# cryptsetup-luksChangeKey

## NAME



           cryptsetup-luksChangeKey - change an existing passphrase
    


## SYNOPSIS



           **cryptsetup** _luksChangeKey_ **[ <options>] <device> [<new key file>]**
    


## DESCRIPTION



           Changes an existing passphrase. The passphrase to be changed must
           be supplied interactively or via --key-file. The new passphrase
           can be supplied interactively or in a file given as the positional
           argument.
    
           If a keyslot is specified (via --key-slot), the passphrase for
           that keyslot must be given, and the new passphrase will overwrite
           the specified keyslot. If no keyslot is specified and there is
           still a free keyslot, then the new passphrase will be put into a
           free keyslot before the keyslot containing the old passphrase is
           purged. If there is no free keyslot, then the keyslot with the old
           passphrase is overwritten directly.
    
           **WARNING:** If a keyslot is overwritten, a media failure during this
           operation can cause the overwrite to fail after the old passphrase
           has been wiped, making the LUKS container inaccessible. LUKS2
           mitigates that by never overwriting the existing keyslot area as
           long as there’s a free space in the keyslots area at least for one
           more LUKS2 keyslot.
    
           If you need to use both luksChangeKey and reencrypt (e.g., to
           recover from a key leak), you need to use them in that order to
           avoid leaking the new volume key.
    
           Some parameters are effective only if used with the LUKS2 format
           that supports per-keyslot parameters. For LUKS1, the PBKDF type
           and hash algorithm are always the same for all keyslots.
    
           **< options> **can be [--key-file, --keyfile-offset, --keyfile-size,
           --new-keyfile-offset, --iter-time, --pbkdf,
           --pbkdf-force-iterations, --pbkdf-memory, --pbkdf-parallel,
           --new-keyfile-size, --key-slot, --force-password, --hash,
           --header, --disable-locks, --type, --keyslot-cipher,
           --keyslot-key-size, --timeout, --verify-passphrase].
    


## OPTIONS



           **--batch-mode** , **-q**
               Suppresses all confirmation questions. Use with care!
    
               If the --verify-passphrase option is not specified, this
               option also switches off the passphrase verification.
    
           **--debug** or **--debug-json**
               Run in debug mode with full diagnostic logs. Debug output
               lines are always prefixed by **#**.
    
               If --debug-json is used, additional LUKS2 JSON data structures
               are printed.
    
           **--disable-locks**
               Disable lock protection for metadata on disk. This option is
               valid only for LUKS2 and is ignored for other formats.
    
               **WARNING:** Do not use this option unless you run cryptsetup in a
               restricted environment where locking is impossible to perform
               (where /run directory cannot be used).
    
           **--force-password**
               Do not use password quality checking for new LUKS passwords.
    
               This option is ignored if cryptsetup is built without password
               quality checking support.
    
               For more info about password quality check, see the manual
               page for **pwquality.conf**(5) and **passwdqc.conf**(5).
    
           **--hash** , **-h** _< hash-spec>_
               The specified hash is used for PBKDF2 and the AF splitter.
    
           **--header** _< device or file storing the LUKS header>_
               Use a detached (separated) metadata device or file where the
               LUKS header is stored. This option allows one to store the
               ciphertext and LUKS header on different devices.
    
               For commands that change the LUKS header (e.g., _luksAddKey_),
               specify the device or file with the LUKS header directly as
               the LUKS device.
    
           **--help** , **-?**
               Show help text and default parameters.
    
           **--iter-time** , **-i** _< number of milliseconds>_
               The number of milliseconds to spend with PBKDF passphrase
               processing. Specifying 0 as a parameter selects the
               compiled-in default.
    
           **--key-file** , **-d** _file_
               Read the passphrase from the file.
    
               If the name given is "-", then the passphrase will be read
               from stdin. In this case, reading will not stop at newline
               characters.
    
               The passphrase supplied via --key-file is always the
               passphrase for the existing keyslot requested by the command.
    
               If you want to set a new passphrase via a key file, you have
               to use a positional argument.
    
