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

NAME

       heimdal-history - Password history via Heimdal external strength checking

SYNOPSIS

       heimdal-history [-hmq] [-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 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 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.

-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 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.