option or to all active key slots in the case
460 --key-slot option is omitted.
461 To remove existing token, specify the token ID which should be
463 removed with --token-id option.
464 WARNING: The action token remove removes any token type, not
466 just keyring type from token slot specified by --token-id
467 option.
468 Action import can store arbitrary valid token json in LUKS2
470 header. It may be passed via standard input or via file passed
471 in --json-file option. If you specify --key-slot then success‐
472 fully imported token is also assigned to the key slot.
473 Action export writes requested token json to a file passed with
475 --json-file or to standard output.
476 <options> can be [--header, --token-id, --key-slot,
478 --key-description, --disable-locks, --disable-keyring,
479 --json-file].
480 convert <device> --type <format>
482 Converts the device between LUKS1 and LUKS2 format (if possi‐
484 ble). The conversion will not be performed if there is an addi‐
485 tional LUKS2 feature or LUKS1 has unsupported header size.
486 Conversion (both directions) must be performed on inactive
488 device. There must not be active dm-crypt mapping established
489 for LUKS header requested for conversion.
490 --type option is mandatory with following accepted values: luks1
492 or luks2.
493 WARNING: The convert action can destroy the LUKS header in the
495 case of a crash during conversion or if a media error occurs.
496 Always create a header backup before performing this operation!
497 <options> can be [--header, --type].
499 config <device>
501 Set permanent configuration options (store to LUKS header). The
503 config command is supported only for LUKS2.
504 The permanent options can be --priority to set priority (normal,
506 prefer, ignore) for keyslot (specified by --key-slot) or --label
507 and --subsystem.
508 <options> can be [--priority, --label, --subsystem, --key-slot,
510 --header].
511
514 cryptsetup supports mapping loop-AES encrypted partition using a com‐
515 patibility mode.
516 open --type loopaes <device> <name> --key-file <keyfile>
518 loopaesOpen <device> <name> --key-file <keyfile> (old syntax)
519 Opens the loop-AES <device> and sets up a mapping <name>.
521 If the key file is encrypted with GnuPG, then you have to use
523 --key-file=- and decrypt it before use, e.g. like this:
524 gpg --decrypt <keyfile> | cryptsetup loopaesOpen --key-file=-
525 <device> <name>
526 WARNING: The loop-AES extension cannot use the direct input of
528 key file on real terminal because the keys are separated by end-
529 of-line and only part of the multi-key file would be read.
530 If you need it in script, just use the pipe redirection:
531 echo $keyfile | cryptsetup loopaesOpen --key-file=- <device>
532 <name>
533 Use --keyfile-size to specify the proper key length if needed.
535 Use --offset to specify device offset. Note that the units need
537 to be specified in number of 512 byte sectors.
538 Use --skip to specify the IV offset. If the original device used
540 an offset and but did not use it in IV sector calculations, you
541 have to explicitly use --skip 0 in addition to the offset param‐
542 eter.
543 Use --hash to override the default hash function for passphrase
545 hashing (otherwise it is detected according to key size).
546 <options> can be [--key-file, --key-size, --offset, --skip,
548 --hash, --readonly, --allow-discards].
549 See also section 7 of the FAQ and http://loop-aes.sourceforge.net for
551 more information regarding loop-AES.
552
554 cryptsetup supports mapping of TrueCrypt, tcplay or VeraCrypt (with
555 --veracrypt option) encrypted partition using a native Linux kernel
556 API. Header formatting and TCRYPT header change is not supported,
557 cryptsetup never changes TCRYPT header on-device.
558 TCRYPT extension requires kernel userspace crypto API to be available
560 (introduced in Linux kernel 2.6.38). If you are configuring kernel
561 yourself, enable "User-space interface for symmetric key cipher algo‐
562 rithms" in "Cryptographic API" section (CRYPTO_USER_API_SKCIPHER .con‐
563 fig option).
564 Because TCRYPT header is encrypted, you have to always provide valid
566 passphrase and keyfiles.
567 Cryptsetup should recognize all header variants, except legacy cipher
569 chains using LRW encryption mode with 64 bits encryption block (namely
570 Blowfish in LRW mode is not recognized, this is limitation of kernel
571 crypto API).
572 To recognize a VeraCrypt device use the --veracrypt option. VeraCrypt
574 is just extension of TrueCrypt header with increased iteration count so
575 unlocking can take quite a lot of time (in comparison with TCRYPT
576 device).
577 To open a VeraCrypt device with a custom Personal Iteration Multiplier
579 (PIM) value, additionally to --veracrypt use either the --ver‐
580 acrypt-pim=<PIM> option to directly specify the PIM on the command-
581 line or use --veracrypt-query-pim to be prompted for the PIM.
582 The PIM value affects the number of iterations applied during key
584 derivation. Please refer to https://www.veracrypt.fr/en/Per‐
585 sonal%20Iterations%20Multiplier%20%28PIM%29.html for more detailed
586 information.
