- krb5-strength 1.1
+ krb5-strength 3.0
(Kerberos password strength checking plugin)
- Maintained by Russ Allbery <rra@stanford.edu>
+ Maintained by Russ Allbery <eagle@eyrie.org>
- Copyright 2006, 2007, 2009, 2010, 2012, 2013 The Board of Trustees of
- the Leland Stanford Junior University. Portions copyright 1993 Alec
+ Copyright 2006, 2007, 2009, 2010, 2012, 2013, 2014 The Board of Trustees
+ of the Leland Stanford Junior University. Portions copyright 1993 Alec
Muffett. Developed by Derrick Brashear and Ken Hornstein of Sine Nomine
- Associates, on behalf of Stanford University.
-
- This software is distributed under a BSD-style license and under the
- Artistic License. Please see the section LICENSE for more information.
+ Associates, on behalf of Stanford University. This software is
+ distributed under a BSD-style license and under the Artistic License.
+ Please see the section LICENSE for more information.
BLURB
- krb5-strength provides mechanisms for checking the strength of Kerberos
- passwords against an external dictionary when a user changes passwords
- in a Kerberos KDC. It is roughly equivalent to checking password
- strength via CrackLib, except that it embeds a copy of Alec Muffett's
- CrackLib that has been modified to perform slightly more strenuous
- tests. It supports both Heimdal and MIT Kerberos (1.9 or later).
+ krb5-strength provides a password quality plugin for the MIT Kerberos
+ KDC (specifically the kadmind server), an external password quality
+ program for use with Heimdal, and a per-principal password history
+ implementation for Heimdal. Passwords can be tested with CrackLib,
+ checked against a CDB or SQLite database of known weak passwords with
+ some transformations, checked for length, checked for non-printable or
+ non-ASCII characters that may be difficult to enter reproducibly,
+ required to contain particular character classes, or any combination of
+ these tests. It supports both Heimdal and MIT Kerberos (1.9 or later).
DESCRIPTION
checks and comes with an example that checks passwords against CrackLib.
However, in testing at Stanford, we found that CrackLib with its default
transform rules does not catch passwords that can be guessed using the
- same dictionary with other tools, such as Jack the Ripper.
+ same dictionary with other tools, such as Jack the Ripper. We then
+ discovered other issues with CrackLib with longer passwords, such as
+ some bad assumptions about how certain measures of complexity will
+ scale, and wanted to impose other limitations that it didn't support.
This plugin provides the ability to check password quality against the
standard version of CrackLib, or against a modified version of CrackLib
that only passes passwords that resist attacks from both Crack and Jack
- the Ripper using the same rule sets. For Heimdal, it includes both a
- program usable as an external password quality check and a plugin that
- implements the dynamic module API. For MIT Kerberos (1.9 or later), it
- includes a plugin for the password quality (pwqual) plugin API.
+ the Ripper using the same rule sets. It also supports doing simpler
+ dictionary checks against a CDB database, which is fast with very large
+ dictionaries, or a SQLite database, which can reject all passwords
+ within edit distance one of a dictionary word. It can also impose other
+ programmatic checks on passwords such as character class requirements.
+
+ For Heimdal, it includes both a program usable as an external password
+ quality check and a plugin that implements the dynamic module API. For
+ MIT Kerberos (1.9 or later), it includes a plugin for the password
+ quality (pwqual) plugin API.
krb5-strength can be built with either the system CrackLib or with the
modified version of CrackLib included in this package. Note, however,
behavior, at which point this package can likely wither away in favor of
much simpler plugins that link to the standard CrackLib library.
+ krb5-strength also includes a password history implementation for
+ Heimdal. This is separate from the password strength implementation but
+ can be stacked with it so that both strength and history checks are
+ performed. This history implementation is available only via the
+ Heimdal external password quality interface. MIT Kerberos includes its
+ own password history implementation.
+
REQUIREMENTS
For Heimdal, you may use either the external password quality check
well-behaved for use inside plugins or libraries. If using a system
CrackLib library, use version 2.8.22 or later to avoid these problems.
+ You can also optionally build against the TinyCDB library, which
+ provides support for simpler and faster password checking against a CDB
+ dictionary file, and the SQLite library (a version new enough to support
+ the sqlite3_open_v2 API; 3.7 should be more than sufficient), which
+ provides support for checking whether passwords are within edit distance
+ one of a dictionary word.
+
For this module to be effective for either Heimdal or MIT Kerberos, you
will also need to construct a dictionary. The mkdict and packer
utilities to build a CrackLib dictionary from a word list are included
that come with the stock CrackLib package (often already packaged in a
Linux distribution); the database format is compatible.
