doc/drafts/draft-behera-ldap-password-policy-xx.txt

Network Working Group                                     J. Sermersheim
Internet-Draft                                               Novell, Inc
Intended status: Standards Track                               L. Poitou
Expires: February 10, 2010                              Sun Microsystems
                                                             H. Chu, Ed.
                                                             Symas Corp.
                                                          August 9, 2009


                  Password Policy for LDAP Directories
                draft-behera-ldap-password-policy-10.txt

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Abstract

   Password policy as described in this document is a set of rules that
   controls how passwords are used and administered in Lightweight
   Directory Access Protocol (LDAP) based directories.  In order to
   improve the security of LDAP directories and make it difficult for
   password cracking programs to break into directories, it is desirable
   to enforce a set of rules on password usage.  These rules are made to
   ensure that users change their passwords periodically, passwords meet
   construction requirements, the re-use of old password is restricted,
   and to deter password guessing attacks.


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Table of Contents

   1.    Overview . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.    Conventions  . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.    Application of Password Policy . . . . . . . . . . . . . . .  6
   4.    Articles of Password Policy  . . . . . . . . . . . . . . . .  7
   4.1.  Password Usage Policy  . . . . . . . . . . . . . . . . . . .  7
   4.2.  Password Modification Policy . . . . . . . . . . . . . . . .  8
   4.3.  Restriction of the Password Policy . . . . . . . . . . . . . 10
   5.    Schema used for Password Policy  . . . . . . . . . . . . . . 12
   5.1.  The pwdPolicy Object Class . . . . . . . . . . . . . . . . . 12
   5.2.  Attribute Types used in the pwdPolicy ObjectClass  . . . . . 12
   5.3.  Attribute Types for Password Policy State Information  . . . 18
   6.    Controls used for Password Policy  . . . . . . . . . . . . . 24
   6.1.  Request Control  . . . . . . . . . . . . . . . . . . . . . . 24
   6.2.  Response Control . . . . . . . . . . . . . . . . . . . . . . 24
   7.    Policy Decision Points . . . . . . . . . . . . . . . . . . . 26
   7.1.  Locked Account Check . . . . . . . . . . . . . . . . . . . . 26
   7.2.  Password Must be Changed Now Check . . . . . . . . . . . . . 26
   7.3.  Password Expiration Check  . . . . . . . . . . . . . . . . . 27
   7.4.  Remaining Grace AuthN Check  . . . . . . . . . . . . . . . . 27
   7.5.  Time Before Expiration Check . . . . . . . . . . . . . . . . 27
   7.6.  Intruder Lockout Check . . . . . . . . . . . . . . . . . . . 27
   7.7.  Intruder Delay Check . . . . . . . . . . . . . . . . . . . . 27
   7.8.  Password Too Young Check . . . . . . . . . . . . . . . . . . 28
   8.    Server Policy Enforcement Points . . . . . . . . . . . . . . 29
   8.1.  Password-based Authentication  . . . . . . . . . . . . . . . 29
   8.2.  Password Update Operations . . . . . . . . . . . . . . . . . 31
   8.3.  Other Operations . . . . . . . . . . . . . . . . . . . . . . 34
   9.    Client Policy Enforcement Points . . . . . . . . . . . . . . 35
   9.1.  Bind Operation . . . . . . . . . . . . . . . . . . . . . . . 35
   9.2.  Modify Operations  . . . . . . . . . . . . . . . . . . . . . 36
   9.3.  Add Operation  . . . . . . . . . . . . . . . . . . . . . . . 37
   9.4.  Compare Operation  . . . . . . . . . . . . . . . . . . . . . 37
   9.5.  Other Operations . . . . . . . . . . . . . . . . . . . . . . 38
   10.   Administration of the Password Policy  . . . . . . . . . . . 39
   11.   Password Policy and Replication  . . . . . . . . . . . . . . 40
   12.   Security Considerations  . . . . . . . . . . . . . . . . . . 42
   13.   IANA Considerations  . . . . . . . . . . . . . . . . . . . . 43
   14.   Acknowledgement  . . . . . . . . . . . . . . . . . . . . . . 44
   15.   Normative References . . . . . . . . . . . . . . . . . . . . 45
         Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 46


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1.  Overview

   LDAP-based directory services are currently accepted by many
   organizations as the access protocol for directories.  The ability to
   ensure the secure read and update access to directory information
   throughout the network is essential to the successful deployment.
   Most LDAP implementations support many authentication schemes - the
   most basic and widely used is the simple authentication i.e., user DN
   and password.  In this case, many LDAP servers have implemented some
   kind of policy related to the password used to authenticate.  Among
   other things, this policy includes:

   o  Whether and when passwords expire.

   o  Whether failed bind attempts cause the account to be locked.

   o  If and how users are able to change their passwords.

   In order to achieve greater security protection and ensure
   interoperability in a heterogeneous environment, LDAP needs to
   standardize on a common password policy model.  This is critical to
   the successful deployment of LDAP directories.


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2.  Conventions

   Imperative keywords defined in [RFC2119] are used in this document,
   and carry the meanings described there.

   All ASN.1 [X.680] Basic Encoding Rules (BER) [X.690] encodings follow
   the conventions found in Section 5.1 of [RFC4511].

   The term "password administrator" refers to a user that has
   sufficient access control privileges to modify users' passwords.  The
   term "password policy administrator" refers to a user that has
   sufficient access control privileges to modify the pwdPolicy object
   defined in this document.  The access control that is used to
   determine whether an identity is a password administrator or password
   policy administrator is beyond the scope of this document, but
   typically implies that the password administrator has 'write'
   privileges to the password attribute.


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3.  Application of Password Policy

   The password policy defined in this document can be applied to any
   attribute holding a user's password used for an authenticated LDAP
   bind operation.  In this document, the term "user" represents any
   LDAP client application that has an identity in the directory.

   This policy is typically applied to the userPassword attribute in the
   case of the LDAP simple authentication method [RFC4511] or the case
   of password based SASL [RFC4422] authentication such as CRAM-MD5
   [RFC2195] and DIGEST-MD5 [RFC2831].

   The policy described in this document assumes that the password
   attribute holds a single value.  No considerations are made for
   directories or systems that allow a user to maintain multi-valued
   password attributes.

   Server implementations MAY institute internal policy whereby certain
   identities (such as directory administrators) are not forced to
   comply with any of password policy.  In this case, the password for a
   directory administrator never expires; the account is never locked,
   etc.


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4.  Articles of Password Policy

   The following sections explain in general terms each aspect of the
   password policy defined in this document as well as the need for
   each.  These policies are subdivided into the general groups of
   password usage and password modification.  Implementation details are
   presented in Section 8 and Section 9.

4.1.  Password Usage Policy

   This section describes policy enforced when a password is used to
   authenticate.  The general focus of this policy is to minimize the
   threat of intruders once a password is in use.

4.1.1.  Password Validity Policy

   These mechanisms allow account usage to be controlled independent of
   any password expiration policies.  The policy defines the absolute
   period of time for which an account may be used.  This allows an
   administrator to define an absolute starting time after which a
   password becomes valid, and an absolute ending time after which the
   password is disabled.

   A mechanism is also provided to define the period of time for which
   an account may remain unused before being disabled.

4.1.2.  Password Guessing Limit

   In order to prevent intruders from guessing a user's password, a
   mechanism exists to track the number of consecutive failed
   authentication attempts, and take action when a limit is reached.
   This policy consists of several parts:

   o  A counter to track the number of failed authentication attempts.

   o  The amount of time to delay on the first authentication failure.

   o  The maximum amount of time to delay on subsequent failures.

   o  A timeframe in which the limit of consecutive failed
      authentication attempts must happen before action is taken.

   o  A configurable limit on failed authentication attempts.

   o  The action to be taken when the limit is reached.  The action will
      either be nothing, or the account will be locked.