587 NOTE: Activation with tcryptOpen is supported only for cipher chains
589 using LRW or XTS encryption modes.
590 The tcryptDump command should work for all recognized TCRYPT devices
592 and doesn't require superuser privilege.
593 To map system device (device with boot loader where the whole encrypted
595 system resides) use --tcrypt-system option. You can use partition
596 device as the parameter (parameter must be real partition device, not
597 an image in a file), then only this partition is mapped.
598 If you have the whole TCRYPT device as a file image and you want to map
600 multiple partition encrypted with system encryption, please create
601 loopback mapping with partitions first (losetup -P, see losetup(8) man
602 page for more info), and use loop partition as the device parameter.
603 If you use the whole base device as a parameter, one device for the
605 whole system encryption is mapped. This mode is available only for
606 backward compatibility with older cryptsetup versions which mapped
607 TCRYPT system encryption using the whole device.
608 To use hidden header (and map hidden device, if available), use
610 --tcrypt-hidden option.
611 To explicitly use backup (secondary) header, use --tcrypt-backup
613 option.
614 NOTE: There is no protection for a hidden volume if the outer volume is
616 mounted. The reason is that if there were any protection, it would
617 require some metadata describing what to protect in the outer volume
618 and the hidden volume would become detectable.
619 open --type tcrypt <device> <name>
622 tcryptOpen <device> <name> (old syntax)
623 Opens the TCRYPT (a TrueCrypt-compatible) <device> and sets up a
625 mapping <name>.
626 <options> can be [--key-file, --tcrypt-hidden, --tcrypt-system,
628 --tcrypt-backup, --readonly, --test-passphrase, --allow-dis‐
629 cards, --veracrypt, --veracrypt-pim, --veracrypt-query-pim].
630 The keyfile parameter allows a combination of file content with
632 the passphrase and can be repeated. Note that using keyfiles is
633 compatible with TCRYPT and is different from LUKS keyfile logic.
634 WARNING: Option --allow-discards cannot be combined with option
636 --tcrypt-hidden. For normal mapping, it can cause the destruc‐
637 tion of hidden volume (hidden volume appears as unused space for
638 outer volume so this space can be discarded).
639 tcryptDump <device>
642 Dump the header information of a TCRYPT device.
644 If the --dump-master-key option is used, the TCRYPT device mas‐
646 ter key is dumped instead of TCRYPT header info. Beware that the
647 master key (or concatenated master keys if cipher chain is used)
648 can be used to decrypt the data stored in the TCRYPT container
649 without a passphrase. This means that if the master key is com‐
650 promised, the whole device has to be erased to prevent further
651 access. Use this option carefully.
652 <options> can be [--dump-master-key, --key-file, --tcrypt-hid‐
654 den, --tcrypt-system, --tcrypt-backup].
655 The keyfile parameter allows a combination of file content with
657 the passphrase and can be repeated.
658 See also https://en.wikipedia.org/wiki/TrueCrypt for more information
660 regarding TrueCrypt.
661 Please note that cryptsetup does not use TrueCrypt code, please report
663 all problems related to this compatibility extension to the cryptsetup
664 project.
665
667 repair <device>
668 Tries to repair the device metadata if possible. Currently sup‐
670 ported only for LUKS device type.
671 This command is useful to fix some known benign LUKS metadata
673 header corruptions. Only basic corruptions of unused keyslot are
674 fixable. This command will only change the LUKS header, not any
675 key-slot data. You may enforce LUKS version by adding --type
676 option.
677 WARNING: Always create a binary backup of the original header
679 before calling this command.
680 benchmark <options>
682 Benchmarks ciphers and KDF (key derivation function). Without
684 parameters, it tries to measure few common configurations.
685 To benchmark other ciphers or modes, you need to specify
687 --cipher and --key-size options or --hash for KDF test.
688 NOTE: This benchmark is using memory only and is only informa‐
690 tive. You cannot directly predict real storage encryption speed
691 from it.
692 For testing block ciphers, this benchmark requires kernel
694 userspace crypto API to be available (introduced in Linux kernel
695 2.6.38). If you are configuring kernel yourself, enable "User-
696 space interface for symmetric key cipher algorithms" in "Crypto‐
697 graphic API" section (CRYPTO_USER_API_SKCIPHER .config option).
698 <options> can be [--cipher, --key-size, --hash].
700
702 --verbose, -v
703 Print more information on command execution.
704 --debug
706 Run in debug mode with full diagnostic logs. Debug output lines
707 are always prefixed by '#'.
708 --type <device-type>
710 Specifies required device type, for more info read BASIC COM‐
711 MANDS section.
712 --hash, -h <hash-spec>
714 Specifies the passphrase hash for open (for plain and loopaes
715 device types).
