draft-ietf-precis-problem-statement-07.txt   draft-ietf-precis-problem-statement-08.txt 
Network Working Group M. Blanchet Network Working Group M. Blanchet
Internet-Draft Viagenie Internet-Draft Viagenie
Intended status: Informational A. Sullivan Intended status: Informational A. Sullivan
Expires: February 4, 2013 Dyn, Inc. Expires: March 23, 2013 Dyn, Inc.
August 3, 2012 September 19, 2012
Stringprep Revision and PRECIS Problem Statement Stringprep Revision and PRECIS Problem Statement
draft-ietf-precis-problem-statement-07.txt draft-ietf-precis-problem-statement-08.txt
Abstract Abstract
If a protocol expects to compare two strings and is prepared only for If a protocol expects to compare two strings and is prepared only for
those strings to be ASCII, then using Unicode codepoints in those those strings to be ASCII, then using Unicode codepoints in those
strings requires they be prepared somehow. Internationalizing Domain strings requires they be prepared somehow. Internationalizing Domain
Names in Applications (here called IDNA2003) defined and used Names in Applications (here called IDNA2003) defined and used
Stringprep and Nameprep. Other protocols subsequently defined Stringprep and Nameprep. Other protocols subsequently defined
Stringprep profiles. A new approach different from Stringprep and Stringprep profiles. A new approach different from Stringprep and
Nameprep is used for a revision of IDNA2003 (called IDNA2008). Other Nameprep is used for a revision of IDNA2003 (called IDNA2008). Other
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 4, 2013. This Internet-Draft will expire on March 23, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 6 2. Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Stringprep Profiles Limitations . . . . . . . . . . . . . . . 6 3. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Major Topics for Consideration . . . . . . . . . . . . . . . . 8 4. Stringprep Profiles Limitations . . . . . . . . . . . . . . . 6
4.1. Comparison . . . . . . . . . . . . . . . . . . . . . . . . 8 5. Major Topics for Consideration . . . . . . . . . . . . . . . . 8
4.1.1. Types of Identifiers . . . . . . . . . . . . . . . . . 8 5.1. Comparison . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1.2. Effect of comparison . . . . . . . . . . . . . . . . . 8 5.1.1. Types of Identifiers . . . . . . . . . . . . . . . . . 8
4.2. Dealing with characters . . . . . . . . . . . . . . . . . 8 5.1.2. Effect of comparison . . . . . . . . . . . . . . . . . 8
4.2.1. Case folding, case sensitivity, and case 5.2. Dealing with characters . . . . . . . . . . . . . . . . . 9
5.2.1. Case folding, case sensitivity, and case
preservation . . . . . . . . . . . . . . . . . . . . . 9 preservation . . . . . . . . . . . . . . . . . . . . . 9
4.2.2. Stringprep and NFKC . . . . . . . . . . . . . . . . . 9 5.2.2. Stringprep and NFKC . . . . . . . . . . . . . . . . . 9
4.2.3. Character mapping . . . . . . . . . . . . . . . . . . 9 5.2.3. Character mapping . . . . . . . . . . . . . . . . . . 10
4.2.4. Prohibited characters . . . . . . . . . . . . . . . . 10 5.2.4. Prohibited characters . . . . . . . . . . . . . . . . 10
4.2.5. Internal structure, delimiters, and special 5.2.5. Internal structure, delimiters, and special
characters . . . . . . . . . . . . . . . . . . . . . . 10 characters . . . . . . . . . . . . . . . . . . . . . . 10
4.2.6. Restrictions because of glyph similarity . . . . . . . 11 5.2.6. Restrictions because of glyph similarity . . . . . . . 11
4.3. Where the data comes from and where it goes . . . . . . . 11 5.3. Where the data comes from and where it goes . . . . . . . 11
4.3.1. User input and the source of protocol elements . . . . 11 5.3.1. User input and the source of protocol elements . . . . 11
4.3.2. User output . . . . . . . . . . . . . . . . . . . . . 11 5.3.2. User output . . . . . . . . . . . . . . . . . . . . . 11
4.3.3. Operations . . . . . . . . . . . . . . . . . . . . . . 12 5.3.3. Operations . . . . . . . . . . . . . . . . . . . . . . 12
5. Considerations for Stringprep replacement . . . . . . . . . . 13 6. Considerations for Stringprep replacement . . . . . . . . . . 13
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13 7. Security Considerations . . . . . . . . . . . . . . . . . . . 14
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
8. Discussion home for this draft . . . . . . . . . . . . . . . . 14 9. Discussion home for this draft . . . . . . . . . . . . . . . . 14
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
10. Informative References . . . . . . . . . . . . . . . . . . . . 14 11. Informative References . . . . . . . . . . . . . . . . . . . . 14
Appendix A. Classification of Stringprep Profiles . . . . . . . . 18 Appendix A. Classification of Stringprep Profiles . . . . . . . . 18
Appendix B. Evaluation of Stringprep Profiles . . . . . . . . . . 19 Appendix B. Evaluation of Stringprep Profiles . . . . . . . . . . 19
B.1. iSCSI Stringprep Profile: RFC3722 (and RFC3721, B.1. iSCSI Stringprep Profile: RFC3722 (and RFC3721,
RFC3720) . . . . . . . . . . . . . . . . . . . . . . . . . 19 RFC3720) . . . . . . . . . . . . . . . . . . . . . . . . . 19
B.2. SMTP/POP3/ManageSieve Stringprep Profiles: B.2. SMTP/POP3/ManageSieve Stringprep Profiles:
RFC4954,RFC5034,RFC 5804 . . . . . . . . . . . . . . . . . 20 RFC4954,RFC5034,RFC 5804 . . . . . . . . . . . . . . . . . 21
B.3. IMAP Stringprep Profiles: RFC5738, RFC4314: Usernames . . 22 B.3. IMAP Stringprep Profiles: RFC5738, RFC4314: Usernames . . 22
B.4. IMAP Stringprep Profiles: RFC5738: Passwords . . . . . . . 23 B.4. IMAP Stringprep Profiles: RFC5738: Passwords . . . . . . . 24
B.5. Anonymous SASL Stringprep Profiles: RFC4505 . . . . . . . 25 B.5. Anonymous SASL Stringprep Profiles: RFC4505 . . . . . . . 25
B.6. XMPP Stringprep Profiles: RFC3920 Nodeprep . . . . . . . . 26 B.6. XMPP Stringprep Profiles: RFC3920 Nodeprep . . . . . . . . 27
B.7. XMPP Stringprep Profiles: RFC3920 Resourceprep . . . . . . 27 B.7. XMPP Stringprep Profiles: RFC3920 Resourceprep . . . . . . 28
B.8. EAP Stringprep Profiles: RFC3748 . . . . . . . . . . . . . 28 B.8. EAP Stringprep Profiles: RFC3748 . . . . . . . . . . . . . 28
Appendix C. Changes between versions . . . . . . . . . . . . . . 29 Appendix C. Changes between versions . . . . . . . . . . . . . . 29
C.1. 00 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 C.1. 00 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
C.2. 01 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 C.2. 01 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
C.3. 02 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 C.3. 02 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
C.4. 03 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 C.4. 03 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
C.5. 04 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 C.5. 04 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