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   o  An amount of time the account is locked (if it is to be locked).
      This can be indefinite.

   Note that using the account lock feature provides an easy avenue for
   Denial-of-Service (DoS) attacks on user accounts.  While some sites'
   policies require accounts to be locked, this feature is discouraged
   in favor of delaying each failed login attempt.

   The delay time will be doubled on each subsequent failure, until it
   reaches the maximum time configured.

   [TBD: we could also provide a syntax for configuring a backoff
   algorithm.  E.g. "+<int>" for linearly incrementing delay, "x<int>"
   for constant multiplier, "^<int> for geometric.  But it's probably
   overkill to add a calculator language to the server.]

4.2.  Password Modification Policy

   This section describes policy enforced while users are modifying
   passwords.  The general focus of this policy is to ensure that when
   users add or change their passwords, the security and effectiveness
   of their passwords is maximized.  In this document, the term "modify
   password operation" refers to any operation that is used to add or
   modify a password attribute.  Often this is done by updating the
   password attribute during an add or modify operation, but MAY be done
   by other means such as an extended operation.

4.2.1.  Password Expiration, Expiration Warning, and Grace
        Authentications

   One of the key properties of a password is the fact that it is not
   well known.  If a password is frequently changed, the chances of that
   user's account being broken into are minimized.

   Password policy administrators may deploy a password policy that
   causes passwords to expire after a given amount of time - thus
   forcing users to change their passwords periodically.

   As a side effect, there needs to be a way in which users are made
   aware of this need to change their password before actually being
   locked out of their accounts.  One or both of the following methods
   handle this:

   o  A warning may be returned to the user sometime before his password
      is due to expire.  If the user fails to heed this warning before
      the expiration time, his account will be locked.


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   o  The user may bind to the directory a preset number of times after
      her password has expired.  If she fails to change her password
      during one of her 'grace' authentications, her account will be
      locked.

4.2.2.  Password History

   When the Password Expiration policy is used, an additional mechanism
   may be employed to prevent users from simply re-using a previous
   password (as this would effectively circumvent the expiration
   policy).

   In order to do this; a history of used passwords is kept.  The
   password policy administrator sets the number of passwords to be
   stored at any given time.  Passwords are stored in this history
   whenever the password is changed.  Users aren't allowed to specify
   any passwords that are in the history list while changing passwords.

4.2.3.  Password Minimum Age

   Users may circumvent the Password History mechanism by quickly
   performing a series of password changes.  If they change their
   password enough times, their 'favorite' password will be pushed out
   of the history list.

   This process may be made less attractive to users by employing a
   minimum age for passwords.  If users are forced to wait 24 hours
   between password changes, they may be less likely to cycle through a
   history of 10 passwords.

4.2.4.  Password Quality and Minimum length

   In order to prevent users from creating or updating passwords that
   are easy to guess, a password quality policy may be employed.  This
   policy consists of two general mechanisms - ensuring that passwords
   conform to a defined quality criterion and ensuring that they are of
   a minimum length.

   Forcing a password to comply with the quality policy may imply a
   variety of things including:

   o  Disallowing trivial or well-known words make up the password.

   o  Forcing a certain number of digits be used.

   o  Disallowing anagrams of the user's name.

   The implementation of this policy meets with the following problems:


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   o  If the password to be added or updated is encrypted by the client
      before being sent, the server has no way of enforcing this policy.
      Therefore, the onus of enforcing this policy falls upon client
      implementations.

   o  There are no specific definitions of what 'quality checking'
      means.  This can lead to unexpected behavior in a heterogeneous
      environment.

4.2.5.  User Defined Passwords

   In some cases, it is desirable to disallow users from adding and
   updating their own passwords.  This policy makes this functionality
   possible.

4.2.6.  Password Change after Reset

   This policy forces the user to update her password after it has been
   set for the first time, or has been reset by a password
   administrator.

   This is needed in scenarios where a password administrator has set or
   reset the password to a well-known value.

4.2.7.  Safe Modification

   As directories become more commonly used, it will not be unusual for
   clients to connect to a directory and leave the connection open for
   an extended period.  This opens up the possibility for an intruder to
   make modifications to a user's password while that user's computer is
   connected but unattended.

   This policy forces the user to prove his identity by specifying the
   old password during a password modify operation.

   {TODO: This allows a dictionary attack unless we specify that this is
   also subject to intruder detection.  One solution is to require users
   to authN prior to changing password.  Another solution is to perform
   intruder detection checks when the password for a non-authenticated
   identity is being updated}

4.3.  Restriction of the Password Policy

   The password policy defined in this document can apply to any
   attribute containing a password.  Password policy state information
   is held in the user's entry, and applies to a password attribute, not
   a particular password attribute value.  Thus the server SHOULD
   enforce that the password attribute subject to password policy,


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   contains one and only one password value.


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5.  Schema used for Password Policy

   The schema elements defined here fall into two general categories.  A
   password policy object class is defined which contains a set of
   administrative password policy attributes, and a set of operational
   attributes are defined that hold general password policy state
   information for each user.

5.1.  The pwdPolicy Object Class

   This object class contains the attributes defining a password policy
   in effect for a set of users.  Section 10 describes the
   administration of this object, and the relationship between it and
   particular objects.

         ( 1.3.6.1.4.1.42.2.27.8.2.1
         NAME 'pwdPolicy'
         SUP top
         AUXILIARY
         MUST ( pwdAttribute )
         MAY ( pwdMinAge $ pwdMaxAge $ pwdInHistory $ pwdCheckQuality $
         pwdMinLength $ pwdMaxLength $ pwdExpireWarning $
         pwdGraceAuthNLimit $ pwdGraceExpiry $ pwdLockout $
         pwdLockoutDuration $ pwdMaxFailure $ pwdFailureCountInterval $
         pwdMustChange $ pwdAllowUserChange $ pwdSafeModify $
         pwdMinDelay $ pwdMaxDelay $ pwdMaxIdle ) )

5.2.  Attribute Types used in the pwdPolicy ObjectClass

   Following are the attribute types used by the pwdPolicy object class.

5.2.1.  pwdAttribute

   This holds the name of the attribute to which the password policy is
   applied.  For example, the password policy may be applied to the
   userPassword attribute.

         ( 1.3.6.1.4.1.42.2.27.8.1.1
         NAME 'pwdAttribute'
         EQUALITY objectIdentifierMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.38 )

5.2.2.  pwdMinAge

   This attribute holds the number of seconds that must elapse between
   modifications to the password.  If this attribute is not present, 0
   seconds is assumed.


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         ( 1.3.6.1.4.1.42.2.27.8.1.2
         NAME 'pwdMinAge'
         EQUALITY integerMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

5.2.3.  pwdMaxAge

   This attribute holds the number of seconds after which a modified
   password will expire.

   If this attribute is not present, or if the value is 0 the password
   does not expire.  If not 0, the value must be greater than or equal
   to the value of the pwdMinAge.

         ( 1.3.6.1.4.1.42.2.27.8.1.3
         NAME 'pwdMaxAge'
         EQUALITY integerMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

5.2.4.  pwdInHistory

   This attribute specifies the maximum number of used passwords stored
   in the pwdHistory attribute.

   If this attribute is not present, or if the value is 0, used
   passwords are not stored in the pwdHistory attribute and thus may be
   reused.

