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pam_passwdqc - Password quality-control PAM module



      pam_passwdqc - Password quality-control PAM module


      [service-name] module-type control-flag pam_passwdqc [options]


      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 passwords.
      The pam_passwdqc module provides functionality for only one PAM category:
      password changing.  In terms of the module-type parameter, this is the
      “password” feature.
      The pam_chauthtok() service function will ask the user for a new pass‐
      word, 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 authentication module:
              (min=disabled,24,12,8,7) 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 char‐
              acter 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 clas‐
              sified, but are assumed to be non-digits.
              N1 is used for passwords consisting of characters from two char‐
              acter classes, which do not meet the requirements for a
              N2 is used for passphrases.  A passphrase must consist of suffi‐
              cient 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 let‐
              ters 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=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 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.
              It is important that you do set max=8 if you are using the tradi‐
              tional hashes, or some weak passwords will pass the checks.
              (passphrase=3) The number of words required for a passphrase, or
              0 to disable passphrase support.
              (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=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 pass‐
              word with the substring removed would be weak.
              (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.
              The only modifier can be used to disallow user-chosen passwords.
              (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 non-root users
              Normally, pam_passwdqc uses getpwnam(3) to obtain the user’s per‐
              sonal login information and use that during the password strength
              checks.  This behavior can be disabled with the non-unix option.
              (retry=3) The number of times the module will ask for a new pass‐
              word 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, 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.
              This tells pam_passwdqc to validate the old password before giv‐
              ing a new password prompt.  Normally, this task is left for sub‐
              sequent modules.
              The primary use for this option is when ask_oldauthtok=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.
      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
      getpwnam(3), pam.conf(5), pam(8)


      The pam_passwdqc module was written by Solar Designer
      〈〉.  This manual page, derived from the author’s docu‐
      mentation, 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.


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