- krb5-strength 1.0
- (kadmind password strength checking plugin)
+ krb5-strength 3.2
+ (Kerberos password strength checking plugin)
+ Maintained by Russ Allbery <eagle@eyrie.org>
- Maintained by Russ Allbery <rra@stanford.edu>
-
- Copyright 2006, 2007, 2009, 2010, 2012 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.
+ Copyright 2016, 2020 Russ Allbery <eagle@eyrie.org>. Copyright
+ 2006-2007, 2009-2010, 2012-2014 The Board of Trustees of the Leland
+ Stanford Junior University. Copyright 1993 Alec Muffett. This software
+ is distributed under a BSD-style license. Please see the section
+ LICENSE below 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 is usable as-is with Heimdal. With MIT Kerberos, it requires
- an included patch to libkadm5srv to support a dynamically loaded
- password check module.
+ krb5-strength provides a password quality plugin for the MIT Kerberos
+ KDC (specifically the kadmind server) and Heimdal KDC, 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.
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.
-
- The MIT Kerberos kadmind supports password strength checking against a
- dictionary out of the box. Unfortunately, that support loads the entire
- dictionary into memory, requires uncompressed dictionaries, and doesn't
- apply any transformations to the password before checking it against the
- dictionary. CrackLib provides more sophisticated strength checking and
- an optimized, compressed on-disk database format.
-
- This toolkit therefore 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, it
- includes two pieces:
-
- * A patch to MIT Kerberos to add a plugin system for password strength
- checking. This patch adds initialization and shutdown hooks plus a
- hook that's run prior to each password change. The code in kadmind
- is independent of what the plugin might do.
-
- * A libkadm5srv or Heimdal kpasswdd plugin that provides a wrapper
- around CrackLib.
+ 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. 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.
+
+ If you're just now starting with password checking, I recommend using
+ the SQLite database with a large wordlist and minimum password lengths.
+ We found this produced the best results with the least user frustration.
+
+ For Heimdal, krb5-strength 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,
the distribution a strength-checking plugin and an external password
check program that use the system CrackLib. With Heimdal, it would
probably be easier to use that plugin or program than build this package
- unless you want the modified CrackLib.
+ unless you want the modified CrackLib, one of the other dictionary
+ types, or the additional character class and length checks.
For information about the changes to the CrackLib included in this
toolkit, see cracklib/HISTORY. The primary changes are tighter rules,
which are more aggressive at finding dictionary words with characters
appended and prepended, which tighten the requirements for password
entropy, and which add stricter rules for longer passwords. They are
- also minor changes to fix portability issues and remove some code that
- doesn't make sense in the kadmind context.
-
- My eventual hope is to submit to CrackLib 2.x modifications that allow
- the rule set to be configured at runtime, at which point this package
- can likely wither away in favor of much simpler plugins that link to the
- standard CrackLib library.
+ also minor changes to fix portability issues, remove some code that
+ doesn't make sense in the kadmind context, and close a few security
+ issues. The standard CrackLib distribution on at least some Linux
+ distributions now supports an additional interface to configure its
+ behavior, and krb5-strength should change in the future to use that
+ interface and drop the embedded copy.
+
+ 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, this package is usable without any special considerations.
- You may use either the external password quality check tool, installed
- as heimdal-strength, or the plugin as you choose. It has been tested
- with Heimdal 1.2.1 and later.
+ For Heimdal, you may use either the external password quality check
+ tool, installed as heimdal-strength, or the plugin as you choose. It
+ has been tested with Heimdal 1.2.1 and later, but has not recently been
+ tested with versions prior to 7.0.
- To use this plugin with MIT Kerberos, you will need to apply the patch
- in the patches directory to MIT Kerberos and rebuild. Due to how
- kadmind is constructed, the changes are actually in the libkadm5srv
- library, not in the kadmind binary, so you'll need to install the
- modified libraries.
+ For MIT Kerberos, version 1.9 or higher is required for the password
+ quality plugin interface. MIT Kerberos does not support an external
+ password quality check tool directly, so you will need to install the
+ plugin.
You can optionally build against the system CrackLib library. Any
version should be supported, but note that some versions, particularly
older versions close to the original code, do things like printing
diagnostics to stderr, calling exit, and otherwise not being
- well-behaved for use inside plugins or libraries.
+ well-behaved for use inside plugins or libraries. They also have known
+ security vulnerabilities. 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
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 5.010 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 (or even better, find
- every word list you can locate on the Internet and combine them). 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.
+ 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
+ * Const::Fast
+ * Crypt::PBKDF2
+ * Getopt::Long::Descriptive
+ * IPC::Run
+ * JSON::MaybeXS
+
+ and their dependencies.
- To bootstrap from a Git checkout, or If you change the Automake files
+ 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 generate man pages and bootstrap the test suite data from
+ a Git checkout.
