HTTP/1.1 200 OK Date: Tue, 09 Apr 2002 12:18:14 GMT Server: Apache/1.3.20 (Unix) Last-Modified: Mon, 21 Feb 2000 15:03:00 GMT ETag: "3ddc98-4523-38b153a4" Accept-Ranges: bytes Content-Length: 17699 Connection: close Content-Type: text/plain INTERNET-DRAFT Kurt D. Zeilenga Intended Category: Standard Track OpenLDAP Foundation Expires: 21 August 2000 21 February 2000 LDAP Authentication Password Attribute 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, to be 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 . Please send editorial comments directly to the author . 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 authentication passwords in a LDAP [RFC2251] directory. The document provides schema definitions for authPassword and related schema definitions. The authPassword is intended to used instead of clear text password storage mechanisms such as userPassword [RFC2256] to support simple bind operations. The Zeilenga [Page 1] INTERNET-DRAFT LDAP AuthPasswd 21 February 2000 attribute may be used to store SASL [RFC2222] authentication passwords in entries of a directory. 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 for plain text storage of user passwords and may be used to implement the LDAP [RFC 2251] bind operation. It is inappropriate for userPassword to have values which are encrypted. 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 password based authentication operations such simple bind and SASL [RFC 2222] / DIGEST-MD5 [DIGEST-MD5]. The attribute type supports multiple storage schemes and provides an equality matching rule which allows clients to assert that a clear text password "matches" one of the attribute's values. Storage schemes may make use of one-way hashing and encryption. No mechanism is defined by this document to provide server side generation of stored values nor to describe or implement password policies. 4. Schema Definitions The following schema definitions are written using the BNF form described in RFC 2252 [RFC2252]. 4.1. authPasswordSyntax ( authPasswordSyntaxOID DESC 'authentication password syntax' ) Values of this syntax are encoded according to the following BNF: authPasswordValue = w scheme w "$" w [authInfo w] "$" w authValue w Zeilenga [Page 2] INTERNET-DRAFT LDAP AuthPasswd 21 February 2000 scheme = authInfo = schemeSpecificValue authValue = schemeSpecfiicValue schemeSpecificValue = ws = *sp 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. Values of this attribute are case sensitive. 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. Each value is matched per its scheme. The rule SHALL return equality if one or more attribute values matches the asserted value, false if zero values matches, and undefined otherwise. If the scheme of an attribute value is unrecognized or the scheme does not prescribe matching behavior, the match against the stored value SHALL be considered undefined. 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. 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 Zeilenga [Page 3] INTERNET-DRAFT LDAP AuthPasswd 21 February 2000 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' EQUALITY authPasswordMatch SYNTAX authPasswordSyntaxOID ) The values of this attribute are representive of the user's password(s) as described in 4.1. The 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. 4.5. authPasswordObject ( authPasswordObjectOID NAME 'authPasswordObject' DESC 'authentication password mixin 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. 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 extension. 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 Zeilenga [Page 4] INTERNET-DRAFT LDAP AuthPasswd 21 February 2000 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 plaintext 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: 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 Zeilenga [Page 5] INTERNET-DRAFT LDAP AuthPasswd 21 February 2000 user/password authentication. It is RECOMMENDED that values of this scheme be protected as if they were plaintext passwords. 5.3. DIGEST-MD5 scheme The DIGEST-MD5 [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 the DIGEST-MD5 specfication. 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 AuthMeth [AuthMeth] specification. 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 plaintext passwords per reasons detailed in DIGEST-MD5, Section 3.9, "Storing Passwords." 6. Implementation Issues For implementations of this specification: Servers MAY restrict schemes used to support a particular authentication process but SHOULD use all values of those 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 in conjunction with authPassword to support authentication process. Servers that support simple bind SHOULD support MD5 scheme and SHOULD support the SHA1 scheme. Zeilenga [Page 6] INTERNET-DRAFT LDAP AuthPasswd 21 February 2000 Servers SHOULD not publish values of authPassword nor allow operations which provide authPassword or AuthPasswordMatch values to unless confidentiality protection is in place. Clients SHOULD not initiate operations which provide, assert, or request values of authPassword 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 compare and search are not authentication nor authorization operations. 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 access to the directory. The AuthPassword values stored SHOULD be protected as if they were plaintext passwords. Simple password authentication SHOULD only be used when privacy protection is in place. Applications SHOULD use strong authentication mechanisms whenever possible. AuthPasswordMatch matching rule allows applications to test the validality 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. 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 offerred 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. Zeilenga [Page 7] INTERNET-DRAFT LDAP AuthPasswd 21 February 2000 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. Acknowledgement 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, 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. [RFC2251] M. Wahl, T. Howes, S. Kille, "Lightweight Zeilenga [Page 8] INTERNET-DRAFT LDAP AuthPasswd 21 February 2000 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. [AUTHMETH] M. Wahl, H. Alvestrand, J. Hodges, RL "Bob" Morgan, "Authentication Methods for LDAP", draft-ietf-ldapext-authmeth-xx.txt, a work in progress. [DIGEST-MD5] P. Leach, C. Newman, "Using Digest Authentication as a SASL Mechanism", draft-leach-digest-sasl-xx.txt, a work in progress. [PASSWD-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 Zeilenga [Page 9]