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Diffstat (limited to 'modules/pam_cracklib/pam_cracklib.8')
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diff --git a/modules/pam_cracklib/pam_cracklib.8 b/modules/pam_cracklib/pam_cracklib.8 new file mode 100644 index 0000000..3ed37e8 --- /dev/null +++ b/modules/pam_cracklib/pam_cracklib.8 @@ -0,0 +1,363 @@ +'\" t +.\" Title: pam_cracklib +.\" Author: [see the "AUTHOR" section] +.\" Generator: DocBook XSL Stylesheets v1.78.1 <http://docbook.sf.net/> +.\" Date: 05/18/2017 +.\" Manual: Linux-PAM Manual +.\" Source: Linux-PAM Manual +.\" Language: English +.\" +.TH "PAM_CRACKLIB" "8" "05/18/2017" "Linux-PAM Manual" "Linux\-PAM Manual" +.\" ----------------------------------------------------------------- +.\" * Define some portability stuff +.\" ----------------------------------------------------------------- +.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +.\" http://bugs.debian.org/507673 +.\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html +.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +.ie \n(.g .ds Aq \(aq +.el .ds Aq ' +.\" ----------------------------------------------------------------- +.\" * set default formatting +.\" ----------------------------------------------------------------- +.\" disable hyphenation +.nh +.\" disable justification (adjust text to left margin only) +.ad l +.\" ----------------------------------------------------------------- +.\" * MAIN CONTENT STARTS HERE * +.\" ----------------------------------------------------------------- +.SH "NAME" +pam_cracklib \- PAM module to check the password against dictionary words +.SH "SYNOPSIS" +.HP \w'\fBpam_cracklib\&.so\fR\ 'u +\fBpam_cracklib\&.so\fR [\fI\&.\&.\&.\fR] +.SH "DESCRIPTION" +.PP +This module can be plugged into the +\fIpassword\fR +stack of a given application to provide some plug\-in strength\-checking for passwords\&. +.PP +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\&. +.PP +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\&. +.PP +The strength checks works in the following manner: at first the +\fBCracklib\fR +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: +.PP +Palindrome +.RS 4 +Is the new password a palindrome? +.RE +.PP +Case Change Only +.RS 4 +Is the new password the the old one with only a change of case? +.RE +.PP +Similar +.RS 4 +Is the new password too much like the old one? This is primarily controlled by one argument, +\fBdifok\fR +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\&. +.RE +.PP +Simple +.RS 4 +Is the new password too small? This is controlled by 6 arguments +\fBminlen\fR, +\fBmaxclassrepeat\fR, +\fBdcredit\fR, +\fBucredit\fR, +\fBlcredit\fR, and +\fBocredit\fR\&. See the section on the arguments for the details of how these work and there defaults\&. +.RE +.PP +Rotated +.RS 4 +Is the new password a rotated version of the old password? +.RE +.PP +Same consecutive characters +.RS 4 +Optional check for same consecutive characters\&. +.RE +.PP +Too long monotonic character sequence +.RS 4 +Optional check for too long monotonic character sequence\&. +.RE +.PP +Contains user name +.RS 4 +Optional check whether the password contains the user\*(Aqs name in some form\&. +.RE +.PP +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\&. +.SH "OPTIONS" +.PP +.PP +\fBdebug\fR +.RS 4 +This option makes the module write information to +\fBsyslog\fR(3) +indicating the behavior of the module (this option does not write password information to the log file)\&. +.RE +.PP +\fBauthtok_type=\fR\fB\fIXXX\fR\fR +.RS 4 +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 +\fIUNIX\fR +can be replaced with this option, by default it is empty\&. +.RE +.PP +\fBretry=\fR\fB\fIN\fR\fR +.RS 4 +Prompt user at most +\fIN\fR +times before returning with error\&. The default is +\fI1\fR\&. +.RE +.PP +\fBdifok=\fR\fB\fIN\fR\fR +.RS 4 +This argument will change the default of +\fI5\fR +for the number of character changes in the new password that differentiate it from the old password\&. +.RE +.PP +\fBminlen=\fR\fB\fIN\fR\fR +.RS 4 +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 (\fIother\fR, +\fIupper\fR, +\fIlower\fR +and +\fIdigit\fR)\&. The default for this parameter is +\fI9\fR +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 +\fICracklib\fR +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 +\fBminlen\fR\&. If you want to allow passwords as short as 5 characters you should not use this module\&. +.RE +.PP +\fBdcredit=\fR\fB\fIN\fR\fR +.RS 4 +(N >= 0) This is the maximum credit for having digits in the new password\&. If you have less than or +\fIN\fR +digits, each digit will count +1 towards meeting the current +\fBminlen\fR +value\&. The default for +\fBdcredit\fR +is 