+ For building a CDB or SQLite dictionary, use the provided
+ krb5-strength-wordlist program. For CDB dictionries, the cdb utility
+ must be on your PATH. For SQLite, the DBI and DBD::SQLite Perl modules
+ are required. krb5-strength-wordlist requires Perl 5.006 or later.
+
For a word list to use as source for the dictionary, you can use
/usr/share/dict/words if it's available on your system, but it would be
better to find a more comprehensive word list. Since word lists are
bulky, often covered by murky copyrights, and easily locatable on the
Internet with a modicum of searching, none are included in this toolkit.
+ The password history program, heimdal-history, requires Perl 5.010 or
+ later plus the following CPAN modules:
+
+ DB_File::Lock
+ Crypt::PBKDF2
+ Getopt::Long::Descriptive
+ IPC::Run
+ JSON
+ Readonly
+
+ and their dependencies.
+
+ To run the test suite, you will need Perl 5.010 or later and the
+ dependencies of the heimdal-history program. The following additional
+ Perl modules will also be used by the test suite if present:
+
+ Perl6::Slurp
+ Test::MinimumVersion
+ Test::Perl::Critic
+ Test::Pod
+ Test::Spelling
+ Test::Strict
+
+ All are available on CPAN. Some tests will be skipped if the modules
+ are not available.
+
+ To enable tests that don't detect functionality problems but are used to
+ sanity-check the release, set the environment variable RELEASE_TESTING
+ to a true value. To enable tests that may be sensitive to the local
+ environment or that produce a lot of false positives without uncovering
+ many problems, set the environment variable AUTHOR_TESTING to a true
+ value.
+
To bootstrap from a Git checkout, or If you change the Automake files
and need to regenerate Makefile.in, you will need Automake 1.11 or
later. For bootstrap or if you change configure.ac or any of the m4
files it includes and need to regenerate configure or config.h.in, you
- will need Autoconf 2.64 or later.
+ will need Autoconf 2.64 or later. You will also need Perl 5.010 or
+ later and the DBI, DBD::SQLite, JSON, Perl6::Slurp, and Readonly modules
+ (from CPAN) to bootstrap the test suite data from a Git checkout.
COMPILING AND INSTALLING
GCC compiler warnings (requires a relatively current version of GCC).
The last step will probably have to be done as root. By default, the
- plugin is installed as /usr/local/lib/kadmind/passwd_strength.so and the
- Heimdal external password check function is installed as
+ plugin is installed as /usr/local/lib/krb5/plugins/pwqual/strength.so
+ and the Heimdal external password check function is installed as
/usr/local/bin/heimdal-strength. You can change these paths with the
--prefix, --libdir, and --bindir options to configure.
directory where CrackLib was installed, or separately set the include
and library path with --with-cracklib-include and --with-cracklib-lib.
+ krb5-strength will automatically build with TinyCDB if it is found. To
+ specify the installation path of TinyCDB, use --with-tinycdb. You can
+ also separately set the include and library path with
+ --with-tinycdb-include and --with-tinycdb-lib.
+
+ Similarly, krb5-strength will automatically build with SQLite if it is
+ found. To specify the installation path of SQLite, use --with-sqlite.
+ You can also separately set the include and library path with
+ --with-sqlite-include and --with-sqlite-lib.
+
Normally, configure will use krb5-config to determine the flags to use
to compile with your Kerberos libraries. If krb5-config isn't found, it
will look for the standard Kerberos libraries in locations already
CONFIGURATION
- First, build and install a CrackLib dictionary as described above. This
+ First, build and install either a CrackLib dictionary as described in
+ REQUIREMENTS above, or build a CDB or SQLite dictionary with
+ krb5-strength-wordlist. (Or any combination thereof.) The CrackLib
dictionary will consist of three files, one each ending in *.hwm, *.pwd,
- and *.pwi. Install those files somewhere on your system. Then, follow
- the relevant instructions below for either Heimdal or MIT Kerberos.
+ and *.pwi. The CDB and SQLite dictionaries will be single files,
+ conventionally ending in *.cdb and *.sqlite respectively. Install those
+ files somewhere on your system. Then, follow the relevant instructions
+ below for either Heimdal or MIT Kerberos.
+
+ See "Other Settings" below for additional krb5.conf setting supported by
+ both Heimdal and MIT Kerberos.
Heimdal
file is located):
krb5-strength = {
- password_dictionary = /usr/local/lib/kadmind/dictionary
+ password_dictionary = /path/to/cracklib/dictionary
+ password_dictionary_cdb = /path/to/cdb/dictionary.cdb
+ password_dictionary_sqlite = /path/to/sqlite/dictionary.sqlite
}
- The provided path should be the full path to the dictionary files,
- omitting the trailing *.hwm, *.pwd, and *.pwi extensions.
