rfc3112.txt

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Network Working Group                                        K. Zeilenga
Request for Comments: 3112                           OpenLDAP Foundation
Category: Informational                                         May 2001


                  LDAP Authentication Password Schema

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

   This document describes schema in support of user/password
   authentication in a LDAP (Lightweight Directory Access Protocol)
   directory including the authPassword attribute type.  This attribute
   type holds values derived from the user's password(s) (commonly using
   cryptographic strength one-way hash).  authPassword is intended to
   used instead of userPassword.

1. Background and Intended Use

   The userPassword attribute type [RFC2256] is intended to be 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 simple password based authentication.
   The attribute type may be used by LDAP servers to implement the LDAP
   Bind operation's "simple" authentication method.

   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 cryptographic strength one-way hashing.
   Though the use of one-way hashing reduces the potential that exposed
   values will allow unauthorized access to the Directory (unless the




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   hash algorithm/implementation is flawed), the hashing of passwords is
   intended to be as an additional layer of protection.  It is
   RECOMMENDED that hashed values be protected as if they were clear
   text passwords.

   This attribute may be used in conjunction with server side password
   generation mechanisms (such as the LDAP Password Modify [RFC3062]
   extended operation).

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

   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].

2. Schema Definitions

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

2.1. authPasswordSyntax

      ( 1.3.6.1.4.1.4203.1.1.2
        DESC 'authentication password syntax' )

   Values of this syntax are encoded according to:

      authPasswordValue = w scheme s authInfo s authValue w
      scheme = %x30-39 / %x41-5A / %x2D-2F / %x5F
            ; 0-9, A-Z, "-", ".", "/", or "_"
      authInfo = schemeSpecificValue
      authValue = schemeSpecificValue
              schemeSpecificValue = *( %x21-23 / %x25-7E )
            ; printable ASCII less "$" and " "
      s = w SEP w
      w = *SP
      SEP = %x24 ; "$"
      SP = %x20 ; " " (space)

   where scheme describes the mechanism and 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.






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

   This document describes a number of schemes, as well as requirements
   for the scheme naming, in section 3.

2.2. authPasswordExactMatch

      ( 1.3.6.1.4.1.4203.1.2.2
        NAME 'authPasswordExactMatch'
        DESC 'authentication password exact matching rule'
        SYNTAX 1.3.6.1.4.1.4203.1.1.2 )

   This matching rule allows a client to assert that an asserted
   authPasswordSyntax value matches authPasswordSyntax values.  It is
   meant to be used as the EQUALITY matching rule of attributes whose
   SYNTAX is authPasswordSyntax.

   The assertion is "TRUE" if there is an attribute value which has the
   same scheme, authInfo, and authValue components as the asserted
   value; "FALSE" if no attribute value has the same components as the
   asserted value; and "Undefined" otherwise.

2.3. authPasswordMatch

       ( 1.3.6.1.4.1.4203.1.2.3
         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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2.4. supportedAuthPasswordSchemes

      ( 1.3.6.1.4.1.4203.1.3.3
        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 2.1.  This attribute may only be present
   in the root DSE.  If the server does not support any password
   schemes, this attribute will not be present.

2.5. authPassword

      ( 1.3.6.1.4.1.4203.1.3.4 NAME 'authPassword'
        DESC 'password authentication information'
        EQUALITY 1.3.6.1.4.1.4203.1.2.2
        SYNTAX 1.3.6.1.4.1.4203.1.1.2 )

   The values of this attribute are representative of the user's
   password(s) and conform to the authPasswordSyntax described in 2.1.
   The values of this attribute may be used for authentication purposes.

   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.

2.6. authPasswordObject

      ( 1.3.6.1.4.1.4203.1.4.7 NAME 'authPasswordObject'
        DESC 'authentication password mix in class'
        MAY 'authPassword'
        AUXILIARY )

   Entries of this object class may contain authPassword attribute
   types.

3. Schemes

   This section describes the "MD5" and "SHA1" schemes.  Other schemes
   may be defined by other documents.  Schemes which are not described
   in an RFC SHOULD be named with a leading "X-" to indicate they are a
   private or implementation specific scheme, or may be named using the
   dotted-decimal representation [RFC2252] of an OID assigned to the
   scheme.



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3.1. 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 salt.  The base64 encoding of the
   salt is provided in the authInfo field.  The salt MUST be at least 64
   bits long.  Implementations of this scheme MUST support salts up to
   128 bits in length.

   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