C.6. 05 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 C.6. 05 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
C.7. 06 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 C.7. 06 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 30 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 30
1. Introduction 1. Introduction
Internationalizing Domain Names in Applications (here called Internationalizing Domain Names in Applications (here called
IDNA2003) [RFC3490], [RFC3491], [RFC3492], [RFC3454] describes a IDNA2003) [RFC3490], [RFC3491], [RFC3492], [RFC3454] describes a
mechanism for encoding Unicode labels making up Internationalized mechanism for encoding Unicode labels making up Internationalized
Domain Names (IDNs) as standard DNS labels. The labels were Domain Names (IDNs) as standard DNS labels. The labels were
processed using a method called Nameprep [RFC3491] and Punycode processed using a method called Nameprep [RFC3491] and Punycode
[RFC3492]. That method was specific to IDNA2003, but is generalized [RFC3492]. That method was specific to IDNA2003, but is generalized
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Unicode 3.2 that was not so listed could be assumed to be allowed Unicode 3.2 that was not so listed could be assumed to be allowed
under the protocol. IDNA2008 begins instead from the assumption that under the protocol. IDNA2008 begins instead from the assumption that
code points are disallowed, and then relies on Unicode properties to code points are disallowed, and then relies on Unicode properties to
derive whether a given code point actually is allowed in the derive whether a given code point actually is allowed in the
protocol. protocol.
This document lists the shortcomings and issues found by protocols This document lists the shortcomings and issues found by protocols
listed above that defined Stringprep profiles. It also lists the listed above that defined Stringprep profiles. It also lists the
requirements for any potential replacement of Stringprep. requirements for any potential replacement of Stringprep.
2. Conventions 2. Keywords
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. Conventions
A single Unicode code point in this memo is denoted by "U+" followed A single Unicode code point in this memo is denoted by "U+" followed
by four to six hexadecimal digits, as used in [Unicode61], Appendix by four to six hexadecimal digits, as used in [Unicode61], Appendix
A. A.
3. Stringprep Profiles Limitations 4. Stringprep Profiles Limitations
During IETF 77 (March 2010), a BOF discussed the current state of the During IETF 77 (March 2010), a BOF discussed the current state of the
protocols that have defined Stringprep profiles [NEWPREP]. The main protocols that have defined Stringprep profiles [NEWPREP]. The main
conclusions from that discussion were as follows: conclusions from that discussion were as follows:
o Stringprep is bound to version 3.2 of Unicode. Stringprep has not o Stringprep is bound to version 3.2 of Unicode. Stringprep has not
been updated to new versions of Unicode. Therefore, the protocols been updated to new versions of Unicode. Therefore, the protocols
using Stringprep are stuck at Unicode 3.2, and their using Stringprep are stuck at Unicode 3.2, and their
specifications need to be updated to support new versions of specifications need to be updated to support new versions of
Unicode. Unicode.
o The protocols would like to not be bound to a specific version of o The protocols would like to not be bound to a specific version of
Unicode, but rather have better Unicode version agility in the way Unicode, but rather have better Unicode version agility in the way
of IDNA2008. This is important partly because it is usually of IDNA2008. This is important partly because it is usually
impossible for an application to require Unicode 3.2; the impossible for an application to require Unicode 3.2; the
application gets whatever version of Unicode is available on the application gets whatever version of Unicode is available on the
host. host.
o The protocols require better bidirectional support (bidi) than o The protocols require better bidirectional support (bidi) than
currently offered by Stringprep. currently offered by Stringprep.
o If the protocols are updated to use a new version of Stringprep or o If the protocols are updated to use a new version of Stringprep or
another framework, then backward compatibility is an important another framework, then backward compatibility is an important
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Notwithstanding the desire evident in [NEWPREP] and the chartering of Notwithstanding the desire evident in [NEWPREP] and the chartering of
a working group, IDNA2008 may be a poor model for what other a working group, IDNA2008 may be a poor model for what other
protocols ought to do, because it is designed to support an old protocols ought to do, because it is designed to support an old
protocol that is designed to operate on the scale of the entire protocol that is designed to operate on the scale of the entire
Internet. Moreover, IDNA2008 is intended to be deployed without any Internet. Moreover, IDNA2008 is intended to be deployed without any
change to the base DNS protocol. Other protocols may aim at change to the base DNS protocol. Other protocols may aim at
deployment in more local environments, or may have protocol version deployment in more local environments, or may have protocol version
negotiation built in. negotiation built in.
4. Major Topics for Consideration 5. Major Topics for Consideration
This section provides an overview of major topics that a Stringprep This section provides an overview of major topics that a Stringprep
replacement needs to address. The headings correspond roughly with replacement needs to address. The headings correspond roughly with
categories under which known Stringprep-using protocol RFCs have been categories under which known Stringprep-using protocol RFCs have been
evaluated. For the details of those evaluations, see Appendix A. evaluated. For the details of those evaluations, see Appendix A.
4.1. Comparison 5.1. Comparison
4.1.1. Types of Identifiers 5.1.1. Types of Identifiers
Following [I-D.iab-identifier-comparison], it is possible to organize Following [I-D.iab-identifier-comparison], it is possible to organize
identifiers into three classes in respect of how they may be compared identifiers into three classes in respect of how they may be compared
with one another: with one another:
Absolute Identifiers Identifiers that can be compared byte-by-byte Absolute Identifiers Identifiers that can be compared byte-by-byte
for equality. for equality.
Definite Identifiers Identifiers that have a well-defined comparison Definite Identifiers Identifiers that have a well-defined comparison
algorithm on which all parties agree. algorithm on which all parties agree.
