In CDB checks, check all passwords within edit distance one

[kerberos/krb5-strength.git] / README

                            krb5-strength 2.2
               (Kerberos password strength checking plugin)

               Maintained by Russ Allbery <eagle@eyrie.org>

  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.

BLURB

  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 password history implementation for
  use with Heimdal.  Passwords can be tested with CrackLib, checked
  against a CDB database of known weak passwords, 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

  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, and imposing 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,
  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.

  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.

  Ideally, the changes to CrackLib should be added to the standard
  CrackLib distribution by adding an additional interface to configure its
  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
  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.  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.

  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 dictionary, use the provided cdbmake-wordlist
  program.  The CDB utility must be on your PATH.  cdbmake-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 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.  Those tests will be skipped if the modules
  are not available.

  To enable tests that may be sensitive to the local environment or that
  produce a lot of false positives without uncovering many problems, set
  RRA_MAINTAINER_TESTS 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 JSON, Perl6::Slurp, and Readonly modules (from CPAN) to
  bootstrap the test suite data from a Git checkout.

COMPILING AND INSTALLING

  You can build and install the plugin 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).

  The last step will probably have to be done as root.  By default, the
  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.

  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.

  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:

      ./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 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

  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.

  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 either a CrackLib dictionary as described in
  REQUIREMENTS above, or build a CDB dictionary with cdbmake-wordlist.
  (Or both.)  The CrackLib dictionary will consist of three files, one
  each ending in *.hwm, *.pwd, and *.pwi.  The CDB dictionary will consist
  of a single file ending in *.cdb.  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

  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     = /path/to/cracklib/dictionary
          password_dictionary_cdb = /path/to/cdb/dictionary.cdb
      }

  The first setting configures a CrackLib dictionary and the second a CDB
  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 either or both settings.  If you use
  both, CrackLib will be checked first, and then CDB.  When checking a CDB
  database, the password, all printable ASCII passwords within edit
  distance one of the password, and the password with the first and last
  characters removed, the first two characters removed, and the last two
  characters removed will all be checked against the dictionary.

  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/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
  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.

  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
  to krb5.conf (or to a separate kdc.conf if you use that) like:

      [plugins]
          pwqual = {
              module = strength:/usr/local/lib/krb5/plugins/pwqual/strength.so
          }

  to register the plugin.

  There are two ways to tell where the dictionary is.  One option is to
  use krb5.conf (and in this case you must use krb5.conf, even if you use
  a separate kdc.conf file).  For this approach, add the following to the
  [appdefaults] section:

      krb5-strength = {
          password_dictionary     = /path/to/cracklib/dictionary
          password_dictionary_cdb = /path/to/cdb/dictionary.cdb
      }

  The first setting configures a CrackLib dictionary and the second a CDB
  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 either or both settings.  If you use
  both, CrackLib will be checked first, and then CDB.  When checking a CDB
  database, the password, all printable ASCII passwords within edit
  distance one of the password, and the password with the first and last
  characters removed, the first two characters removed, and the last two
  characters removed will all be checked against the dictionary.

  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

  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 dictionary path.  If
  both settings are used, 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 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_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.  Also be aware that,
      when testing passwords within edit distance one against a CDB
      database, only characters in the printable ASCII character set will
      be attempted.

  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.