Provided by: libpam-cracklib_1.1.8-3.2ubuntu2.3_amd64 bug

NAME

       pam_cracklib - PAM module to check the password against dictionary words

SYNOPSIS

       pam_cracklib.so [...]

DESCRIPTION

       This module can be plugged into the password stack of a given application to provide some
       plug-in strength-checking for passwords.

       The action of this module is to prompt the user for a password and check its strength
       against a system dictionary and a set of rules for identifying poor choices.

       The first action is to prompt for a single password, check its strength and then, if it is
       considered strong, prompt for the password a second time (to verify that it was typed
       correctly on the first occasion). All being well, the password is passed on to subsequent
       modules to be installed as the new authentication token.

       The strength checks works in the following manner: at first the Cracklib routine is called
       to check if the password is part of a dictionary; if this is not the case an additional
       set of strength checks is done. These checks are:

       Palindrome
           Is the new password a palindrome?

       Case Change Only
           Is the new password the the old one with only a change of case?

       Similar
           Is the new password too much like the old one? This is primarily controlled by one
           argument, difok which is a number of character changes (inserts, removals, or
           replacements) between the old and new password that are enough to accept the new
           password. This defaults to 5 changes.

       Simple
           Is the new password too small? This is controlled by 6 arguments minlen,
           maxclassrepeat, dcredit, ucredit, lcredit, and ocredit. See the section on the
           arguments for the details of how these work and there defaults.

       Rotated
           Is the new password a rotated version of the old password?

       Same consecutive characters
           Optional check for same consecutive characters.

       Too long monotonic character sequence
           Optional check for too long monotonic character sequence.

       Contains user name
           Optional check whether the password contains the user's name in some form.

       This module with no arguments will work well for standard unix password encryption. With
       md5 encryption, passwords can be longer than 8 characters and the default settings for
       this module can make it hard for the user to choose a satisfactory new password. Notably,
       the requirement that the new password contain no more than 1/2 of the characters in the
       old password becomes a non-trivial constraint. For example, an old password of the form
       "the quick brown fox jumped over the lazy dogs" would be difficult to change... In
       addition, the default action is to allow passwords as small as 5 characters in length. For
       a md5 systems it can be a good idea to increase the required minimum size of a password.
       One can then allow more credit for different kinds of characters but accept that the new
       password may share most of these characters with the old password.

OPTIONS

       debug
           This option makes the module write information to syslog(3) indicating the behavior of
           the module (this option does not write password information to the log file).

       authtok_type=XXX
           The default action is for the module to use the following prompts when requesting
           passwords: "New UNIX password: " and "Retype UNIX password: ". The example word UNIX
           can be replaced with this option, by default it is empty.

       retry=N
           Prompt user at most N times before returning with error. The default is 1.

       difok=N
           This argument will change the default of 5 for the number of character changes in the
           new password that differentiate it from the old password.

       minlen=N
           The minimum acceptable size for the new password (plus one if credits are not disabled
           which is the default). In addition to the number of characters in the new password,
           credit (of +1 in length) is given for each different kind of character (other, upper,
           lower and digit). The default for this parameter is 9 which is good for a old style
           UNIX password all of the same type of character but may be too low to exploit the
           added security of a md5 system. Note that there is a pair of length limits in Cracklib
           itself, a "way too short" limit of 4 which is hard coded in and a defined limit (6)
           that will be checked without reference to minlen. If you want to allow passwords as
           short as 5 characters you should not use this module.

       dcredit=N
           (N >= 0) This is the maximum credit for having digits in the new password. If you have
           less than or N digits, each digit will count +1 towards meeting the current minlen
           value. The default for dcredit is 1 which is the recommended value for minlen less
           than 10.

           (N < 0) This is the minimum number of digits that must be met for a new password.

       ucredit=N
           (N >= 0) This is the maximum credit for having upper case letters in the new password.
           If you have less than or N upper case letters each letter will count +1 towards
           meeting the current minlen value. The default for ucredit is 1 which is the
           recommended value for minlen less than 10.