716 Specifies the hash used in the LUKS key setup scheme and volume
718 key digest for luksFormat. The specified hash is used as hash-
719 parameter for PBKDF2 and for the AF splitter.
720 The specified hash name is passed to the compiled-in crypto
722 backend. Different backends may support different hashes. For
723 luksFormat, the hash algorithm must provide at least 160 bits of
724 output, which excludes, e.g., MD5. Do not use a non-crypto hash
725 like "crc32" as this breaks security.
726 Values compatible with old version of cryptsetup are "ripemd160"
728 for open --type plain and "sha1" for luksFormat.
729 Use cryptsetup --help to show the defaults.
731 --cipher, -c <cipher-spec>
733 Set the cipher specification string.
734 cryptsetup --help shows the compiled-in defaults. The current
736 default in the distributed sources is "aes-cbc-essiv:sha256" for
737 plain dm-crypt and "aes-xts-plain64" for LUKS.
738 If a hash is part of the cipher specification, then it is used
740 as part of the IV generation. For example, ESSIV needs a hash
741 function, while "plain64" does not and hence none is specified.
742 For XTS mode you can optionally set a key size of 512 bits with
744 the -s option. Key size for XTS mode is twice that for other
745 modes for the same security level.
746 XTS mode requires kernel 2.6.24 or later and plain64 requires
748 kernel 2.6.33 or later. More information can be found in the
749 FAQ.
750 --verify-passphrase, -y
752 When interactively asking for a passphrase, ask for it twice and
753 complain if both inputs do not match. Advised when creating a
754 regular mapping for the first time, or when running luksFormat.
755 Ignored on input from file or stdin.
756 --key-file, -d name
758 Read the passphrase from file.
759 If the name given is "-", then the passphrase will be read from
761 stdin. In this case, reading will not stop at newline charac‐
762 ters.
763 With LUKS, passphrases supplied via --key-file are always the
765 existing passphrases requested by a command, except in the case
766 of luksFormat where --key-file is equivalent to the positional
767 key file argument.
768 If you want to set a new passphrase via key file, you have to
770 use a positional argument to luksAddKey.
771 See section NOTES ON PASSPHRASE PROCESSING for more information.
773 --keyfile-offset value
775 Skip value bytes at the beginning of the key file. Works with
776 all commands that accept key files.
777 --keyfile-size, -l value
779 Read a maximum of value bytes from the key file. The default is
780 to read the whole file up to the compiled-in maximum that can be
781 queried with --help. Supplying more data than the compiled-in
782 maximum aborts the operation.
783 This option is useful to cut trailing newlines, for example. If
785 --keyfile-offset is also given, the size count starts after the
786 offset. Works with all commands that accept key files.
787 --new-keyfile-offset value
789 Skip value bytes at the start when adding a new passphrase from
790 key file with luksAddKey.
791 --new-keyfile-size value
793 Read a maximum of value bytes when adding a new passphrase from
794 key file with luksAddKey. The default is to read the whole file
795 up to the compiled-in maximum length that can be queried with
796 --help. Supplying more than the compiled in maximum aborts the
797 operation. When --new-keyfile-offset is also given, reading
798 starts after the offset.
799 --master-key-file
801 Use a master key stored in a file.
802 For luksFormat this allows creating a LUKS header with this spe‐
804 cific master key. If the master key was taken from an existing
805 LUKS header and all other parameters are the same, then the new
806 header decrypts the data encrypted with the header the master
807 key was taken from.
808 Action luksDump together with --dump-master-key option: The vol‐
810 ume (master) key is stored in a file instead of being printed
811 out to standard output.
812 WARNING: If you create your own master key, you need to make
814 sure to do it right. Otherwise, you can end up with a low-
815 entropy or otherwise partially predictable master key which will
816 compromise security.
817 For luksAddKey this allows adding a new passphrase without hav‐
819 ing to know an existing one.
820 For open this allows one to open the LUKS device without giving
822 a passphrase.
823 --dump-master-key
825 For luksDump this option includes the master key in the dis‐
826 played information. Use with care, as the master key can be used
827 to bypass the passphrases, see also option --master-key-file.
828 --json-file
830 Read token json from a file or write token to it. See token
831 action for more information. --json-file=- reads json from stan‐
832 dard input or writes it to standard output respectively.
833 --use-random
835 --use-urandom
837 For luksFormat these options define which kernel random number
838 generator will be used to create the master key (which is a
839 long-term key).
840 See NOTES ON RANDOM NUMBER GENERATORS for more information. Use
842 cryptsetup --help to show the compiled-in default random number
843 generator.
844 WARNING: In a low-entropy situation (e.g. in an embedded sys‐
846 tem), both selections are problematic. Using /dev/urandom can
847 lead to weak keys. Using /dev/random can block a long time,
848 potentially forever, if not enough entropy can be harvested by
849 the kernel.
