Ubuntu Manpage: heimdal-history - Password history via Heimdal external strength checking

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, 2023 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
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       SPDX-License-Identifier: MIT