1 INTERNET-DRAFT Kurt D. Zeilenga
2 Intended Category: Standard Track OpenLDAP Foundation
3 Expires: 11 January 2001 11 July 2000
6 LDAP Authentication Password Attribute
7 <draft-zeilenga-ldap-authpasswd-03.txt>
11 1. Status of this Memo
13 This document is an Internet-Draft and is in full conformance with all
14 provisions of Section 10 of RFC2026.
16 This document is intended to be, after appropriate review and
17 revision, submitted to the RFC Editor as a Standard Track document.
18 Distribution of this memo is unlimited. Technical discussion of this
19 document will take place on the IETF LDAP Extension Working Group
20 mailing list <ietf-ldapext@netscape.com>. Please send editorial
21 comments directly to the author <Kurt@OpenLDAP.org>.
23 Internet-Drafts are working documents of the Internet Engineering Task
24 Force (IETF), its areas, and its working groups. Note that other
25 groups may also distribute working documents as Internet-Drafts.
26 Internet-Drafts are draft documents valid for a maximum of six months
27 and may be updated, replaced, or obsoleted by other documents at any
28 time. It is inappropriate to use Internet-Drafts as reference
29 material or to cite them other than as ``work in progress.''
31 The list of current Internet-Drafts can be accessed at
32 http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft
33 Shadow Directories can be accessed at http://www.ietf.org/shadow.html.
35 Copyright 2000, The Internet Society. All Rights Reserved.
37 Please see the Copyright section near the end of this document for
43 This document describes schema for storing information in support of
44 user/password authentication in a LDAP [RFC2251] directory. The
45 document defines the authPassword attribute type and related schema.
46 The attribute type is used to store values derived from the user's
47 password(s) (commonly using cryptographic strength one-way hash).
48 authPassword is intended to used instead of clear text password
54 INTERNET-DRAFT LDAP AuthPasswd 11 July 2000
57 storage mechanisms such as userPassword [RFC2256]. The values of
58 authPassword may be used to support both LDAP "simple" and SASL
59 [RFC2222] password authentication mechanisms [RFC2829].
61 The key words ``MUST'', ``MUST NOT'', ``REQUIRED'', ``SHALL'', ``SHALL
62 NOT'', ``SHOULD'', ``SHOULD NOT'', ``RECOMMENDED'', and ``MAY'' in
63 this document are to be interpreted as described in RFC 2119
67 3. Background and Intended Use
69 The userPassword attribute type [RFC 2256] is intended be used to used
70 to support the LDAP [RFC2251] "simple" bind operation. However,
71 values of userPassword must be clear text passwords. It is often
72 desirable to store values derived from the user's password(s) instead
75 The authPassword attribute type is intended to be used to store
76 information used to implement password based authentication. The
77 attribute type may be used by LDAP servers to implement user/password
78 authentication operations [RFC2829] such "simple" and SASL [RFC2222] /
81 The attribute type supports multiple storage schemes. A matching rule
82 is provided for use with extensible search filters to allow clients to
83 assert that a clear text password "matches" one of the attribute's
84 values. Storage schemes often use of cryptographic strength one-way
87 This attribute may be used in conjunction with server side password
88 generation mechanisms (such as [PW-EXOP]).
90 Access to this attribute may governed by administrative controls such
91 as those which implement password change policies.
96 The following schema definitions are described in terms of LDAPv3
97 Attribute Syntax Definitions [RFC2252] with specific syntax detailed
98 using Augmented BNF [RFC2234].
100 Editor's Note: object identifiers (OIDs) will be assigned before this
101 document is published as an RFC.
