CRYPTSETUP-LUKSCHANGEKEY(8)  Maintenance Commands  CRYPTSETUP-LUKSCHANGEKEY(8)

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.

REPORTING BUGS
       Report bugs at cryptsetup mailing list <cryptsetup@lists.linux.dev> or
       in Issues project section
       <https://gitlab.com/cryptsetup/cryptsetup/-/issues/new>.

       Please attach the output of the failed command with --debug option
       added.

SEE ALSO
       Cryptsetup FAQ
       <https://gitlab.com/cryptsetup/cryptsetup/wikis/FrequentlyAskedQuestions>

       cryptsetup(8), integritysetup(8) and veritysetup(8)

CRYPTSETUP
       Part of cryptsetup project <https://gitlab.com/cryptsetup/cryptsetup/>.

cryptsetup 2.8.1		  2025-08-13	   CRYPTSETUP-LUKSCHANGEKEY(8)