NAME

       heimdal-history - Password history via Heimdal external strength checking

SYNOPSIS

       heimdal-history [-chmq] [-b target-time] [-d database]
           [-S length-stats-db] [-s strength-program] [principal]

DESCRIPTION

       heimdal-history is an implementation of password history via the Heimdal external password strength
       checking interface.  It stores separate history for each principal, hashed using Crypt::PBKDF2 with
       randomly-generated salt.  (The randomness is from a weak pseudorandom number generator, not strongly
       random.)  Password history is stored indefinitely (implementing infinite history); older password hashes
       are never removed by this program.

       Password history is stored in a BerkeleyDB DB_HASH file.  The key is the principal.  The value is a JSON
       array of objects, each of which has two keys.  "timestamp" contains the time when the history entry was
       added (in POSIX seconds since UNIX epoch), and "hash" contains the hash of a previously-used password in
       the Crypt::PBKDF2 LDAP-compatible format.  Passwords are hashed using PBKDF2 (from PKCS#5) with SHA-256
       as the underlying hash function using a number of rounds configured in this script.  See Crypt::PBKDF2
       for more information.

       heimdal-history also checks password strength before checking history.  It does so by invoking another
       program that also uses the Heimdal external password strength checking interface.  By default, it runs
       /usr/bin/heimdal-strength.  Only if that program approves the password does it hash it and check history.

       For more information on how to set up password history, see "CONFIGURATION" below.

       As with any implementation of the Heimdal external password strength checking protocol, heimdal-history
       expects, on standard input:

           principal: <principal>
           new-password: <password>
           end

       (with no leading whitespace).  <principal> is the principal changing its password (passed to the other
       password strength checking program but otherwise unused here), and <password> is the new password.  There
       must be exactly one space after the colon.  Any subsequent spaces are taken to be part of the principal
       or password.

       If the password is accepted, heimdal-history will assume that it will be used and will update the history
       database to record the new password.  It will also update the password length statistics database to
       account for the new password.

       If invoked as root, heimdal-history will run the external strength checking program as user "nobody" and
       group "nogroup", and will check and write to the history database as user "_history" and group
       "_history".  These users must exist on the system if it is run as root.

       The result of each password check will be logged to syslog (priority LOG_INFO, facility LOG_AUTH).  Each
       log line will be a set of key/value pairs in the format "key=value".  The keys are:

       action
           The action performed (currently always "check").

       principal
           The principal for which a password was checked.

       error
           An internal error message that did not stop the history check, but which may indicate that something
           is wrong with the history database (such as corrupted entries or invalid hashes).  If this key is
           present, neither "result" nor "reason" will be present.  There will be a subsequent log message from
           the same invocation giving the final result of the history check (assuming heimdal-history doesn't
           exit with a fatal error).

       result
           Either "accepted" or "rejected".

       reason
           If the password was rejected, the reason for the rejection.

       The value will be surrounded with double quotes if it contains a double quote or space.  Any double
       quotes in the value will be doubled, so """ becomes "".

OPTIONS

       -b target-time, --benchmark=target-time
           Do not do a password history check.  Instead, benchmark the hash algorithm with various possible
           iteration counts and find an iteration count that results in target-time seconds of computation time
           required to hash a password (which should be a real number).  A result will be considered acceptable
           if it is within 0.005 seconds of the target time.  The results will be printed to standard output and
           then heimdal-history will exit successfully.

       -c, --check-only
           Check password history and password strength and print the results as normal, but do not update the
           history or length statistics databases.  This is a read-only mode of operation that will not make any
           changes to the underlying database, only report if a password would currently be accepted.

       -d database, --database=database
           Use database as the history database file instead of the default
           (/var/lib/heimdal-history/history.db).  Primarily used for testing, since Heimdal won't pass this
           argument.

       -h, --help
           Print a short usage message and exit.

       -m, --manual, --man
           Display this manual and exit.

