INTERNET-DRAFT Kurt D. Zeilenga Intended Category: Standard Track OpenLDAP Foundation Expires: 11 June 2000 11 December 1999 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 attribute may be used to store SASL [RFC2222] authentication passwords in entries of a directory. Zeilenga [Page 1] INTERNET-DRAFT LDAP AuthPasswd 11 December 1999 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 hashed password values for authentication purposes. 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. The attribute may be used by LDAP servers to implement simple bind and SASL [RFC 2222] user/password mechanisms such as DIGEST-MD5 [DIGEST- MD5]. Though values of authPassword are generally secured by use of a cryptographically safe one-way hash, they SHOULD be protected as if the password was stored in plain text. In particular, if the values used by some SASL mechanisms are compromised for a given user, then the attacker may falsely authenticate as this user and gain immediate access to all information to which that user is authorized. 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 = scheme "$" [ info ] "$" hashedValue scheme = info = Zeilenga [Page 2] INTERNET-DRAFT LDAP AuthPasswd 11 December 1999 hashedValue = where scheme describes the hash mechanism, info is a scheme specific, and hashedValue is the hashed value. The info field is often a salt. 4.2. authPasswordMatch ( authPasswordMatchOID NAME 'authPasswordMatch' DESC 'authentication password matching rule' SYNTAX 1.3.6.1.4.1.1466.115.121.1.40 ) This matching rule allows a client to assert that a password matches values of authPasswordSyntax. The server SHALL compare the stored hashedValue with a value derived from the asserted value and the stored info field according to the scheme of the stored value. This syntax may only be used for equality comparisons. 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 hash schemes' SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 USAGE dSAOperation ) The values of this attribute are case insensitive names of supported authentication password schemes which the server supports. 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 abbribute are derived from the user's password per the indicated scheme. The attribute may be used for authentication purposes. Zeilenga [Page 3] INTERNET-DRAFT LDAP AuthPasswd 11 December 1999 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 'hashed password mixin class' MAY 'authPassword' AUXILIARY ) Entries of this object class contain authentication passwords. 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. Scheme names are case insensitive. 5.1. MD5 scheme The MD5 [RFC1321] scheme name is "MD5". The hashedValue is the base64 encoding of an MD5 Digest of the concatenation the user password and optional salt. The salt is provided in the info 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 info field would be the base64 encoding of "salt" and the hashValue field would be the base64 encoding of the MD5 digest of "marysalt". 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 Zeilenga [Page 4] INTERNET-DRAFT LDAP AuthPasswd 11 December 1999 The SHA1 [SHA1] scheme name is "SHA1". The hashedValue is the base64 encoding of an SHA1 Digest of the concatenation the user password and the optional salt. The salt is provided in the info 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 info field would be the base64 encoding of "salt" and the hashValue field would be the base64 encoding of the SHA1 digest of "marysalt". 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. 5.3. DIGEST-MD5 scheme The DIGEST-MD5 [DIGEST-MD5] scheme name is "SASL/DIGEST-MD5". The hashedValue is the base64 encoding of H( { username-value, ":", realm-value, ":", passwd } ) and info 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 hashValue 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. 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 Zeilenga [Page 5] INTERNET-DRAFT LDAP AuthPasswd 11 December 1999 For implementations of this specification: Servers MAY restrict schemes used to support a particular authentication process but SHOULD use all values of those schemes. 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. 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. 7. Security Considerations This document describes how authentication information to support simple password authentication may be stored in directories. Use of simple password authentication should only be used when privacy protection is in place. Applications should use strong authentication mechanisms whenever possible. AuthPassword values stored SHOULD be protected as if they were plaintext passwords. 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. 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. 8. Copyright Copyright 2000, The Internet Society. All Rights Reserved. Zeilenga [Page 6] INTERNET-DRAFT LDAP AuthPasswd 11 December 1999 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 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, Zeilenga [Page 7] INTERNET-DRAFT LDAP AuthPasswd 11 December 1999 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-04.txt, June 1999. [DIGEST-MD5] P. Leach, C. Newman, "Using Digest Authentication as a SASL Mechanism", draft-leach-digest-sasl-05.txt, October 1999. [SHA1] NIST, FIPS PUB 180-1: Secure Hash Standard, April 1995. 11. Author's Address Kurt D. Zeilenga OpenLDAP Foundation Zeilenga [Page 8]