INTERNET-DRAFT                                      Kurt D. Zeilenga
Intended Category: Standard Track                   OpenLDAP Foundation
Expires: 11 January 2001                            11 July 2000


                  LDAP Authentication Password Attribute
                 <draft-zeilenga-ldap-authpasswd-03.txt>



1. Status of this Memo

  This document is an Internet-Draft and is in full conformance with all
  provisions of Section 10 of RFC2026.

  This document is intended to be, after appropriate review and
  revision, submitted to the RFC Editor as a Standard Track document.
  Distribution of this memo is unlimited.  Technical discussion of this
  document will take place on the IETF LDAP Extension Working Group
  mailing list <ietf-ldapext@netscape.com>.  Please send editorial
  comments directly to the author <Kurt@OpenLDAP.org>.

  Internet-Drafts are working documents of the Internet Engineering Task
  Force (IETF), its areas, and its working groups.  Note that other
  groups may also distribute working documents as Internet-Drafts.
  Internet-Drafts are draft documents valid for a maximum of six months
  and may be updated, replaced, or obsoleted by other documents at any
  time.  It is inappropriate to use Internet-Drafts as reference
  material or to cite them other than as ``work in progress.''

  The list of current Internet-Drafts can be accessed at
  http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft
  Shadow Directories can be accessed at http://www.ietf.org/shadow.html.

  Copyright 2000, The Internet Society.  All Rights Reserved.

  Please see the Copyright section near the end of this document for
  more information.


2. Abstract

  This document describes schema for storing information in support of
  user/password authentication in a LDAP [RFC2251] directory.  The
  document defines the authPassword attribute type and related schema.
  The attribute type is used to store values derived from the user's
  password(s) (commonly using cryptographic strength one-way hash).
  authPassword is intended to used instead of clear text password



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  storage mechanisms such as userPassword [RFC2256].  The values of
  authPassword may be used to support both LDAP "simple" and SASL
  [RFC2222] password authentication mechanisms [RFC2829].

  The key words ``MUST'', ``MUST NOT'', ``REQUIRED'', ``SHALL'', ``SHALL
  NOT'', ``SHOULD'', ``SHOULD NOT'', ``RECOMMENDED'',  and ``MAY'' in
  this document are to be interpreted as described in RFC 2119
  [RFC2119].


3. Background and Intended Use

  The userPassword attribute type [RFC 2256] is intended be used to used
  to support the LDAP [RFC2251] "simple" bind operation.  However,
  values of userPassword must be clear text passwords.  It is often
  desirable to store values derived from the user's password(s) instead
  of actual passwords.

  The authPassword attribute type is intended to be used to store
  information used to implement password based authentication.  The
  attribute type may be used by LDAP servers to implement user/password
  authentication operations [RFC2829] such "simple" and SASL [RFC2222] /
  DIGEST-MD5 [RFC2831].

  The attribute type supports multiple storage schemes.  A matching rule
  is provided for use with extensible search filters to allow clients to
  assert that a clear text password "matches" one of the attribute's
  values.  Storage schemes often use of cryptographic strength one-way
  hashing.

  This attribute may be used in conjunction with server side password
  generation mechanisms (such as [PW-EXOP]).

  Access to this attribute may governed by administrative controls such
  as those which implement password change policies.


4. Schema Definitions

  The following schema definitions are described in terms of LDAPv3
  Attribute Syntax Definitions [RFC2252] with specific syntax detailed
  using Augmented BNF [RFC2234].

  Editor's Note: object identifiers (OIDs) will be assigned before this
                 document is published as an RFC.