+ The first setting configures a CrackLib dictionary, the second a CDB
+ dictionary, and the third a SQLite dictionary. The provided path should
+ be the full path to the dictionary files, omitting the trailing *.hwm,
+ *.pwd, and *.pwi extensions for the CrackLib dictionary. You can use
+ any combination of the three settings. If you use more than one,
+ CrackLib will be checked first, then CDB, and then SQLite as
+ appropriate.
+
+ When checking against a CDB database, the password, the password with
+ the first character removed, the last character removed, the first and
+ last characters removed, the first two characters removed, and the last
+ two characters removed will all be checked against the dictionary.
+
+ When checking a SQLite database, the password will be rejected if it is
+ within edit distance one of any word in the dictionary, meaning that the
+ database word can be formed from the password by deleting, adding, or
+ changing a single character.
Then, for the external password checking program, add a new section (or
modify the existing [password_quality] section) to look like the
[password_quality]
policies = krb5-strength
- policy_libraries = /usr/local/lib/kadmind/passwd_strength.so
+ policy_libraries = /usr/local/lib/krb5/plugins/pwqual/strength.so
in either krb5.conf or kdc.conf. Note that some older versions of
Heimdal have a bug in the support for loading modules when
pass the --check-library argument to kpasswdd specifying the library to
load.
+ Additional configuration is required to use the history implementation.
+ 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, 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
+ 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/local/bin, /usr/bin, and /bin. Change
+ the PATH setting at the top of the script if you have different
+ requirements. You should continue to configure heimdal-strength as if
+ you were running it directly.
+
MIT Kerberos
To add this module to the list of password quality checks, add a section
[plugins]
pwqual = {
- module = strength:/usr/local/lib/kadmind/passwd_strength.so
+ module = strength:/usr/local/lib/krb5/plugins/pwqual/strength.so
}
to register the plugin.
[appdefaults] section:
krb5-strength = {
- password_dictionary = /path/to/cracklib/dictionary
+ password_dictionary = /path/to/cracklib/dictionary
+ password_dictionary_cdb = /path/to/cdb/dictionary.cdb
+ password_dictionary_sqlite = /path/to/sqlite/dictionary.sqlite
}
+ The first setting configures a CrackLib dictionary, the second a CDB
+ dictionary, and the third a SQLite dictionary. The provided path should
+ be the full path to the dictionary files, omitting the trailing *.hwm,
+ *.pwd, and *.pwi extensions for the CrackLib dictionary. You can use
+ any combination of the three settings. If you use more than one,
+ CrackLib will be checked first, then CDB, and then SQLite as
+ appropriate.
+
+ When checking against a CDB database, the password, the password with
+ the first character removed, the last character removed, the first and
+ last characters removed, the first two characters removed, and the last
+ two characters removed will all be checked against the dictionary.
+
+ When checking a SQLite database, the password will be rejected if it is
+ within edit distance one of any word in the dictionary, meaning that the
+ database word can be formed from the password by deleting, adding, or
+ changing a single character.
+
The second option is to use the normal dict_path setting. In the
[realms] section of your krb5.conf kdc.conf, under the appropriate realm
or realms, specify the path to the dictionary:
dict_file = /path/to/cracklib/dictionary
- The provided path should be the full path to the dictionary files,
- omitting the trailing *.hwm, *.pwd, or *.pwi extension. However, be
- aware that, if you use this approach, you will probably want to disable
- the built-in standard dict pwqual plugin by adding the line:
+ This will be taken as a CrackLib dictionary path, the same as the
+ setting for password_dictionary above. The provided path should be the
+ full path to the dictionary files, omitting the trailing *.hwm, *.pwd,
+ or *.pwi extension. However, be aware that, if you use this approach,
+ you will probably want to disable the built-in standard dict pwqual
+ plugin by adding the line:
disable = dict
to the pwqual block of the [plugins] section as shown above. Otherwise,
it will also try to load a dictionary at the same path to do simple
dictionary matching.
+
+ You can also mix and match these settings, by using dict_path for the
+ CrackLib dictionary path and krb5.conf for the CDB or SQLite dictionary
+ paths. If both settings are used for the CrackLib path, krb5.conf
+ overrides the dict_path setting (so that dict_path can be used for other
+ password quality modules). There is no way to specify a CDB or SQLite
+ dictionary via the dict_path setting.
+
+ Other Settings
+
+ The following additional settings are supported in the [appdefaults]
+ section of krb5.conf when running under either Heimdal or MIT Kerberos.
