draft-ietf-precis-problem-statement-05.txt   draft-ietf-precis-problem-statement-06.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: September 13, 2012 Dyn, Inc. Expires: January 10, 2013 Dyn, Inc.
March 12, 2012 July 9, 2012
Stringprep Revision Problem Statement Stringprep Revision and PRECIS Problem Statement
draft-ietf-precis-problem-statement-05.txt draft-ietf-precis-problem-statement-06.txt
Abstract Abstract
Using Unicode codepoints in protocol strings that expect comparison If a protocol expects to compare two strings and is prepared only for
with other strings requires preparation of the string that contains those strings to be ASCII, then using Unicode codepoints in those
the Unicode codepoints. Internationalizing Domain Names in string requires they be prepared somehow. Internationalizing Domain
Applications (IDNA2003) defined and used Stringprep and Nameprep. Names in Applications (here called IDNA2003) defined and used
Other protocols subsequently defined Stringprep profiles. A new Stringprep and Nameprep. Other protocols subsequently defined
approach different from Stringprep and Nameprep is used for a Stringprep profiles. A new approach different from Stringprep and
revision of IDNA2003 (called IDNA2008). Other Stringprep profiles Nameprep is used for a revision of IDNA2003 (called IDNA2008). Other
need to be similarly updated or a replacement of Stringprep needs to Stringprep profiles need to be similarly updated or a replacement of
be designed. This document outlines the issues to be faced by those Stringprep needs to be designed. This document outlines the issues
designing a Stringprep replacement. to be faced by those designing a Stringprep replacement.
Status of this Memo Status of this Memo
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Stringprep Profiles Limitations . . . . . . . . . . . . . . . 5 3. Stringprep Profiles Limitations . . . . . . . . . . . . . . . 8
4. Major Topics for Consideration . . . . . . . . . . . . . . . . 6 4. Major Topics for Consideration . . . . . . . . . . . . . . . . 10
4.1. Comparison . . . . . . . . . . . . . . . . . . . . . . . . 6 4.1. Comparison . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1.1. Types of Identifiers . . . . . . . . . . . . . . . . . 6 4.1.1. Types of Identifiers . . . . . . . . . . . . . . . . . 10
4.1.2. Effect of comparison . . . . . . . . . . . . . . . . . 7 4.1.2. Effect of comparison . . . . . . . . . . . . . . . . . 10
4.2. Dealing with characters . . . . . . . . . . . . . . . . . 7 4.2. Dealing with characters . . . . . . . . . . . . . . . . . 10
4.2.1. Case folding, case sensitivity, and case 4.2.1. Case folding, case sensitivity, and case
preservation . . . . . . . . . . . . . . . . . . . . . 7 preservation . . . . . . . . . . . . . . . . . . . . . 11
4.2.2. Stringprep and NFKC . . . . . . . . . . . . . . . . . 8 4.2.2. Stringprep and NFKC . . . . . . . . . . . . . . . . . 11
4.2.3. Character mapping . . . . . . . . . . . . . . . . . . 8 4.2.3. Character mapping . . . . . . . . . . . . . . . . . . 11
4.2.4. Prohibited characters . . . . . . . . . . . . . . . . 8 4.2.4. Prohibited characters . . . . . . . . . . . . . . . . 12
4.2.5. Internal structure, delimiters, and special 4.2.5. Internal structure, delimiters, and special
characters . . . . . . . . . . . . . . . . . . . . . . 9 characters . . . . . . . . . . . . . . . . . . . . . . 12
4.2.6. Restrictions because of glyph similarity . . . . . . . 10 4.2.6. Restrictions because of glyph similarity . . . . . . . 13
4.3. Where the data comes from and where it goes . . . . . . . 10 4.3. Where the data comes from and where it goes . . . . . . . 13
4.3.1. User input and the source of protocol elements . . . . 10 4.3.1. User input and the source of protocol elements . . . . 13
4.3.2. User output . . . . . . . . . . . . . . . . . . . . . 10 4.3.2. User output . . . . . . . . . . . . . . . . . . . . . 13
4.3.3. Operations . . . . . . . . . . . . . . . . . . . . . . 10 4.3.3. Operations . . . . . . . . . . . . . . . . . . . . . . 14
4.3.4. Some useful classes of strings . . . . . . . . . . . . 11 5. Considerations for Stringprep replacement . . . . . . . . . . 16
5. Considerations for Stringprep replacement . . . . . . . . . . 12 6. Security Considerations . . . . . . . . . . . . . . . . . . . 17
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 8. Discussion home for this draft . . . . . . . . . . . . . . . . 19
8. Discussion home for this draft . . . . . . . . . . . . . . . . 13 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 10. Informative References . . . . . . . . . . . . . . . . . . . . 21
10. Informative References . . . . . . . . . . . . . . . . . . . . 13 Appendix A. Classification of Stringprep Profiles . . . . . . . . 25
Appendix A. Classification of Stringprep Profiles . . . . . . . . 17 Appendix B. Evaluation of Stringprep Profiles . . . . . . . . . . 26
Appendix B. Evaluation of Stringprep Profiles . . . . . . . . . . 18 B.1. iSCSI Stringprep Profiles: RFC3722, RFC3721, RFC3720 . . . 26
B.1. iSCSI Stringprep Profiles: RFC3722, RFC3721, RFC3720 . . . 18
B.2. SMTP/POP3/ManageSieve Stringprep Profiles: B.2. SMTP/POP3/ManageSieve Stringprep Profiles:
RFC4954,RFC5034,RFC 5804 . . . . . . . . . . . . . . . . . 20 RFC4954,RFC5034,RFC 5804 . . . . . . . . . . . . . . . . . 28
B.3. IMAP Stringprep Profiles: RFC5738, RFC4314: Usernames . . 21 B.3. IMAP Stringprep Profiles: RFC5738, RFC4314: Usernames . . 30
B.4. IMAP Stringprep Profiles: RFC5738: Passwords . . . . . . . 23 B.4. IMAP Stringprep Profiles: RFC5738: Passwords . . . . . . . 31
