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krb5-strength 3.1
(Kerberos password strength checking plugin)
Maintained by Russ Allbery <eagle@eyrie.org>
Copyright 2016 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 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
Heimdal includes a capability to plug in external password quality
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. 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,
that if you're building against the system CrackLib, Heimdal includes in
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, 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, 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, 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 1.5.
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. 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
utilities to build a CrackLib dictionary from a word list are included
in this toolkit but not installed by default. You can run them out of
the cracklib directory after building. You can also use the utilities
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. 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.
BUILDING AND INSTALLATION
You can build and install krb5-strength with the standard commands:
./configure
make
make install
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.
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. 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
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.
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 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
GCC compiler warnings (requires a relatively current version of GCC).
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 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.
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=devel/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 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 Derrick 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.
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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