Indefinite Identifiers Identifiers that have no single comparison Indefinite Identifiers Identifiers that have no single comparison
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Definite Identifiers include cases like the comparison of Unicode Definite Identifiers include cases like the comparison of Unicode
code points in different encodings: they do not match byte for byte, code points in different encodings: they do not match byte for byte,
but can all be converted to a single encoding which then does match but can all be converted to a single encoding which then does match
byte for byte. Indefinite Identifiers are sometimes algorithmically byte for byte. Indefinite Identifiers are sometimes algorithmically
comparable by well-specified subsets of parties. For more discussion comparable by well-specified subsets of parties. For more discussion
of these categories, see [I-D.iab-identifier-comparison]. of these categories, see [I-D.iab-identifier-comparison].
The section on treating the existing known cases, Appendix A uses the The section on treating the existing known cases, Appendix A uses the
categories above. categories above.
4.1.2. Effect of comparison 5.1.2. Effect of comparison
The three classes of comparison style outlined in Section 4.1.1 may The three classes of comparison style outlined in Section 5.1.1 may
have different effects when applied. It is necessary to evaluate the have different effects when applied. It is necessary to evaluate the
effects if a comparison results in a false positive, and what the effects if a comparison results in a false positive, and what the
effects are if a comparison results in a false negative, especially effects are if a comparison results in a false negative, especially
in terms of the consequences to security and usability. in terms of the consequences to security and usability.
4.2. Dealing with characters 5.2. Dealing with characters
This section outlines a range of issues having to do with characters This section outlines a range of issues having to do with characters
in the target protocols, and outlines the ways in which IDNA2008 in the target protocols, and outlines the ways in which IDNA2008
might be a good analogy to other protocols, and ways in which it might be a good analogy to other protocols, and ways in which it
might be a poor one. might be a poor one.
4.2.1. Case folding, case sensitivity, and case preservation 5.2.1. Case folding, case sensitivity, and case preservation
In IDNA2003, labels are always mapped to lower case before the In IDNA2003, labels are always mapped to lower case before the
Punycode transformation. In IDNA2008, there is no mapping at all: Punycode transformation. In IDNA2008, there is no mapping at all:
input is either a valid U-label or it is not. At the same time, input is either a valid U-label or it is not. At the same time,
upper-case characters are by definition not valid U-labels, because upper-case characters are by definition not valid U-labels, because
they fall into the Unstable category (category B) of [RFC5892]. they fall into the Unstable category (category B) of [RFC5892].
If there are protocols that require upper and lower cases be If there are protocols that require upper and lower cases be
preserved, then the analogy with IDNA2008 will break down. preserved, then the analogy with IDNA2008 will break down.
Accordingly, existing protocols are to be evaluated according to the Accordingly, existing protocols are to be evaluated according to the
following criteria: following criteria:
1. Does the protocol use case folding? For all blocks of code 1. Does the protocol use case folding? For all blocks of code
points, or just for certain subsets? points, or just for certain subsets?
2. Is the system or protocol case sensitive? 2. Is the system or protocol case sensitive?
3. Does the system or protocol preserve case? 3. Does the system or protocol preserve case?
4.2.2. Stringprep and NFKC 5.2.2. Stringprep and NFKC
Stringprep profiles may use normalization. If they do, they use NFKC Stringprep profiles may use normalization. If they do, they use NFKC
[UAX15] (most profiles do). It is not clear that NFKC is the right [UAX15] (most profiles do). It is not clear that NFKC is the right
normalization to use in all cases. In [UAX15], there is the normalization to use in all cases. In [UAX15], there is the
following observation regarding Normalization Forms KC and KD: "It is following observation regarding Normalization Forms KC and KD: "It is
best to think of these Normalization Forms as being like uppercase or best to think of these Normalization Forms as being like uppercase or
lowercase mappings: useful in certain contexts for identifying core lowercase mappings: useful in certain contexts for identifying core
meanings, but also performing modifications to the text that may not meanings, but also performing modifications to the text that may not
always be appropriate." In general, it can be said that NFKC is more always be appropriate." In general, it can be said that NFKC is more
aggressive about finding matches between codepoints than NFC. For aggressive about finding matches between codepoints than NFC. For
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best form to use. At the same time, one of the nice things about best form to use. At the same time, one of the nice things about
NFKC is that it deals with the width of characters that are otherwise NFKC is that it deals with the width of characters that are otherwise
similar, by canonicalizing half-width to full-width. This mapping similar, by canonicalizing half-width to full-width. This mapping
step can be crucial in practice. A replacement for stringprep step can be crucial in practice. A replacement for stringprep
depends on analyzing the different use profiles and considering depends on analyzing the different use profiles and considering
whether NFKC or NFC is a better normalization for each profile. whether NFKC or NFC is a better normalization for each profile.
For the purposes of evaluating an existing example of Stringprep use, For the purposes of evaluating an existing example of Stringprep use,
it is helpful to know whether it uses no normalization, NFKC, or NFC. it is helpful to know whether it uses no normalization, NFKC, or NFC.
4.2.3. Character mapping 5.2.3. Character mapping
Along with the case mapping issues raised in Section 4.2.1, there is Along with the case mapping issues raised in Section 5.2.1, there is
the question of whether some characters are mapped either to other the question of whether some characters are mapped either to other
characters or to nothing during Stringprep. [RFC3454], Section 3, characters or to nothing during Stringprep. [RFC3454], Section 3,
outlines a number of characters that are mapped to nothing, and also outlines a number of characters that are mapped to nothing, and also
permits Stringprep profiles to define their own mappings. permits Stringprep profiles to define their own mappings.
4.2.4. Prohibited characters 5.2.4. Prohibited characters
Along with case folding and other character mappings, many protocols Along with case folding and other character mappings, many protocols
have characters that are simply disallowed. For example, control have characters that are simply disallowed. For example, control
characters and special characters such as "@" or "/" may be characters and special characters such as "@" or "/" may be
prohibited in a protocol. prohibited in a protocol.
One of the primary changes of IDNA2008 is in the way it approaches One of the primary changes of IDNA2008 is in the way it approaches
Unicode code points, using the new inclusion-based approach (see Unicode code points, using the new inclusion-based approach (see
Section 1). Section 1).