B.5. Anonymous SASL Stringprep Profiles: RFC4505 . . . . . . . 24 B.5. Anonymous SASL Stringprep Profiles: RFC4505 . . . . . . . 33
B.6. XMPP Stringprep Profiles: RFC3920 Nodeprep . . . . . . . . 26 B.6. XMPP Stringprep Profiles: RFC3920 Nodeprep . . . . . . . . 35
B.7. XMPP Stringprep Profiles: RFC3920 Resourceprep . . . . . . 27 B.7. XMPP Stringprep Profiles: RFC3920 Resourceprep . . . . . . 36
B.8. EAP Stringprep Profiles: RFC3748 . . . . . . . . . . . . . 27 B.8. EAP Stringprep Profiles: RFC3748 . . . . . . . . . . . . . 37
Appendix C. Changes between versions . . . . . . . . . . . . . . 28 Appendix C. Changes between versions . . . . . . . . . . . . . . 39
C.1. 00 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 C.1. 00 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
C.2. 01 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 C.2. 01 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
C.3. 02 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 C.3. 02 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
C.4. 03 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 C.4. 03 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
C.5. 04 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 C.5. 04 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
C.6. 05 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 C.6. 05 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29 C.7. 06 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 41
1. Introduction 1. Introduction
Internationalizing Domain Names in Applications (IDNA2003) [RFC3490], Internationalizing Domain Names in Applications (here called
[RFC3491], [RFC3492], [RFC3454] describes a mechanism for encoding IDNA2003) [RFC3490], [RFC3491], [RFC3492], [RFC3454] describes a
Unicode labels making up Internationalized Domain Names (IDNs) as mechanism for encoding Unicode labels making up Internationalized
standard DNS labels. The labels were processed using a method called Domain Names (IDNs) as standard DNS labels. The labels were
Nameprep [RFC3491] and Punycode [RFC3492]. That method was specific processed using a method called Nameprep [RFC3491] and Punycode
to IDNA2003, but is generalized as Stringprep [RFC3454]. The general [RFC3492]. That method was specific to IDNA2003, but is generalized
mechanism is used by other protocols with similar needs, but with as Stringprep [RFC3454]. The general mechanism is used by other
different constraints than IDNA2003. protocols with similar needs, but with different constraints than
IDNA2003.
Stringprep defines a framework within which protocols define their Stringprep defines a framework within which protocols define their
Stringprep profiles. Known IETF specifications using Stringprep are Stringprep profiles. Known IETF specifications using Stringprep are
listed below: listed below:
o The Nameprep profile [RFC3490] for use in Internationalized Domain o The Nameprep profile [RFC3490] for use in Internationalized Domain
Names (IDNs); Names (IDNs);
o NFSv4 [RFC3530] and NFSv4.1 [RFC5661]; o NFSv4 [RFC3530] and NFSv4.1 [RFC5661];
o The iSCSI profile [RFC3722] for use in Internet Small Computer o The iSCSI profile [RFC3722] for use in Internet Small Computer
Systems Interface (iSCSI) Names; Systems Interface (iSCSI) Names;
o EAP [RFC3748]; o EAP [RFC3748];
o The Nodeprep and Resourceprep profiles [RFC3920] for use in the o The Nodeprep and Resourceprep profiles [RFC3920] for use in the
Extensible Messaging and Presence Protocol (XMPP), and the XMPP to Extensible Messaging and Presence Protocol (XMPP), and the XMPP to
CPIM mapping [RFC3922] (the latter of these relies on the former); CPIM mapping [RFC3922] (the latter of these relies on the former);
o The Policy MIB profile [RFC4011] for use in the Simple Network o The Policy MIB profile [RFC4011] for use in the Simple Network
Management Protocol (SNMP); Management Protocol (SNMP);
o The SASLprep profile [RFC4013] for use in the Simple o The SASLprep profile [RFC4013] for use in the Simple
Authentication and Security Layer (SASL), and SASL itself Authentication and Security Layer (SASL), and SASL itself
[RFC4422]; [RFC4422];
o TLS [RFC4279]; o TLS [RFC4279];
o IMAP4 using SASLprep [RFC4314]; o IMAP4 using SASLprep [RFC4314];
o The trace profile [RFC4505] for use with the SASL ANONYMOUS o The trace profile [RFC4505] for use with the SASL ANONYMOUS
mechanism; mechanism;
o The LDAP profile [RFC4518] for use with LDAP [RFC4511] and its o The LDAP profile [RFC4518] for use with LDAP [RFC4511] and its
authentication methods [RFC4513]; authentication methods [RFC4513];
o Plain SASL using SASLprep [RFC4616]; o Plain SASL using SASLprep [RFC4616];
o NNTP using SASLprep [RFC4643]; o NNTP using SASLprep [RFC4643];
o PKIX subject identification using LDAPprep [RFC4683]; o PKIX subject identification using LDAPprep [RFC4683];
o Internet Application Protocol Collation Registry [RFC4790]; o Internet Application Protocol Collation Registry [RFC4790];
o SMTP Auth using SASLprep [RFC4954]; o SMTP Auth using SASLprep [RFC4954];
o POP3 Auth using SASLprep [RFC5034]; o POP3 Auth using SASLprep [RFC5034];
o TLS SRP using SASLprep [RFC5054]; o TLS SRP using SASLprep [RFC5054];
o IRI and URI in XMPP [RFC5122]; o IRI and URI in XMPP [RFC5122];
o PKIX CRL using LDAPprep [RFC5280]; o PKIX CRL using LDAPprep [RFC5280];
o IAX using Nameprep [RFC5456]; o IAX using Nameprep [RFC5456];
o SASL SCRAM using SASLprep [RFC5802]; o SASL SCRAM using SASLprep [RFC5802];
o Remote management of Sieve using SASLprep [RFC5804]; o Remote management of Sieve using SASLprep [RFC5804];
o The unicode-casemap Unicode Collation [RFC5051]. o The unicode-casemap Unicode Collation [RFC5051].