103 4.1. authPasswordSyntax
110 INTERNET-DRAFT LDAP AuthPasswd 11 July 2000
113 ( authPasswordSyntaxOID
114 DESC 'authentication password syntax' )
116 Values of this syntax are encoded according to the following BNF:
118 authPasswordValue = w scheme s [authInfo] s authValue w
119 scheme = <an IA5 string of uppercase letters, numbers,
120 and "-", "_", and "/">
121 authInfo = schemeSpecificValue
122 authValue = schemeSpecfiicValue
123 schemeSpecificValue = <an IA5 printable string
124 not containing "$" or " ">
127 sep = "$" ; an IA5 dollar sign (36)
128 sp = " " ; an IA5 space (20)
130 where scheme describes the storage mechanism, authInfo and authValue
131 are a scheme specific. The authInfo field is often a base64 encoded
132 salt. The authValue field is often a base64 encoded value derived
133 from a user's password(s). Values of this attribute are case
136 This document describes a number of schemes, as well as requirements
137 for the scheme naming, in section 5.
140 4.2. authPasswordMatch
142 ( authPasswordMatchOID
143 NAME 'authPasswordMatch'
144 DESC 'authentication password matching rule'
145 SYNTAX 1.3.6.1.4.1.1466.115.121.1.40{128} )
147 This matching rule allows a client to assert that a password matches
148 values of authPasswordSyntax using an extensibleMatch filter
149 component. Each value is matched per its scheme. The assertion is
150 TRUE if one or more attribute values matches the asserted value, FALSE
151 if all values do not matches, and Undefined otherwise.
153 Servers which support use of this matching rule SHOULD publish
154 appropriate matchingRuleUse values per [RFC2252], 4.4.
156 Transfer of authPasswordMatch assertion values is strongly discouraged
157 where the underlying transport service cannot guarantee
158 confidentiality and may result in disclosure of the values to
159 unauthorized parties.
166 INTERNET-DRAFT LDAP AuthPasswd 11 July 2000
169 4.3. supportedAuthPasswordSchemes
171 ( supportedAuthPasswordSchemesOID
172 NAME 'supportedAuthPasswordSchemes'
173 DESC 'supported password storage schemes'
174 EQUALITY caseExactIA5Match
175 SYNTAX 1.3.6.1.4.1.1466.115.121.1.26{32}
178 The values of this attribute are names of supported authentication
179 password schemes which the server supports. The syntax of a scheme
180 name is described in section 4.1. This attribute may only be present
181 in the root DSE. If the server does not support any mechanisms this
182 attribute will not be present.
187 ( authPasswordOID NAME 'authPassword'
188 SYNTAX authPasswordSyntaxOID )
190 The values of this attribute are representative of the user's
191 password(s) and conform to the authPasswordSyntax described in 4.1.
192 The values of this attribute may be used for authentication purposes.
194 This attribute type is defined without any built-in matching rules.
195 The absence of an EQUALITY matching rules disallows modification of
198 Transfer of authPassword values is strongly discouraged where the
199 underlying transport service cannot guarantee confidentiality and may
200 result in disclosure of the values to unauthorized parties.
203 4.5. authPasswordObject
205 ( authPasswordObjectOID NAME 'authPasswordObject'
206 DESC 'authentication password mix in class'
207 MAY 'authPassword' AUXILIARY )
209 Entries of this object class may contain authPassword attribute types.
214 This section describes the "MD5", "SHA1", and "SASL/DIGEST-MD5".
215 Other schemes may be defined by other documents. Schemes starting
216 with string "SASL/" indicate association with a SASL mechanism.
222 INTERNET-DRAFT LDAP AuthPasswd 11 July 2000
225 Schemes which are not described by standard track documents SHOULD be
226 named with a leading "X-" or, if associated with a SASL mechanism,
227 "SASL/X-" to indicate they are a private or implementation specific
228 mechanism, or may be named using the dotted-decimal representation
229 [RFC2252] of an OID assigned to the mechanism.
234 The MD5 [RFC1321] scheme name is "MD5".
236 The authValue is the base64 encoding of an MD5 digest of the
237 concatenation the user password and optional salt. The base64
238 encoding of the salt is provided in the authInfo field.
239 Implementations of this scheme must support salts up to 128-bit in
240 length. Use with a 64-bit or larger salt is RECOMMENDED.