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ZERO WIDTH NON-JOINER (ZWJ, U+200D and ZWNJ, U+200C) are allowed with ZERO WIDTH NON-JOINER (ZWJ, U+200D and ZWNJ, U+200C) are allowed with
contextual rules because they are required in some circumstances, yet contextual rules because they are required in some circumstances, yet
are considered punctuation by Unicode and would therefore be are considered punctuation by Unicode and would therefore be
DISALLOWED under the usual IDNA2008 derivation rules. The goal of DISALLOWED under the usual IDNA2008 derivation rules. The goal of
IDNA2008 is to provide the widest repertoire of code points possible IDNA2008 is to provide the widest repertoire of code points possible
and consistent with the traditional DNS "LDH" (letters, digits, and consistent with the traditional DNS "LDH" (letters, digits,
hyphen; see [RFC0952]) rule, trusting to the operators of individual hyphen; see [RFC0952]) rule, trusting to the operators of individual
zones to make sensible (and usually more restrictive) policies for zones to make sensible (and usually more restrictive) policies for
their zones. their zones.
4.2.5. Internal structure, delimiters, and special characters 5.2.5. Internal structure, delimiters, and special characters
IDNA2008 has a special problem with delimiters, because the delimiter IDNA2008 has a special problem with delimiters, because the delimiter
"character" in the DNS wire format is not really part of the data. "character" in the DNS wire format is not really part of the data.
In DNS, labels are not separated exactly; instead, a label carries In DNS, labels are not separated exactly; instead, a label carries
with it an indicator that says how long the label is. When the label with it an indicator that says how long the label is. When the label
is presented in presentation format as part of a fully qualified is presented in presentation format as part of a fully qualified
domain name, the label separator FULL STOP, U+002E (.) is used to domain name, the label separator FULL STOP, U+002E (.) is used to
break up the labels. But because that label separator does not break up the labels. But because that label separator does not
travel with the wire format of the domain name, there is no way to travel with the wire format of the domain name, there is no way to
encode a different, "internationalized" separator in IDNA2008. encode a different, "internationalized" separator in IDNA2008.
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as well. as well.
An important issue to tackle here is whether it is valuable to map to An important issue to tackle here is whether it is valuable to map to
or from these special characters as part of the Stringprep or from these special characters as part of the Stringprep
replacement. In some locales, the analogue to FULL STOP, U+002E is replacement. In some locales, the analogue to FULL STOP, U+002E is
some other character, and users may expect to be able to substitute some other character, and users may expect to be able to substitute
their normal stop for FULL STOP, U+002E. At the same time, there are their normal stop for FULL STOP, U+002E. At the same time, there are
predictability arguments in favour of treating identifiers with FULL predictability arguments in favour of treating identifiers with FULL
STOP, U+002E in them just the way they are treated under IDNA2008. STOP, U+002E in them just the way they are treated under IDNA2008.
4.2.6. Restrictions because of glyph similarity 5.2.6. Restrictions because of glyph similarity
Homoglyphs are similarly (or identically) rendered glyphs of Homoglyphs are similarly (or identically) rendered glyphs of
different codepoints. For DNS names, homoglyphs may enable phishing. different codepoints. For DNS names, homoglyphs may enable phishing.
If a protocol requires some visual comparison by end-users, then the If a protocol requires some visual comparison by end-users, then the
issue of homoglyphs are to be considered. In the DNS context, theses issue of homoglyphs are to be considered. In the DNS context, theses
issues are documented in [RFC5894] and [RFC4690]. IDNA2008 does not, issues are documented in [RFC5894] and [RFC4690]. IDNA2008 does not,
however, have a mechanism to deal with them, trusting to DNS zone however, have a mechanism to deal with them, trusting to DNS zone
operators to enact sensible policies for the subset of Unicode they operators to enact sensible policies for the subset of Unicode they
wish to support, given their user community. A similar policy/ wish to support, given their user community. A similar policy/
protocol split may not be desirable in every protocol. protocol split may not be desirable in every protocol.
4.3. Where the data comes from and where it goes 5.3. Where the data comes from and where it goes
4.3.1. User input and the source of protocol elements 5.3.1. User input and the source of protocol elements
Some protocol elements are provided by users, and others are not. Some protocol elements are provided by users, and others are not.
Those that are not may presumably be subject to greater restrictions, Those that are not may presumably be subject to greater restrictions,
whereas those that users provide likely need to permit the broadest whereas those that users provide likely need to permit the broadest
range of code points. The following questions are helpful: range of code points. The following questions are helpful:
1. Do users input the strings directly? 1. Do users input the strings directly?
2. If so, how? (keyboard, stylus, voice, copy-paste, etc.) 2. If so, how? (keyboard, stylus, voice, copy-paste, etc.)
3. Where do we place the dividing line between user interface and 3. Where do we place the dividing line between user interface and
protocol? (see [RFC5895]) protocol? (see [RFC5895])
4.3.2. User output 5.3.2. User output
Just as only some protocol elements are expected to be entered Just as only some protocol elements are expected to be entered
directly by users, only some protocol elements are intended to be directly by users, only some protocol elements are intended to be
consumed directly by users. It is important to know how users are consumed directly by users. It is important to know how users are
expected to be able to consume the protocol elements, because expected to be able to consume the protocol elements, because
different environments present different challenges. An element that different environments present different challenges. An element that
is only ever delivered as part of a vCard remains in machine-readable is only ever delivered as part of a vCard remains in machine-readable
format, so the problem of visual confusion is not a great one. Is format, so the problem of visual confusion is not a great one. Is
the protocol element published as part of a vCard, a web directory, the protocol element published as part of a vCard, a web directory,
on a business card, or on "the side of a bus"? Do users use the on a business card, or on "the side of a bus"? Do users use the
protocol element as an identifier (which means that they might enter protocol element as an identifier (which means that they might enter
it again in some other context)? (See also Section 4.2.6.) it again in some other context)? (See also Section 5.2.6.)
4.3.3. Operations 5.3.3. Operations
Some strings are useful as part of the protocol but are not used as Some strings are useful as part of the protocol but are not used as
input to other operations (for instance, purely informative or input to other operations (for instance, purely informative or
descriptive text). Other strings are used directly as input to other descriptive text). Other strings are used directly as input to other
operations (such as cryptographic hash functions), or are used operations (such as cryptographic hash functions), or are used
together with other strings to (such as concatenating a string with together with other strings to (such as concatenating a string with
some others to form a unique identifier). some others to form a unique identifier).
4.3.3.1. String classes 5.3.3.1. String classes
Strings often have a similar function in different protocols. For Strings often have a similar function in different protocols. For
instance, many different protocols contain user identifiers or instance, many different protocols contain user identifiers or
passwords. A single profile for all such uses might be desirable. passwords. A single profile for all such uses might be desirable.
