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RFC4013-SASLprep: Stringprep Profile for User Names and Passwords

王朝other·作者佚名  2008-05-31
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Network Working Group K. Zeilenga

Request for Comments: 4013 OpenLDAP Foundation

Category: Standards Track February 2005

SASLprep: Stringprep Profile for User Names and PassWords

Status of This Memo

This document specifies an Internet standards track protocol for the

Internet community, and requests discussion and suggestions for

improvements. Please refer to the current edition of the "Internet

Official Protocol Standards" (STD 1) for the standardization state

and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2005).

Abstract

This document describes how to prepare Unicode strings representing

user names and passwords for comparison. The document defines the

"SASLprep" profile of the "stringprep" algorithm to be used for both

user names and passwords. This profile is intended to be used by

Simple Authentication and Security Layer (SASL) mechanisms (sUCh as

PLAIN, CRAM-MD5, and DIGEST-MD5), as well as other protocols

exchanging simple user names and/or passwords.

1. Introduction

The use of simple user names and passwords in authentication and

authorization is pervasive on the Internet. To increase the

likelihood that user name and password input and comparison work in

ways that make sense for typical users throughout the world, this

document defines rules for preparing internationalized user names and

passwords for comparison. For simplicity and implementation ease, a

single algorithm is defined for both user names and passwords.

The algorithm assumes all strings are comprised of characters from

the Unicode [Unicode] character set.

This document defines the "SASLprep" profile of the "stringprep"

algorithm [StringPrep].

The profile is designed for use in Simple Authentication and Security

Layer ([SASL]) mechanisms, such as [PLAIN], [CRAM-MD5], and

[DIGEST-MD5]. It may be applicable where simple user names and

passwords are used. This profile is not intended for use in

preparing identity strings that are not simple user names (e.g.,

email addresses, domain names, distinguished names), or where

identity or password strings that are not character data, or require

different handling (e.g., case folding).

This document does not alter the technical specification of any

existing protocols. Any specification that wishes to use the

algorithm described in this document needs to eXPlicitly incorporate

this document and provide precise details as to where and how this

algorithm is used by implementations of that specification.

2. The SASLprep Profile

This section defines the "SASLprep" profile of the "stringprep"

algorithm [StringPrep]. This profile is intended for use in

preparing strings representing simple user names and passwords.

This profile uses Unicode 3.2 [Unicode].

Character names in this document use the notation for code points and

names from the Unicode Standard [Unicode]. For example, the letter

"a" may be represented as either or .

In the lists of mappings and the prohibited characters, the "U+" is

left off to make the lists easier to read. The comments for

character ranges are shown in square brackets (such as "[CONTROL

CHARACTERS]") and do not come from the standard.

Note: A glossary of terms used in Unicode can be found in [Glossary].

Information on the Unicode character encoding model can be found in

[CharModel].

2.1. Mapping

This profile specifies:

- non-ASCII space characters [StringPrep, C.1.2] that can be

mapped to SPACE (U+0020), and

- the "commonly mapped to nothing" characters [StringPrep, B.1]

that can be mapped to nothing.

2.2. Normalization

This profile specifies using Unicode normalization form KC, as

described in Section 4 of [StringPrep].

2.3. Prohibited Output

This profile specifies the following characters as prohibited input:

- Non-ASCII space characters [StringPrep, C.1.2]

- ASCII control characters [StringPrep, C.2.1]

- Non-ASCII control characters [StringPrep, C.2.2]

- Private Use characters [StringPrep, C.3]

- Non-character code points [StringPrep, C.4]

- Surrogate code points [StringPrep, C.5]

- Inappropriate for plain text characters [StringPrep, C.6]

- Inappropriate for canonical representation characters

[StringPrep, C.7]

- Change display properties or deprecated characters

[StringPrep, C.8]

- Tagging characters [StringPrep, C.9]

2.4. Bidirectional Characters

This profile specifies checking bidirectional strings as described in

[StringPrep, Section 6].

2.5. Unassigned Code Points

This profile specifies the [StringPrep, A.1] table as its list of

unassigned code points.

3. Examples

The following table provides examples of how various character data

is transformed by the SASLprep string preparation algorithm

# Input Output Comments

- ----- ------ --------

1 IX IX SOFT HYPHEN mapped to nothing

2 user user no transformation

3 USER USER case preserved, will not match #2

4 a output is NFKC, input in ISO 8859-1

5 IX output is NFKC, will match #1

6 Error - prohibited character

7 Error - bidirectional check

4. Security Considerations

This profile is intended to prepare simple user name and password

strings for comparison or use in cryptographic functions (e.g.,

message digests). The preparation algorithm was specifically

designed such that its output is canonical, and it is well-formed.