850 --key-slot, -S <0-7>
852 For LUKS operations that add key material, this options allows
853 you to specify which key slot is selected for the new key. This
854 option can be used for luksFormat, and luksAddKey.
855 In addition, for open, this option selects a specific key-slot
856 to compare the passphrase against. If the given passphrase
857 would only match a different key-slot, the operation fails.
858 --key-size, -s <bits>
860 Sets key size in bits. The argument has to be a multiple of 8.
861 The possible key-sizes are limited by the cipher and mode used.
862 See /proc/crypto for more information. Note that key-size in
864 /proc/crypto is stated in bytes.
865 This option can be used for open --type plain or luksFormat.
867 All other LUKS actions will use the key-size specified in the
868 LUKS header. Use cryptsetup --help to show the compiled-in
869 defaults.
870 --size, -b <number of 512 byte sectors>
872 Set the size of the device in sectors of 512 bytes. This option
873 is only relevant for the open and resize actions.
874 --offset, -o <number of 512 byte sectors>
876 Start offset in the backend device in 512-byte sectors. This
877 option is only relevant for the open action with plain or
878 loopaes device types.
879 --skip, -p <number of 512 byte sectors>
881 Start offset used in IV calculation in 512-byte sectors (how
882 many sectors of the encrypted data to skip at the beginning).
883 This option is only relevant for the open action with plain or
884 loopaes device types.
885 Hence, if --offset n, and --skip s, sector n (the first sector
887 of the encrypted device) will get a sector number of s for the
888 IV calculation.
889 --readonly, -r
891 set up a read-only mapping.
892 --shared
894 Creates an additional mapping for one common ciphertext device.
895 Arbitrary mappings are supported. This option is only relevant
896 for the open --type plain action. Use --offset, --size and
897 --skip to specify the mapped area.
898 --pbkdf <PBKDF spec>
900 Set Password-Based Key Derivation Function (PBKDF) algorithm for
901 LUKS keyslot. The PBKDF can be: pbkdf2 (for PBKDF2 according to
902 RFC2898), argon2i for Argon2i or argon2id for Argon2id (see
903 https://www.cryptolux.org/index.php/Argon2 for more info).
904 For LUKS1, only PBKDF2 is accepted (no need to use this option).
906 The default PBKDF2 for LUKS2 is set during compilation time and
907 is available in cryptsetup --help output.
908 A PBKDF is used for increasing dictionary and brute-force attack
910 cost for keyslot passwords. The parameters can be time, memory
911 and parallel cost.
912 For PBKDF2, only time cost (number of iterations) applies. For
914 Argon2i/id, there is also memory cost (memory required during
915 the process of key derivation) and parallel cost (number of
916 threads that run in parallel during the key derivation.
917 Note that increasing memory cost also increases time, so the
919 final parameter values are measured by a benchmark. The bench‐
920 mark tries to find iteration time (--iter-time) with required
921 memory cost --pbkdf-memory. If it is not possible, the memory
922 cost is decreased as well. The parallel cost --pbkdf-parallel
923 is constant, is is checked against available CPU cores (if not
924 available, it is decreased) and the maximum parallel cost is 4.
925 You can see all PBKDF parameters for particular LUKS2 keyslot
927 with luksDump command.
928 NOTE: If you do not want to use benchmark and want to specify
930 all parameters directly, use --pbkdf-force-iterations with
931 --pbkdf-memory and --pbkdf-parallel. This will override the
932 values without benchmarking. Note it can cause extremely long
933 unlocking time. Use only is specified cases, for example, if you
934 know that the formatted device will be used on some small embed‐
935 ded system. In this case, the LUKS PBKDF2 digest will be set to
936 the minimum iteration count.
937 --iter-time, -i <number of milliseconds>
939 The number of milliseconds to spend with PBKDF passphrase pro‐
940 cessing. This option is only relevant for LUKS operations that
941 set or change passphrases, such as luksFormat or luksAddKey.
942 Specifying 0 as parameter selects the compiled-in default.
943 --pbkdf-memory <number>
945 Set the memory cost for PBKDF (for Argon2i/id the number repre‐
946 sents kilobytes). Note that it is maximal value, PBKDF bench‐
947 mark or available physical memory can decrease it. This option
948 is not available for PBKDF2.
949 --pbkdf-parallel <number>
951 Set the parallel cost for PBKDF (number of threads, up to 4).
952 Note that it is maximal value, it is decreased automatically if
953 CPU online count is lower. This option is not available for
954 PBKDF2.
955 --pbkdf-force-iterations <num>
957 Avoid PBKDF benchmark and set time cost (iterations) directly.
958 It can be used for LUKS/LUKS2 device only. See --pbkdf option
959 for more info.