         ( 1.3.6.1.4.1.42.2.27.8.1.4
         NAME 'pwdInHistory'
         EQUALITY integerMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

5.2.5.  pwdCheckQuality

   {TODO: Consider changing the syntax to OID.  Each OID will list a
   quality rule (like min len, # of special characters, etc).  These
   rules can be specified outside this document.}

   {TODO: Note that even though this is meant to be a check that happens
   during password modification, it may also be allowed to happen during
   authN.  This is useful for situations where the password is encrypted
   when modified, but decrypted when used to authN.}

   This attribute indicates how the password quality will be verified


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   while being modified or added.  If this attribute is not present, or
   if the value is '0', quality checking will not be enforced.  A value
   of '1' indicates that the server will check the quality, and if the
   server is unable to check it (due to a hashed password or other
   reasons) it will be accepted.  A value of '2' indicates that the
   server will check the quality, and if the server is unable to verify
   it, it will return an error refusing the password.

         ( 1.3.6.1.4.1.42.2.27.8.1.5
         NAME 'pwdCheckQuality'
         EQUALITY integerMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

5.2.6.  pwdMinLength

   When quality checking is enabled, this attribute holds the minimum
   number of characters that must be used in a password.  If this
   attribute is not present, no minimum password length will be
   enforced.  If the server is unable to check the length (due to a
   hashed password or otherwise), the server will, depending on the
   value of the pwdCheckQuality attribute, either accept the password
   without checking it ('0' or '1') or refuse it ('2').

         ( 1.3.6.1.4.1.42.2.27.8.1.6
         NAME 'pwdMinLength'
         EQUALITY integerMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

5.2.7.  pwdMaxLength

   When quality checking is enabled, this attribute holds the maximum
   number of characters that may be used in a password.  If this
   attribute is not present, no maximum password length will be
   enforced.  If the server is unable to check the length (due to a
   hashed password or otherwise), the server will, depending on the
   value of the pwdCheckQuality attribute, either accept the password
   without checking it ('0' or '1') or refuse it ('2').

         ( 1.3.6.1.4.1.42.2.27.8.1.31
         NAME 'pwdMaxLength'
         EQUALITY integerMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )


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5.2.8.  pwdExpireWarning

   This attribute specifies the maximum number of seconds before a
   password is due to expire that expiration warning messages will be
   returned to an authenticating user.

   If this attribute is not present, or if the value is 0 no warnings
   will be returned.  If not 0, the value must be smaller than the value
   of the pwdMaxAge attribute.

         ( 1.3.6.1.4.1.42.2.27.8.1.7
         NAME 'pwdExpireWarning'
         EQUALITY integerMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

5.2.9.  pwdGraceAuthNLimit

   This attribute specifies the number of times an expired password can
   be used to authenticate.  If this attribute is not present or if the
   value is 0, authentication will fail.

         ( 1.3.6.1.4.1.42.2.27.8.1.8
         NAME 'pwdGraceAuthNLimit'
         EQUALITY integerMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

5.2.10.  pwdGraceExpiry

   This attribute specifies the number of seconds the grace
   authentications are valid.  If this attribute is not present or if
   the value is 0, there is no time limit on the grace authentications.

         ( 1.3.6.1.4.1.42.2.27.8.1.30
         NAME 'pwdGraceExpire'
         EQUALITY integerMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

5.2.11.  pwdLockout

   This attribute indicates, when its value is "TRUE", that the password
   may not be used to authenticate after a specified number of
   consecutive failed bind attempts.  The maximum number of consecutive
   failed bind attempts is specified in pwdMaxFailure.

   If this attribute is not present, or if the value is "FALSE", the


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   password may be used to authenticate when the number of failed bind
   attempts has been reached.

         ( 1.3.6.1.4.1.42.2.27.8.1.9
         NAME 'pwdLockout'
         EQUALITY booleanMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.7
         SINGLE-VALUE )

5.2.12.  pwdLockoutDuration

   This attribute holds the number of seconds that the password cannot
   be used to authenticate due to too many failed bind attempts.  If
   this attribute is not present, or if the value is 0 the password
   cannot be used to authenticate until reset by a password
   administrator.

         ( 1.3.6.1.4.1.42.2.27.8.1.10
         NAME 'pwdLockoutDuration'
         EQUALITY integerMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

5.2.13.  pwdMaxFailure

   This attribute specifies the number of consecutive failed bind
   attempts after which the password may not be used to authenticate.
   If this attribute is not present, or if the value is 0, this policy
   is not checked, and the value of pwdLockout will be ignored.

         ( 1.3.6.1.4.1.42.2.27.8.1.11
         NAME 'pwdMaxFailure'
         EQUALITY integerMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

5.2.14.  pwdFailureCountInterval

   This attribute holds the number of seconds after which the password
   failures are purged from the failure counter, even though no
   successful authentication occurred.

   If this attribute is not present, or if its value is 0, the failure
   counter is only reset by a successful authentication.


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         ( 1.3.6.1.4.1.42.2.27.8.1.12
         NAME 'pwdFailureCountInterval'
         EQUALITY integerMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

5.2.15.  pwdMustChange

   This attribute specifies with a value of "TRUE" that users must
   change their passwords when they first bind to the directory after a
   password is set or reset by a password administrator.  If this
   attribute is not present, or if the value is "FALSE", users are not
   required to change their password upon binding after the password
   administrator sets or resets the password.  This attribute is not set
   due to any actions specified by this document, it is typically set by
   a password administrator after resetting a user's password.

         ( 1.3.6.1.4.1.42.2.27.8.1.13
         NAME 'pwdMustChange'
         EQUALITY booleanMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.7
         SINGLE-VALUE )

5.2.16.  pwdAllowUserChange

   This attribute indicates whether users can change their own
   passwords, although the change operation is still subject to access
   control.  If this attribute is not present, a value of "TRUE" is
   assumed.  This attribute is intended to be used in the absence of an
   access control mechanism.

         ( 1.3.6.1.4.1.42.2.27.8.1.14
         NAME 'pwdAllowUserChange'
         EQUALITY booleanMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.7
         SINGLE-VALUE )

5.2.17.  pwdSafeModify

   This attribute specifies whether or not the existing password must be
   sent along with the new password when being changed.  If this
   attribute is not present, a "FALSE" value is assumed.

         ( 1.3.6.1.4.1.42.2.27.8.1.15
         NAME 'pwdSafeModify'
         EQUALITY booleanMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.7
         SINGLE-VALUE )


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5.2.18.  pwdMinDelay

   This attribute specifies the number of seconds to delay responding to
   the first failed authentication attempt.  If this attribute is not
   set or is 0, no delays will be used. pwdMaxDelay must also be
   specified if pwdMinDelay is set.

         ( 1.3.6.1.4.1.42.2.27.8.1.24
         NAME 'pwdMinDelay'
         EQUALITY integerMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

5.2.19.  pwdMaxDelay

   This attribute specifies the maximum number of seconds to delay when
   responding to a failed authentication attempt.  The time specified in
   pwdMinDelay is used as the starting time and is then doubled on each
   failure until the delay time is greater than or equal to pwdMaxDelay
   (or a successful authentication occurs, which resets the failure
   counter). pwdMinDelay must be specified if pwdMaxDelay is set.

         ( 1.3.6.1.4.1.42.2.27.8.1.25
         NAME 'pwdMaxDelay'
         EQUALITY integerMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

5.2.20.  pwdMaxIdle

   This attribute specifies the number of seconds an account may remain
   unused before it becomes locked.  If this attribute is not set or is
   0, no check is performed.