       -q, --quiet
           Suppress logging to syslog and only return the results on standard output and standard error.
           Primarily used for testing, since Heimdal won't pass this argument.

       -S length-stats-db, --stats=length-stats-db
           Use length-stats-db as the database file for password length statistics instead of the default
           (/var/lib/heimdal-history/lengths.db).  Primarily used for testing, since Heimdal won't pass this
           argument.

       -s strength-program, --strength=strength-program
           Run strength-program as the external strength-checking program instead of the default
           (/usr/bin/heimdal-strength).  Primarily used for testing, since Heimdal won't pass this argument.

CONFIGURATION

       Additional setup is required to use this history implementation with your Heimdal KDC.

       First, ensure that its dependencies are installed, and then examine the local configuration settings at
       the top of the heimdal-history program.  By default, it requires a "_history" user and "_history" group
       be present on the system, and all history information will be read and written as that user and group.
       It also requires a "nobody" user and "nogroup" group to be present (this should be the default with most
       variants of UNIX), and all strength checking will be done as that user and group.  It uses various files
       in /var/lib/heimdal-history to store history and statistical information by default, so if using the
       defaults, create that directory and ensure it is writable by the "_history" user.

       Once that setup is done, change your "[password_quality]" configuration in krb5.conf or kdc.conf to:

           [password_quality]
               policies         = external-check
               external_program = /usr/local/bin/heimdal-history

       The heimdal-history program will automatically also run heimdal-strength as well, looking for it in
       /usr/bin.  Change the $STRENGTH_PROGRAM setting at the top of the script if you have that program in a
       different location.  You should continue to configure heimdal-strength as if you were running it
       directly.

RETURN STATUS

       On approval of the password, heimdal-history will print "APPROVED" and a newline to standard output and
       exit with status 0.

       If the password is rejected by the strength checking program or if it (or a version with a single
       character removed) matches one of the hashes stored in the password history, heimdal-history will print
       the reason for rejection to standard error and exit with status 0.

       On any internal error, heimdal-history will print the error to standard error and exit with a non-zero
       status.

FILES

       /usr/bin/heimdal-strength
           The default password strength checking program.  This program must follow the Heimdal external
           password strength checking API.

       /var/lib/heimdal-history/history.db
           The default database path.  If heimdal-strength is run as root, this file needs to be readable and
           writable by user "_history" and group "_history".  If it doesn't exist, it will be created with mode
           0600.

       /var/lib/heimdal-history/history.db.lock
           The lock file used to synchronize access to the history database.  As with the history database, if
           heimdal-strength is run as root, this file needs to be readable and writable by user "_history" and
           group "_history".

       /var/lib/heimdal-history/lengths.db
           The default length statistics path, which will be a BerkeleyDB DB_HASH file of password lengths to
           counts of passwords with that length.  If heimdal-strength is run as root, this file needs to be
           readable and writable by user "_history" and group "_history".  If it doesn't exist, it will be
           created with mode 0600.

       /var/lib/heimdal-history/lengths.db.lock
           The lock file used to synchronize access to the length statistics database.  As with the length
           statistics database, if heimdal-strength is run as root, this file needs to be readable and writable
           by user "_history" and group "_history".

AUTHOR

       Russ Allbery <eagle@eyrie.org>

COPYRIGHT AND LICENSE

       Copyright 2016-2017, 2020 Russ Allbery <eagle@eyrie.org>

       Copyright 2013-2014 The Board of Trustees of the Leland Stanford Junior University

       Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
       associated documentation files (the "Software"), to deal in the Software without restriction, including
       without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
       copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the
       following conditions:

       The above copyright notice and this permission notice shall be included in all copies or substantial
       portions of the Software.

       THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT
       LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN
       NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
       WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
       SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

       SPDX-License-Identifier: MIT

SEE ALSO

       Crypt::PBKDF2, heimdal-strength(1)