However, due to an anomaly [PR29] in the specification of Unicode

normalization, canonical equivalence is not guaranteed for a select

few character sequences. These sequences, however, do not appear in

well-formed text. This specification was published despite this

known technical problem. It is expected that this specification will

be revised before further progression on the Standards Track (after

[Unicode] and/or [StringPrep] specifications have been updated to

address this problem).

It is not intended for preparing identity strings that are not simple

user names (e.g., distinguished names, domain names), nor is the

profile intended for use of simple user names that require different

handling (such as case folding). Protocols (or applications of those

protocols) that have application-specific identity forms and/or

comparison algorithms should use mechanisms specifically designed for

these forms and algorithms.

Application of string preparation may have an impact upon the

feasibility of brute force and dictionary attacks. While the number

of possible prepared strings is less than the number of possible

Unicode strings, the number of usable names and passwords is greater

than as if only ASCII was used. Though SASLprep eliminates some

Unicode code point sequences as possible prepared strings, that

elimination generally makes the (canonical) output forms practicable

and prohibits nonsensical inputs.

User names and passwords should be protected from eavesdropping.

General "stringprep" and Unicode security considerations apply. Both

are discussed in [StringPrep].

5. IANA Considerations

This document details the "SASLprep" profile of the [StringPrep]

protocol. This profile has been registered in the stringprep profile

registry.

Name of this profile: SASLprep

RFC in which the profile is defined: RFC 4013

Indicator whether or not this is the newest version of the

profile: This is the first version of the SASPprep profile.

6. Acknowledgement

This document borrows text from "Preparation of Internationalized

Strings ('stringprep')" and "Nameprep: A Stringprep Profile for

Internationalized Domain Names", both by Paul Hoffman and Marc

Blanchet. This document is a product of the IETF SASL WG.

7. Normative References

[StringPrep] Hoffman, P. and M. Blanchet, "Preparation of

Internationalized Strings ("stringprep")", RFC 3454,

December 2002.

[Unicode] The Unicode Consortium, "The Unicode Standard, Version

3.2.0" is defined by "The Unicode Standard, Version

3.0" (Reading, MA, Addison-Wesley, 2000. ISBN 0-201-

61633-5), as amended by the "Unicode Standard Annex

#27: Unicode 3.1"

(http://www.unicode.org/reports/tr27/) and by the

"Unicode Standard Annex #28: Unicode 3.2"

(http://www.unicode.org/reports/tr28/).

8. Informative References

[Glossary] The Unicode Consortium, "Unicode Glossary",

.

[CharModel] Whistler, K. and M. Davis, "Unicode Technical Report

#17, Character Encoding Model", UTR17,

, August

2000.

[SASL] Melnikov, A., Ed., "Simple Authentication and Security

Layer (SASL)", Work in Progress.

[CRAM-MD5] Nerenberg, L., "The CRAM-MD5 SASL Mechanism", Work in

Progress.

[DIGEST-MD5] Leach, P., Newman, C., and A. Melnikov, "Using Digest

Authentication as a SASL Mechanism", Work in Progress.

[PLAIN] Zeilenga, K., Ed., "The Plain SASL Mechanism", Work in

Progress.

[PR29] "Public Review Issue #29: Normalization Issue",

, February

2004.

Author's Address

Kurt D. Zeilenga

OpenLDAP Foundation

EMail: Kurt@OpenLDAP.org

Full Copyright Statement

Copyright (C) The Internet Society (2005).

This document is subject to the rights, licenses and restrictions

contained in BCP 78, and except as set forth therein, the authors

retain all their rights.

This document and the information contained herein are provided on an

"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS

OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET

ENGINEERING TASK FORCE DISCLAIM 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.

Intellectual Property

The IETF takes no position regarding the validity or scope of any

Intellectual Property Rights or other rights that might be claimed to

pertain to the implementation or use of the technology described in

this document or the extent to which any license under such rights

might or might not be available; nor does it represent that it has

made any independent effort to identify any such rights. Information

on the IETF's procedures with respect to rights in IETF Documents can

be found in BCP 78 and BCP 79.

Copies of IPR disclosures made to the IETF Secretariat and any

assurances of licenses to be made available, or the result of an

attempt made to oBTain a general license or permission for the use of

such proprietary rights by implementers or users of this

specification can be obtained from the IETF on-line IPR repository at

http://www.ietf.org/ipr.

The IETF invites any interested party to bring to its attention any

copyrights, patents or patent applications, or other proprietary

rights that may cover technology that may be required to implement

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Acknowledgement

Funding for the RFC Editor function is currently provided by the

Internet Society.

 
 
 
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