info > CRYPTSETUP

📖 NAME

cryptsetup - manage plain dm-crypt and LUKS encrypted volumes

🚀 Quick Reference

Use CaseCommandDescription
Create LUKS2 containercryptsetup --type luks2 luksFormat /dev/sdXInitialize a LUKS2 partition with a passphrase
Open LUKS containercryptsetup open /dev/sdX sdX_cryptDecrypt and map the device to /dev/mapper/sdX_crypt
Add a passphrasecryptsetup luksAddKey /dev/sdXAdd a new passphrase to a key slot
Remove a passphrasecryptsetup luksRemoveKey /dev/sdXRemove an existing passphrase
Backup LUKS headercryptsetup luksHeaderBackup /dev/sdX --header-backup-file backupSave header and keyslot area to a file
Restore LUKS headercryptsetup luksHeaderRestore /dev/sdX --header-backup-file backupRestore header from backup file
Erase all keyslotscryptsetup erase /dev/sdXPermanently destroy access to LUKS container
Check device statuscryptsetup status <name>Show mapping details for an active device
Resize an active mappingcryptsetup resize <name>Change the size of the mapped device
Benchmark ciphers/KDFcryptsetup benchmarkMeasure performance of cryptographic algorithms

🔧 SYNOPSIS

cryptsetup <options> <action> <action args>

📄 DESCRIPTION

cryptsetup is used to conveniently setup dm-crypt managed device-mapper mappings. These include plain dm-crypt volumes and LUKS volumes. The difference is that LUKS uses a metadata header and can hence offer more features than plain dm-crypt. On the other hand, the header is visible and vulnerable to damage.

In addition, cryptsetup provides limited support for the use of loop-AES volumes, TrueCrypt, VeraCrypt and BitLocker compatible volumes.

🔍 PLAIN DM-CRYPT OR LUKS?

Unless you understand the cryptographic background well, use LUKS. With plain dm-crypt there are a number of possible user errors that massively decrease security. While LUKS cannot fix them all, it can lessen the impact for many of them.

⚠️ WARNINGS

A lot of good information on the risks of using encrypted storage, on handling problems and on security aspects can be found in the Cryptsetup FAQ. Read it. Nonetheless, some risks deserve to be mentioned here.

⚙️ BASIC ACTIONS

The following are valid actions for all supported device types.

🛠️ PLAIN MODE

Plain dm-crypt encrypts the device sector-by-sector with a single, non-salted hash of the passphrase. No checks are performed, no metadata is used. There is no formatting operation. When the raw device is mapped (opened), the usual device operations can be used on the mapped device, including filesystem creation. Mapped devices usually reside in /dev/mapper/<name>.

The following are valid plain device type actions:

Example: 'cryptsetup open --type plain /dev/sda10 e1' maps the raw encrypted device /dev/sda10 to the mapped (decrypted) device /dev/mapper/e1, which can then be mounted, fsck-ed or have a filesystem created on it.

🏷️ LUKS EXTENSION

LUKS, the Linux Unified Key Setup, is a standard for disk encryption. It adds a standardized header at the start of the device, a key-slot area directly behind the header and the bulk data area behind that. The whole set is called a 'LUKS container'. The device that a LUKS container resides on is called a 'LUKS device'. For most purposes, both terms can be used interchangeably. But note that when the LUKS header is at a nonzero offset in a device, then the device is not a LUKS device anymore, but has a LUKS container stored in it at an offset.

LUKS can manage multiple passphrases that can be individually revoked or changed and that can be securely scrubbed from persistent media due to the use of anti-forensic stripes. Passphrases are protected against brute-force and dictionary attacks by PBKDF2, which implements hash iteration and salting in one function.

LUKS2 is a new version of header format that allows additional extensions like different PBKDF algorithm or authenticated encryption. You can format device with LUKS2 header if you specify --type luks2 in luksFormat command. For activation, the format is already recognized automatically.