4.1. authPasswordSyntax




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    ( authPasswordSyntaxOID
      DESC 'authentication password syntax' )

  Values of this syntax are encoded according to the following BNF:

    authPasswordValue = w scheme s [authInfo] s authValue w
    scheme = <an IA5 string of uppercase letters, numbers,
             and "-", "_", and "/">
    authInfo = schemeSpecificValue
    authValue = schemeSpecfiicValue
    schemeSpecificValue = <an IA5 printable string
                          not containing "$" or " ">
    s = w sep w
    w = *sp
    sep = "$" ; an IA5 dollar sign (36)
    sp = " "     ; an IA5 space (20)

  where scheme describes the storage mechanism, authInfo and authValue
  are a scheme specific.  The authInfo field is often a base64 encoded
  salt.  The authValue field is often a base64 encoded value derived
  from a user's password(s). Values of this attribute are case
  sensitive.

  This document describes a number of schemes, as well as requirements
  for the scheme naming, in section 5.


4.2. authPasswordMatch

    ( authPasswordMatchOID
      NAME 'authPasswordMatch'
      DESC 'authentication password matching rule'
      SYNTAX 1.3.6.1.4.1.1466.115.121.1.40{128} )

  This matching rule allows a client to assert that a password matches
  values of authPasswordSyntax using an extensibleMatch filter
  component.  Each value is matched per its scheme.  The assertion is
  TRUE if one or more attribute values matches the asserted value, FALSE
  if all values do not matches, and Undefined otherwise.

  Servers which support use of this matching rule SHOULD publish
  appropriate matchingRuleUse values per [RFC2252], 4.4.

  Transfer of authPasswordMatch assertion values is strongly discouraged
  where the underlying transport service cannot guarantee
  confidentiality and may result in disclosure of the values to
  unauthorized parties.




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4.3. supportedAuthPasswordSchemes

    ( supportedAuthPasswordSchemesOID
      NAME 'supportedAuthPasswordSchemes'
      DESC 'supported password storage schemes'
      EQUALITY caseExactIA5Match
      SYNTAX 1.3.6.1.4.1.1466.115.121.1.26{32}
      USAGE dSAOperation )

  The values of this attribute are names of supported authentication
  password schemes which the server supports.  The syntax of a scheme
  name is described in section 4.1.  This attribute may only be present
  in the root DSE.  If the server does not support any mechanisms this
  attribute will not be present.


4.4. authPassword

    ( authPasswordOID NAME 'authPassword'
      SYNTAX authPasswordSyntaxOID )

  The values of this attribute are representative of the user's
  password(s) and conform to the authPasswordSyntax described in 4.1.
  The values of this attribute may be used for authentication purposes.

  This attribute type is defined without any built-in matching rules.
  The absence of an EQUALITY matching rules disallows modification of
  individual values.

  Transfer of authPassword values is strongly discouraged where the
  underlying transport service cannot guarantee confidentiality and may
  result in disclosure of the values to unauthorized parties.


4.5. authPasswordObject

    ( authPasswordObjectOID NAME 'authPasswordObject'
      DESC 'authentication password mix in class'
      MAY 'authPassword'      AUXILIARY )

  Entries of this object class may contain authPassword attribute types.


5. Schemes

  This section describes the "MD5", "SHA1", and "SASL/DIGEST-MD5".
  Other schemes may be defined by other documents.  Schemes starting
  with string "SASL/" indicate association with a SASL mechanism.



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  Schemes which are not described by standard track documents SHOULD be
  named with a leading "X-" or, if associated with a SASL mechanism,
  "SASL/X-" to indicate they are a private or implementation specific
  mechanism, or may be named using the dotted-decimal representation
  [RFC2252] of an OID assigned to the mechanism.


5.1. MD5 scheme

  The MD5 [RFC1321] scheme name is "MD5".

  The authValue is the base64 encoding of an MD5 digest of the
  concatenation the user password and optional salt.  The base64
  encoding of the salt is provided in the authInfo field.
  Implementations of this scheme must support salts up to 128-bit in
  length.  Use with a 64-bit or larger salt is RECOMMENDED.

