| HEIMDAL-HISTORY(1) | krb5-strength | HEIMDAL-HISTORY(1) |
heimdal-history - Password history via Heimdal external strength checking
heimdal-history [-chmq] [-b
target-time] [-d database]
[-S length-stats-db] [-s strength-program]
[principal]
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:
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 "".
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.
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.
Russ Allbery <eagle@eyrie.org>
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
Crypt::PBKDF2, heimdal-strength(1)
| 2021-02-28 | 3.2 |