Often, a string in a protocol is effectively a protocol element from Often, a string in a protocol is effectively a protocol element from
another protocol. For instance, different systems might use the same another protocol. For instance, different systems might use the same
credentials database for authentication. credentials database for authentication.
4.3.3.2. Community Considerations 5.3.3.2. Community Considerations
A Stringprep replacement that does anything more than just update A Stringprep replacement that does anything more than just update
Stringprep to the latest version of Unicode will probably entail some Stringprep to the latest version of Unicode will probably entail some
changes. It is important to identify the willingness of the changes. It is important to identify the willingness of the
protocol-using community to accept backwards-incompatible changes. protocol-using community to accept backwards-incompatible changes.
By the same token, it is important to evaluate the desire of the By the same token, it is important to evaluate the desire of the
community for features not available under Stringprep. community for features not available under Stringprep.
4.3.3.3. Unicode Incompatible Changes 5.3.3.3. Unicode Incompatible Changes
IDNA2008 uses an algorithm to derive the validity of a Unicode code IDNA2008 uses an algorithm to derive the validity of a Unicode code
point for use under IDNA2008. It does this by using the properties point for use under IDNA2008. It does this by using the properties
of each code point to test its validity. of each code point to test its validity.
This approach depends crucially on the idea that code points, once This approach depends crucially on the idea that code points, once
valid for a protocol profile, will not later be made invalid. That valid for a protocol profile, will not later be made invalid. That
is not a guarantee currently provided by Unicode. Properties of code is not a guarantee currently provided by Unicode. Properties of code
points may change between versions of Unicode. Rarely, such a change points may change between versions of Unicode. Rarely, such a change
could cause a given code point to become invalid under a protocol could cause a given code point to become invalid under a protocol
profile, even though the code point would be valid with an earlier profile, even though the code point would be valid with an earlier
version of Unicode. This is not merely a theoretical possibility, version of Unicode. This is not merely a theoretical possibility,
because it has occurred ([RFC6452]). because it has occurred ([RFC6452]).
Accordingly, as in IDNA2008, a Stringprep replacement that intends to Accordingly, as in IDNA2008, a Stringprep replacement that intends to
be Unicode version agnostic will need to work out a mechanism to be Unicode version agnostic will need to work out a mechanism to
address cases where incompatible changes occur because of new Unicode address cases where incompatible changes occur because of new Unicode
versions. versions.
5. Considerations for Stringprep replacement 6. Considerations for Stringprep replacement
The above suggests the following guidance for replacing Stringprep: The above suggests the following guidance for replacing Stringprep:
o A stringprep replacement should be defined. o A stringprep replacement should be defined.
o The replacement should take an approach similar to IDNA2008, (e.g. o The replacement should take an approach similar to IDNA2008, (e.g.
by using codepoint properties instead of codepoint whitelisting) by using codepoint properties instead of codepoint whitelisting)
in that it enables better Unicode agility. in that it enables better Unicode agility.
o Protocols share similar characteristics of strings. Therefore, o Protocols share similar characteristics of strings. Therefore,
defining internationalization preparation algorithms for the defining internationalization preparation algorithms for the
smallest set of string classes may be sufficient for most cases, smallest set of string classes may be sufficient for most cases,
providing coherence among a set of related protocols or protocols providing coherence among a set of related protocols or protocols
where identifiers are exchanged. where identifiers are exchanged.
o The sets of string classes need to be evaluated according to the o The sets of string classes need to be evaluated according to the
considerations that make up the headings in Section 4 considerations that make up the headings in Section 5
o It is reasonable to limit scope to Unicode code points, and rule o It is reasonable to limit scope to Unicode code points, and rule
the mapping of data from other character encodings outside the the mapping of data from other character encodings outside the
scope of this effort. scope of this effort.
o The replacement ought at least to provide guidance to applications o The replacement ought at least to provide guidance to applications
using the replacement on how to handle protocol incompatibilities using the replacement on how to handle protocol incompatibilities
resulting from changes to Unicode. In an ideal world, the resulting from changes to Unicode. In an ideal world, the
stringprep replacement would handle the changes automatically, but stringprep replacement would handle the changes automatically, but
it appears that such automatic handling would require magic and it appears that such automatic handling would require magic and
cannot be expected. cannot be expected.
o Compatibility within each protocol between a technique that is o Compatibility within each protocol between a technique that is
skipping to change at page 13, line 45 skipping to change at page 14, line 5
strategy on existing deployments. By way of comparison, it is worth strategy on existing deployments. By way of comparison, it is worth
noting that some characters were acceptable in IDNA labels under noting that some characters were acceptable in IDNA labels under
IDNA2003, but are not protocol-valid under IDNA2008 (and conversely); IDNA2003, but are not protocol-valid under IDNA2008 (and conversely);
disagreement about what to do during the transition has resulted in disagreement about what to do during the transition has resulted in
different approaches to mapping. Different implementers may make different approaches to mapping. Different implementers may make
different decisions about what to do in such cases; this could have different decisions about what to do in such cases; this could have
interoperability effects. It is necessary to trade better support interoperability effects. It is necessary to trade better support
for different linguistic environments against the potential side for different linguistic environments against the potential side
effects of backward incompatibility. effects of backward incompatibility.
6. Security Considerations 7. Security Considerations
This document merely states what problems are to be solved, and does This document merely states what problems are to be solved, and does
not define a protocol. There are undoubtedly security implications not define a protocol. There are undoubtedly security implications
of the particular results that will come from the work to be of the particular results that will come from the work to be
completed. completed.
7. IANA Considerations 8. IANA Considerations
This document has no actions for IANA. This document has no actions for IANA.
8. Discussion home for this draft 9. Discussion home for this draft
Note: RFC-Editor, please remove this section before publication. Note: RFC-Editor, please remove this section before publication.
This document is intended to define the problem space discussed on This document is intended to define the problem space discussed on
the precis@ietf.org mailing list. the precis@ietf.org mailing list.
9. Acknowledgements 10. Acknowledgements
This document is the product of the PRECIS IETF Working Group, and This document is the product of the PRECIS IETF Working Group, and
participants in that Working Group were helpful in addressing issues participants in that Working Group were helpful in addressing issues
with the text. with the text.
Specific contributions came from David Black, Alan DeKok, Simon Specific contributions came from David Black, Alan DeKok, Simon
Josefsson, Bill McQuillan, Alexey Melnikov, Peter Saint-Andre, Dave Josefsson, Bill McQuillan, Alexey Melnikov, Peter Saint-Andre, Dave
Thaler, and Yoshiro Yoneya. Thaler, and Yoshiro Yoneya.