However, a review [1] of these protocol specifications found that However, a review (see [ietf78precis]) of these protocol
they are very similar and can be grouped into a short number of specifications found that they are very similar and can be grouped
classes. Moreover, many reuse the same Stringprep profile, such as into a short number of classes. Moreover, many reuse the same
the SASL one. Stringprep profile, such as the SASL one.
IDNA2003 was replaced because of some limitations described in IDNA2003 was replaced because of some limitations described in
[RFC4690]. The new IDN specification, called IDNA2008 [RFC5890], [RFC4690]. The new IDN specification, called IDNA2008 [RFC5890],
[RFC5891], [RFC5892], [RFC5893] was designed based on the [RFC5891], [RFC5892], [RFC5893] was designed based on the
considerations found in [RFC5894]. One of the effects of IDNA2008 is considerations found in [RFC5894]. One of the effects of IDNA2008 is
that Nameprep and Stringprep are not used at all. Instead, an that Nameprep and Stringprep are not used at all. Instead, an
algorithm based on Unicode properties of codepoints is defined. That algorithm based on Unicode properties of codepoints is defined. That
algorithm generates a stable and complete table of the supported algorithm generates a stable and complete table of the supported
Unicode codepoints for each Unicode version. This algorithm is based Unicode codepoints for each Unicode version. This algorithm is based
on an inclusion-based approach, instead of the exclusion-based on an inclusion-based approach, instead of the exclusion-based
approach of Stringprep/Nameprep. approach of Stringprep/Nameprep. That is, IDNA2003 created an
explicit list of excluded or mapped-away characters; anything in
Unicode 3.2 that was not so listed could be assumed to be allowed
under the protocol. IDNA2008 begins instead from the assumption that
code points are disallowed, and then relies on Unicode properties to
derive whether a given code point actually is allowed in the
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. Conventions
This document uses the Unicode convention [2] to specify Unicode A single Unicode code point in this memo is denoted by "U+" followed
codepoint with the following syntax: U+ABCD where ABCD is the by four to six hexadecimal digits. Compare to [Unicode61], Appendix
codepoint in hexadecimal. A.
3. Stringprep Profiles Limitations 3. Stringprep Profiles Limitations
During IETF 77, a BOF [3] discussed the current state of the During IETF 77, a BOF discussed the current state of the protocols
protocols that have defined Stringprep profiles [NEWPREP]. The main 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 to Unicode 3.2. using Stringprep are stuck to Unicode 3.2.
o The protocols need to be updated to support new versions of o The protocols need to be updated to support new versions of
Unicode. The protocols would like to not be bound to a specific Unicode. The protocols would like to not be bound to a specific
version of Unicode, but rather have better Unicode agility in the version of Unicode, but rather have better Unicode agility in the
way of IDNA2008. This is important partly because it is usually way 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
requirement. For example, Stringprep is based on and profiles may requirement. For example, Stringprep is based on and profiles may
use NFKC [UAX15], while IDNA2008 mostly uses NFC [UAX15]. use NFKC [UAX15], while IDNA2008 mostly uses NFC [UAX15].
o Identifiers are passed between protocols. For example, the same o Identifiers are passed between protocols. For example, the same
username string of codepoints may be passed between SASL, XMPP, username string of codepoints may be passed between SASL, XMPP,
LDAP and EAP. Therefore, common set of rules or classes of LDAP and EAP. Therefore, common set of rules or classes of
strings are preferred over specific rules for each protocol. strings are preferred over specific rules for each protocol.
Without real planning in advance, many stringprep profiles reuse Without real planning in advance, many stringprep profiles reuse
other profiles, so this goal was accomplished by accident with other profiles, so this goal was accomplished by accident with
Stringprep. Stringprep.
Protocols that use Stringprep profiles use strings for different Protocols that use Stringprep profiles use strings for different
purposes: purposes:
skipping to change at page 6, line 19 skipping to change at page 8, line 41
o Identifiers are passed between protocols. For example, the same o Identifiers are passed between protocols. For example, the same
username string of codepoints may be passed between SASL, XMPP, username string of codepoints may be passed between SASL, XMPP,
LDAP and EAP. Therefore, common set of rules or classes of LDAP and EAP. Therefore, common set of rules or classes of
strings are preferred over specific rules for each protocol. strings are preferred over specific rules for each protocol.
Without real planning in advance, many stringprep profiles reuse Without real planning in advance, many stringprep profiles reuse
other profiles, so this goal was accomplished by accident with other profiles, so this goal was accomplished by accident with
Stringprep. Stringprep.
