Ubuntu Manpage: heimdal-strength - Heimdal password quality check embedding CrackLib

NAME

       heimdal-strength - Heimdal password quality check embedding CrackLib

SYNOPSIS

       heimdal-strength [principal]

DESCRIPTION

heimdal-strength is an external password quality check program for Heimdal that verifies
the strength of a password. 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 is normally run via
kpasswdd(8) using the Heimdal password quality check interface rather than directly.

To use this program, it must be configured in krb5.conf via settings in "[appdefaults]"
for the application name "krb5-strength". A typical setting would be:

krb5-strength = {
password_dictionary = /usr/local/lib/kadmind/dictionary
}

which says to check passwords with CrackLib using the given path as the base path of the
CrackLib dictionary. See "CONFIGURATION" below for details on the supported configuration
options.

heimdal-strength then expects the Heimdal password quality check information on standard
input, specifically:

principal: <principal>
new-password: <password>
end

where <principal> is the principal whose password would be changed and <password> is the
new password. If the password appears to be strong, it prints "APPROVED" on standard
output and exits with a status of 0. If the password is rejected as being too weak, it
will print the reason for rejecting the password on standard error and exit with a status
of 0. If some fatal error occurs, it will print that error to standard error and exit
with a non-zero status.

CONFIGURATION

The following krb5.conf configuration options are supported:

cracklib_maxlen
Normally, all passwords are checked with CrackLib if a CrackLib dictionary is defined.
However, CrackLib's rules were designed for a world in which most passwords were four
to eight characters long, and tends to spuriously reject a lot of passphrases. If
this option is set to something other than its default of 0, passwords longer than
that length bypass CrackLib checks. (Using a SQLite dictionary for longer passwords
is strongly recommended.)

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.

password_dictionary
Specifies the base path to a CrackLib dictionary and enables password strength testing
using CrackLib. The provided path should be the full path to the dictionary files,
omitting the trailing *.hwm, *.pwd, and *.pwi extensions for the CrackLib dictionary.

password_dictionary_cdb
Specifies the base path to a CDB dictionary and enables CDB password dictionary
lookups. The path must point to a CDB-format database whose keys are the known
passwords or dictionary words. The values are ignored. You can use the
krb5-strength-wordlist utility to generate the CDB database from a word list.

The CDB dictionary lookups do not do the complex password mangling that CrackLib does.
Instead, the password itself will be checked against the dictionary, and then
variations of the password formed by removing the first character, the last character,
the first and last characters, the first two characters, and the last two characters.
If any of these strings are found in the CDB database, the password will be rejected;
otherwise, it will be accepted, at least by this check.

A CrackLib dictionary, a CDB dictionary, and a SQLite dictionary may all be configured
at the same time or in any combination, in which case CrackLib will be run first,
followed by CDB and then SQLite as appropriate.

password_dictionary_sqlite
Specifies the base path to a SQLite dictionary and enables SQLite password dictionary
lookups. The path must point to a SQLite 3 database with a table named "passwords".
This table should have two columns, "password" and "drowssap", which, for each
dictionary word, holds the word and the reversed form of the word. You can use the
krb5-strength-wordlist utility to generate the SQLite database from a word list.

The SQLite dictionary lookups do not do the complex password mangling that CrackLib
does, but they will detect and reject any password that is within edit distance one of
a word in the dictionary, meaning that the dictionary word can be formed from the
password by adding, deleting, or modifying a single character.

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". 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.
Passwords 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.

AUTHOR

       Russ Allbery <eagle@eyrie.org>

COPYRIGHT AND LICENSE