Dave Thaler provided the "buckets" insight in Section 4.1.1, central Dave Thaler provided the "buckets" insight in Section 5.1.1, central
to the organization of the problem. to the organization of the problem.
Evaluations of Stringprep profiles that are included in Appendix B Evaluations of Stringprep profiles that are included in Appendix B
were done by: David Black, Alexey Melnikov, Peter Saint-Andre, Dave were done by: David Black, Alexey Melnikov, Peter Saint-Andre, Dave
Thaler. Thaler.
10. Informative References 11. Informative References
[I-D.iab-identifier-comparison] [I-D.iab-identifier-comparison]
Thaler, D., "Issues in Identifier Comparison for Security Thaler, D., "Issues in Identifier Comparison for Security
Purposes", draft-iab-identifier-comparison-00 (work in Purposes", draft-iab-identifier-comparison-04 (work in
progress), July 2011. progress), August 2012.
[NEWPREP] "Newprep BoF Meeting Minutes", March 2010. [NEWPREP] "Newprep BoF Meeting Minutes", March 2010.
[RFC0952] Harrenstien, K., Stahl, M., and E. Feinler, "DoD Internet [RFC0952] Harrenstien, K., Stahl, M., and E. Feinler, "DoD Internet
host table specification", RFC 952, October 1985. host table specification", RFC 952, October 1985.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3454] Hoffman, P. and M. Blanchet, "Preparation of [RFC3454] Hoffman, P. and M. Blanchet, "Preparation of
Internationalized Strings ("stringprep")", RFC 3454, Internationalized Strings ("stringprep")", RFC 3454,
December 2002. December 2002.
[RFC3490] Faltstrom, P., Hoffman, P., and A. Costello, [RFC3490] Faltstrom, P., Hoffman, P., and A. Costello,
"Internationalizing Domain Names in Applications (IDNA)", "Internationalizing Domain Names in Applications (IDNA)",
RFC 3490, March 2003. RFC 3490, March 2003.
[RFC3491] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep [RFC3491] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep
Profile for Internationalized Domain Names (IDN)", Profile for Internationalized Domain Names (IDN)",
skipping to change at page 18, line 28 skipping to change at page 18, line 36
Blanchet, M., "PRECIS Framework", Proceedings of the Blanchet, M., "PRECIS Framework", Proceedings of the
Seventy-Eighth Internet Engineering Task Seventy-Eighth Internet Engineering Task
Force https://www.ietf.org/proceedings/78/, July 2010, Force https://www.ietf.org/proceedings/78/, July 2010,
<http://www.ietf.org/proceedings/78/slides/precis-2.pdf>. <http://www.ietf.org/proceedings/78/slides/precis-2.pdf>.
Appendix A. Classification of Stringprep Profiles Appendix A. Classification of Stringprep Profiles
A number of the known cases of Stringprep use were evaluated during A number of the known cases of Stringprep use were evaluated during
the preparation of this document. The known cases are here described the preparation of this document. The known cases are here described
in two ways. The types of identifiers the protocol uses is first in two ways. The types of identifiers the protocol uses is first
called out in the ID type column (from Section 4.1.1), using the called out in the ID type column (from Section 5.1.1), using the
short forms "a" for Absolute, "d" for Definite, and "i" for short forms "a" for Absolute, "d" for Definite, and "i" for
Indefinite. Next, there is a column that contains an "i" if the Indefinite. Next, there is a column that contains an "i" if the
protocol string comes from user input, an "o" if the protocol string protocol string comes from user input, an "o" if the protocol string
becomes user-facing output, "b" if both are true, and "n" if neither becomes user-facing output, "b" if both are true, and "n" if neither
is true. is true.
+------+--------+-------+ +------+--------+-------+
| RFC | IDtype | User? | | RFC | IDtype | User? |
+------+--------+-------+ +------+--------+-------+
| 3722 | a | b | | 3722 | a | b |
skipping to change at page 19, line 20 skipping to change at page 19, line 35
themselves. A template was used for reviewers to get a coherent view themselves. A template was used for reviewers to get a coherent view
of all evaluations. of all evaluations.
B.1. iSCSI Stringprep Profile: RFC3722 (and RFC3721, RFC3720) B.1. iSCSI Stringprep Profile: RFC3722 (and RFC3721, RFC3720)
Description: An iSCSI session consists of an initiator (i.e., host Description: An iSCSI session consists of an initiator (i.e., host
or server that uses storage) communicating with a target (i.e., a or server that uses storage) communicating with a target (i.e., a
storage array or other system that provides storage). Both the storage array or other system that provides storage). Both the
iSCSI initiator and target are named by iSCSI Names. The iSCSI iSCSI initiator and target are named by iSCSI Names. The iSCSI
stringprep profile is used for iSCSI names. stringprep profile is used for iSCSI names.
How it is used iSCSI initiators and targets (see above). They can How it is used: iSCSI initiators and targets (see above). They can
also be used to identify SCSI ports (these are software entities also be used to identify SCSI ports (these are software entities
in the iSCSI protocol, not hardware ports), and iSCSI logical in the iSCSI protocol, not hardware ports), and iSCSI logical
units (storage volumes), although both are unusual in practice. units (storage volumes), although both are unusual in practice.
What entities create these identifiers? Generally a Human user (1) What entities create these identifiers? Generally a Human user (1)
configures an Automated system (2) that generates the names. configures an Automated system (2) that generates the names.
Advance configuration of the system is required due to the Advance configuration of the system is required due to the
embedded use of external unique identifier (from the DNS or IEEE). embedded use of external unique identifier (from the DNS or IEEE).
How is the string input in the system? Keyboard and copy-paste are How is the string input in the system? Keyboard and copy-paste are
common. Copy-paste is common because iSCSI names are long enough common. Copy-paste is common because iSCSI names are long enough
to be problematic for humans to remember, causing use of email, to be problematic for humans to remember, causing use of email,
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Internal Structure: None Internal Structure: None
User Output: Unlikely, but possible. For example, if it is the same User Output: Unlikely, but possible. For example, if it is the same
as an email address. as an email address.
Operations: - Sometimes concatenated with other data and then used Operations: - Sometimes concatenated with other data and then used
as input to a cryptographic hash function as input to a cryptographic hash function
How much tolerance for change from existing stringprep approach? Not How much tolerance for change from existing stringprep approach? Not
sure. sure.