Each passphrase, also called a key in this document, is associated with one of 8 key-slots. Key operations that do not specify a slot affect the first slot that matches the supplied passphrase or the first empty slot if a new passphrase is added.

The <device> parameter can also be specified by a LUKS UUID in the format UUID=<uuid>. Translation to real device name uses symlinks in /dev/disk/by-uuid directory.

To specify a detached header, the --header parameter can be used in all LUKS commands and always takes precedence over the positional <device> parameter.

The following are valid LUKS actions:

🔁 loop-AES EXTENSION

cryptsetup supports mapping loop-AES encrypted partition using a compatibility mode.

See also section 7 of the FAQ and http://loop-aes.sourceforge.net for more information regarding loop-AES.

🔒 TCRYPT (TrueCrypt-compatible and VeraCrypt) EXTENSION

cryptsetup supports mapping of TrueCrypt, tcplay or VeraCrypt encrypted partition using a native Linux kernel API. Header formatting and TCRYPT header change is not supported, cryptsetup never changes TCRYPT header on-device.

TCRYPT extension requires kernel userspace crypto API to be available (introduced in Linux kernel 2.6.38). If you are configuring kernel yourself, enable "User-space interface for symmetric key cipher algorithms" in "Cryptographic API" section (CRYPTO_USER_API_SKCIPHER .config option).

Because TCRYPT header is encrypted, you have to always provide valid passphrase and keyfiles.

Cryptsetup should recognize all header variants, except legacy cipher chains using LRW encryption mode with 64 bits encryption block (namely Blowfish in LRW mode is not recognized, this is limitation of kernel crypto API).

VeraCrypt is just extension of TrueCrypt header with increased iteration count so unlocking can take quite a lot of time (in comparison with TCRYPT device).

To open a VeraCrypt device with a custom Personal Iteration Multiplier (PIM) value, use either the --veracrypt-pim=<PIM> option to directly specify the PIM on the command- line or use --veracrypt-query-pim to be prompted for the PIM.

The PIM value affects the number of iterations applied during key derivation. Please refer to https://www.veracrypt.fr/en/Personal%20Iterations%20Multiplier%20%28PIM%29.html for more detailed information.

If you need to disable VeraCrypt device support, use --disable-veracrypt option.

NOTE: Activation with tcryptOpen is supported only for cipher chains using LRW or XTS encryption modes.

The tcryptDump command should work for all recognized TCRYPT devices and doesn't require superuser privilege.

To map system device (device with boot loader where the whole encrypted system resides) use --tcrypt-system option. You can use partition device as the parameter (parameter must be real partition device, not an image in a file), then only this partition is mapped.

If you have the whole TCRYPT device as a file image and you want to map multiple partition encrypted with system encryption, please create loopback mapping with partitions first (losetup -P, see losetup(8) man page for more info), and use loop partition as the device parameter.

If you use the whole base device as a parameter, one device for the whole system encryption is mapped. This mode is available only for backward compatibility with older cryptsetup versions which mapped TCRYPT system encryption using the whole device.

To use hidden header (and map hidden device, if available), use --tcrypt-hidden option.

To explicitly use backup (secondary) header, use --tcrypt-backup option.

NOTE: There is no protection for a hidden volume if the outer volume is mounted. The reason is that if there were any protection, it would require some metadata describing what to protect in the outer volume and the hidden volume would become detectable.

See also https://en.wikipedia.org/wiki/TrueCrypt for more information regarding TrueCrypt. Please note that cryptsetup does not use TrueCrypt code, please report all problems related to this compatibility extension to the cryptsetup project.

🧪 BITLK (Windows BitLocker-compatible) EXTENSION (EXPERIMENTAL)

cryptsetup supports mapping of BitLocker and BitLocker to Go encrypted partition using a native Linux kernel API. Header formatting and BITLK header changes are not supported, cryptsetup never changes BITLK header on-device. WARNING: This extension is EXPERIMENTAL.