Protocols that use Stringprep profiles use strings for different Protocols that use Stringprep profiles use strings for different
purposes: purposes:
o XMPP uses a different Stringprep profile for each part of the XMPP o XMPP uses a different Stringprep profile for each part of the XMPP
address (JID): a localpart which is similar to a username and used address (JID): a localpart which is similar to a username and used
for authentication, a domainpart which is a domain name and a for authentication, a domainpart which is a domain name and a
resource part which is less restrictive than the localpart. resource part which is less restrictive than the localpart.
o iSCSI uses a Stringprep profile for the IQN, which is very similar o iSCSI uses a Stringprep profile for the IQN, which is very similar
to (often is) a DNS domain name. to (often is) a DNS domain name.
o SASL and LDAP uses a Stringprep profile for usernames. o SASL and LDAP uses a Stringprep profile for usernames.
o LDAP uses a set of Stringprep profiles. o LDAP uses a set of Stringprep profiles.
The consensus [4] of the BOF attendees is that it would be highly The apparent judgement of the BOF attendees [NEWPREP] was that it
desirable to have a replacement of Stringprep, with similar would be highly desirable to have a replacement of Stringprep, with
characteristics to IDNA2008. That replacement should be defined so similar characteristics to IDNA2008. That replacement should be
that the protocols could use internationalized strings without a lot defined so that the protocols could use internationalized strings
of specialized internationalization work, since internationalization without a lot of specialized internationalization work, since
expertise is not available in the respective protocols or working internationalization expertise is not available in the respective
groups. protocols or working groups. Accordingly, the IESG formed the PRECIS
working group to undertake the task.
Notwithstanding the desire evident in [NEWPREP] and the chartering of
a working group, IDNA2008 may be a poor model for what other
protocols ought to do, because it is designed to support an old
protocol that is designed to operate on the scale of the entire
Internet. Moreover, IDNA2008 is intended to be deployed without any
change to the base DNS protocol. Other protocols may aim at
deployment in more local environments, or may have protocol version
negotiation built in.
4. Major Topics for Consideration 4. 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 4.1. Comparison
skipping to change at page 8, line 17 skipping to change at page 11, line 34
4.2.2. Stringprep and NFKC 4.2.2. 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." For things like the spelling of users' always be appropriate." In general, it can be said that NFKC is more
names, then, NFKC may not be the best form to use. At the same time, aggressive about finding matches between codepoints than NFC. For
one of the nice things about NFKC is that it deals with the width of things like the spelling of users' names, then, NFKC may not be the
characters that are otherwise similar, by canonicalizing half-width best form to use. At the same time, one of the nice things about
to full-width. This mapping step can be crucial in practice. A NFKC is that it deals with the width of characters that are otherwise
replacement for stringprep depends on analyzing the different use similar, by canonicalizing half-width to full-width. This mapping
profiles and considering whether NFKC or NFC is a better step can be crucial in practice. A replacement for stringprep
normalization for each profile. depends on analyzing the different use profiles and considering
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 4.2.3. 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 4.2.1, 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 4.2.4. 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. IDNA2003 created an explicit list of excluded Unicode code points, using the new inclusion-based approach (see
or mapped-away characters; anything in Unicode 3.2 that was not so Section 1).
listed could be assumed to be allowed under the protocol. IDNA2008
begins instead from the assumption that code points are disallowed,
and then relies on Unicode properties to derive whether a given code
point actually is allowed in the protocol.
Moreover, there is more than one class of "allowed in the protocol" Because of the default assumption in IDNA2008 that a code point is
in IDNA2008 (but not in IDNA2003). While some code points are not allowed by the protocol, it has more than one class of "allowed
disallowed outright, some are allowed only in certain contexts. The by the protocol"; this is unlike IDNA2003. While some code points
reasons for the context-dependent rules have to do with the way some are disallowed outright, some are allowed only in certain contexts.
characters are used. For instance, the ZERO WIDTH JOINER and ZERO The reasons for the context-dependent rules have to do with the way
WIDTH NON-JOINER (ZWJ, U+200D and ZWNJ, U+200C) are allowed with some characters are used. For instance, the ZERO WIDTH JOINER and
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 rule, trusting to the and consistent with the traditional DNS "LDH" (letters, digits,
operators of individual zones to make sensible (and usually more hyphen; see [RFC0952]) rule, trusting to the operators of individual
restrictive) policies for their zones. zones to make sensible (and usually more restrictive) policies for
their zones.
IDNA2008 may be a poor model for what other protocols ought to do in
this case, because it is designed to support an old protocol that is
designed to operate on the scale of the entire Internet. Moreover,
IDNA2008 is intended to be deployed without any change to the base
DNS protocol. Other protocols may aim at deployment in more local
environments, or may have protocol version negotiation built in.
4.2.5. Internal structure, delimiters, and special characters 4.2.5. 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
skipping to change at page 11, line 39 skipping to change at page 14, line 51
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 IDNA2008,a Stringprep replacement that intends to be Accordingly, as in IDNA2008, a Stringprep replacement that intends to
Unicode version agnostic will need to work out a mechanism to address be Unicode version agnostic will need to work out a mechanism to
cases where incompatible changes occur because of new Unicode address cases where incompatible changes occur because of new Unicode
versions. versions.
4.3.4. Some useful classes of strings
With the above considerations in hand, we can usefully classify
strings into the following categories:
DomainClass Strings that are intended for use in a domain name slot,
as defined in [RFC5890]. Note that strings of DomainClass could
be used outside a domain name slot: the question here is what the
eventual intended use for the string is, and not whether the
string is actually functioning as a domain name at any moment.
NameClass Strings that are intended for use as identifiers but that
are not DomainClass strings. NameClass strings are normally
public data within the protocol where they are used: these are
intended as identifiers that can be passed around to identify
something.
FreeClass Strings that are intended to be used by the protocol as
free-form strings, but that have some significant handling within
the protocol. This includes things that are normally not public
data in a protocol (like passwords), and things that might have
additional restrictions within the protocol in question, such as a
friendly name in a chat room.