Background information: In RFC 5034, when describing the POP3 AUTH Background information: In RFC 5034, when describing the POP3 AUTH
command: The authorization identity generated by the SASL exchange command: The authorization identity generated by the SASL exchange
is a simple username, and SHOULD use the SASLprep profile (see is a simple username, and SHOULD use the SASLprep profile (see
[RFC4013]) of the StringPrep algorithm (see [RFC3454]) to prepare RFC4013) of the StringPrep algorithm (see RFC3454) to prepare
these names for matching. If preparation of the authorization these names for matching. If preparation of the authorization
identity fails or results in an empty string (unless it was identity fails or results in an empty string (unless it was
transmitted as the empty string), the server MUST fail the transmitted as the empty string), the server MUST fail the
authentication. In RFC 4954, when describing the SMTP AUTH authentication. In RFC 4954, when describing the SMTP AUTH
command: The authorization identity generated by this [SASL] command: The authorization identity generated by this SASL
exchange is a "simple username" (in the sense defined in exchange is a "simple username" (in the sense defined in
[SASLprep]), and both client and server SHOULD (*) use the SASLprep), and both client and server SHOULD (*) use the SASLprep
[SASLprep] profile of the [StringPrep] algorithm to prepare these profile of the StringPrep algorithm to prepare these names for
names for transmission or comparison. If preparation of the transmission or comparison. If preparation of the authorization
authorization identity fails or results in an empty string (unless identity fails or results in an empty string (unless it was
it was transmitted as the empty string), the server MUST fail the transmitted as the empty string), the server MUST fail the
authentication. (*) Note: Future revision of this specification authentication. (*) Note: Future revision of this specification
may change this requirement to MUST. Currently, the SHOULD is may change this requirement to MUST. Currently, the SHOULD is
used in order to avoid breaking the majority of existing used in order to avoid breaking the majority of existing
implementations. In RFC 5804, when describing the ManageSieve implementations. In RFC 5804, when describing the ManageSieve
AUTHENTICATE command: The authorization identity generated by this AUTHENTICATE command: The authorization identity generated by this
[SASL] exchange is a "simple username" (in the sense defined in SASL exchange is a "simple username" (in the sense defined in
[SASLprep]), and both client and server MUST use the [SASLprep] SASLprep), and both client and server MUST use the SASLprep
profile of the [StringPrep] algorithm to prepare these names for profile of the StringPrep algorithm to prepare these names for
transmission or comparison. If preparation of the authorization transmission or comparison. If preparation of the authorization
identity fails or results in an empty string (unless it was identity fails or results in an empty string (unless it was
transmitted as the empty string), the server MUST fail the transmitted as the empty string), the server MUST fail the
authentication. authentication.
B.3. IMAP Stringprep Profiles: RFC5738, RFC4314: Usernames B.3. IMAP Stringprep Profiles: RFC5738, RFC4314: Usernames
Evaluation Note These documents have 2 types of strings (usernames Evaluation Note These documents have 2 types of strings (usernames
and passwords), so there are two separate templates. and passwords), so there are two separate templates.
Description: "username" parameter to the IMAP LOGIN command, Description: "username" parameter to the IMAP LOGIN command,
skipping to change at page 24, line 36 skipping to change at page 25, line 4
Internal Structure: None Internal Structure: None
User Output: - text of email messages (e.g. in "you forgot your User Output: - text of email messages (e.g. in "you forgot your
password" email messages) - web page / directory - side of the bus password" email messages) - web page / directory - side of the bus
/ in ads -- possible / in ads -- possible
Operations: Sometimes concatenated with other data and then used as Operations: Sometimes concatenated with other data and then used as
input to a cryptographic hash function. Frequently stored as is, input to a cryptographic hash function. Frequently stored as is,
or hashed. or hashed.
How much tolerance for change from existing stringprep approach? Not How much tolerance for change from existing stringprep approach? Not
sure. Non-ASCII IMAP passwords are currently prohibited by IMAP sure. Non-ASCII IMAP passwords are currently prohibited by IMAP
(RFC 3501), however they are likely to be in widespread use. (RFC 3501), however they are likely to be in widespread use.
Background information: RFC 5738 (IMAP INTERNATIONALIZATION): 5. Background information: RFC 5738 (IMAP INTERNATIONALIZATION): 5.
UTF8=USER Capability If the "UTF8=USER" capability is advertised, UTF8=USER Capability If the "UTF8=USER" capability is advertised,
that indicates the server accepts UTF-8 user names and passwords that indicates the server accepts UTF-8 user names and passwords
and applies SASLprep [RFC4013] to both arguments of the LOGIN and applies SASLprep RFC4013 to both arguments of the LOGIN
command. The server MUST reject UTF-8 that fails to comply with command. The server MUST reject UTF-8 that fails to comply with
the formal syntax in RFC 3629 [RFC3629] or if it encounters the formal syntax in RFC 3629 RFC3629 or if it encounters Unicode
Unicode characters listed in Section 2.3 of SASLprep RFC 4013 characters listed in Section 2.3 of SASLprep RFC 4013 RFC4013.
[RFC4013]. RFC 4314 (IMAP4 Access Control List (ACL) Extension): RFC 4314 (IMAP4 Access Control List (ACL) Extension): 3. Access
3. Access control management commands and responses Servers, when control management commands and responses Servers, when processing
processing a command that has an identifier as a parameter (i.e., a command that has an identifier as a parameter (i.e., any of
any of SETACL, DELETEACL, and LISTRIGHTS commands), SHOULD first SETACL, DELETEACL, and LISTRIGHTS commands), SHOULD first prepare
prepare the received identifier using "SASLprep" profile the received identifier using "SASLprep" profile SASLprep of the
[SASLprep] of the "stringprep" algorithm [Stringprep]. If the "stringprep" algorithm Stringprep. If the preparation of the
preparation of the identifier fails or results in an empty string, identifier fails or results in an empty string, the server MUST
the server MUST refuse to perform the command with a BAD response. refuse to perform the command with a BAD response. Note that
Note that Section 6 recommends additional identifier's Section 6 recommends additional identifier's verification steps.