BITLK extension requires kernel userspace crypto API to be available (for details see TCRYPT section).

Cryptsetup should recognize all BITLK header variants, except legacy header used in Windows Vista systems and partially decrypted BitLocker devices. Activation of legacy devices encrypted in CBC mode requires at least Linux kernel version 5.3 and for devices using Elephant diffuser kernel 5.6.

The bitlkDump command should work for all recognized BITLK devices and doesn't require superuser privilege.

For unlocking with the open a password or a recovery passphrase or a startup key must be provided.

Additionally unlocking using master key is supported. You must provide BitLocker Full Volume Encryption Key (FVEK) using the --master-key-file option. The key must be decrypted and without the header (only 128/256/512 bits of key data depending on used cipher and mode).

Other unlocking methods (TPM, SmartCard) are not supported.

Please note that cryptsetup does not use any Windows BitLocker code, please report all problems related to this compatibility extension to the cryptsetup project.

🧰 MISCELLANEOUS

⚙️ OPTIONS

📝 EXAMPLE

Example 1: Create LUKS 2 container on block device /dev/sdX.
sudo cryptsetup --type luks2 luksFormat /dev/sdX

Example 2: Add an additional passphrase to key slot 5.
sudo cryptsetup luksAddKey --key-slot 5 /dev/sdX

Example 3: Create LUKS header backup and save it to file.
sudo cryptsetup luksHeaderBackup /dev/sdX --header-backup-file /var/tmp/NameOfBackupFile

Example 4: Open LUKS container on /dev/sdX and map it to sdX_crypt.
sudo cryptsetup open /dev/sdX sdX_crypt

WARNING: The command in example 5 will erase all key slots.
You cannot use your luks container afterwards anymore unless
you have a backup to restore.

Example 5: Erase all key slots on /dev/sdX.
sudo cryptsetup erase /dev/sdX

Example 6: Restore LUKS header from backup file.
sudo cryptsetup luksHeaderRestore /dev/sdX --header-backup-file /var/tmp/NameOfBackupFile

🚪 Exit Codes

Cryptsetup returns 0 on success and a non-zero value on error.

📝 NOTES ON PASSPHRASE PROCESSING FOR PLAIN MODE

Note that no iterated hashing or salting is done in plain mode. If hashing is done, it is a single direct hash. This means that low-entropy passphrases are easy to attack in plain mode.

From a terminal: The passphrase is read until the first newline, i.e. '\n'. The input without the newline character is processed with the default hash or the hash specified with --hash. The hash result will be truncated to the key size of the used cipher, or the size specified with -s.

From stdin: Reading will continue until a newline (or until the maximum input size is reached), with the trailing newline stripped. The maximum input size is defined by the same compiled-in default as for the maximum key file size and can be overwritten using --keyfile-size option. The data read will be hashed with the default hash or the hash specified with --hash. The hash result will be truncated to the key size of the used cipher, or the size specified with -s.

Note that if --key-file=- is used for reading the key from stdin, trailing newlines are not stripped from the input.

If "plain" is used as argument to --hash, the input data will not be hashed. Instead, it will be zero padded (if shorter than the key size) or truncated (if longer than the key size) and used directly as the binary key. This is useful for directly specifying a binary key. No warning will be given if the amount of data read from stdin is less than the key size.

From a key file: It will be truncated to the key size of the used cipher or the size given by -s and directly used as a binary key. WARNING: The --hash argument is being ignored. The --hash option is usable only for stdin input in plain mode. If the key file is shorter than the key, cryptsetup will quit with an error. The maximum input size is defined by the same compiled-in default as for the maximum key file size and can be overwritten using --keyfile-size option.

📝 NOTES ON PASSPHRASE PROCESSING FOR LUKS

LUKS uses PBKDF2 to protect against dictionary attacks and to give some protection to low-entropy passphrases (see RFC 2898 and the cryptsetup FAQ).