960 --batch-mode, -q
962 Suppresses all confirmation questions. Use with care!
963 If the -y option is not specified, this option also switches off
965 the passphrase verification for luksFormat.
966 --progress-frequency <seconds>
968 Print separate line every <seconds> with wipe progress.
969 --timeout, -t <number of seconds>
971 The number of seconds to wait before timeout on passphrase input
972 via terminal. It is relevant every time a passphrase is asked,
973 for example for open, luksFormat or luksAddKey. It has no
974 effect if used in conjunction with --key-file.
975 This option is useful when the system should not stall if the
976 user does not input a passphrase, e.g. during boot. The default
977 is a value of 0 seconds, which means to wait forever.
978 --tries, -T
980 How often the input of the passphrase shall be retried. This
981 option is relevant every time a passphrase is asked, for example
982 for open, luksFormat or luksAddKey. The default is 3 tries.
983 --align-payload <number of 512 byte sectors>
985 Align payload at a boundary of value 512-byte sectors. This
986 option is relevant for luksFormat.
987 If not specified, cryptsetup tries to use the topology info pro‐
989 vided by the kernel for the underlying device to get the optimal
990 alignment. If not available (or the calculated value is a mul‐
991 tiple of the default) data is by default aligned to a 1MiB
992 boundary (i.e. 2048 512-byte sectors).
993 For a detached LUKS header, this option specifies the offset on
995 the data device. See also the --header option.
996 --uuid=UUID
998 Use the provided UUID for the luksFormat command instead of gen‐
999 erating a new one. Changes the existing UUID when used with the
1000 luksUUID command.
1001 The UUID must be provided in the standard UUID format, e.g.
1003 12345678-1234-1234-1234-123456789abc.
1004 --allow-discards
1006 Allow the use of discard (TRIM) requests for the device. This
1007 option is only relevant for open action.
1008 WARNING: This command can have a negative security impact
1010 because it can make filesystem-level operations visible on the
1011 physical device. For example, information leaking filesystem
1012 type, used space, etc. may be extractable from the physical
1013 device if the discarded blocks can be located later. If in
1014 doubt, do not use it.
1015 A kernel version of 3.1 or later is needed. For earlier kernels,
1017 this option is ignored.
1018 --perf-same_cpu_crypt
1020 Perform encryption using the same cpu that IO was submitted on.
1021 The default is to use an unbound workqueue so that encryption
1022 work is automatically balanced between available CPUs. This
1023 option is only relevant for open action.
1024 NOTE: This option is available only for low-level dm-crypt per‐
1026 formance tuning, use only if you need a change to default dm-
1027 crypt behaviour. Needs kernel 4.0 or later.
1028 --perf-submit_from_crypt_cpus
1030 Disable offloading writes to a separate thread after encryption.
1031 There are some situations where offloading write bios from the
1032 encryption threads to a single thread degrades performance sig‐
1033 nificantly. The default is to offload write bios to the same
1034 thread. This option is only relevant for open action.
1035 NOTE: This option is available only for low-level dm-crypt per‐
1037 formance tuning, use only if you need a change to default dm-
1038 crypt behaviour. Needs kernel 4.0 or later.
1039 --test-passphrase
1041 Do not activate the device, just verify passphrase. This option
1042 is only relevant for open action (the device mapping name is not
1043 mandatory if this option is used).
1044 --header <device or file storing the LUKS header>
1046 Use a detached (separated) metadata device or file where the
1047 LUKS header is stored. This option allows one to store cipher‐
1048 text and LUKS header on different devices.
1049 This option is only relevant for LUKS devices and can be used
1051 with the luksFormat, open, luksSuspend, luksResume, status and
1052 resize commands.
1053 For luksFormat with a file name as the argument to --header, the
1055 file will be automatically created if it does not exist. See
1056 the cryptsetup FAQ for header size calculation.
1057 For other commands that change the LUKS header (e.g. luksAdd‐
1059 Key), specify the device or file with the LUKS header directly
1060 as the LUKS device.
1061 If used with luksFormat, the --align-payload option is taken as
1063 absolute sector alignment on ciphertext device and can be zero.
1064 WARNING: There is no check whether the ciphertext device speci‐
1066 fied actually belongs to the header given. In fact, you can
1067 specify an arbitrary device as the ciphertext device for open
1068 with the --header option. Use with care.
1069 --header-backup-file <file>
1071 Specify file with header backup for luksHeaderBackup or luk‐
1072 sHeaderBackup actions.
1073 --force-password
1075 Do not use password quality checking for new LUKS passwords.
1076 This option applies only to luksFormat, luksAddKey and
1078 luksChangeKey and is ignored if cryptsetup is built without
1079 password quality checking support.
1080 For more info about password quality check, see the manual page
1082 for pwquality.conf(5) and passwdqc.conf(5).