verification steps. and in Section 6: This document relies on and in Section 6: This document relies on SASLprep to describe
steps required to perform identifier canonicalization
[SASLprep] to describe steps required to perform identifier (preparation). The preparation algorithm in SASLprep was
canonicalization (preparation). The preparation algorithm in specifically designed such that its output is canonical, and it is
SASLprep was specifically designed such that its output is well-formed. However, due to an anomaly PR29 in the specification
canonical, and it is well-formed. However, due to an anomaly of Unicode normalization, canonical equivalence is not guaranteed
[PR29] in the specification of Unicode normalization, canonical for a select few character sequences. Identifiers prepared with
equivalence is not guaranteed for a select few character SASLprep can be stored and returned by an ACL server. The anomaly
sequences. Identifiers prepared with SASLprep can be stored and affects ACL manipulation and evaluation of identifiers containing
returned by an ACL server. The anomaly affects ACL manipulation the selected character sequences. These sequences, however, do
and evaluation of identifiers containing the selected character not appear in well-formed text. In order to address this problem,
sequences. These sequences, however, do not appear in well-formed an ACL server MAY reject identifiers containing sequences
text. In order to address this problem, an ACL server MAY reject described in PR29 by sending the tagged BAD response. This is in
identifiers containing sequences described in [PR29] by sending addition to the requirement to reject identifiers that fail
the tagged BAD response. This is in addition to the requirement SASLprep preparation as described in Section 3.
to reject identifiers that fail SASLprep preparation as described
in Section 3.
B.5. Anonymous SASL Stringprep Profiles: RFC4505 B.5. Anonymous SASL Stringprep Profiles: RFC4505
Description: RFC 4505 defines a "trace" field: Description: RFC 4505 defines a "trace" field:
Comparison: this field is not intended for comparison (only used for Comparison: this field is not intended for comparison (only used for
logging) logging)
Case folding; case sensitivity, preserve case: No case folding/case Case folding; case sensitivity, preserve case: No case folding/case
sensitive sensitive
Do users input the strings directly? Yes. Possibly entered in Do users input the strings directly? Yes. Possibly entered in
configuration UIs, or on a command line. Can also be stored in configuration UIs, or on a command line. Can also be stored in
skipping to change at page 26, line 18 skipping to change at page 26, line 35
user can be confused with another user. False negative: two user can be confused with another user. False negative: two
distinct users are treated as the same user. But note that the distinct users are treated as the same user. But note that the
trace field is not authenticated, so it can be easily falsified. trace field is not authenticated, so it can be easily falsified.
Tolerance of changes in the community The community would be Tolerance of changes in the community The community would be
flexible. flexible.
Delimiters No internal structure, but see comments above about Delimiters No internal structure, but see comments above about
frequent use of email addresses. frequent use of email addresses.
Background information: The Anonymous Mechanism The mechanism Background information: The Anonymous Mechanism The mechanism
consists of a single message from the client to the server. The consists of a single message from the client to the server. The
client may include in this message trace information in the form client may include in this message trace information in the form
of a string of [UTF-8]-encoded [Unicode] characters prepared in of a string of UTF-8-encoded Unicode characters prepared in
accordance with [StringPrep] and the "trace" stringprep profile accordance with StringPrep and the "trace" stringprep profile
defined in Section 3 of this document. The trace information, defined in Section 3 of this document. The trace information,
which has no semantical value, should take one of two forms: an which has no semantical value, should take one of two forms: an
Internet email address, or an opaque string that does not contain Internet email address, or an opaque string that does not contain
the '@' (U+0040) character and that can be interpreted by the the '@' (U+0040) character and that can be interpreted by the
system administrator of the client's domain. For privacy reasons, system administrator of the client's domain. For privacy reasons,
an Internet email address or other information identifying the an Internet email address or other information identifying the
user should only be used with permission from the user. 3. The user should only be used with permission from the user. 3. The
"trace" Profile of "Stringprep" This section defines the "trace" "trace" Profile of "Stringprep" This section defines the "trace"
profile of [StringPrep]. This profile is designed for use with profile of StringPrep. This profile is designed for use with the
the SASL ANONYMOUS Mechanism. Specifically, the client is to SASL ANONYMOUS Mechanism. Specifically, the client is to prepare
prepare the message production in accordance with this profile. the message production in accordance with this profile. The
The character repertoire of this profile is Unicode 3.2 [Unicode]. character repertoire of this profile is Unicode 3.2. No mapping
No mapping is required by this profile. No Unicode normalization is required by this profile. No Unicode normalization is required
is required by this profile. The list of unassigned code points by this profile. The list of unassigned code points for this
for this profile is that provided in Appendix A of [StringPrep]. profile is that provided in Appendix A of StringPrep. Unassigned
Unassigned code points are not prohibited. Characters from the code points are not prohibited. Characters from the following
following tables of [StringPrep] are prohibited: - C.2.1 (ASCII tables of StringPrep are prohibited: - C.2.1 (ASCII control
control characters) - C.2.2 (Non-ASCII control characters) - C.3 characters) - C.2.2 (Non-ASCII control characters) - C.3 (Private
(Private use characters) - C.4 (Non-character code points) - C.5 use characters) - C.4 (Non-character code points) - C.5 (Surrogate
(Surrogate codes) - C.6 (Inappropriate for plain text) - C.8 codes) - C.6 (Inappropriate for plain text) - C.8 (Change display
(Change display properties are deprecated) - C.9 (Tagging properties are deprecated) - C.9 (Tagging characters) No
characters) No additional characters are prohibited. This profile additional characters are prohibited. This profile requires
requires bidirectional character checking per Section 6 of bidirectional character checking per Section 6 of StringPrep.
[StringPrep].
B.6. XMPP Stringprep Profiles: RFC3920 Nodeprep B.6. XMPP Stringprep Profiles: RFC3920 Nodeprep
Description: Localpart of JabberID ("JID"), as in: Description: Localpart of JabberID ("JID"), as in:
localpart@domainpart/resourcepart localpart@domainpart/resourcepart
How It's Used: - Usernames (e.g., stpeter@jabber.org) - Chatroom How It's Used: - Usernames (e.g., stpeter@jabber.org) - Chatroom
names (e.g., precis@jabber.ietf.org) - Publish-subscribe nodes - names (e.g., precis@jabber.ietf.org) - Publish-subscribe nodes -
Bot names Bot names
Who Generates It: - Typically, end users via an XMPP client - Who Generates It: - Typically, end users via an XMPP client -
Sometimes created in an automated fashion Sometimes created in an automated fashion
User Input Methods: - Typed by user - Copy-and-paste - Perhaps voice User Input Methods: - Typed by user - Copy-and-paste - Perhaps voice
input - Clicking a URI/IRI input - Clicking a URI/IRI
Enforcement: - Rules enforced by server / add-on service (e.g., Enforcement: - Rules enforced by server / add-on service (e.g.,
chatroom service) on registration of account, creation of room, chatroom service) on registration of account, creation of room,
etc. etc.
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