5. Considerations for Stringprep replacement 5. 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 i18n preparation algorithms for the smallest set of defining internationalization preparation algorithms for the
string classes may be sufficient for most cases, providing smallest set of string classes may be sufficient for most cases,
coherence among a set of related protocols or protocols where providing coherence among a set of related protocols or protocols
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 4
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 Recommendations for handling protocol incompatibilities resulting
from changes to Unicode are required. o The replacement ought at least to provide guidance to applications
o Comptability within each protocol between a technique that is using the replacement on how to handle protocol incompatibilities
resulting from changes to Unicode. In an ideal world, the
stringprep replacement would handle the changes automatically, but
it appears that such automatic handling would require magic and
cannot be expected.
o Compatibility within each protocol between a technique that is
stringprep-based and the technique's replacement has to be stringprep-based and the technique's replacement has to be
considered very carefully. considered very carefully.
Existing deployments already depend on Stringprep profiles. Existing deployments already depend on Stringprep profiles.
Therefore, a replacement must consider the effects of any new Therefore, a replacement must consider the effects of any new
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
skipping to change at page 13, line 33 skipping to change at page 20, line 11
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 9. 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, Bill Specific contributions came from David Black, Alan DeKok, Simon
McQuillan, Alexey Melnikov, Peter Saint-Andre, Dave Thaler, and Josefsson, Bill McQuillan, Alexey Melnikov, Peter Saint-Andre, Dave
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 4.1.1, 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 10. 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-00 (work in
progress), July 2011. progress), July 2011.
[NEWPREP] "Newprep BoF Meeting Minutes", March 2010. [NEWPREP] "Newprep BoF Meeting Minutes", March 2010.
[RFC0952] Harrenstien, K., Stahl, M., and E. Feinler, "DoD Internet
host table specification", RFC 952, October 1985.
[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 17, line 18 skipping to change at page 24, line 22
Internationalized Domain Names in Applications (IDNA) Internationalized Domain Names in Applications (IDNA)
2008", RFC 5895, September 2010. 2008", RFC 5895, September 2010.
[RFC6452] Faltstrom, P. and P. Hoffman, "The Unicode Code Points and [RFC6452] Faltstrom, P. and P. Hoffman, "The Unicode Code Points and
Internationalized Domain Names for Applications (IDNA) - Internationalized Domain Names for Applications (IDNA) -
Unicode 6.0", RFC 6452, November 2011. Unicode 6.0", RFC 6452, November 2011.
[UAX15] "Unicode Standard Annex #15: Unicode Normalization Forms", [UAX15] "Unicode Standard Annex #15: Unicode Normalization Forms",
UAX 15, September 2009. UAX 15, September 2009.
[1] <http://www.ietf.org/proceedings/78/slides/precis-2.pdf> [Unicode61]
The Unicode Consortium. The Unicode Standard, Version
[2] <http://www.unicode.org/standard/principles.html> 6.1, defined by:, "The Unicode Standard -- Version 6.1",
(Mountain View, CA: The Unicode Consortium, 2012. ISBN
[3] <http://www.ietf.org/proceedings/77/newprep.html> 978-1-936213-02-3), September 2009,
<http://www.unicode.org/versions/Unicode6.1.0/>.
[4] <http://www.ietf.org/proceedings/77/minutes/newprep.txt>
[5] <http://trac.tools.ietf.org/wg/precis/trac/report/6> [ietf78precis]
Blanchet, M., "PRECIS Framework", Proceedings of the
Seventy-Eighth Internet Engineering Task
Force https://www.ietf.org/proceedings/78/, July 2010,
<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 4.1.1), 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. The remaining columns have an "x" if and only if the is true.
protocol uses that class, as described in Section 4.3.4. Values
marked "-" indicate that an answer is not useful; in this case, see
detailed discussion in Appendix B.
+------+--------+-------+-------------+-----------+-----------+ +------+--------+-------+
| RFC | IDtype | User? | DomainClass | NameClass | FreeClass | | RFC | IDtype | User? |
+------+--------+-------+-------------+-----------+-----------+ +------+--------+-------+
| 3722 | a | o | | x | x | | 3722 | a | o |
| 3748 | - | - | - | x | - | | | | |
| 3920 | a,d | b | | x | x | | 3748 | - | - |
| 4505 | a | i | | | x | | | | |
| 4314 | a,d | b | | x | x | | 3920 | a,d | b |
| 4954 | a,d | b | | x | | | | | |
| 5034 | a,d | b | | x | | | 4505 | a | i |
| 5804 | a,d | b | | x | | | | | |
+------+--------+-------+-------------+-----------+-----------+ | 4314 | a,d | b |
| | | |
| 4954 | a,d | b |
| | | |
| 5034 | a,d | b |
| | | |
| 5804 | a,d | b |
+------+--------+-------+
Table 1 Table 1
[[anchor22: This table now contains results of any reviews the WG
did. Unreviewed things in the tracker are not reflected here.
--ajs@anvilwalrusden.com]]
Appendix B. Evaluation of Stringprep Profiles Appendix B. Evaluation of Stringprep Profiles
This section is a summary of the evaluation of Stringprep This section is a summary of evaluation of Stringprep profiles that
profiles [5] that was done to get a good understanding of the usage was done to get a good understanding of the usage of Stringprep.
of Stringprep. This summary is by no means normative nor the actual This summary is by no means normative nor the actual evaluations
evaluations themselves. A template was used for reviewers to get a themselves. A template was used for reviewers to get a coherent view
coherent view of all evaluations. of all evaluations.