1083 --deferred
1085 Defers device removal in close command until the last user
1086 closes it.
1087 --disable-locks
1089 Disable lock protection for metadata on disk. This option is
1090 valid only for LUKS2 and ignored for other formats.
1091 WARNING: Do not use this option unless you run cryptsetup in a
1093 restricted environment where locking is impossible to perform
1094 (where /run directory cannot be used).
1095 --disable-keyring
1097 Do not load volume key in kernel keyring but use store key
1098 directly in the dm-crypt target. This option is supported only
1099 for the LUKS2 format.
1100 --key-description <text>
1102 Set key description in keyring for use with token command.
1103 --priority <normal|prefer|ignore>
1105 Set a priority for LUKS2 keyslot. The prefer priority marked
1106 slots are tried before normal priority. The ignored priority
1107 means, that slot is never used, if not explicitly requested by
1108 --key-slot option.
1109 --token-id
1111 Specify what token to use in actions token, open or resize. If
1112 omitted, all available tokens will be checked before proceeding
1113 further with passphrase prompt.
1114 --token-only
1116 Do not proceed further with action (any of token, open or
1117 resize) if token activation failed. Without the option, action
1118 asks for passphrase to proceed further.
1119 --sector-size <bytes>
1121 Set sector size for use with disk encryption. It must be power
1122 of two and in range 512 - 4096 bytes. The default is 512 bytes
1123 sectors. This option is available only in the LUKS2 mode.
1124 Note that if sector size is higher than underlying device hard‐
1126 ware sector and there is not integrity protection that uses data
1127 journal, using this option can increase risk on incomplete sec‐
1128 tor writes during a power fail.
1129 If used together with --integrity option and dm-integrity jour‐
1131 nal, the atomicity of writes is guaranteed in all cases (but it
1132 cost write performance - data has to be written twice).
1133 Increasing sector size from 512 bytes to 4096 bytes can provide
1135 better performance on most of the modern storage devices and
1136 also with some hw encryption accelerators.
1137 --persistent
1139 If used with LUKS2 devices and activation commands like open,
1140 the specified activation flags are persistently written into
1141 metadata and used next time automatically even for normal acti‐
1142 vation. (No need to use cryptab or other system configuration
1143 files.) Only --allow-discards, --perf-same_cpu_crypt,
1144 --perf-submit_from_crypt_cpus and --integrity-no-journal can be
1145 stored persistently.
1146 --label <LABEL>
1148 --subsystem <SUBSYSTEM> Set label and subsystem description for
1149 LUKS2 device, can be used in config and format actions. The
1150 label and subsystem are optional fields and can be later used in
1151 udev scripts for triggering user actions once device marked by
1152 these labels is detected.
1153 --integrity <integrity algorithm>
1155 Specify integrity algorithm to be used for authenticated disk
1156 encryption in LUKS2.
1157 WARNING: This extension is EXPERIMENTAL and requires dm-
1159 integrity kernel target (available since kernel version 4.12).
1160 For native AEAD modes, also enable "User-space interface for
1161 AEAD cipher algorithms" in "Cryptographic API" section (CON‐
1162 FIG_CRYPTO_USER_API_AEAD .config option).
1163 For more info, see AUTHENTICATED DISK ENCRYPTION section.
1165 --integrity-no-journal
1167 Activate device with integrity protection without using data
1168 journal (direct write of data and integrity tags). Note that
1169 without journal power fail can cause non-atomic write and data
1170 corruption. Use only if journalling is performed on a different
1171 storage layer.
1172 --integrity-no-wipe
1174 Skip wiping of device authentication (integrity) tags. If you
1175 skip this step, sectors will report invalid integrity tag until
1176 an application write to the sector.
1177 NOTE: Even some writes to the device can fail if the write is
1179 not aligned to page size and page-cache initiates read of a sec‐
1180 tor with invalid integrity tag.
1181 --unbound
1183 Creates new LUKS2 unbound keyslot. See luksAddKey action for
1185 more details.
1186 --tcrypt-hidden
1188 --tcrypt-system --tcrypt-backup Specify which TrueCrypt on-disk
1189 header will be used to open the device. See TCRYPT section for
1190 more info.
1191 --veracrypt
1193 Allow VeraCrypt compatible mode. Only for TCRYPT extension. See
1194 TCRYPT section for more info.
1195 --veracrypt-pim
1197 --veracrypt-query-pim Use a custom Personal Iteration Multiplier
1198 (PIM) for VeraCrypt device. See TCRYPT section for more info.
1199 --version
1201 Show the program version.
1202 --usage
1204 Show short option help.
1205 --help, -?
1207 Show help text and default parameters.
1208
1210 Cryptsetup returns 0 on success and a non-zero value on error.
1211 Error codes are: 1 wrong parameters, 2 no permission (bad passphrase),
1213 3 out of memory, 4 wrong device specified, 5 device already exists or
1214 device is busy.