From a terminal: The passphrase is read until the first newline and then processed by PBKDF2 without the newline character.

From stdin: LUKS will read passphrases from stdin up to the first newline character or the compiled-in maximum key file length. If --keyfile-size is given, it is ignored.

From key file: The complete keyfile is read up to the compiled-in maximum size. Newline characters do not terminate the input. The --keyfile-size option can be used to limit what is read.

Passphrase processing: Whenever a passphrase is added to a LUKS header (luksAddKey, luksFormat), the user may specify how much the time the passphrase processing should consume. The time is used to determine the iteration count for PBKDF2 and higher times will offer better protection for low-entropy passphrases, but open will take longer to complete. For passphrases that have entropy higher than the used key length, higher iteration times will not increase security.

The default setting of one or two seconds is sufficient for most practical cases. The only exception is a low-entropy passphrase used on a device with a slow CPU, as this will result in a low iteration count. On a slow device, it may be advisable to increase the iteration time using the --iter-time option in order to obtain a higher iteration count. This does slow down all later luksOpen operations accordingly.

⚠️ INCOHERENT BEHAVIOR FOR INVALID PASSPHRASES/KEYS

LUKS checks for a valid passphrase when an encrypted partition is unlocked. The behavior of plain dm-crypt is different. It will always decrypt with the passphrase given. If the given passphrase is wrong, the device mapped by plain dm-crypt will essentially still contain encrypted data and will be unreadable.

🔐 NOTES ON SUPPORTED CIPHERS, MODES, HASHES AND KEY SIZES

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.

For the --hash option, if the crypto backend is libgcrypt, then all algorithms supported by the gcrypt library are available. For other crypto backends, some algorithms may be missing.

🔑 NOTES ON PASSPHRASES

Mathematics can't be bribed. Make sure you keep your passphrases safe. There are a few nice tricks for constructing a fallback, when suddenly out of the blue, your brain refuses to cooperate. These fallbacks need LUKS, as it's only possible with LUKS to have multiple passphrases. Still, if your attacker model does not prevent it, storing your passphrase in a sealed envelope somewhere may be a good idea as well.

🎲 NOTES ON RANDOM NUMBER GENERATORS

Random Number Generators (RNG) used in cryptsetup are always the kernel RNGs without any modifications or additions to data stream produced.

There are two types of randomness cryptsetup/LUKS needs. One type (which always uses /dev/urandom) is used for salts, the AF splitter and for wiping deleted keyslots. The second type is used for the volume (master) key. You can switch between using /dev/random and /dev/urandom here, see --use-random and --use-urandom options. Using /dev/random on a system without enough entropy sources can cause luksFormat to block until the requested amount of random data is gathered. In a low-entropy situation (embedded system), this can take a very long time and potentially forever. At the same time, using /dev/urandom in a low-entropy situation will produce low-quality keys. This is a serious problem, but solving it is out of scope for a mere man-page. See urandom(4) for more information.

🛡️ AUTHENTICATED DISK ENCRYPTION (EXPERIMENTAL)

Since Linux kernel version 4.12 dm-crypt supports authenticated disk encryption.

Normal disk encryption modes are length-preserving (plaintext sector is of the same size as a ciphertext sector) and can provide only confidentiality protection, but not cryptographically sound data integrity protection.

Authenticated modes require additional space per-sector for authentication tag and use Authenticated Encryption with Additional Data (AEAD) algorithms.

If you configure LUKS2 device with data integrity protection, there will be an underlying dm-integrity device, which provides additional per-sector metadata space and also provide data journal protection to ensure atomicity of data and metadata update. Because there must be additional space for metadata and journal, the available space for the device will be smaller than for length-preserving modes.

The dm-crypt device then resides on top of such a dm-integrity device. All activation and deactivation of this device stack is performed by cryptsetup, there is no difference in using luksOpen for integrity protected devices. If you want to format LUKS2 device with data integrity protection, use --integrity option.