-COMPILING AND INSTALLING
+BUILDING AND INSTALLATION
- You can build and install the plugin with the standard commands:
+ You can build and install krb5-strength with the standard commands:
./configure
make
make install
- Pass --enable-silent-rules to configure for a quieter build (similar to
- the Linux kernel). Use make warnings instead of make to build with full
- GCC compiler warnings (requires a relatively current version of GCC).
+ If you are building from a Git clone, first run ./bootstrap in the
+ source directory to generate the build files. make install will
+ probably have to be done as root. Building outside of the source
+ directory is also supported, if you wish, by creating an empty directory
+ and then running configure with the correct relative path.
+
+ By default, the Heimdal external password check function is installed as
+ /usr/local/bin/heimdal-strength, and the plugin is installed as
+ /usr/local/lib/krb5/plugins/pwqual/strength.so. You can change these
+ paths with the --prefix, --libdir, and --bindir options to configure.
+
+ By default, the embedded version of CrackLib will be used. To build
+ with the system version of CrackLib, pass --with-cracklib to configure.
+ You can optionally add a directory, giving the root directory where
+ CrackLib was installed, or separately set the include and library path
+ with --with-cracklib-include and --with-cracklib-lib. You can also
+ build without any CrackLib support by passing --without-cracklib to
+ configure.
+
+ 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.
- 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
- /usr/local/bin/heimdal-strength. You can change these paths with the
- --prefix, --libdir, and --bindir options to configure.
-
- For MIT Kerberos, you also have to apply the patch provided in the
- patches directory to the MIT Kerberos source and install the new
- libkadm5srv library. See patches/README for more information about the
- patch. If you're using a different version of MIT Kerberos, you may
- need to adjust the patch accordingly.
+ Normally, configure will use krb5-config to determine the flags to use
+ to compile with your Kerberos libraries. To specify a particular
+ krb5-config script to use, either set the PATH_KRB5_CONFIG environment
+ variable or pass it to configure like:
- To build with the system version of CrackLib, pass --with-cracklib to
- configure. You can optionally add a directory, giving the root
- directory where CrackLib was installed, or separately set the include
- and library path with --with-cracklib-include and --with-cracklib-lib.
+ ./configure PATH_KRB5_CONFIG=/path/to/krb5-config
- 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
- searched by your compiler. If the the krb5-config script first in your
- path is not the one corresponding to the Kerberos libraries you want to
- use or if your Kerberos libraries and includes aren't in a location
- searched by default by your compiler, you need to specify a different
- Kerberos installation root via --with-krb5=PATH. For example:
+ If krb5-config isn't found, configure will look for the standard
+ Kerberos libraries in locations already searched by your compiler. If
+ the the krb5-config script first in your path is not the one
+ corresponding to the Kerberos libraries you want to use, or if your
+ Kerberos libraries and includes aren't in a location searched by default
+ by your compiler, you need to specify a different Kerberos installation
+ root via --with-krb5=PATH. For example:
./configure --with-krb5=/usr/pubsw
You can also individually set the paths to the include directory and the
library directory with --with-krb5-include and --with-krb5-lib. You may
need to do this if Autoconf can't figure out whether to use lib, lib32,
- or lib64 on your platform. Note that these settings aren't used if a
- krb5-config script is found, so you may need to disable the krb5-config
- script as described below.
-
- To specify a particular krb5-config script to use, either set the
- PATH_KRB5_CONFIG environment variable or pass it to configure like:
-
- ./configure PATH_KRB5_CONFIG=/path/to/krb5-config
+ or lib64 on your platform.
To not use krb5-config and force library probing even if there is a
krb5-config script on your path, set PATH_KRB5_CONFIG to a nonexistent
path:
- ./configure KRB5_CONFIG=/nonexistent
+ ./configure PATH_KRB5_CONFIG=/nonexistent
+
+ krb5-config is not used and library probing is always done if either
+ --with-krb5-include or --with-krb5-lib are given.
+
+ Pass --enable-silent-rules to configure for a quieter build (similar to
+ the Linux kernel). Use make warnings instead of make to build with full
+ compiler warnings (requires either GCC or Clang and may require a
+ relatively current version of the compiler).
You can pass the --enable-reduced-depends flag to configure to try to
minimize the shared library dependencies encoded in the binaries. This
- omits from the link line all the libraries included solely because the
- Kerberos libraries depend on them and instead links the programs only
- against libraries whose APIs are called directly. This will only work
- with shared Kerberos libraries and will only work on platforms where
- shared libraries properly encode their own dependencies (such as Linux).
- It is intended primarily for building packages for Linux distributions
- to avoid encoding unnecessary shared library dependencies that make
- shared library migrations more difficult. If none of the above made any
- sense to you, don't bother with this flag.
-
-CONFIGURATION
-
- First, build and install a CrackLib dictionary as described above. This
- 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.
-
- Heimdal
-
- There are two options: using an external password check program, or
- using the plugin. I recommend the external password check program
- unless you encounter speed problems with that approach that cause
- kpasswd to time out.
