passwdqc.conf man page

passwdqc.conf — libpasswdqc configuration file


libpasswdqc is a simple password strength checking library. In addition to checking regular passwords, it offers support for passphrases and can provide randomly generated ones. A passwdqc.conf configuration file may be used to override default libpasswdqc settings.


A passwdqc.conf file consists of 0 or more lines of the following format:


Empty lines and lines beginning with “#” are ignored. Whitespace characters between the option, “=”, and value are not allowed.

Directive Options

Load the specified configuration FILE in the passwdqc.conf format. This file may define any options described in this manual, including load of yet another configuration file, but loops are not allowed.

Password Quality Control Options

(default: min=disabled,24,11,8,7) 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 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.

(default: max=40) 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: 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 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.

(default: passphrase=3) The number of words required for a passphrase, or 0 to disable the support for user-chosen passphrases.
(default: 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.

(default: 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.
(default: random=47) The size of randomly-generated passphrases in bits (24 to 85), 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.

Pam Module Options

(default: enforce=everyone) The PAM 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.
Normally, the PAM 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.
(default: retry=3) The number of times the PAM 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 for the old password as well. Normally, the PAM module leaves this task for subsequent modules. With no argument, the ask_oldauthtok option will cause the PAM module to ask for the old password during the preliminary check phase. If the ask_oldauthtok option is specified with the update argument, the PAM module will do that during the update phase.
This tells the PAM module 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 other modules stacked before the PAM module. This disables user interaction within the PAM module. The only difference between use_first_pass and use_authtok is that the former is incompatible with ask_oldauthtok.



See Also

getpwnam(3), pam_passwdqc(8).



The pam_passwdqc module was written for Openwall GNU/*/Linux by Solar Designer ⟨solar at openwall.com⟩. This manual page was derived from pam_passwdqc(8). The latter, 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.

Referenced By

cryptsetup(8), pam_passwdqc(8), pwqcheck(1), pwqgen(1).

Explore man page connections for passwdqc.conf(5).

March 13, 2010