243 Given a user "joe" who's password is "mary" and a salt of "salt",
244 the authInfo field would be the base64 encoding of "salt" and the
245 authValue field would be the base64 encoding of the MD5 digest of
248 A match against an asserted password and an attribute value of this
249 scheme SHALL be true if and only if the MD5 digest of concatenation of
250 the asserted value and the salt is equal to the MD5 digest contained
251 in AuthValue. The match SHALL be undefined if the server is unable to
252 complete the equality test for any reason. Otherwise the match SHALL
255 Values of this scheme SHOULD only be used to implement simple
256 user/password authentication.
258 It is RECOMMENDED that values of this scheme be protected as if they
259 were clear text passwords.
264 The SHA1 [SHA1] scheme name is "SHA1".
266 The authValue is the base64 encoding of an SHA1 digest of the
267 concatenation the user password and the optional salt. The base64
268 encoding of the salt is provided in the authInfo field.
269 Implementations of this scheme must support salts up to 128-bit in
270 length. Use with a 64-bit or larger salt is RECOMMENDED.
278 INTERNET-DRAFT LDAP AuthPasswd 11 July 2000
281 Given a user "joe" who's password is "mary" and a salt of "salt",
282 the authInfo field would be the base64 encoding of "salt" and the
283 authValue field would be the base64 encoding of the SHA1 digest of
286 A match against an asserted password and an attribute value of this
287 scheme SHALL be true if and only if the SHA1 digest of concatenation
288 of the asserted value and the salt is equal to the SHA1 digest
289 contained in AuthValue. The match SHALL be undefined if the server is
290 unable to complete the equality test for any reason. Otherwise the
291 match SHALL be false.
293 Values of this scheme SHOULD only be used to implement simple
294 user/password authentication.
296 It is RECOMMENDED that values of this scheme be protected as if they
297 were clear text passwords.
300 5.3. DIGEST-MD5 scheme
302 The DIGEST-MD5 scheme name is "SASL/DIGEST-MD5".
304 The authValue is the base64 encoding of
305 H( { username-value, ":", realm-value, ":", passwd } )
307 and authInfo is the base64 encoding of
308 { username-value, ":", realm-value }
310 as defined by RFC2831.
313 Given a user "joe" within the realm "localhost" who's password is
314 "mary", the info field would be the base64 encoding of
315 "joe:localhost" and the authValue field would be the base64 encoding
316 of the MD5 digest of "joe:localhost:mary".
318 Values of this scheme SHOULD only be used to implement the
319 SASL/DIGEST-MD5 as described by the Authentication Methods for LDAP
320 [RFC2829]. A simple password assertion against a value of this scheme
321 SHALL be considered undefined.
323 Values of this scheme MUST be protected as if it the values were clear
324 text passwords per reasons detailed in DIGEST-MD5, Section 3.9,
328 6. Implementation Issues
334 INTERNET-DRAFT LDAP AuthPasswd 11 July 2000
337 For implementations of this specification:
339 Servers MAY restrict which schemes are used in conjunction with a
340 particular authentication process but SHOULD use all values of
341 selected schemes. If the asserted password matches any of the
342 stored values, the asserted password SHOULD be considered valid.
343 Servers MAY use other authentication storage mechanisms, such as
344 userPassword or an external password store, in conjunction with
345 authPassword to support the authentication process.
347 Servers that support simple bind MUST support the MD5 scheme and
348 SHOULD support the SHA1 scheme.
350 Servers SHOULD not publish values of authPassword nor allow
351 operations which expose authPassword or AuthPasswordMatch values to
352 unless confidentiality protection is in place.
354 Clients SHOULD not initiate operations which provide or request
355 values of authPassword or make authPasswordMatch assertions unless
356 confidentiality protection is in place.
358 Clients SHOULD not assume that a successful AuthPasswordMatch,
359 whether by compare or search, is sufficient to gain directory
360 access. The bind operation MUST be used to authentication to the
364 7. Security Considerations
366 This document describes how authentication information may be stored
367 in a directory. Authentication information must be adequately
368 protected as unintended disclosure will allow attackers to gain
369 immediate access to the directory as described by [RFC2829].
