xref: /dragonfly/contrib/pam_passwdqc/README (revision 7d3e9a5b)

pam_passwdqc is a simple password strength checking module for
PAM-aware password changing programs, such as passwd(1).  In addition
to checking regular passwords, it offers support for passphrases and
can provide randomly generated ones.  All features are optional and
can be (re-)configured without rebuilding.

This module should be stacked before your usual password changing
module (such as pam_unix or pam_pwdb) in the password management group
(the "password" lines in /etc/pam.d/passwd or /etc/pam.conf).  The
password changing module should then be told to use the provided new
authentication token (new password) rather than request it from the
user.  There's usually the "use_authtok" option to do that.  If your
password changing module lacks the "use_authtok" option or its prompts
are inconsistent with pam_passwdqc's, you may tell pam_passwdqc to ask
for the old password as well, with "ask_oldauthtok".  In that case the
option to use with the password changing module is "use_first_pass".

There are a number of supported options, which can be used to modify the
behavior of pam_passwdqc (defaults are given in square brackets):

	config=FILE			[]

Load the specified configuration FILE, which must be in the
passwdqc.conf format (described in the passwdqc.conf(5) manual page).
This file may define any options described in here, including load of
yet another configuration file, but loops are not allowed.

	min=N0,N1,N2,N3,N4		[min=disabled,24,11,8,7]

The minimum allowed password lengths for different kinds of passwords
and 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 character
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 character
classes that do not meet the requirements for a passphrase.

N2 is used for passphrases.  Note that besides meeting this length
requirement, a passphrase must also consist of a sufficient number of
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=72]

The maximum allowed password length.  This can be used to prevent
users from setting passwords that may be too long for some system
services.

The value 8 is treated specially: with max=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 password at 8 characters.

It is important that you do set max=8 if you are using the traditional
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 user-chosen 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 substring is found; it will instead be
subjected to the usual strength requirements with the weak substring
partially discounted.

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 password with the substring partially
discounted would be weak.

	wordlist=FILE			[]

Deny passwords that are based on lines of a tiny external text file,
which can reasonably be e.g. a list of a few thousand common passwords.
Common dictionary words may also reasonably be included, especially in a
local language other than English, or longer yet common English words.
(passwdqc includes a list of a few thousand common English words of
lengths from 3 to 6 built in.  Any word list possibly specified with
this option is used in addition to the built-in word list.)

Substring matching and discounting will be used if the "match" setting
above is non-zero.  Please note that this is very inefficient, and isn't
to be used with large wordlists.

	denylist=FILE			[]

Deny passwords or passphrases directly appearing in a tiny external text
file.  That file can reasonably be e.g. a list of common passwords if
only a relaxed policy is desired and stricter checks are thus disabled
(using their separate options).  Such policy would only be somewhat
effective against online/remote attacks, but not against offline attacks
on hashed passwords.

	filter=FILE			[]

Deny passwords or passphrases directly appearing in a maybe huge binary
filter file created with pwqfilter.  This is very efficient, needing at
most two random disk reads per query.  A filter created from millions of
leaked passwords can reasonably be used on top of passwdqc's other
checks to further reduce the number of passing yet weak passwords
without causing unreasonable inconvenience (as e.g. higher minimum
lengths and character set requirements could).

	random=N[,only]			[random=47]

The size of randomly-generated passphrases in bits (24 to 136), or 0 to
disable this feature.  Any passphrase that contains 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, the module 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.  With "ask_oldauthtok=update", pam_passwdqc
will do that during the update phase.

	check_oldauthtok		[]

This tells pam_passwdqc to validate the old password before giving a
new password prompt.  Normally, this task is left for subsequent
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.  With this module,
the only difference between "use_first_pass" and "use_authtok" is that
the former is incompatible with "ask_oldauthtok".

	noaudit				[]

If audit is enabled at build time, the PAM module logs audit events once
user tries to change their credentials.  This option disables that audit
logging.