         ( 1.3.6.1.4.1.42.2.27.8.1.26
         NAME 'pwdMaxIdle'
         EQUALITY integerMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
         SINGLE-VALUE )

5.3.  Attribute Types for Password Policy State Information

   Password policy state information must be maintained for each user.
   The information is located in each user entry as a set of operational
   attributes.  These operational attributes are: pwdChangedTime,
   pwdAccountLockedTime, pwdFailureTime, pwdHistory, pwdGraceUseTime,
   pwdReset, pwdPolicySubEntry, pwdStartTime, pwdEndTime,
   pwdLastSuccess.


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5.3.1.  Password Policy State Attribute Option

   Since the password policy could apply to several attributes used to
   store passwords, each of the above operational attributes must have
   an option to specify which pwdAttribute it applies to.  The password
   policy option is defined as the following:

   pwd-<passwordAttribute>

   where passwordAttribute a string following the OID syntax
   (1.3.6.1.4.1.1466.115.121.1.38).  The attribute type descriptor
   (short name) MUST be used.

   For example, if the pwdPolicy object has for pwdAttribute
   "userPassword" then the pwdChangedTime operational attribute, in a
   user entry, will be:

   pwdChangedTime;pwd-userPassword: 20000103121520Z

   This attribute option follows sub-typing semantics.  If a client
   requests a password policy state attribute to be returned in a search
   operation, and does not specify an option, all subtypes of that
   policy state attribute are returned.

5.3.2.  pwdChangedTime

   This attribute specifies the last time the entry's password was
   changed.  This is used by the password expiration policy.  If this
   attribute does not exist, the password will never expire.

         ( 1.3.6.1.4.1.42.2.27.8.1.16
         NAME 'pwdChangedTime'
         DESC 'The time the password was last changed'
         EQUALITY generalizedTimeMatch
         ORDERING generalizedTimeOrderingMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.24
         SINGLE-VALUE
         NO-USER-MODIFICATION
         USAGE directoryOperation )

5.3.3.  pwdAccountLockedTime

   This attribute holds the time that the user's account was locked.  A
   locked account means that the password may no longer be used to
   authenticate.  A 000001010000Z value means that the account has been
   locked permanently, and that only a password administrator can unlock
   the account.


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         ( 1.3.6.1.4.1.42.2.27.8.1.17
         NAME 'pwdAccountLockedTime'
         DESC 'The time an user account was locked'
         EQUALITY generalizedTimeMatch
         ORDERING generalizedTimeOrderingMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.24
         SINGLE-VALUE
         NO-USER-MODIFICATION
         USAGE directoryOperation )

5.3.4.  pwdFailureTime

   This attribute holds the timestamps of the consecutive authentication
   failures.

         ( 1.3.6.1.4.1.42.2.27.8.1.19
         NAME 'pwdFailureTime'
         DESC 'The timestamps of the last consecutive authentication
         failures'
         EQUALITY generalizedTimeMatch
         ORDERING generalizedTimeOrderingMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.24
         NO-USER-MODIFICATION
         USAGE directoryOperation )

5.3.5.  pwdHistory

   This attribute holds a history of previously used passwords.  Values
   of this attribute are transmitted in string format as given by the
   following ABNF:

      pwdHistory = time "#" syntaxOID "#" length "#" data

      time       = GeneralizedTime

      syntaxOID  = numericoid    ; the string representation of the
                                 ; dotted-decimal OID that defines the
                                 ; syntax used to store the password.

      length     = number        ; the number of octets in data.

      data       = <octets representing the password in the format
                    specified by syntaxOID>.

   GeneralizedTime is specified in 3.3.13 of [RFC4517]. numericoid and
   number are specified in 1.4 of [RFC4512].

   This format allows the server to store, and transmit a history of


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   passwords that have been used.  In order for equality matching to
   function properly, the time field needs to adhere to a consistent
   format.  For this purpose, the time field MUST be in GMT format.

         ( 1.3.6.1.4.1.42.2.27.8.1.20
         NAME 'pwdHistory'
         DESC 'The history of user s passwords'
         EQUALITY octetStringMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.40
         NO-USER-MODIFICATION
         USAGE directoryOperation )

5.3.6.  pwdGraceUseTime

   This attribute holds the timestamps of grace authentications after a
   password has expired.

         ( 1.3.6.1.4.1.42.2.27.8.1.21
         NAME 'pwdGraceUseTime'
         DESC 'The timestamps of the grace authentication after the
         password has expired'
         EQUALITY generalizedTimeMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.24
         NO-USER-MODIFICATION
         USAGE directoryOperation )

5.3.7.  pwdReset

   This attribute holds a flag to indicate (when TRUE) that the password
   has been updated by the password administrator and must be changed by
   the user.

         ( 1.3.6.1.4.1.42.2.27.8.1.22
         NAME 'pwdReset'
         DESC 'The indication that the password has been reset'
         EQUALITY booleanMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.7
         SINGLE-VALUE
         USAGE directoryOperation )

5.3.8.  pwdPolicySubentry

   This attribute points to the pwdPolicy subentry in effect for this
   object.


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         ( 1.3.6.1.4.1.42.2.27.8.1.23
         NAME 'pwdPolicySubentry'
         DESC 'The pwdPolicy subentry in effect for this object'
         EQUALITY distinguishedNameMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.12
         SINGLE-VALUE
         NO-USER-MODIFICATION
         USAGE directoryOperation )

5.3.9.  pwdStartTime

   This attribute specifies the time the entry's password becomes valid
   for authentication.  Authentication attempts made before this time
   will fail.  If this attribute does not exist, then no restriction
   applies.

         ( 1.3.6.1.4.1.42.2.27.8.1.27
         NAME 'pwdStartTime'
         DESC 'The time the password becomes enabled'
         EQUALITY generalizedTimeMatch
         ORDERING generalizedTimeOrderingMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.24
         SINGLE-VALUE
         NO-USER-MODIFICATION
         USAGE directoryOperation )

5.3.10.  pwdEndTime

   This attribute specifies the time the entry's password becomes
   invalid for authentication.  Authentication attempts made after this
   time will fail, regardless of expiration or grace settings.  If this
   attribute does not exist, then this restriction does not apply.

         ( 1.3.6.1.4.1.42.2.27.8.1.28
         NAME 'pwdEndTime'
         DESC 'The time the password becomes disabled'
         EQUALITY generalizedTimeMatch
         ORDERING generalizedTimeOrderingMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.24
         SINGLE-VALUE
         NO-USER-MODIFICATION
         USAGE directoryOperation )

   Note that pwdStartTime may be set to a time greater than or equal to
   pwdEndTime; this simply disables the account.


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5.3.11.  pwdLastSuccess

   This attribute holds the timestamp of the last successful
   authentication.

         ( 1.3.6.1.4.1.42.2.27.8.1.29
         NAME 'pwdLastSuccess'
         DESC 'The timestamp of the last successful authentication'
         EQUALITY generalizedTimeMatch
         ORDERING generalizedTimeOrderingMatch
         SYNTAX 1.3.6.1.4.1.1466.115.121.1.24
         SINGLE-VALUE
         NO-USER-MODIFICATION
         USAGE directoryOperation )


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6.  Controls used for Password Policy

   This section details the controls used while enforcing password
   policy.  A request control is defined that is sent by a client with a
   request operation in order to elicit a response control.  The
   response control contains various warnings and errors associated with
   password policy.

   {TODO: add a note about advertisement and discovery}

6.1.  Request Control

   This control MAY be sent with any LDAP request message in order to
   convey to the server that this client is aware of, and can process
   the response control described in this document.  When a server
   receives this control, it will return the response control when
   appropriate and with the proper data.