  Example:
    Given a user "joe" who's password is "mary" and a salt of "salt",
    the authInfo field would be the base64 encoding of "salt" and the
    authValue field would be the base64 encoding of the MD5 digest of
    "marysalt".

  A match against an asserted password and an attribute value of this
  scheme SHALL be true if and only if the MD5 digest of concatenation of
  the asserted value and the salt is equal to the MD5 digest contained
  in AuthValue.  The match SHALL be undefined if the server is unable to
  complete the equality test for any reason.  Otherwise the match SHALL
  be false.

  Values of this scheme SHOULD only be used to implement simple
  user/password authentication.

  It is RECOMMENDED that values of this scheme be protected as if they
  were clear text passwords.


5.2. SHA1 scheme

  The SHA1 [SHA1] scheme name is "SHA1".

  The authValue is the base64 encoding of an SHA1 digest of the
  concatenation the user password and the optional salt.  The base64
  encoding of the salt is provided in the authInfo field.
  Implementations of this scheme must support salts up to 128-bit in
  length.  Use with a 64-bit or larger salt is RECOMMENDED.

  Example:



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    Given a user "joe" who's password is "mary" and a salt of "salt",
    the authInfo field would be the base64 encoding of "salt" and the
    authValue field would be the base64 encoding of the SHA1 digest of
    "marysalt".

  A match against an asserted password and an attribute value of this
  scheme SHALL be true if and only if the SHA1 digest of concatenation
  of the asserted value and the salt is equal to the SHA1 digest
  contained in AuthValue.  The match SHALL be undefined if the server is
  unable to complete the equality test for any reason.  Otherwise the
  match SHALL be false.

  Values of this scheme SHOULD only be used to implement simple
  user/password authentication.

  It is RECOMMENDED that values of this scheme be protected as if they
  were clear text passwords.


5.3. DIGEST-MD5 scheme

  The DIGEST-MD5 scheme name is "SASL/DIGEST-MD5".

  The authValue is the base64 encoding of
    H( { username-value, ":", realm-value, ":", passwd } )

  and authInfo is the base64 encoding of
    { username-value, ":", realm-value }

  as defined by RFC2831.

  Example:
    Given a user "joe" within the realm "localhost" who's password is
    "mary", the info field would be the base64 encoding of
    "joe:localhost" and the authValue field would be the base64 encoding
    of the MD5 digest of "joe:localhost:mary".

  Values of this scheme SHOULD only be used to implement the
  SASL/DIGEST-MD5 as described by the Authentication Methods for LDAP
  [RFC2829].  A simple password assertion against a value of this scheme
  SHALL be considered undefined.

  Values of this scheme MUST be protected as if it the values were clear
  text passwords per reasons detailed in DIGEST-MD5, Section 3.9,
  "Storing Passwords."


6. Implementation Issues



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  For implementations of this specification:

    Servers MAY restrict which schemes are used in conjunction with a
    particular authentication process but SHOULD use all values of
    selected schemes.  If the asserted password matches any of the
    stored values, the asserted password SHOULD be considered valid.
    Servers MAY use other authentication storage mechanisms, such as
    userPassword or an external password store, in conjunction with
    authPassword to support the authentication process.

    Servers that support simple bind MUST support the MD5 scheme and
    SHOULD support the SHA1 scheme.

    Servers SHOULD not publish values of authPassword nor allow
    operations which expose authPassword or AuthPasswordMatch values to
    unless confidentiality protection is in place.

    Clients SHOULD not initiate operations which provide or request
    values of authPassword or make authPasswordMatch assertions unless
    confidentiality protection is in place.

    Clients SHOULD not assume that a successful AuthPasswordMatch,
    whether by compare or search, is sufficient to gain directory
    access.  The bind operation MUST be used to authentication to the
    directory.


7. Security Considerations

  This document describes how authentication information may be stored
  in a directory.  Authentication information must be adequately
  protected as unintended disclosure will allow attackers to gain
  immediate access to the directory as described by [RFC2829].