Since dm-integrity doesn't support discards (TRIM), dm-crypt device on top of it inherits this, so integrity protection mode doesn't support discards either.

Some integrity modes requires two independent keys (key for encryption and for authentication). Both these keys are stored in one LUKS keyslot.

WARNING: All support for authenticated modes is experimental and there are only some modes available for now. Note that there are a very few authenticated encryption algorithms that are suitable for disk encryption. You also cannot use CRC32 or any other non-cryptographic checksums (other than the special integrity mode "none"). If for some reason you want to have integrity control without using authentication mode, then you should separately configure dm-integrity independently of LUKS2.

💿 NOTES ON LOOPBACK DEVICE USE

Cryptsetup is usually used directly on a block device (disk partition or LVM volume). However, if the device argument is a file, cryptsetup tries to allocate a loopback device and map it into this file. This mode requires Linux kernel 2.6.25 or more recent which supports the loop autoclear flag (loop device is cleared on the last close automatically). Of course, you can always map a file to a loop-device manually. See the cryptsetup FAQ for an example.

When device mapping is active, you can see the loop backing file in the status command output. Also see losetup(8).

🔒 LUKS2 header locking

The LUKS2 on-disk metadata is updated in several steps and to achieve proper atomic update, there is a locking mechanism. For an image in file, code uses flock(2) system call. For a block device, lock is performed over a special file stored in a locking directory (by default /run/lock/cryptsetup). The locking directory should be created with the proper security context by the distribution during the boot-up phase. Only LUKS2 uses locks, other formats do not use this mechanism.

🗑️ DEPRECATED ACTIONS

🐛 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 originally written by Jana Saout <jana@saout.de>

The LUKS extensions and original man page were written by Clemens Fruhwirth <clemens@endorphin.org>.

Man page extensions by Milan Broz <gmazyland@gmail.com>.

Man page rewrite and extension by Arno Wagner <arno@wagner.name>.

©️ COPYRIGHT

Copyright (C) 2004 Jana Saout

Copyright (C) 2004-2006 Clemens Fruhwirth

Copyright (C) 2012-2014 Arno Wagner

Copyright (C) 2009-2021 Red Hat, Inc.

Copyright (C) 2009-2021 Milan Broz

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

CRYPTSETUP □✕
📖 NAME 🚀 Quick Reference 🔧 SYNOPSIS 📄 DESCRIPTION
🔍 PLAIN DM-CRYPT OR LUKS?
⚠️ WARNINGS ⚙️ BASIC ACTIONS 🛠️ PLAIN MODE 🏷️ LUKS EXTENSION 🔁 loop-AES EXTENSION 🔒 TCRYPT (TrueCrypt-compatible and VeraCrypt) EXTENSION 🧪 BITLK (Windows BitLocker-compatible) EXTENSION (EXPERIMENTAL) 🧰 MISCELLANEOUS ⚙️ OPTIONS 📝 EXAMPLE 🚪 Exit Codes 📝 NOTES ON PASSPHRASE PROCESSING FOR PLAIN MODE 📝 NOTES ON PASSPHRASE PROCESSING FOR LUKS ⚠️ INCOHERENT BEHAVIOR FOR INVALID PASSPHRASES/KEYS 🔐 NOTES ON SUPPORTED CIPHERS, MODES, HASHES AND KEY SIZES 🔑 NOTES ON PASSPHRASES 🎲 NOTES ON RANDOM NUMBER GENERATORS 🛡️ AUTHENTICATED DISK ENCRYPTION (EXPERIMENTAL) 💿 NOTES ON LOOPBACK DEVICE USE 🔒 LUKS2 header locking 🗑️ DEPRECATED ACTIONS 🐛 REPORTING BUGS 👤 AUTHORS ©️ COPYRIGHT 🔗 SEE ALSO

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