   The controlType is 1.3.6.1.4.1.42.2.27.8.5.1 and the criticality may
   be TRUE or FALSE.  There is no controlValue.

6.2.  Response Control

   If the client has sent a passwordPolicyRequest control, the server
   (when solicited by the inclusion of the request control) sends this
   control with the following operation responses: bindResponse,
   modifyResponse, addResponse, compareResponse and possibly
   extendedResponse, to inform of various conditions, and MAY be sent
   with other operations (in the case of the changeAfterReset error).
   The controlType is 1.3.6.1.4.1.42.2.27.8.5.1 and the controlValue is
   the BER encoding of the following type:

      PasswordPolicyResponseValue ::= SEQUENCE {
         warning [0] CHOICE {
            timeBeforeExpiration [0] INTEGER (0 .. maxInt),
            graceAuthNsRemaining [1] INTEGER (0 .. maxInt) } OPTIONAL,
         error   [1] ENUMERATED {
            passwordExpired             (0),
            accountLocked               (1),
            changeAfterReset            (2),
            passwordModNotAllowed       (3),
            mustSupplyOldPassword       (4),
            insufficientPasswordQuality (5),
            passwordTooShort            (6),
            passwordTooYoung            (7),
            passwordInHistory           (8) } OPTIONAL }

   The timeBeforeExpiration warning specifies the number of seconds


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   before a password will expire.  The graceAuthNsRemaining warning
   specifies the remaining number of times a user will be allowed to
   authenticate with an expired password.  The passwordExpired error
   signifies that the password has expired and must be reset.  The
   changeAfterReset error signifies that the password must be changed
   before the user will be allowed to perform any operation other than
   bind and modify.  The passwordModNotAllowed error is set when a user
   is restricted from changing her password.  The
   insufficientPasswordQuality error is set when a password doesn't pass
   quality checking.  The passwordTooYoung error is set if the age of
   the password to be modified is not yet old enough.

   Typically, only either a warning or an error will be encoded though
   there may be exceptions.  For example, if the user is required to
   change a password after the password administrator set it, and the
   password will expire in a short amount of time, the control may
   include the timeBeforeExpiration warning and the changeAfterReset
   error.


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7.  Policy Decision Points

   Following are a number of procedures used to make policy decisions.
   These procedures are typically performed by the server while
   processing an operation.

   The following sections contain detailed instructions that refer to
   attributes of the pwdPolicy object class.  When doing so, the
   attribute of the pwdPolicy object that governs the entry being
   discussed is implied.

7.1.  Locked Account Check

   A status of true is returned to indicate that the account is locked
   if any of these conditions are met:

   o  The value of the pwdAccountLockedTime attribute is 000001010000Z.

   o  The current time is less than the value of the pwdStartTime
      attribute.

   o  The current time is greater than or equal to the value of the
      pwdEndTime attribute.

   o  The current time is greater than or equal to the value of the
      pwdLastSuccess attribute added to the value of the pwdMaxIdle
      attribute.

   o  The current time is less than the value of the
      pwdAccountLockedTime attribute added to the value of the
      pwdLockoutDuration.

   Otherwise a status of false is returned.

7.2.  Password Must be Changed Now Check

   A status of true is returned to indicate that the password must be
   changed if all of these conditions are met:

   o  The pwdMustChange attribute is set to TRUE.

   o  The pwdReset attribute is set to TRUE.

   Otherwise a status of false is returned.


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7.3.  Password Expiration Check

   A status of true is returned indicating that the password has expired
   if the current time minus the value of pwdChangedTime is greater than
   the value of the pwdMaxAge.

   Otherwise, a status of false is returned.

7.4.  Remaining Grace AuthN Check

   If the pwdGraceUseTime attribute is present, the number of values in
   that attribute subtracted from the value of pwdGraceAuthNLimit is
   returned.  Otherwise zero is returned.  A positive result specifies
   the number of remaining grace authentications.

7.5.  Time Before Expiration Check

   If the pwdExpireWarning attribute is not present a zero status is
   returned.  Otherwise the following steps are followed:

   Subtract the time stored in pwdChangedTime from the current time to
   arrive at the password's age.  If the password's age is greater than
   than the value of the pwdMaxAge attribute, a zero status is returned.
   Subtract the value of the pwdExpireWarning attribute from the value
   of the pwdMaxAge attribute to arrive at the warning age.  If the
   password's age is equal to or greater than the warning age, the value
   of pwdMaxAge minus the password's age is returned.

7.6.  Intruder Lockout Check

   A status of true indicating that an intruder has been detected is
   returned if the following conditions are met:

   o  The pwdLockout attribute is TRUE.

   o  The number of values in the pwdFailureTime attribute that are
      younger than pwdFailureCountInterval is greater or equal to the
      pwdMaxFailure attribute.

   Otherwise a status of false is returned.

   While performing this check, values of pwdFailureTime that are old by
   more than pwdFailureCountInterval are purged and not counted.

7.7.  Intruder Delay Check

   If the pwdMinDelay attribute is 0 or not set, zero is returned.


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   Otherwise, a delay time is computed based on the number of values in
   the pwdFailureTime attribute.  If the computed value is greater than
   the pwdMaxDelay attribute, the pwdMaxDelay value is returned.

   While performing this check, values of pwdFailureTime that are old by
   more than pwdFailureCountInterval are purged and not counted.

7.8.  Password Too Young Check

   If the Section 7.2 check returned true then this check will return
   false, to allow the password to be changed.

   A status of true indicating that not enough time has passed since the
   password was last updated is returned if:

   o  The value of pwdMinAge is non-zero and pwdChangedTime is present.

   o  The value of pwdMinAge is greater than the current time minus the
      value of pwdChangedTime.

   Otherwise a false status is returned.


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8.  Server Policy Enforcement Points

   The server SHOULD enforce that the password attribute subject to a
   password policy as defined in this document, contains one and only
   one password value.

   Note: The case where a single password value is stored in multiple
   formats simultaneously is still considered to be only one password
   value.

   The scenarios in the following operations assume that the client has
   attached a passwordPolicyRequest control to the request message of
   the operation.  In the event that the passwordPolicyRequest control
   was not sent, no passwordPolicyResponse control is returned.  All
   other instructions remain the same.

   For successfully completed operations, unless otherwise stated, no
   passwordPolicyResponse control is returned.

8.1.  Password-based Authentication

   This section contains the policy enforcement rules and policy data
   updates used while validating a password.  Operations that validate
   passwords include, but are not limited to, the Bind operation where
   the simple choice specifies a password, and the Compare operation
   where the attribute being compared holds a password.  Note that while
   the Compare operation does not authenticate a user to the LDAP
   server, it may be used by an external application for purposes of
   authentication.

8.1.1.  Fail if the account is locked

   If the account is locked as specified in Section 7.1, the server
   fails the operation with an appropriate resultCode (i.e.
   invalidCredentials (49) in the case of a bind operation, compareFalse
   (5) in the case of a compare operation, etc.).  The server MAY set
   the error: accountLocked (1) in the passwordPolicyResponse in the
   controls field of the message.

8.1.2.  Validated Password Procedures

   If the validation operation indicates that the password validated,
   these procedures are followed in order:

8.1.2.1.  Policy state updates

   Delete the pwdFailureTime and pwdAccountLockedTime attributes.


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   Set the value of the pwdLastSuccess attribute to the current time.

   Note: setting pwdLastSuccess is optional, but it is required if the
   policy has pwdMaxIdle defined.