  Values of authPassword SHOULD be protected as if they were clear text
  passwords.  When values are transferred, privacy protections, such as
  IPSEC or TLS, SHOULD be in place.

  Clients SHOULD use strong authentication mechanisms [RFC2829].

  AuthPasswordMatch matching rule allows applications to test the
  validity of a user password and, hence, may be used to mount a
  dictionary attack.  Servers SHOULD take appropriate measures to
  protect the directory from such attacks.

  Some password schemes may require CPU intensive operations.  Servers
  SHOULD take appropriate measures to protect against Denial of Service
  attacks.



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  AuthPassword does not restrict an authentication identity to a single
  password.  An attacker who gains write access to this attribute may
  store additional values without disabling the user's true password(s).
  Use of policy aware clients and servers is RECOMMENDED.

  The level of protection offered against various attacks differ from
  scheme to scheme.  It is RECOMMENDED that servers support scheme
  selection as a configuration item.  This allows for a scheme to be
  easily disabled if a significant security flaw is discovered.


8. Copyright

  Copyright 2000, The Internet Society.  All Rights Reserved.

  This document and translations of it may be copied and furnished to
  others, and derivative works that comment on or otherwise explain it
  or assist in its implementation may be prepared, copied, published and
  distributed, in whole or in part, without restriction of any kind,
  provided that the above copyright notice and this paragraph are
  included on all such copies and derivative works.  However, this
  document itself may not be modified in any way, such as by removing
  the copyright notice or references to the Internet Society or other
  Internet organizations, except as needed for the  purpose of
  developing Internet standards in which case the procedures for
  copyrights defined in the Internet Standards process must be followed,
  or as required to translate it into languages other than English.

  The limited permissions granted above are perpetual and will not be
  revoked by the Internet Society or its successors or assigns.

  This document and the information contained herein is provided on an
  "AS IS" basis and THE AUTHORS, THE INTERNET SOCIETY, AND THE INTERNET
  ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED,
  INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
  INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
  WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


9. Acknowledgment

  This document borrows from a number of IETF documents and is based
  upon input from the IETF LDAPext working group.


10. Bibliography

  [RFC1321] R. Rivest, "The MD5 Message-Digest Algorithm", RFC 1321,



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            April 1992

  [RFC2219] S. Bradner, "Key words for use in RFCs to Indicate
            Requirement Levels", RFC 2119, March 1997.

  [RFC2222] J. Myers, "Simple Authentication and Security Layer (SASL)",
            RFC 2222, October 1997.

  [RFC2234] D. Crocker (editor), P. Overell, "Augmented BNF for Syntax
            Specifications: ABNF", RFC 2234, November 1997.

  [RFC2251] M. Wahl, T. Howes, S. Kille, "Lightweight Directory Access
            Protocol (v3)", RFC 2251, December 1997.

  [RFC2252] M. Wahl, A. Coulbeck, T. Howes, S. Kille, "Lightweight
            Directory Access Protocol (v3):  Attribute Syntax
            Definitions", RFC 2252, December 1997.

  [RFC2256] M. Wahl, "A Summary of the X.500(96) User Schema for use
            with LDAPv3", RFC 2256, December 1997.

  [RFC2307] L. Howard, "An Approach for Using LDAP as a Network
            Information Service", RFC 2307, March 1998.

  [RFC2829] M. Wahl, H. Alvestrand, J. Hodges, RL "Bob" Morgan,
            "Authentication Methods for LDAP", RFC 2829, June 2000.

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

  [PW-EXOP] K. Zeilenga, "LDAP Password Modify Extended Operation"
            draft-zeilenga-ldap-passwd-exop-xx.txt, a work in progress.

  [SHA1]    NIST, FIPS PUB 180-1: Secure Hash Standard, April 1995.


11.  Author's Address

  Kurt D. Zeilenga
  OpenLDAP Foundation
  <Kurt@OpenLDAP.org>










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