B.1. iSCSI Stringprep Profiles: RFC3722, RFC3721, RFC3720 B.1. iSCSI Stringprep Profiles: RFC3722, 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,
sneaker-net, text files, etc. to avoid mistype mistakes. sneaker-net, text files, etc. to avoid mistype mistakes.
Where do we place the dividing line between user interface and Where do we place the dividing line between user interface and
protocol? The iSCSI protocol requires that all i18n string protocol? The iSCSI protocol requires that all internationalization
preparation occur in the user interface. The iSCSI protocol string preparation occur in the user interface. The iSCSI
treats iSCSI names as opaque identifiers that are compared byte- protocol treats iSCSI names as opaque identifiers that are
by-byte for equality. iSCSI names are generally not checked for compared byte-by-byte for equality. iSCSI names are generally not
correct formatting by the protocol. checked for correct formatting by the protocol.
What entities enforce the rules? There are no iSCSI-specific What entities enforce the rules? There are no iSCSI-specific
enforcement entities, although the use of unique identifier enforcement entities, although the use of unique identifier
information in the names relies on DNS registrars and the IEEE information in the names relies on DNS registrars and the IEEE
Registration Authority. Registration Authority.
Comparison Byte-by-byte Comparison Byte-by-byte
Case Folding, Sensitivity, Preservation Case folding is required for Case Folding, Sensitivity, Preservation Case folding is required for
the code blocks specified in RFC 3454, Table B.2. The overall the code blocks specified in RFC 3454, Table B.2. The overall
iSCSI naming system (UI + protocol) is case-insensitive. iSCSI naming system (UI + protocol) is case-insensitive.
What is the impact if the comparison results in a false positive? What is the impact if the comparison results in a false positive?
Potential access to the wrong storage. - If the initiator has no Potential access to the wrong storage. - If the initiator has no
access to the wrong storage, an authentication failure is the access to the wrong storage, an authentication failure is the
probable result. - If the initiator has access to the worng probable result. - If the initiator has access to the worng
storage, the resulting mis-identificaiton could result in use of storage, the resulting mis-identificaiton could result in use of
the wrong data and possible corruption of stored data. the wrong data and possible corruption of stored data.
What is the impact if the comparison results in a false negative? What is the impact if the comparison results in a false negative?
Denial of authorized storage access. Denial of authorized storage access.
What are the security impacts? iSCSI names are often used as the What are the security impacts? iSCSI names are often used as the
authentication identities for storage systems. Comparison authentication identities for storage systems. Comparison
problems could result in authentication problems, although note problems could result in authentication problems, although note
that authentication failure ameliorates some of the false positive that authentication failure ameliorates some of the false positive
cases. cases.
Normalization NFKC, as specified by RFC 3454. Normalization NFKC, as specified by RFC 3454.
Mapping Yes, as specified by table B.1 in RFC 3454 Mapping Yes, as specified by table B.1 in RFC 3454
Disallowed Characters Only the following characters are allowed: - Disallowed Characters Only the following characters are allowed: -
ASCII dash, dot, colon - ASCII lower case letters and digits - ASCII dash, dot, colon - ASCII lower case letters and digits -
Unicode lower case characters as specified by RFC 3454 All other Unicode lower case characters as specified by RFC 3454 All other
characters are disallowed. characters are disallowed.
Which other strings or identifiers are these most similar to? None - Which other strings or identifiers are these most similar to? None -
iSCSI names are unique to iSCSI. iSCSI names are unique to iSCSI.
Are these strings or identifiers sometimes the same as strings or Are these strings or identifiers sometimes the same as strings or
identifiers from other protocols? No identifiers from other protocols? No
Does the identifier have internal structure that needs to be Does the identifier have internal structure that needs to be
respected? Yes - ASCII dot, dash and colon are used for internal respected? Yes - ASCII dot, dash and colon are used for internal
name structure. These are not reserved characters in that they name structure. These are not reserved characters in that they
can occur in the name in locations other than those used for can occur in the name in locations other than those used for
structuring purposes (e.g., only the first occurrence of a colon structuring purposes (e.g., only the first occurrence of a colon
character is structural, others are not). character is structural, others are not).
How are users exposed to these strings? How are they published? How are users exposed to these strings? How are they published?
iSCSI names appear in server and storage system configuration iSCSI names appear in server and storage system configuration
interfaces. They also appear in system logs. interfaces. They also appear in system logs.
Is the string / identifier used as input to other operations? Is the string / identifier used as input to other operations?
Effectively, no. The rarely used port and logical unit names Effectively, no. The rarely used port and logical unit names
involve concatenation, which effectively extends a unique iSCSI involve concatenation, which effectively extends a unique iSCSI
Name for a target to uniquely identify something within that Name for a target to uniquely identify something within that
target. target.
How much tolerance for change from existing stringprep approach? How much tolerance for change from existing stringprep approach?
Good tolerance; the community would prefer that i18n experts solve Good tolerance; the community would prefer that
i18n problems ;-). internationalization experts solve internationalization problems
;-).
How strong a desire for change (e.g., for Unicode agility)? Unicode How strong a desire for change (e.g., for Unicode agility)? Unicode
agility is desired in principle as long as nothing significant agility is desired in principle as long as nothing significant
breaks. breaks.
