One document matched: draft-zeilenga-ldap-authpasswd-02.txt
Differences from draft-zeilenga-ldap-authpasswd-01.txt
INTERNET-DRAFT Kurt D. Zeilenga
Intended Category: Standard Track OpenLDAP Foundation
Expires: 21 August 2000 21 February 2000
LDAP Authentication Password Attribute
<draft-zeilenga-ldap-authpasswd-02.txt>
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 <ietf-ldapext@netscape.com>. Please send
editorial comments directly to the author <Kurt@OpenLDAP.org>.
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
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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
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scheme = <an IA5 string of uppercase letters, numbers,
and "-", "_", and "/">
authInfo = schemeSpecificValue
authValue = schemeSpecfiicValue
schemeSpecificValue = <an IA5 printable string
not containing "$" or " ">
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
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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
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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
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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.
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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.
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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
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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
<Kurt@OpenLDAP.org>
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