371 Values of authPassword SHOULD be protected as if they were clear text
372 passwords. When values are transferred, privacy protections, such as
373 IPSEC or TLS, SHOULD be in place.
375 Clients SHOULD use strong authentication mechanisms [RFC2829].
377 AuthPasswordMatch matching rule allows applications to test the
378 validity of a user password and, hence, may be used to mount a
379 dictionary attack. Servers SHOULD take appropriate measures to
380 protect the directory from such attacks.
382 Some password schemes may require CPU intensive operations. Servers
383 SHOULD take appropriate measures to protect against Denial of Service
390 INTERNET-DRAFT LDAP AuthPasswd 11 July 2000
393 AuthPassword does not restrict an authentication identity to a single
394 password. An attacker who gains write access to this attribute may
395 store additional values without disabling the user's true password(s).
396 Use of policy aware clients and servers is RECOMMENDED.
398 The level of protection offered against various attacks differ from
399 scheme to scheme. It is RECOMMENDED that servers support scheme
400 selection as a configuration item. This allows for a scheme to be
401 easily disabled if a significant security flaw is discovered.
406 Copyright 2000, The Internet Society. All Rights Reserved.
408 This document and translations of it may be copied and furnished to
409 others, and derivative works that comment on or otherwise explain it
410 or assist in its implementation may be prepared, copied, published and
411 distributed, in whole or in part, without restriction of any kind,
412 provided that the above copyright notice and this paragraph are
413 included on all such copies and derivative works. However, this
414 document itself may not be modified in any way, such as by removing
415 the copyright notice or references to the Internet Society or other
416 Internet organizations, except as needed for the purpose of
417 developing Internet standards in which case the procedures for
418 copyrights defined in the Internet Standards process must be followed,
419 or as required to translate it into languages other than English.
421 The limited permissions granted above are perpetual and will not be
422 revoked by the Internet Society or its successors or assigns.
424 This document and the information contained herein is provided on an
425 "AS IS" basis and THE AUTHORS, THE INTERNET SOCIETY, AND THE INTERNET
426 ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED,
427 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
428 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
429 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
434 This document borrows from a number of IETF documents and is based
435 upon input from the IETF LDAPext working group.
440 [RFC1321] R. Rivest, "The MD5 Message-Digest Algorithm", RFC 1321,
446 INTERNET-DRAFT LDAP AuthPasswd 11 July 2000
451 [RFC2219] S. Bradner, "Key words for use in RFCs to Indicate
452 Requirement Levels", RFC 2119, March 1997.
454 [RFC2222] J. Myers, "Simple Authentication and Security Layer (SASL)",
455 RFC 2222, October 1997.
457 [RFC2234] D. Crocker (editor), P. Overell, "Augmented BNF for Syntax
458 Specifications: ABNF", RFC 2234, November 1997.
460 [RFC2251] M. Wahl, T. Howes, S. Kille, "Lightweight Directory Access
461 Protocol (v3)", RFC 2251, December 1997.
463 [RFC2252] M. Wahl, A. Coulbeck, T. Howes, S. Kille, "Lightweight
464 Directory Access Protocol (v3): Attribute Syntax
465 Definitions", RFC 2252, December 1997.
467 [RFC2256] M. Wahl, "A Summary of the X.500(96) User Schema for use
468 with LDAPv3", RFC 2256, December 1997.
470 [RFC2307] L. Howard, "An Approach for Using LDAP as a Network
471 Information Service", RFC 2307, March 1998.
473 [RFC2829] M. Wahl, H. Alvestrand, J. Hodges, RL "Bob" Morgan,
474 "Authentication Methods for LDAP", RFC 2829, June 2000.
476 [RFC2831] P. Leach, C. Newman, "Using Digest Authentication as a SASL
477 Mechanism", RFC 2831, June 2000.
479 [PW-EXOP] K. Zeilenga, "LDAP Password Modify Extended Operation"
480 draft-zeilenga-ldap-passwd-exop-xx.txt, a work in progress.
482 [SHA1] NIST, FIPS PUB 180-1: Secure Hash Standard, April 1995.