1 which is the recommended value for +\fBminlen\fR +less than 10\&. +.sp +(N < 0) This is the minimum number of digits that must be met for a new password\&. +.RE +.PP +\fBucredit=\fR\fB\fIN\fR\fR +.RS 4 +(N >= 0) This is the maximum credit for having upper case letters in the new password\&. If you have less than or +\fIN\fR +upper case letters each letter will count +1 towards meeting the current +\fBminlen\fR +value\&. The default for +\fBucredit\fR +is +\fI1\fR +which is the recommended value for +\fBminlen\fR +less than 10\&. +.sp +(N < 0) This is the minimum number of upper case letters that must be met for a new password\&. +.RE +.PP +\fBlcredit=\fR\fB\fIN\fR\fR +.RS 4 +(N >= 0) This is the maximum credit for having lower case letters in the new password\&. If you have less than or +\fIN\fR +lower case letters, each letter will count +1 towards meeting the current +\fBminlen\fR +value\&. The default for +\fBlcredit\fR +is 1 which is the recommended value for +\fBminlen\fR +less than 10\&. +.sp +(N < 0) This is the minimum number of lower case letters that must be met for a new password\&. +.RE +.PP +\fBocredit=\fR\fB\fIN\fR\fR +.RS 4 +(N >= 0) This is the maximum credit for having other characters in the new password\&. If you have less than or +\fIN\fR +other characters, each character will count +1 towards meeting the current +\fBminlen\fR +value\&. The default for +\fBocredit\fR +is 1 which is the recommended value for +\fBminlen\fR +less than 10\&. +.sp +(N < 0) This is the minimum number of other characters that must be met for a new password\&. +.RE +.PP +\fBminclass=\fR\fB\fIN\fR\fR +.RS 4 +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 +\fBcredit\fR +check is that a specific class if of characters is not required\&. Instead +\fIN\fR +out of four of the classes are required\&. +.RE +.PP +\fBmaxrepeat=\fR\fB\fIN\fR\fR +.RS 4 +Reject passwords which contain more than N same consecutive characters\&. The default is 0 which means that this check is disabled\&. +.RE +.PP +\fBmaxsequence=\fR\fB\fIN\fR\fR +.RS 4 +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 \*(Aq12345\*(Aq or \*(Aqfedcb\*(Aq\&. Note that most such passwords will not pass the simplicity check unless the sequence is only a minor part of the password\&. +.RE +.PP +\fBmaxclassrepeat=\fR\fB\fIN\fR\fR +.RS 4 +Reject passwords which contain more than N consecutive characters of the same class\&. The default is 0 which means that this check is disabled\&. +.RE +.PP +\fBreject_username\fR +.RS 4 +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\&. +.RE +.PP +\fBgecoscheck\fR +.RS 4 +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\&. +.RE +.PP +\fBenforce_for_root\fR +.RS 4 +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\&. +.RE +.PP +\fBuse_authtok\fR +.RS 4 +This argument is used to +\fIforce\fR +the module to not prompt the user for a new password but use the one provided by the previously stacked +\fIpassword\fR +module\&. +.RE +.PP +\fBdictpath=\fR\fB\fI/path/to/dict\fR\fR +.RS 4 +Path to the cracklib dictionaries\&. +.RE +.SH "MODULE TYPES PROVIDED" +.PP +Only the +\fBpassword\fR +module type is provided\&. +.SH "RETURN VALUES" +.PP +.PP +PAM_SUCCESS +.RS 4 +The new password passes all checks\&. +.RE +.PP +PAM_AUTHTOK_ERR +.RS 4 +No new password was entered, the username could not be determined or the new password fails the strength checks\&. +.RE +.PP +PAM_AUTHTOK_RECOVERY_ERR +.RS 4 +The old password was not supplied by a previous stacked module or got not requested from the user\&. The first error can happen if +\fBuse_authtok\fR +is specified\&. +.RE +.PP +PAM_SERVICE_ERR +.RS 4 +A internal error occurred\&. +.RE +.SH "EXAMPLES" +.PP +For an example of the use of this module, we show how it may be stacked with the password component of +\fBpam_unix\fR(8) +.sp +.if n \{\ +.RS 4 +.\} +.nf +# +# 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 + +.fi +.if n \{\ +.RE +.\} +.PP +Another example (in the +/etc/pam\&.d/passwd +format) is for the case that you want to use md5 password encryption: +.sp +.if n \{\ +.RS 4 +.\} +.nf +#%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 \e + difok=3 minlen=15 dcredit= 2 ocredit=2 +password required pam_unix\&.so use_authtok nullok md5 + +.fi +.if n \{\ +.RE +.\} +.PP +And here is another example in case you don\*(Aqt want to use credits: +.sp +.if n \{\ +.RS 4 +.\} +.nf +#%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 \e + dcredit=\-1 ucredit=\-1 ocredit=\-1 lcredit=0 minlen=8 +password required pam_unix\&.so use_authtok nullok md5 + +.fi +.if n \{\ +.RE +.\} +.sp +.SH "SEE ALSO" +.PP +\fBpam.conf\fR(5), +\fBpam.d\fR(5), +\fBpam\fR(8) +.SH "AUTHOR" +.PP +pam_cracklib was written by Cristian Gafton <gafton@redhat\&.com> |