B.2. SMTP/POP3/ManageSieve Stringprep Profiles: RFC4954,RFC5034,RFC B.2. SMTP/POP3/ManageSieve Stringprep Profiles: RFC4954,RFC5034,RFC
5804 5804
Description: Authorization identity (user identifier) exchanged Description: Authorization identity (user identifier) exchanged
during SASL authentication: AUTH (SMTP/POP3) or AUTHENTICATE during SASL authentication: AUTH (SMTP/POP3) or AUTHENTICATE
(ManageSieve) command. (ManageSieve) command.
skipping to change at page 23, line 6 skipping to change at page 31, line 31
details on restrictions. Note that some implementations allow details on restrictions. Note that some implementations allow
spaces in these. While IMAP implementations are not required to spaces in these. While IMAP implementations are not required to
use a specific format, an IMAP username frequently has the same use a specific format, an IMAP username frequently has the same
format as an email address (and EAI email address in the future), format as an email address (and EAI email address in the future),
or as a left hand side of an email address. Note: whatever is or as a left hand side of an email address. Note: whatever is
recommended for IMAP username should also be used for ManageSieve, recommended for IMAP username should also be used for ManageSieve,
POP3 and SMTP authorization identities, as IMAP/POP3/SMTP/ POP3 and SMTP authorization identities, as IMAP/POP3/SMTP/
ManageSieve are frequently implemented together. ManageSieve are frequently implemented together.
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. - access control lists (e.g. in IMAP ACL as an email address. - access control lists (e.g. in IMAP ACL
extension), both when managing membership and listing membership extension), both when managing membership and listing membership
of existing access control lists. - often show up as mailbox names of existing access control lists. - often show up as mailbox names
(under Other Users IMAP namespace) (under Other Users IMAP namespace)
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. Non-ASCII IMAP usernames are currently prohibited by IMAP sure. Non-ASCII IMAP usernames are currently prohibited by IMAP
(RFC 3501). However they are allowed when used in IMAP ACL (RFC 3501). However they are allowed when used in IMAP ACL
extension. extension.
B.4. IMAP Stringprep Profiles: RFC5738: Passwords B.4. IMAP Stringprep Profiles: RFC5738: Passwords
Description: "Password" parameter to the IMAP LOGIN command Description: "Password" parameter to the IMAP LOGIN command
How It's Used: Used for authentication (Passwords) How It's Used: Used for authentication (Passwords)
Who Generates It: Either generated by email system administrators Who Generates It: Either generated by email system administrators
using some tools/conventions, or specified by the human user. using some tools/conventions, or specified by the human user.
User Input Methods: - Typed by user - Copy-and-paste - Perhaps voice User Input Methods: - Typed by user - Copy-and-paste - Perhaps voice
input - Can also be specified in configuration files or on a input - Can also be specified in configuration files or on a
command line command line
Enforcement: Rules enforced by server / add-on service (e.g., Enforcement: Rules enforced by server / add-on service (e.g.,
gateway service or backend databse) on registration of account gateway service or backend databse) on registration of account
Comparison Method: "Type 1" (byte-for-byte) Comparison Method: "Type 1" (byte-for-byte)
Case Folding, Sensitivity, Preservation: Most likely case sensitive. Case Folding, Sensitivity, Preservation: Most likely case sensitive.
Impact of Comparison: False positives: - an unauthorized user is Impact of Comparison: False positives: - an unauthorized user is
allowed IMAP access (login) False negatives: - an authorized user allowed IMAP access (login) False negatives: - an authorized user
is denied IMAP access is denied IMAP access
Normalization: NFKC (as per RFC 4013) Normalization: NFKC (as per RFC 4013)
Mapping: (see Section 2 of RFC 4013 for the full list): non ASCII Mapping: (see Section 2 of RFC 4013 for the full list): non ASCII
spaces are mapped to space spaces are mapped to space
Disallowed Characters: (see Section 2 of RFC 4013 for the full Disallowed Characters: (see Section 2 of RFC 4013 for the full
list): Unicode Control characters, etc. list): Unicode Control characters, etc.
String Classes: Currently defined as "simple username" (see Section String Classes: Currently defined as "simple username" (see Section
2 of RFC 4013 for details on restrictions.), however this is 2 of RFC 4013 for details on restrictions.), however this is
likely to be a different class from usernames. Note that some likely to be a different class from usernames. Note that some
implementations allow spaces in these. Password in all email implementations allow spaces in these. Password in all email
related protocols should be treated in the same way. Same related protocols should be treated in the same way. Same
passwords are frequently shared with web, IM, etc. applications. passwords are frequently shared with web, IM, etc. applications.
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 I18N): 5. UTF8=USER
Capability If the "UTF8=USER" capability is advertised, that Background information: RFC 5738 (IMAP INTERNATIONALIZATION): 5.
indicates the server accepts UTF-8 user names and passwords and UTF8=USER Capability If the "UTF8=USER" capability is advertised,
applies SASLprep [RFC4013] to both arguments of the LOGIN command. that indicates the server accepts UTF-8 user names and passwords
The server MUST reject UTF-8 that fails to comply with the formal and applies SASLprep [RFC4013] to both arguments of the LOGIN
syntax in RFC 3629 [RFC3629] or if it encounters Unicode command. The server MUST reject UTF-8 that fails to comply with
characters listed in Section 2.3 of SASLprep RFC 4013 [RFC4013]. the formal syntax in RFC 3629 [RFC3629] or if it encounters
RFC 4314 (IMAP4 Access Control List (ACL) Extension): 3. Access Unicode characters listed in Section 2.3 of SASLprep RFC 4013
control management commands and responses Servers, when processing [RFC4013]. RFC 4314 (IMAP4 Access Control List (ACL) Extension):
a command that has an identifier as a parameter (i.e., any of 3. Access control management commands and responses Servers, when
SETACL, DELETEACL, and LISTRIGHTS commands), SHOULD first prepare processing a command that has an identifier as a parameter (i.e.,
the received identifier using "SASLprep" profile [SASLprep] of the any of SETACL, DELETEACL, and LISTRIGHTS commands), SHOULD first
"stringprep" algorithm [Stringprep]. If the preparation of the prepare the received identifier using "SASLprep" profile
identifier fails or results in an empty string, the server MUST [SASLprep] of the "stringprep" algorithm [Stringprep]. If the
refuse to perform the command with a BAD response. Note that preparation of the identifier fails or results in an empty string,
Section 6 recommends additional identifier's verification steps. the server MUST refuse to perform the command with a BAD response.