8.1.2.2.  Password must be changed now

   If the decision in Section 7.2 returns true, the server sends to the
   client a response with an appropriate successful resultCode (i.e.
   success (0), compareTrue (6), etc.), and includes the
   passwordPolicyResponse in the controls field of the bindResponse
   message with the warning: changeAfterReset specified.

   For bind, the server MUST then disallow all operations issued by this
   user except modify password, bind, unbind, abandon and StartTLS
   extended operation.

8.1.2.3.  Expired password

   If the password has expired as per Section 7.3, the server either
   returns a success or failure based on the state of grace
   authentications.

8.1.2.3.1.  Remaining Grace Authentications

   If there are remaining grace authentications as per Section 7.4, the
   server adds a new value with the current time in pwdGraceUseTime.
   Then it sends to the client a response with an appropriate successful
   resultCode (i.e. success (0), compareTrue (6), etc.), and includes
   the passwordPolicyResponse in the controls field of the response
   message with the warning: graceAuthNsRemaining choice set to the
   number of grace authentications left.

   Implementor's note: The system time of the host machine may be more
   granular than is needed to ensure unique values of this attribute.
   It is recommended that a mechanism is used to ensure unique
   generalized time values.  The fractional seconds field may be used
   for this purpose.

8.1.2.3.2.  No Remaining Grace Authentications

   If there are no remaining grace authentications, the server fails the
   operation with an appropriate resultCode (invalidCredentials (49),
   compareFalse (5), etc.), and includes the passwordPolicyResponse in
   the controls field of the bindResponse message with the error:
   passwordExpired (0) set.


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8.1.2.4.  Expiration Warning

   If the result of Section 7.5 is a positive number, the server sends
   to the client a response with an appropriate successful resultCode
   (i.e. success (0), compareTrue (6), etc.), and includes the
   passwordPolicyResponse in the controls field of the bindResponse
   message with the warning: timeBeforeExiration set to the value as
   described above.  Otherwise, the server sends a successful response,
   and omits the passwordPolicyResponse.

8.1.3.  AuthN Failed Procedures

   If the authentication process indicates that the password failed
   validation due to invalid credentials, these procedures are followed:

8.1.3.1.  Policy state update

   Add the current time as a value of the pwdFailureTime attribute.

   Implementor's note: The system time of the host machine may be more
   granular than is needed to ensure unique values of this attribute.
   It is recommended that a mechanism is used to ensure unique
   generalized time values.  The fractional seconds field may be used
   for this purpose.

8.1.3.2.  Handle Intruder Detection

   If the check in Section 7.6 returns a true state, the server locks
   the account by setting the value of the pwdAccountLockedTime
   attribute to the current time.  After locking the account, the server
   fails the operation with an appropriate resultCode
   (invalidCredentials (49), compareFalse (5), etc.), and includes the
   passwordPolicyResponse in the controls field of the message with the
   error: accountLocked (1).

   If the check in Section 7.7 returns a non-zero value, the server
   waits that number of seconds before sending the authentication
   response back to the client.

8.2.  Password Update Operations

   Because the password is stored in an attribute, various operations
   (like add and modify) may be used to create or update a password.
   But some alternate mechanisms have been defined or may be defined,
   such as the LDAP Password Modify Extended Operation [RFC3062].

   While processing a password update, the server performs the following
   steps:


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8.2.1.  Safe Modification

   If pwdSafeModify is set to TRUE and if there is an existing password
   value, the server ensures that the password update operation includes
   the user's existing password.

   When the LDAP modify operation is used to modify a password, this is
   done by specifying both a delete action and an add or replace action,
   where the delete action specifies the existing password, and the add
   or replace action specifies the new password.  Other password update
   operations SHOULD employ a similar mechanism.  Otherwise this policy
   will fail.

   If the existing password is not specified, the server does not
   process the operation and sends the appropriate response message to
   the client with the resultCode: insufficientAccessRights (50), and
   includes the passwordPolicyResponse in the controls field of the
   response message with the error: mustSupplyOldPassword (4).

8.2.2.  Change After Reset

   If the decision in Section 7.2 returns true, the server ensures that
   the password update operation contains no modifications other than
   the modification of the password attribute.  If other modifications
   exist, the server sends a response message to the client with the
   resultCode: insufficientAccessRights (50), and includes the
   passwordPolicyResponse in the controls field of the response message
   with the error: changeAfterReset (2).

8.2.3.  Rights Check

   Check to see whether the bound identity has sufficient rights to
   update the password.  If the bound identity is a user changing its
   own password, this MAY be done by checking the pwdAllowUserChange
   attribute or using an access control mechanism.  The determination of
   this is implementation specific.  If the user is not allowed to
   update her password, the server sends a response message to the
   client with the resultCode: insufficientAccessRights (50), and
   includes the passwordPolicyResponse in the controls field of the
   response message with the error: passwordModNotAllowed (3).

8.2.4.  Too Early to Update

   If the check in Section 7.8 results in a true status The server sends
   a response message to the client with the resultCode:
   constraintViolation (19), and includes the passwordPolicyResponse in
   the controls field of the response message with the error:
   passwordTooYoung (7).


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8.2.5.  Password Quality

   Check the value of the pwdCheckQuality attribute.  If the value is
   non-zero, the server:

   o  Ensure that the password meets the quality criteria enforced by
      the server.  This enforcement is implementation specific.  If the
      server is unable to check the quality (due to a hashed password or
      otherwise), the value of pwdCheckQuality is evaluated.  If the
      value is 1, operation continues.  If the value is 2, the server
      sends a response message to the client with the resultCode:
      constraintViolation (19), and includes the passwordPolicyResponse
      in the controls field of the response message with the error:
      insufficientPasswordQuality (5).  If the server is able to check
      the password quality, and the check fails, the server sends a
      response message to the client with the resultCode:
      constraintViolation (19), and includes the passwordPolicyResponse
      in the controls field of the response message with the error:
      insufficientPasswordQuality (5).

   o  checks the value of the pwdMinLength attribute.  If the value is
      non-zero, it ensures that the new password is of at least the
      minimum length.  If the server is unable to check the length (due
      to a hashed password or otherwise), the value of pwdCheckQuality
      is evaluated.  If the value is 1, operation continues.  If the
      value is 2, the server sends a response message to the client with
      the resultCode: constraintViolation (19), and includes the
      passwordPolicyResponse in the controls field of the response
      message with the error: passwordTooShort (6).  If the server is
      able to check the password length, and the check fails, the server
      sends a response message to the client with the resultCode:
      constraintViolation (19), and includes the passwordPolicyResponse
      in the controls field of the response message with the error:
      passwordTooShort (6).

8.2.6.  Invalid Reuse

   If pwdInHistory is present and its value is non-zero, the server
   checks whether this password exists in the entry's pwdHistory
   attribute or in the current password attribute.  If the password does
   exist in the pwdHistory attribute or in the current password
   attribute, the server sends a response message to the client with the
   resultCode: constraintViolation (19), and includes the
   passwordPolicyResponse in the controls field of the response message
   with the error: passwordInHistory (8).


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8.2.7.  Policy State Updates

   If the steps have completed without causing an error condition, the
   server performs the following steps in order to update the necessary
   password policy state attributes:

   If the value of either pwdMaxAge or pwdMinAge is non-zero, the server
   updates the pwdChangedTime attribute on the entry to the current
   time.

   If the value of pwdInHistory is non-zero, the server adds the
   previous password (if one existed) to the pwdHistory attribute.  If
   the number of attributes held in the pwdHistory attribute exceeds the
   value of pwdInHistory, the server removes the oldest excess
   passwords.

