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Network Working Group                                        K. ZeilengaRequest for Comments: 3112                           OpenLDAP FoundationCategory: Informational                                         May 2001LDAP Authentication Password SchemaStatus 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 theZeilenga                     Informational                      [Page 1]

RFC 3112          LDAP Authentication Password Schema           May 2001   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 inRFC 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.Zeilenga                     Informational                      [Page 2]

RFC 3112          LDAP Authentication Password Schema           May 2001   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, insection 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.Zeilenga                     Informational                      [Page 3]

RFC 3112          LDAP Authentication Password Schema           May 20012.4. 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 insection 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.Zeilenga                     Informational                      [Page 4]

RFC 3112          LDAP Authentication Password Schema           May 20013.1. 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   user/password authentication.3.2. SHA1 scheme   The SHA1 [SHA1] scheme name is "SHA1".   The authValue is the base64 encoding of a SHA1 digest of the   concatenation the user password and the 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 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.Zeilenga                     Informational                      [Page 5]

RFC 3112          LDAP Authentication Password Schema           May 2001   Values of this scheme SHOULD only be used to implement simple   user/password authentication.4. Implementation Issues   For all 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 SHA1 scheme and      SHOULD support the MD5 scheme.      Servers SHOULD NOT publish values of authPassword nor allow      operations which expose authPassword values or AuthPasswordMatch      assertions 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 authenticate to the      directory.5. 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].   As flaws may be discovered in the hashing algorithm or with a   particular implementation of the algorithm or values could be subject   to various attacks if exposed, 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].Zeilenga                     Informational                      [Page 6]

RFC 3112          LDAP Authentication Password Schema           May 2001   AuthPasswordMatch matching rule allows applications to test the   validity of a user password and, hence, may be used to mount an   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.   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.6. Acknowledgment   This document borrows from a number of IETF documents and is based   upon input from the IETF LDAPext working group.7. Bibliography   [RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm",RFC 1321,             April 1992   [RFC2219] Bradner, S., "Key words for use in RFCs to Indicate             Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC2234] Crocker, D., Editor, P. Overell, "Augmented BNF for Syntax             Specifications: ABNF",RFC 2234, November 1997.   [RFC2251] Wahl, M., Howes, T. and S. Kille, "Lightweight Directory             Access Protocol (v3)",RFC 2251, December 1997.   [RFC2252] Wahl, M., Coulbeck, A., Howes, T., and S. Kille,             "Lightweight Directory Access Protocol (v3): Attribute             Syntax Definitions",RFC 2252, December 1997.   [RFC2256] Wahl, A., "A Summary of the X.500(96) User Schema for use             with LDAPv3",RFC 2256, December 1997.   [RFC2307] Howard, L., "An Approach for Using LDAP as a Network             Information Service",RFC 2307, March 1998.Zeilenga                     Informational                      [Page 7]

RFC 3112          LDAP Authentication Password Schema           May 2001   [RFC2829] Wahl, M., Alvestrand, H., Hodges, J. and R. Morgan,             "Authentication Methods for LDAP",RFC 2829, June 2000.   [RFC3062] Zeilenga, K., "LDAP Password Modify Extended Operation",RFC 3062, February 2001.   [SHA1]    NIST, FIPS PUB 180-1: Secure Hash Standard, April 1995.8. Author's Address   Kurt D. Zeilenga   OpenLDAP Foundation   EMail: Kurt@OpenLDAP.orgZeilenga                     Informational                      [Page 8]

RFC 3112          LDAP Authentication Password Schema           May 20019.  Full Copyright Statement   Copyright (C) The Internet Society (2001).  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 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.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Zeilenga                     Informational                      [Page 9]