           (N < 0) This is the minimum number of upper case letters that must be met for a new
           password.

       lcredit=N
           (N >= 0) This is the maximum credit for having lower case letters in the new password.
           If you have less than or N lower case letters, each letter will count +1 towards
           meeting the current minlen value. The default for lcredit is 1 which is the
           recommended value for minlen less than 10.

           (N < 0) This is the minimum number of lower case letters that must be met for a new
           password.

       ocredit=N
           (N >= 0) This is the maximum credit for having other characters in the new password.
           If you have less than or N other characters, each character will count +1 towards
           meeting the current minlen value. The default for ocredit is 1 which is the
           recommended value for minlen less than 10.

           (N < 0) This is the minimum number of other characters that must be met for a new
           password.

       minclass=N
           The minimum number of required classes of characters for the new password. The default
           number is zero. The four classes are digits, upper and lower letters and other
           characters. The difference to the credit check is that a specific class if of
           characters is not required. Instead N out of four of the classes are required.

       maxrepeat=N
           Reject passwords which contain more than N same consecutive characters. The default is
           0 which means that this check is disabled.

       maxsequence=N
           Reject passwords which contain monotonic character sequences longer than N. The
           default is 0 which means that this check is disabled. Examples of such sequence are
           '12345' or 'fedcb'. Note that most such passwords will not pass the simplicity check
           unless the sequence is only a minor part of the password.

       maxclassrepeat=N
           Reject passwords which contain more than N consecutive characters of the same class.
           The default is 0 which means that this check is disabled.

       reject_username
           Check whether the name of the user in straight or reversed form is contained in the
           new password. If it is found the new password is rejected.

       gecoscheck
           Check whether the words from the GECOS field (usualy full name of the user) longer
           than 3 characters in straight or reversed form are contained in the new password. If
           any such word is found the new password is rejected.

       enforce_for_root
           The module will return error on failed check also if the user changing the password is
           root. This option is off by default which means that just the message about the failed
           check is printed but root can change the password anyway. Note that root is not asked
           for an old password so the checks that compare the old and new password are not
           performed.

       use_authtok
           This argument is used to force the module to not prompt the user for a new password
           but use the one provided by the previously stacked password module.

       dictpath=/path/to/dict
           Path to the cracklib dictionaries.

MODULE TYPES PROVIDED

       Only the password module type is provided.

RETURN VALUES

       PAM_SUCCESS
           The new password passes all checks.

       PAM_AUTHTOK_ERR
           No new password was entered, the username could not be determined or the new password
           fails the strength checks.

       PAM_AUTHTOK_RECOVERY_ERR
           The old password was not supplied by a previous stacked module or got not requested
           from the user. The first error can happen if use_authtok is specified.

       PAM_SERVICE_ERR
           A internal error occurred.

EXAMPLES

       For an example of the use of this module, we show how it may be stacked with the password
       component of pam_unix(8)

           #
           # These lines stack two password type modules. In this example the
           # user is given 3 opportunities to enter a strong password. The
           # "use_authtok" argument ensures that the pam_unix module does not
           # prompt for a password, but instead uses the one provided by
           # pam_cracklib.
           #
           passwd  password required       pam_cracklib.so retry=3
           passwd  password required       pam_unix.so use_authtok

       Another example (in the /etc/pam.d/passwd format) is for the case that you want to use md5
       password encryption:

           #%PAM-1.0
           #
           # These lines allow a md5 systems to support passwords of at least 14
           # bytes with extra credit of 2 for digits and 2 for others the new
           # password must have at least three bytes that are not present in the
           # old password
           #
           password  required pam_cracklib.so \
                          difok=3 minlen=15 dcredit= 2 ocredit=2
           password  required pam_unix.so use_authtok nullok md5

       And here is another example in case you don't want to use credits:

           #%PAM-1.0
           #
           # These lines require the user to select a password with a minimum
           # length of 8 and with at least 1 digit number, 1 upper case letter,
           # and 1 other character
           #
           password  required pam_cracklib.so \
                          dcredit=-1 ucredit=-1 ocredit=-1 lcredit=0 minlen=8
           password  required pam_unix.so use_authtok nullok md5

SEE ALSO

       pam.conf(5), pam.d(5), pam(7)

AUTHOR

       pam_cracklib was written by Cristian Gafton <gafton@redhat.com>