   If the value the pwdMustChange is TRUE and the modification is
   performed by a password administrator, then the pwdReset attribute is
   set to TRUE.  Otherwise, the pwdReset is removed from the user's
   entry if it exists.

   The pwdFailureTime and pwdGraceUseTime attributes is removed from the
   user's entry if they exist.

8.3.  Other Operations

   For operations other than bind, password update, unbind, abandon or
   StartTLS, if the decision in Section 7.2 returns true, the server
   sends a response message to the client with the resultCode:
   insufficientAccessRights (50), and includes the
   passwordPolicyResponse in the controls field of the response message
   with the error: changeAfterReset (2).


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9.  Client Policy Enforcement Points

   These sections illustrate possible scenarios for each LDAP operation
   and define the types of responses that identify those scenarios.

   The scenarios in the following operations assume that the client
   attached a passwordPolicyRequest control to the request message of
   the operation, and thus may receive a passwordPolicyResponse control
   in the response message.  In the event that the passwordPolicyRequest
   control was not sent, no passwordPolicyResponse control is returned.
   All other instructions remain the same.

9.1.  Bind Operation

   For every bind response received, the client checks the resultCode of
   the bindResponse and checks for a passwordPolicyResponse control to
   determine if any of the following conditions are true and MAY prompt
   the user accordingly.

   o  bindResponse.resultCode = insufficientAccessRights (50),
      passwordPolicyResponse.error = accountLocked (1): The password
      failure limit has been reached and the account is locked.  The
      user needs to retry later or contact the password administrator to
      reset the password.

   o  bindResponse.resultCode = success (0),
      passwordPolicyResponse.error = changeAfterReset (2): The user is
      binding for the first time after the password administrator set
      the password.  In this scenario, the client SHOULD prompt the user
      to change his password immediately.

   o  bindResponse.resultCode = success (0),
      passwordPolicyResponse.warning = graceAuthNsRemaining: The
      password has expired but there are remaining grace
      authentications.  The user needs to change it.

   o  bindResponse.resultCode = invalidCredentials (49),
      passwordPolicyResponse.error = passwordExpired (0): The password
      has expired and there are no more grace authentications.  The user
      contacts the password administrator in order to have its password
      reset.

   o  bindResponse.resultCode = success (0),
      passwordPolicyResponse.warning = timeBeforeExpiration: The user's
      password will expire in n number of seconds.


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9.2.  Modify Operations

9.2.1.  Modify Request

   If the application or client encrypts the password prior to sending
   it in a password modification operation (whether done through
   modifyRequest or another password modification mechanism), it SHOULD
   check the values of the pwdMinLength, and pwdCheckQuality attributes
   and SHOULD enforce these policies.

9.2.2.  Modify Response

   If the modifyRequest operation was used to change the password, or if
   another mechanism is used --such as an extendedRequest-- the
   modifyResponse or other appropriate response MAY contain information
   pertinent to password policy.  The client checks the resultCode of
   the response and checks for a passwordPolicyResponse control to
   determine if any of the following conditions are true and optionally
   notify the user of the condition.

   o  pwdModResponse.resultCode = insufficientAccessRights (50),
      passwordPolicyResponse.error = mustSupplyOldPassword (4): The user
      attempted to change her password without specifying the old
      password but the password policy requires this.

   o  pwdModResponse.resultCode = insufficientAccessRights (50),
      passwordPolicyResponse.error = changeAfterReset (2): The user must
      change her password before submitting any other LDAP requests.

   o  pwdModResponse.resultCode = insufficientAccessRights (50),
      passwordPolicyResponse.error = passwordModNotAllowed (3): The user
      doesn't have sufficient rights to change his password.

   o  pwdModResponse.resultCode = constraintViolation (19),
      passwordPolicyResponse.error = passwordTooYoung (7): It is too
      soon after the last password modification to change the password.

   o  pwdModResponse.resultCode = constraintViolation (19),
      passwordPolicyResponse.error = insufficientPasswordQuality (5):
      The password failed quality checking.

   o  pwdModResponse.resultCode = constraintViolation (19),
      passwordPolicyResponse.error = passwordTooShort (6): The length of
      the password is too short.

   o  pwdModResponse.resultCode = constraintViolation (19),
      passwordPolicyResponse.error = passwordInHistory (8): The password
      has already been used; the user must choose a different one.


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9.3.  Add Operation

   If a password is specified in an addRequest, the client checks the
   resultCode of the addResponse and checks for a passwordPolicyResponse
   control to determine if any of the following conditions are true and
   may prompt the user accordingly.

   o  addResponse.resultCode = insufficientAccessRights (50),
      passwordPolicyResponse.error = passwordModNotAllowed (3): The user
      doesn't have sufficient rights to add this password.

   o  addResponse.resultCode = constraintViolation (19),
      passwordPolicyResponse.error = insufficientPasswordQuality (5):
      The password failed quality checking.

   o  addResponse.resultCode = constraintViolation (19),
      passwordPolicyResponse.error = passwordTooShort (6): The length of
      the password is too short.

9.4.  Compare Operation

   When a compare operation is used to compare a password, the client
   checks the resultCode of the compareResponse and checks for a
   passwordPolicyResponse to determine if any of the following
   conditions are true and MAY prompt the user accordingly.  These
   conditions assume that the result of the comparison was true.

   o  compareResponse.resultCode = compareFalse (5),
      passwordPolicyResponse.error = accountLocked (1): The password
      failure limit has been reached and the account is locked.  The
      user needs to retry later or contact the password administrator to
      reset the password.

   o  compareResponse.resultCode = compareTrue (6),
      passwordPolicyResponse.warning = graceAuthNsRemaining: The
      password has expired but there are remaining grace
      authentications.  The user needs to change it.

   o  compareResponse.resultCode = compareFalse (5),
      passwordPolicyResponse.error = passwordExpired (0): The password
      has expired and there are no more grace authentications.  The user
      must contact the password administrator to reset the password.

   o  compareResponse.resultCode = compareTrue (6),
      passwordPolicyResponse.warning = timeBeforeExpiration: The user's
      password will expire in n number of seconds.


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9.5.  Other Operations

   For operations other than bind, unbind, abandon or StartTLS, the
   client checks the result code and control to determine if any other
   actions are needed.

   o  <Response>.resultCode = insufficientAccessRights (50),
      passwordPolicyResponse.error = accountLocked (1) : The password
      failure limit has been reached and the account is locked.  The
      user needs to retry later or contact the password administrator to
      reset the password.

   o  <Response>.resultCode = insufficientAccessRights (50),
      passwordPolicyResponse.error = changeAfterReset (2) : The user
      needs to change the password immediately.


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10.  Administration of the Password Policy

   {TODO: Need to define an administrativeRole (need OID).  Need to
   describe whether pwdPolicy admin areas can overlap}

   A password policy is defined for a particular subtree of the DIT by
   adding to an LDAP subentry whose immediate superior is the root of
   the subtree, the pwdPolicy auxiliary object class.  The scope of the
   password policy is defined by the SubtreeSpecification attribute of
   the LDAP subentry as specified in [RFC3672].

   It is possible to define password policies for different password
   attributes within the same pwdPolicy entry, by specifying multiple
   values of the pwdAttribute.  But password policies could also be in
   separate sub entries as long as they are contained under the same
   LDAP subentry.

   Only one policy may be in effect for a given password attribute in
   any entry.  If multiple policies exist which overlap in the range of
   entries affected, the resulting behavior is undefined.

   Modifying the password policy MUST NOT result in any change in users'
   entries to which the policy applies.

