path: root/lib/libpam/modules/pam_passwdqc/pam_passwdqc.8

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.\" Associates, Inc.  under DARPA/SPAWAR contract N66001-01-C-8035
.\" ("CBOSS"), as part of the DARPA CHATS research program.
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.Dd April 15, 2002
.Dt PAM_PASSWDQC 8
.Os
.Sh NAME
.Nm pam_passwdqc
.Nd Password quality-control PAM module
.Sh SYNOPSIS
.Op Ar service-name
.Ar module-type
.Ar control-flag
.Pa pam_passwdqc
.Op Ar options
.Sh DESCRIPTION
The
.Nm
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.
.Pp
The
.Nm
module provides functionality for only one PAM category:
password changing.
In terms of the
.Ar module-type
parameter, this is the
.Dq Li password
feature.
.Pp
The
.Fn pam_chauthtok
service function will ask the user for a new password, and verify that
it meets certain minimum standards.
If the chosen password is unsatisfactory, the service function returns
.Dv PAM_AUTHTOK_ERR .
.Pp
The following options may be passed to the authentication module:
.Bl -tag -width 18n
.It Cm min Ns = Ns Ar N0 Ns , Ns Ar N1 Ns , Ns Ar N2 Ns , Ns Ar N3 Ns , Ns Ar N4
(min=disabled,24,12,8,7)
The minimum allowed password lengths for different kinds of passwords
/ passphrases.
The keyword
.Dq 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.
.Pp
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 couldn't
be classified, but are assumed to be non-digits.
.Pp
N1 is used for passwords consisting of characters from two character
classes, which don't meet the requirements for a passphrase.
.Pp
N2 is used for passphrases.
A passphrase must consist of sufficient words (see the
.Cm passphrase
option below).
.Pp
N3 and N4 are used for passwords consisting of characters from three
and four character classes, respectively.
.Pp
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.
.Pp
In addition to being sufficiently long, passwords are required to
contain enough different characters for the character classes and
the minimum length they've been checked against.
.Pp
.It Cm max Ns = Ns Ar 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
.Cm 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 for compatibility with the traditional DES password hashes,
which truncate the password at 8 characters.
.Pp
It is important that you do set max=8 if you're using the traditional
hashes, or some weak passwords will pass the checks.
.It Cm passphrase Ns = Ns Ar N
(passphrase=3)
The number of words required for a passphrase, or 0 to disable
passphrase support.
.It Cm match Ns = Ns Ar 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 removed.
.Pp
The substring search is case-insensitive and is able to detect and
remove a common substring spelled backwards.
.It Cm similar Ns = Ns Ar permit Ns | Ns Ar 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's a sufficiently
long common substring and the new password with the substring removed
would be weak.
.It Cm random Ns = Ns Ar N Ns Op , Ns Ar 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.
.Pp
The
.Dq only
modifier can be used to disallow user-chosen passwords.
.It Cm enforce Ns = Ns Ar none Ns | Ns Ar users Ns | Ns Ar everyone
(enforce=everyone)
The module can be configured to warn of weak passwords only, but not
actually enforce strong passwords.
The
.Dq users
setting will enforce strong passwords for non-root users only.
.It Cm non-unix
Normally,
.Nm
uses
.Xr 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
.Cm non-unix
option.
.It Cm retry Ns = Ns Ar 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.
.It Cm ask_oldauthtok Ns Op = Ns Ar update
Ask for the old password as well.
Normally, pam_passwdqc leaves this task for subsequent modules.
With no argument, the
.Cm ask_oldauthtok
option will cause
.Nm
to ask for the old password during the preliminary check phase.
If the
.Cm ask_oldauthtok
option is specified with the
.Dq update
argument,
.Nm
will do that during the update phase.
.It Cm 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.
.Pp
The primary use for this option is when
.Cm ask_oldauthtok Ns = Ns Ar update
is also specified, in which case no other modules gets a chance to ask
for and validate the password.
Of course, this will only work with Unix passwords.
.It Cm use_first_pass Ns , Ns Cm use_authtok
Use the new password obtained by modules stacked before
.Nm .
This disables user interaction within
.Nm .
The only difference between
.Cm use_first_pass
and
.Cm use_authtok
is that the former is incompatible with
.Cm ask_oldauthtok .
.Sh SEE ALSO
.Xr getpwnnam 3 ,
.Xr pam.conf 5 ,
.Xr pam 8
.Sh AUTHORS
The
.Nm
module was written by
.An Solar Designer Aq solar@openwall.com .
This manual page, derived from the author's documentation, was written
for the
.Fx
Project by
ThinkSec AS and NAI Labs, the Security Research Division of Network
Associates, Inc. under DARPA/SPAWAR contract N66001-01-C-8035
.Pq Dq CBOSS ,
as part of the DARPA CHATS research program.