               See section _NOTES ON PASSPHRASE PROCESSING_ in cryptsetup(8)
               for more information.
    
           **--keyfile-offset** _value_
               Skip _value_ bytes at the beginning of the key file.
    
           **--keyfile-size** , **-l** _value_
               Read a maximum of _value_ bytes from the key file. The default
               is to read the whole file up to the compiled-in maximum that
               can be queried with --help. Supplying more data than the
               compiled-in maximum aborts the operation.
    
               This option is useful to cut trailing newlines, for example.
               If --keyfile-offset is also given, the size count starts after
               the offset.
    
           **--key-slot** , **-S** _< 0-N>_
               For LUKS operations that add key material, this option allows
               you to specify which keyslot is selected for the new key.
    
               The maximum number of keyslots depends on the LUKS version.
               LUKS1 can have up to 8 keyslots. LUKS2 can have up to 32
               keyslots based on keyslot area size and key size, but a valid
               keyslot ID can always be between 0 and 31 for LUKS2.
    
           **--keyslot-cipher** _< cipher-spec>_
               This option can be used to set specific cipher encryption for
               the LUKS2 keyslot area.
    
           **--keyslot-key-size** _< bits>_
               This option can be used to set a specific key size for the
               LUKS2 keyslot area.
    
           **--new-keyfile-offset** _value_
               Skip _value_ bytes at the start when adding a new passphrase
               from the key file.
    
           **--new-keyfile-size** _value_
               Read a maximum of _value_ bytes when adding a new passphrase
               from the key file. The default is to read the whole file up to
               the compiled-in maximum length that can be queried with
               --help. Supplying more than the compiled-in maximum aborts the
               operation. When --new-keyfile-offset is also given, reading
               starts after the offset.
    
           **--pbkdf** _< PBKDF spec>_
               Set Password-Based Key Derivation Function (PBKDF) algorithm
               for LUKS keyslot. The PBKDF can be: _pbkdf2_ (for PBKDF2
               according to RFC2898), _argon2i_ for Argon2i or _argon2id_ for
               Argon2id (see Argon2
               <https://www.cryptolux.org/index.php/Argon2> for more info).
    
               For LUKS1, only PBKDF2 is accepted (no need to use this
               option). The default PBKDF for LUKS2 is set during compilation
               time and is available in the _cryptsetup --help_ output.
    
               A PBKDF is used for increasing the dictionary and brute-force
               attack cost for keyslot passwords. The parameters can be time,
               memory and parallel cost.
    
               For PBKDF2, only the time cost (number of iterations) applies.
               For Argon2i/id, there is also memory cost (memory required
               during the process of key derivation) and parallel cost
               (number of threads that run in parallel during the key
               derivation.
    
               Note that increasing memory cost also increases time, so the
               final parameter values are measured by a benchmark. The
               benchmark tries to find iteration time (--iter-time) with
               required memory cost --pbkdf-memory. If it is not possible,
               the memory cost is decreased as well. The parallel cost
               --pbkdf-parallel is constant and is checked against available
               CPU cores.
    
               You can see all PBKDF parameters for a particular LUKS2
               keyslot with the cryptsetup-luksDump(8) command.
    
               If you do not want to use benchmark and want to specify all
               parameters directly, use --pbkdf-force-iterations with
               --pbkdf-memory and --pbkdf-parallel. This will override the
               values without benchmarking. Note it can cause extremely long
               unlocking time or cause out-of-memory conditions with
               unconditional process termination. Use only in specific cases,
               for example, if you know that the formatted device will be
               used on some small embedded system.
    
               **MINIMAL AND MAXIMAL PBKDF COSTS:** For **PBKDF2** , the minimum
               iteration count is 1000 and the maximum is 4294967295 (maximum
               for 32-bit unsigned integer). Memory and parallel costs are
               not supported for PBKDF2. For **Argon2i** and **Argon2id** , the
               minimum iteration count (CPU cost) is 4, and the maximum is
               4294967295 (maximum for a 32-bit unsigned integer). Minimum
               memory cost is 32 KiB and maximum is 4 GiB. If the memory cost
               parameter is benchmarked (not specified by a parameter), it is
               always in the range from 64 MiB to 1 GiB. Memory cost above
               1GiB (up to the 4GiB maximum) can be setup only by the
               --pbkdf-memory parameter. The parallel cost minimum is 1 and
               maximum 4 (if enough CPU cores are available, otherwise it is
               decreased by the available CPU cores).
    