1215
1217 Note that no iterated hashing or salting is done in plain mode. If
1218 hashing is done, it is a single direct hash. This means that low-
1219 entropy passphrases are easy to attack in plain mode.
1220 From a terminal: The passphrase is read until the first newline, i.e.
1222 '\n'. The input without the newline character is processed with the
1223 default hash or the hash specified with --hash. The hash result will
1224 be truncated to the key size of the used cipher, or the size specified
1225 with -s.
1226 From stdin: Reading will continue until a newline (or until the maximum
1228 input size is reached), with the trailing newline stripped. The maximum
1229 input size is defined by the same compiled-in default as for the maxi‐
1230 mum key file size and can be overwritten using --keyfile-size option.
1231 The data read will be hashed with the default hash or the hash speci‐
1233 fied with --hash. The hash result will be truncated to the key size of
1234 the used cipher, or the size specified with -s.
1235 Note that if --key-file=- is used for reading the key from stdin,
1237 trailing newlines are not stripped from the input.
1238 If "plain" is used as argument to --hash, the input data will not be
1240 hashed. Instead, it will be zero padded (if shorter than the key size)
1241 or truncated (if longer than the key size) and used directly as the
1242 binary key. This is useful for directly specifying a binary key. No
1243 warning will be given if the amount of data read from stdin is less
1244 than the key size.
1245 From a key file: It will be truncated to the key size of the used
1247 cipher or the size given by -s and directly used as a binary key.
1248 WARNING: The --hash argument is being ignored. The --hash option is
1250 usable only for stdin input in plain mode.
1251 If the key file is shorter than the key, cryptsetup will quit with an
1253 error. The maximum input size is defined by the same compiled-in
1254 default as for the maximum key file size and can be overwritten using
1255 --keyfile-size option.
1256
1260 LUKS uses PBKDF2 to protect against dictionary attacks and to give some
1261 protection to low-entropy passphrases (see RFC 2898 and the cryptsetup
1262 FAQ).
1263 From a terminal: The passphrase is read until the first newline and
1265 then processed by PBKDF2 without the newline character.
1266 From stdin: LUKS will read passphrases from stdin up to the first new‐
1268 line character or the compiled-in maximum key file length. If --key‐
1269 file-size is given, it is ignored.
1270 From key file: The complete keyfile is read up to the compiled-in maxi‐
1272 mum size. Newline characters do not terminate the input. The --key‐
1273 file-size option can be used to limit what is read.
1274 Passphrase processing: Whenever a passphrase is added to a LUKS header
1276 (luksAddKey, luksFormat), the user may specify how much the time the
1277 passphrase processing should consume. The time is used to determine the
1278 iteration count for PBKDF2 and higher times will offer better protec‐
1279 tion for low-entropy passphrases, but open will take longer to com‐
1280 plete. For passphrases that have entropy higher than the used key
1281 length, higher iteration times will not increase security.
1282 The default setting of one or two seconds is sufficient for most prac‐
1284 tical cases. The only exception is a low-entropy passphrase used on a
1285 device with a slow CPU, as this will result in a low iteration count.
1286 On a slow device, it may be advisable to increase the iteration time
1287 using the --iter-time option in order to obtain a higher iteration
1288 count. This does slow down all later luksOpen operations accordingly.
1289
1291 LUKS checks for a valid passphrase when an encrypted partition is
1292 unlocked. The behavior of plain dm-crypt is different. It will always
1293 decrypt with the passphrase given. If the given passphrase is wrong,
1294 the device mapped by plain dm-crypt will essentially still contain
1295 encrypted data and will be unreadable.
1296
1298 The available combinations of ciphers, modes, hashes and key sizes
1299 depend on kernel support. See /proc/crypto for a list of available
1300 options. You might need to load additional kernel crypto modules in
1301 order to get more options.
1302 For the --hash option, if the crypto backend is libgcrypt, then all
1304 algorithms supported by the gcrypt library are available. For other
1305 crypto backends, some algorithms may be missing.
1306
1308 Mathematics can't be bribed. Make sure you keep your passphrases safe.
1309 There are a few nice tricks for constructing a fallback, when suddenly
1310 out of the blue, your brain refuses to cooperate. These fallbacks need
1311 LUKS, as it's only possible with LUKS to have multiple passphrases.
1312 Still, if your attacker model does not prevent it, storing your
1313 passphrase in a sealed envelope somewhere may be a good idea as well.
1314
1316 Random Number Generators (RNG) used in cryptsetup are always the kernel
1317 RNGs without any modifications or additions to data stream produced.
1318 There are two types of randomness cryptsetup/LUKS needs. One type
1320 (which always uses /dev/urandom) is used for salts, the AF splitter and
1321 for wiping deleted keyslots.