-
- For either approach, first add a stanza like the following to the
- [appdefaults] section of your /etc/krb5.conf (or wherever your krb5.conf
- file is located):
-
- krb5-strength = {
- password_dictionary = /usr/local/lib/kadmind/dictionary
- }
-
- The provided path should be the full path to the dictionary files,
- omitting the trailing *.hwm, *.pwd, and *.pwi extensions.
-
- Then, for the external password checking program, add a new section (or
- modify the existing [password_quality] section) to look like the
- following:
-
- [password_quality]
- policies = external-check
- external_program = /usr/local/bin/heimdal-strength
-
- You can, of course, combine this policy with others. Replace the path
- with the full path to wherever you have installed heimdal-strength. You
- can put this section in your kdc.conf instead of krb5.conf if you
- prefer.
-
- If you want to instead use the module, use the following section
- instead:
-
- [password_quality]
- policies = krb5-strength
- policy_libraries = /usr/local/lib/kadmind/passwd_strength.so
-
- in either krb5.conf or kdc.conf. Note that some versions of Heimdal
- have a bug in the support for loading modules when policy_libraries is
- set. If you get an error like:
-
- didn't find `kadm5_password_verifier' symbol in `(null)'
-
- you may have to omit policy_libraries in your configuration and instead
- pass the --check-library argument to kpasswdd specifying the library to
- load.
-
- MIT Kerberos
-
- In the [realms] section of your 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. Then, specify
- the path to the plugin by adding:
-
- pwcheck_plugin = /usr/local/lib/kadmind/passwd_strength.so
-
- to the same section of the kdc.conf, giving the correct full path to the
- plugin. Restart kadmind and password strength checking should be
- enabled.
-
- Be aware that, for MIT Kerberos, password strength checking is only
- applied to principals with a policy set. If you want to check all user
- passwords, assign all user principals a password policy. (Similarly,
- you can avoid checking the strength of passwords for particular
- principals by clearing their policy.) Also be aware that enabling this
- plugin will disable the normal kadmind dictionary check. There
- currently is no way to have them both enabled at the same time.
-
- Finally, note that the default rules of this plugin will reject the
- temporary password used by addprinc -randkey or ktadd -randkey when
- initializing a principal. When generating service principals using that
- flag, you will need to pass in the -clearpolicy flag as well to avoid
- rejecting the initial temporary password. You can then add a policy
- later with modprinc if desired.
+ omits from the link line all the libraries included solely because other
+ libraries depend on them and instead links the programs only against
+ libraries whose APIs are called directly. This will only work with
+ shared libraries and will only work on platforms where shared libraries
+ properly encode their own dependencies (this includes most modern
+ platforms such as all Linux). It is intended primarily for building
+ packages for Linux distributions to avoid encoding unnecessary shared
+ library dependencies that make shared library migrations more difficult.
+ If none of the above made any sense to you, don't bother with this flag.
+
+ After installing this software, see the man pages for krb5-strength,
+ heimdal-strength, and heimdal-history for configuration information.
+
+TESTING
+
+ krb5-strength comes with a test suite, which you can run after building
+ with:
+
+ make check
+
+ If a test fails, you can run a single test with verbose output via:
+
+ tests/runtests -o <name-of-test>
+
+ Do this instead of running the test program directly since it will
+ ensure that necessary environment variables are set up.
+
+ 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.
+
+SUPPORT
+
+ The krb5-strength web page at:
+
+ https://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.
+
+ For bug tracking, use the issue tracker on GitHub:
+
+ https://github.com/rra/krb5-strength/issues
+
+ However, please be aware that I tend to be extremely busy and work
+ projects often take priority. I'll save your report 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 on GitHub at:
+
+ https://github.com/rra/krb5-strength
+
+ or by cloning the repository at:
+
+ https://git.eyrie.org/git/kerberos/krb5-strength.git
+
+ or view the repository via the web at:
+
+ https://git.eyrie.org/?p=kerberos/krb5-strength.git
+
+ The eyrie.org repository is the canonical one, maintained by the author,
+ but using GitHub is probably more convenient for most purposes. Pull
+ requests are gratefully reviewed and normally accepted.
+
+LICENSE
+
+ The krb5-strength package as a whole is covered by the following
+ copyright statement and license:
+
+ Copyright 2016, 2020 Russ Allbery <eagle@eyrie.org>
+ Copyright 2006-2007, 2009-2010, 2012-2014
+ The Board of Trustees of the Leland Stanford Junior University
+ Copyright 1993 Alec Muffett
+
+ 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.
+
+ Developed by Daria Phoebe Brashear and Ken Hornstein of Sine Nomine
+ Associates, on behalf of Stanford University.
+
+ 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.
+
+ 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, and detailed information about the
+ licensing of each file, are recorded in the LICENSE file.
+
+ Files covered by a license with an assigned SPDX License Identifier
+ include SPDX-License-Identifier tags to enable automated processing of
+ license information. See https://spdx.org/licenses/ for more
+ information.
+
+ For any copyright range specified by files in this package as YYYY-ZZZZ,
+ the range specifies every single year in that closed interval.
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