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 ones.

The pam_passwdqc module provides functionality for only one PAM management 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 password, 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,24,11,8,7) 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.

Required password complexity is proportional to its length. Passwords must have at least N4 characters. Passwords shorter than N3 characters need to have lower case letters, upper case letters, digits and symbols. Passwords shorter than N2 characters must have 3 or more classes of characters. Passwords shorter than N1 characters must have 2 or more classes of characters. Passwords longer than N1 characters can have just one type of characters in them.

In other words, the number of required unique characters depends how long or complex the password is.

max=N

(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.

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 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 password with the substring removed would be weak.

random=N[,only]

(random=42) The size of randomly-generated passphrases in bits (24 to 72), 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, 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 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.

disable_firstupper_lastdigit_check

This tells pam_passwdqc to include upper-case letters used as the first character and digits used as the last character of a password when calculating the number of character classes.

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.

oldpass_prompt_file, newpass_prompt_file = absolute-file-path

These can be used to override prompts while requesting old password and new password, respectively. The maximum size of the prompt files can be 4096 characters at present. If the file size is more than 4096 characters, the output will be truncated to 4096 characters.

SEE ALSO¶

getpwnam(3), pam.conf(5), pam(8)

AUTHORS¶

The pam_passwdqc module was written for Openwall GNU/*/Linux by Solar Designer ⟨solar at 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.