1322 The second type is used for the volume (master) key. You can switch
1324 between using /dev/random and /dev/urandom here, see --use-random and
1325 --use-urandom options. Using /dev/random on a system without enough
1326 entropy sources can cause luksFormat to block until the requested
1327 amount of random data is gathered. In a low-entropy situation (embedded
1328 system), this can take a very long time and potentially forever. At the
1329 same time, using /dev/urandom in a low-entropy situation will produce
1330 low-quality keys. This is a serious problem, but solving it is out of
1331 scope for a mere man-page. See urandom(4) for more information.
1332
1334 Since Linux kernel version 4.12 dm-crypt supports authenticated disk
1335 encryption.
1336 Normal disk encryption modes are length-preserving (plaintext sector is
1338 of the same size as a ciphertext sector) and can provide only confiden‐
1339 tiality protection, but not cryptographically sound data integrity pro‐
1340 tection.
1341 Authenticated modes require additional space per-sector for authentica‐
1343 tion tag and use Authenticated Encryption with Additional Data (AEAD)
1344 algorithms.
1345 If you configure LUKS2 device with data integrity protection, there
1347 will be an underlying dm-integrity device, which provides additional
1348 per-sector metadata space and also provide data journal protection to
1349 ensure atomicity of data and metadata update. Because there must be
1350 additional space for metadata and journal, the available space for the
1351 device will be smaller than for length-preserving modes.
1352 The dm-crypt device then resides on top of such a dm-integrity device.
1354 All activation and deactivation of this device stack is performed by
1355 cryptsetup, there is no difference in using luksOpen for integrity pro‐
1356 tected devices. If you want to format LUKS2 device with data integrity
1357 protection, use --integrity option.
1358 Some integrity modes requires two independent keys (key for encryption
1360 and for authentication). Both these keys are stored in one LUKS
1361 keyslot.
1362 WARNING: All support for authenticated modes is experimental and there
1364 are only some modes available for now. Note that there are a very few
1365 authenticated encryption algorithms that are suitable for disk encryp‐
1366 tion.
1367
1370 Cryptsetup is usually used directly on a block device (disk partition
1371 or LVM volume). However, if the device argument is a file, cryptsetup
1372 tries to allocate a loopback device and map it into this file. This
1373 mode requires Linux kernel 2.6.25 or more recent which supports the
1374 loop autoclear flag (loop device is cleared on the last close automati‐
1375 cally). Of course, you can always map a file to a loop-device manually.
1376 See the cryptsetup FAQ for an example.
1377 When device mapping is active, you can see the loop backing file in the
1379 status command output. Also see losetup(8).
1380
1382 The LUKS2 on-disk metadata is updated in several steps and to achieve
1383 proper atomic update, there is a locking mechanism. For an image in
1384 file, code uses flock(2) system call. For a block device, lock is per‐
1385 formed over a special file stored in a locking directory (by default
1386 /run/lock/cryptsetup). The locking directory should be created with
1387 the proper security context by the distribution during the boot-up
1388 phase. Only LUKS2 uses locks, other formats do not use this mechanism.
1389
1391 The reload action is no longer supported. Please use dmsetup(8) if you
1392 need to directly manipulate with the device mapping table.
1393 The luksDelKey was replaced with luksKillSlot.
1395
1397 Report bugs, including ones in the documentation, on the cryptsetup
1398 mailing list at <dm-crypt@saout.de> or in the 'Issues' section on LUKS
1399 website. Please attach the output of the failed command with the
1400 --debug option added.
1401
1403 cryptsetup originally written by Jana Saout <jana@saout.de>
1404 The LUKS extensions and original man page were written by Clemens Fruh‐
1405 wirth <clemens@endorphin.org>.
1406 Man page extensions by Milan Broz <gmazyland@gmail.com>.
1407 Man page rewrite and extension by Arno Wagner <arno@wagner.name>.
1408
1410 Copyright © 2004 Jana Saout
1411 Copyright © 2004-2006 Clemens Fruhwirth
1412 Copyright © 2009-2018 Red Hat, Inc.
1413 Copyright © 2009-2018 Milan Broz
1414 Copyright © 2012-2014 Arno Wagner
1415 This is free software; see the source for copying conditions. There is
1417 NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
1418 PURPOSE.
1419
1421 The LUKS website at https://gitlab.com/cryptsetup/cryptsetup/
1422 The cryptsetup FAQ, contained in the distribution package and online at
1424 https://gitlab.com/cryptsetup/cryptsetup/wikis/FrequentlyAskedQuestions
1425 The cryptsetup mailing list and list archive, see FAQ entry 1.6.
1427 The LUKS on-disk format specification available at https://git‐
1429 lab.com/cryptsetup/cryptsetup/wikis/Specification
1430cryptsetup January 2018 CRYPTSETUP(8)