Ubuntu Manpage: pwqcheck — Check passphrase quality

NAME

       pwqcheck — Check passphrase quality

SYNOPSIS

       pwqcheck [options]

DESCRIPTION

       The  pwqcheck program checks passphrase quality using the libpasswdqc library.  By default, it expects to
       read 3 lines from standard input:

             first line is a new password,
             second line is an old password, and
             third line is either an existing account name or a passwd(5) entry.

       There are a number of supported options, which can be used to control the pwqcheck behavior.

       pwqcheck prints OK on success.  Scripts invoking pwqcheck are suggested to check for  both  a  zero  exit
       status and the OK line.

OPTIONS

min=N0,N1,N2,N3,N4
(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.

max=N (default: 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: 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
(default: passphrase=3) The number of words required for a passphrase.

match=N
(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.

similar=permit|deny
(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.

wordlist=FILE
Deny passwords that are based on lines of the 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 the 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).

config=FILE
Load config FILE in the passwdqc.conf format. This file may define any options described in
passwdqc.conf(5), but only the min, max, passphrase, match, and config options are honored by
pwqcheck.

-1 Read just 1 line (new passphrase). This is needed to use pwqcheck as the passwordcheck program
on OpenBSD - e.g., with ":passwordcheck=/usr/bin/pwqcheck -1:\" (without the quotes, but with the
trailing backslash) in the "default" section in /etc/login.conf.

-2 Read just 2 lines (new and old passphrases).

--multi
Check multiple passphrases (until EOF). This option may be used on its own or along with the -1
or -2 options. pwqcheck will read 1, 2, or 3 lines and will output one line per passphrase to
check. The lines will start with either OK or a message explaining why the passphrase did not
pass the checks, followed by a colon and a space, and finally followed by the passphrase. The
explanatory message is guaranteed to not include a colon. With this option, the exit status of
pwqcheck depends solely on whether there were any errors preventing the strength of passphrases
from being fully checked or not. A primary use for this option is to test different policies
and/or different versions of passwdqc on large passphrase lists.

--version
Output pwqcheck program version and exit.

-h, --help
Output pwqcheck help text and exit.

EXIT STATUS

       pwqcheck  exits  with  non-zero  status  when  it encounters invalid config file, invalid option, invalid
       parameter value, invalid data in standard input, and in any  case  when  it  fails  to  check  passphrase
       strength.   Without  the  --multi option, pwqcheck also exits with non-zero status when it detects a weak
       passphrase.

FILES

       /etc/passwdqc.conf  (not  read  unless   this   suggested   file   location   is   specified   with   the
       config=/etc/passwdqc.conf option).

AUTHORS

       The pam_passwdqc module was written for Openwall GNU/*/Linux by Solar Designer.  The pwqcheck program was
       originally written for ALT GNU/*/Linux by Dmitry V. Levin, indirectly reusing code from pam_passwdqc (via
       libpasswdqc).   This  manual  page (derived from the pam_passwdqc documentation) was written for Openwall
       GNU/*/Linux by Dmitry V. Levin.

Openwall Project                                December 30, 2020                                    PWQCHECK(1)