               **WARNING:** Increasing PBKDF computational costs above the
               mentioned limits provides negligible additional security
               improvement. While elevated costs significantly increase
               brute-force overhead, they offer negligible protection against
               dictionary attacks. The marginal cost increase for processing
               an entire dictionary remains fundamentally insufficient.
    
               The hardcoded PBKDF limits represent engineered trade-offs
               between cryptographic security and operational usability. LUKS
               maintains portability and must be used within a reasonable
               time on resource-constrained systems.
    
               Cryptsetup deliberately restricts maximum memory cost (4 GiB)
               and parallel cost (4) parameters due to architectural
               limitations (like embedded and legacy systems).
    
               PBKDF memory cost mandates actual physical RAM allocation with
               intensive write operations that must remain in physical RAM.
               Any swap usage results in unacceptable performance
               degradation. Memory management often overcommits allocations
               beyond available physical memory, expecting most allocated
               memory to remain unused. In such situations, as PBKDF always
               uses all allocated memory, it frequently causes out-of-memory
               failures that abort cryptsetup operations.
    
           **--pbkdf-force-iterations** _number_
               Avoid the PBKDF benchmark and set the time cost (iterations)
               directly. It can be used only for a LUKS/LUKS2 device. See
               --pbkdf option for more info.
    
           **--pbkdf-memory** _number_
               Set the memory cost for PBKDF (for Argon2i/id, the number
               represents kilobytes). Note that it is the maximal value;
               PBKDF benchmark or available physical memory can decrease it.
               This option is not available for PBKDF2.
    
           **--pbkdf-parallel** _number_
               Set the parallel cost for PBKDF (number of threads, up to 4).
               Note that it is the maximal value; it is decreased
               automatically if the CPU online count is lower. This option is
               not available for PBKDF2.
    
           **--timeout** , **-t** _seconds_
               The number of seconds to wait before a timeout on passphrase
               input via terminal. It is relevant every time a passphrase is
               asked. It has no effect if used in conjunction with
               --key-file.
    
               This option is useful when the system should not stall if the
               user does not input a passphrase, e.g., during boot. The
               default is a value of 0 seconds, which means to wait forever.
    
           **--type** _type_
               Specifies required device type, for more info, read the _BASIC_
               _ACTIONS_ section in cryptsetup(8).
    
           **--usage**
               Show short option help.
    
           **--verify-passphrase** , **-y**
               When interactively asking for a passphrase, ask for it twice
               and complain if both inputs do not match. Ignored on input
               from file or stdin.
    
           **--version** , **-V**
               Show the program version.
    


## CRYPTSETUP



           Part of cryptsetup project
           <https://gitlab.com/cryptsetup/cryptsetup/>. This page is part of
           the _Cryptsetup_ ((open-source disk encryption)) project.
           Information about the project can be found at 
           ⟨https://gitlab.com/cryptsetup/cryptsetup⟩. If you have a bug
           report for this manual page, send it to dm-crypt@saout.de. This
           page was obtained from the project's upstream Git repository
           ⟨https://gitlab.com/cryptsetup/cryptsetup.git⟩ on 2025-08-11. (At
           that time, the date of the most recent commit that was found in
           the repository was 2025-08-01.) If you discover any rendering
           problems in this HTML version of the page, or you believe there is
           a better or more up-to-date source for the page, or you have
           corrections or improvements to the information in this COLOPHON
           (which is _not_ part of the original manual page), send a mail to
           man-pages@man7.org
    
    cryptsetup 2.8.1-git            2025-08-09     _CRYPTSETUP...SCHANGEKEY_(8)
    


* * *