+
+ minimum_different
+
+ If set to a numeric value, passwords with fewer than this number of
+ unique characters will be rejected. This can be used to reject, for
+ example, passwords that are long strings of the same character or
+ repetitions of small numbers of characters, which may be too easy to
+ guess.
+
+ minimum_length
+
+ If set to a numeric value, passwords with fewer than that number of
+ characters will be rejected, independent of any length restrictions
+ in CrackLib. Note that this setting does not bypass the minimum
+ length requirements in CrackLib itself (which, for the version
+ embedded in this package, is eight characters).
+
+ require_ascii_printable
+
+ If set to a true boolean value, rejects any password that contains
+ non-ASCII characters or ASCII control characters. Spaces are
+ allowed; tabs are not (at least assuming the POSIX C locale). No
+ canonicalization or character set is defined for Kerberos passwords
+ in general, so you may want to reject non-ASCII characters to avoid
+ interoperability problems with computers with different default
+ character sets or Unicode normalization forms.
+
+ require_classes
+
+ This option allows specification of more complex character class
+ requirements. The value of this parameter should be one or more
+ whitespace-separated rule. Each rule has the syntax:
+
+ [<min>-<max>:]<class>[,<class>...]
+
+ where <class> is one of "upper", "lower", "digit", or "symbol"
+ (without the quote marks). The symbol class includes all characters
+ other than alphanumeric characters, including space. The listed
+ classes must appear in the password. Separate multiple required
+ classes with a comma (and no space).
+
+ The character class checks will be done in whatever locale the
+ plugin or password check program is run in, which will normally be
+ the POSIX C locale but may be different depending on local
+ configuration.
+
+ A simple example:
+
+ require_classes = upper,lower,digit
+
+ This requires all passwords contain at least one uppercase letter,
+ at least one lowercase letter, and at least one digit.
+
+ If present, <min> and <max> specify the minimum password length and
+ maximum password length to which this rule applies. This allows one
+ to specify character class requirements that change with password
+ length. So, for example:
+
+ require_classes = 8-19:upper,lower 8-15:digit 8-11:symbol
+
+ requires all passwords from 8 to 11 characters long contain all four
+ character classes, passwords from 12 to 15 characters long contain
+ upper and lower case and a digit, and passwords from 16 to 19
+ characters long contain both upper and lower case. Passowrds longer
+ than 20 characters have no character class restrictions. (This
+ example is probably used in conjunction with minimum_length = 8.)
+
+ require_non_letter
+
+ If set to a true boolean value, the password must contain at least
+ one character that is not a letter (uppercase or lowercase) or a
+ space. This may be helpful in combination with passphrases; users
+ may choose a stock English phrase, and this will force at least some
+ additional complexity.
+
+ You can omit any dictionary setting and only use the above settings, in
+ which case only the above checks and checks for passwords based on the
+ principal will be done, bypassing any dictionary check. (But for that
+ simple style of password strength checking, there are probably better
+ strength checking plugins already available.)
+
+SUPPORT
+
+ The krb5-strength web page at:
+
+ http://www.eyrie.org/~eagle/software/krb5-strength/
+
+ will always have the current version of this package, the current
+ documentation, and pointers to any additional resources.
+
+ I welcome bug reports and patches for this package at eagle@eyrie.org.
+ However, please be aware that I tend to be extremely busy and work
+ projects often take priority. I'll save your mail and get to it as soon
+ as I can, but it may take me a couple of months.
+
+SOURCE REPOSITORY
+
+ krb5-strength is maintained using Git. You can access the current
+ source by cloning the repository at:
+
+ git://git.eyrie.org/kerberos/krb5-strength.git
+
+ or view the repository via the web at:
+
+ http://git.eyrie.org/?p=kerberos/krb5-strength.git
+
+ When contributing modifications, either patches (possibly generated by
+ git format-patch) or Git pull requests are welcome.
+
+LICENSE
+
+ The krb5-strength package as a whole is covered by the following
+ copyright statement and license:
+
+ Copyright 2006, 2007, 2009, 2010, 2012, 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.
+
+ The embedded version of CrackLib (all files in the cracklib
+ subdirectory) is covered by the Artistic license. See the file
+ cracklib/LICENCE for more information. Combined derivative works that
+ include this code, such as binaries built with the embedded CrackLib,
+ will need to follow the terms of the Artistic license as well as the
+ above license.
+
+ All other individual files without an explicit exception below are
+ released under this license. Some files may have additional copyright
+ holders as noted in those files. There is detailed information about
+ the licensing of each file in the LICENSE file in this distribution.
+
+ Some files in this distribution are individually released under
+ different licenses, all of which are compatible with the above general
+ package license but which may require preservation of additional
+ notices. All required notices are preserved in the LICENSE file.
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