pam_passwdqc
PAM_PASSWDQC(8) BSD System Manager’s Manual PAM_PASSWDQC(8)
NAME
pam_passwdqc - Password quality-control PAM module
SYNOPSIS
[service-name] module-type control-flag pam_passwdqc [options]
DESCRIPTION
The pam_passwdqc module is a simple password strength checking module
for PAM. In addition to checking regular passwords, it offers support
for passphrases and can provide randomly generated passwords.
The pam_passwdqc module provides functionality for only one PAM manage-
ment group: password changing. In terms of the module-type parameter,
this is the “password” feature.
The pam_chauthtok() service function may ask the user for a new pass-
word, and verify that it meets certain minimum standards. If the chosen
password is unsatisfactory, the service function returns
PAM_AUTHTOK_ERR.
The following options may be passed to the module:
min=N0,N1,N2,N3,N4
(min=disabled,24,12,8,7) The minimum allowed password lengths
for different kinds of passwords/passphrases. The keyword
disabled can be used to disallow passwords of a given kind
regardless of their length. Each subsequent number is required
to be no larger than the preceding one.
N0 is used for passwords consisting of characters from one char-
acter class only. The character classes are: digits, lower-case
letters, upper-case letters, and other characters. There is
also a special class for non-ASCII characters which could not be
classified, but are assumed to be non-digits.
N1 is used for passwords consisting of characters from two char-
acter classes, which do not meet the requirements for a
passphrase.
N2 is used for passphrases. A passphrase must consist of suffi-
cient words (see the passphrase option below).
N3 and N4 are used for passwords consisting of characters from
three and four character classes, respectively.
When calculating the number of character classes, upper-case
letters used as the first character and digits used as the last
character of a password are not counted.
In addition to being sufficiently long, passwords are required
to contain enough different characters for the character classes
and the minimum length they have been checked against.
max=N (max=40) The maximum allowed password length. This can be used
to prevent users from setting passwords which may be too long
for some system services. The value 8 is treated specially: if
max is set to 8, passwords longer than 8 characters will not be
rejected, but will be truncated to 8 characters for the strength
checks and the user will be warned. This is to be used with the
traditional DES-based password hashes, which truncate the pass-
word at 8 characters.
It is important that you do set max=8 if you are using the tra-
ditional hashes, or some weak passwords will pass the checks.
passphrase=N
(passphrase=3) The number of words required for a passphrase, or
0 to disable the support for passphrases.
match=N
(match=4) The length of common substring required to conclude
that a password is at least partially based on information found
in a character string, or 0 to disable the substring search.
Note that the password will not be rejected once a weak sub-
string is found; it will instead be subjected to the usual
strength requirements with the weak substring removed.
The substring search is case-insensitive and is able to detect
and remove a common substring spelled backwards.
similar=permit|deny
(similar=deny) Whether a new password is allowed to be similar
to the old one. The passwords are considered to be similar when
there is a sufficiently long common substring and the new pass-
word with the substring removed would be weak.
random=N[,only]
(random=42) The size of randomly-generated passwords in bits, or
0 to disable this feature. Passwords that contain the offered
randomly-generated string will be allowed regardless of other
possible restrictions.
The only modifier can be used to disallow user-chosen passwords.
enforce=none|users|everyone
(enforce=everyone) The module can be configured to warn of weak
passwords only, but not actually enforce strong passwords. The
users setting will enforce strong passwords for invocations by
non-root users only.
non-unix
Normally, pam_passwdqc uses getpwnam(3) to obtain the user’s
personal login information and use that during the password
strength checks. This behavior can be disabled with the
non-unix option.
retry=N
(retry=3) The number of times the module will ask for a new
password if the user fails to provide a sufficiently strong
password and enter it twice the first time.
ask_oldauthtok[=update]
Ask for the old password as well. Normally, pam_passwdqc leaves
this task for subsequent modules. With no argument, the
ask_oldauthtok option will cause pam_passwdqc to ask for the old
password during the preliminary check phase. If the
ask_oldauthtok option is specified with the update argument,
pam_passwdqc will do that during the update phase.
check_oldauthtok
This tells pam_passwdqc to validate the old password before giv-
ing a new password prompt. Normally, this task is left for sub-
sequent modules.
The primary use for this option is when ask_oldauthtok=update is
also specified, in which case no other module gets a chance to
ask for and validate the password. Of course, this will only
work with UNIX passwords.
use_first_pass, use_authtok
Use the new password obtained by modules stacked before
pam_passwdqc. This disables user interaction within
pam_passwdqc. The only difference between use_first_pass and
use_authtok is that the former is incompatible with
ask_oldauthtok.
SEE ALSO
getpwnam(3), pam.conf(5), pam(8)
AUTHORS
The pam_passwdqc module was written for Openwall GNU/*/Linux by Solar
Designer 〈solar@openwall.com〉. This manual page, derived from the
author’s documentation, was written for the FreeBSD Project by ThinkSec
AS and NAI Labs, the Security Research Division of Network Associates,
Inc. under DARPA/SPAWAR contract N66001-01-C-8035 (“CBOSS”), as part of
the DARPA CHATS research program.
BSD November 1, 2003 BSD