   It SHOULD be possible to overwrite the password policy for one user
   by defining a new policy in a subentry of the user entry.

   Each object that is controlled by password policy advertises the
   subentry that is being used to control its policy in its
   pwdPolicySubentry attribute.  Clients wishing to examine or manage
   password policy for an object may interrogate the pwdPolicySubentry
   for that object in order to arrive at the proper pwdPolicy subentry.


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11.  Password Policy and Replication

   {TODO: This section needs to be changed to highlight the pitfalls of
   replication, suggest some implementation choices to overcome those
   pitfalls, but remove prescriptive language relating to the update of
   state information}

   The pwdPolicy object defines the password policy for a portion of the
   DIT and MUST be replicated on all the replicas of this subtree, as
   any subentry would be, in order to have a consistent policy among all
   replicated servers.

   The elements of the password policy that are related to the users are
   stored in the entry themselves as operational attributes.  As these
   attributes are subject to modifications even on a read-only replica,
   replicating them must be carefully considered.

   The pwdChangedTime attribute MUST be replicated on all replicas, to
   allow expiration of the password.

   The pwdReset attribute MUST be replicated on all replicas, to deny
   access to operations other than bind and modify password.

   The pwdHistory attribute MUST be replicated to writable replicas.  It
   doesn't have to be replicated to a read-only replica, since the
   password will never be directly modified on this server.

   The pwdAccountLockedTime, pwdFailureTime and pwdGraceUseTime
   attributes SHOULD be replicated to writable replicas, making the
   password policy global for all servers.  When the user entry is
   replicated to a read-only replica, these attributes SHOULD NOT be
   replicated.  This means that the number of failures, of grace
   authentications and the locking will take place on each replicated
   server.  For example, the effective number of failed attempts on a
   user password will be N x M (where N is the number of servers and M
   the value of pwdMaxFailure attribute).  Replicating these attributes
   to a read-only replica MAY reduce the number of tries globally but
   MAY also introduce some inconstancies in the way the password policy
   is applied.

   Note: there are some situations where global replication of these
   state attributes may not be desired.  For example, if two clusters of
   replicas are geographically remote and joined by a slow network link,
   and their users only login from one of the two locations, it may be
   unnecessary to propagate all of the state changes from one cluster to
   the other.  Servers SHOULD allow administrators to control which
   attributes are replicated on a case-by-case basis.


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   Servers participating in a loosely consistent multi-master
   replication agreement SHOULD employ a mechanism which ensures
   uniqueness of values when populating the attributes pwdFailureTime
   and pwdGraceUseTime.  The method of achieving this is a local matter
   and may consist of using a single authoritative source for the
   generation of unique time values, or may consist of the use of the
   fractional seconds part to hold a replica identifier.


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12.  Security Considerations

   This document defines a set of rules to implement in an LDAP server,
   in order to mitigate some of the security risks associated with the
   use of passwords and to make it difficult for password cracking
   programs to break into directories.

   Authentication with a password MUST follow the recommendations made
   in [RFC4513].

   Modifications of passwords SHOULD only occur when the connection is
   protected with confidentiality and secure authentication.

   Access controls SHOULD be used to restrict access to the password
   policy attributes.  The attributes defined to maintain the password
   policy state information SHOULD only be modifiable by the password
   administrator or higher authority.  The pwdHistory attribute MUST be
   subject to the same level of access control as the attrbute holding
   the password.

   As it is possible to define a password policy for one specific user
   by adding a subentry immediately under the user's entry, Access
   Controls SHOULD be used to restrict the use of the pwdPolicy object
   class or the LDAP subentry object class.

   When the intruder detection password policy is enforced, the LDAP
   directory is subject to a denial of service attack.  A malicious user
   could deliberately lock out one specific user's account (or all of
   them) by sending bind requests with wrong passwords.  There is no way
   to protect against this kind of attack.  The LDAP directory server
   SHOULD log as much information as it can (such as client IP address)
   whenever an account is locked, in order to be able to identify the
   origin of the attack.  Denying anonymous access to the LDAP directory
   is also a way to restrict this kind of attack.  Using the login delay
   instead of the lockout mechanism will also help avoid this denial of
   service.

   Returning certain status codes (such as passwordPolicyResponse.error
   = accountLocked) allows a denial of service attacker to know that it
   has successfully denied service to an account.  Servers SHOULD
   implement additional checks which return the same status when it is
   sensed that some number of failed authentication requests has occured
   on a single connection, or from a client address.  Server
   implementors are encouraged to invent other checks similar to this in
   order to thwart this type of DoS attack.


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13.  IANA Considerations

   <<<TBD>>>


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14.  Acknowledgement

   This document is based in part on prior work done by Valerie Chu from
   Netscape Communications Corp, published as
   draft-vchu-ldap-pwd-policy-00.txt (December 1998).  Prasanta Behera
   participated in early revisions of this document.


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15.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2195]  Klensin, J., Catoe, R., and P. Krumviede, "IMAP/POP
              AUTHorize Extension for Simple Challenge/Response",
              RFC 2195, September 1997.

   [RFC2831]  Leach, P. and C. Newman, "Using Digest Authentication as a
              SASL Mechanism", RFC 2831, May 2000.

   [RFC3062]  Zeilenga, K., "LDAP Password Modify Extended Operation",
              RFC 3062, February 2001.

   [RFC3383]  Zeilenga, K., "Internet Assigned Numbers Authority (IANA)
              Considerations for the Lightweight Directory Access
              Protocol (LDAP)", RFC 3383, September 2002.

   [RFC3672]  Zeilenga, K., "Subentries in the Lightweight Directory
              Access Protocol (LDAP)", RFC 3672, December 2003.

   [RFC4422]  Melnikov, A. and K. Zeilenga, "Simple Authentication and
              Security Layer (SASL)", RFC 4422, June 2006.

   [RFC4511]  Sermersheim, J., "Lightweight Directory Access Protocol
              (LDAP): The Protocol", RFC 4511, June 2006.

   [RFC4512]  Zeilenga, K., "Lightweight Directory Access Protocol
              (LDAP): Directory Information Models", RFC 4512,
              June 2006.

   [RFC4513]  Harrison, R., "Lightweight Directory Access Protocol
              (LDAP): Authentication Methods and Security Mechanisms",
              RFC 4513, June 2006.

   [RFC4517]  Legg, S., "Lightweight Directory Access Protocol (LDAP):
              Syntaxes and Matching Rules", RFC 4517, June 2006.

   [X.680]    International Telecommunications Union, "Abstract Syntax
              Notation One (ASN.1): Specification of basic notation",
              ITU-T Recommendation X.680, July 2002.

   [X.690]    International Telecommunications Union, "Information
              Technology - ASN.1 encoding rules: Specification of Basic
              Encoding Rules (BER),  Canonical Encoding Rules (CER) and
              Distinguished Encoding Rules (DER)", ITU-T
              Recommendation X.690, July 2002.


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Authors' Addresses

   Jim Sermersheim
   Novell, Inc
   1800 South Novell Place
   Provo, Utah  84606
   US

   Phone: +1 801 861-3088
   Email: jimse@novell.com


   Ludovic Poitou
   Sun Microsystems
   180, Avenue de l'Europe
   Zirst de Montbonnot, Saint Ismier cedex  38334
   FR

   Phone: +33 476 188 212
   Email: ludovic.poitou@sun.com


   Howard Chu (editor)
   Symas Corp.
   18740 Oxnard Street, Suite 313A
   Tarzana, California  91356
   US

   Phone: +1 818 757-7087
   Email: hyc@symas.com


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