and in Section 6: This document relies on [SASLprep] to describe Note that Section 6 recommends additional identifier's
steps required to perform identifier canonicalization verification steps. and in Section 6: This document relies on
(preparation). The preparation algorithm in SASLprep was [SASLprep] to describe steps required to perform identifier
specifically designed such that its output is canonical, and it is canonicalization (preparation). The preparation algorithm in
well-formed. However, due to an anomaly [PR29] in the SASLprep was specifically designed such that its output is
specification of Unicode normalization, canonical equivalence is canonical, and it is well-formed. However, due to an anomaly
not guaranteed for a select few character sequences. Identifiers [PR29] in the specification of Unicode normalization, canonical
prepared with SASLprep can be stored and returned by an ACL equivalence is not guaranteed for a select few character
server. The anomaly affects ACL manipulation and evaluation of sequences. Identifiers prepared with SASLprep can be stored and
identifiers containing the selected character sequences. These returned by an ACL server. The anomaly affects ACL manipulation
sequences, however, do not appear in well-formed text. In order and evaluation of identifiers containing the selected character
to address this problem, an ACL server MAY reject identifiers sequences. These sequences, however, do not appear in well-formed
containing sequences described in [PR29] by sending the tagged BAD text. In order to address this problem, an ACL server MAY reject
response. This is in addition to the requirement to reject identifiers containing sequences described in [PR29] by sending
identifiers that fail SASLprep preparation as described in Section the tagged BAD response. This is in addition to the requirement
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
configuration files. The value can also be automatically configuration files. The value can also be automatically
generated by clients (e.g. a fixed string is used, or a user's generated by clients (e.g. a fixed string is used, or a user's
email address). email address).
How users input strings? Keyboard/voice, stylus (pick from a list). How users input strings? Keyboard/voice, stylus (pick from a list).
Copy-paste - possibly. Copy-paste - possibly.
Normalization: None Normalization: None
Disallowed Characters Control characters are disallowed. (See Disallowed Characters Control characters are disallowed. (See
Section 3 of RFC 4505) Section 3 of RFC 4505)
Which other strings or identifiers are these most similar to? RFC Which other strings or identifiers are these most similar to? RFC
4505 says that the trace "should take one of two forms: an 4505 says that the trace "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." In practice, this system administrator of the client's domain." In practice, this
is a freeform text, so it belongs to a different class from "email is a freeform text, so it belongs to a different class from "email
address" or "username". address" or "username".
Are these strings or identifiers sometimes the same as strings or Are these strings or identifiers sometimes the same as strings or
identifiers from other protocols (e.g., does an IM system sometimes identifiers from other protocols (e.g., does an IM system sometimes
use the same credentials database for authentication as an email use the same credentials database for authentication as an email
system)? Yes: see above. However there is no strong need to keep system)? Yes: see above. However there is no strong need to keep
them consistent in the future. them consistent in the future.
How are users exposed to these strings, how are they published? No. How are users exposed to these strings, how are they published? No.
However, The value can be seen in server logs However, The value can be seen in server logs
Impacts of false positives and false negatives: False positive: a Impacts of false positives and false negatives: False positive: a
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,
skipping to change at page 29, line 4 skipping to change at page 39, line 16
Note to RFC Editor: This section should be removed prior to Note to RFC Editor: This section should be removed prior to
publication. publication.
C.1. 00 C.1. 00
First WG version. Based on First WG version. Based on
draft-blanchet-precis-problem-statement-00. draft-blanchet-precis-problem-statement-00.
C.2. 01 C.2. 01
o Made clear that the document is talking only about Unicode code o Made clear that the document is talking only about Unicode code
points, and not any particular encoding. points, and not any particular encoding.
o Substantially reorganized the document along the lines of the o Substantially reorganized the document along the lines of the
review template at <http://trac.tools.ietf.org/wg/precis/trac/ review template at <http://trac.tools.ietf.org/wg/precis/trac/
wiki/StringprepReviewTemplate>. wiki/StringprepReviewTemplate>.
o Included specific questions for each topic for consideration. o Included specific questions for each topic for consideration.
o Moved spot for individual protocol review to appendix. Not o Moved spot for individual protocol review to appendix. Not
populated yet. populated yet.
C.3. 02 C.3. 02
o Cleared up details of comparison classes o Cleared up details of comparison classes
o Added a section on changes in Unicode o Added a section on changes in Unicode
C.4. 03 C.4. 03
o Aligned comparison discussion with identifier discussion from o Aligned comparison discussion with identifier discussion from
draft-iab-identifier-comparison-00 draft-iab-identifier-comparison-00
o Added section on classes of strings ("Namey" and so on) o Added section on classes of strings ("Namey" and so on)
C.5. 04 C.5. 04
Keepalive version Keepalive version
C.6. 05 C.6. 05
o Changed classes of strings to align with framework doc o Changed classes of strings to align with framework doc
o Altered table in Appendix A o Altered table in Appendix A
o Added all profiles evaluations from the wg wiki in appendix B o Added all profiles evaluations from the wg wiki in appendix B
C.7. 06
o Respond to comments received in WGLC
o Removed classes of strings (also from Appendix A)
o Moved inclusion/exclusion distinction to Introduction
o Fix some sentences to clarify terminology and add or fix
references
Authors' Addresses Authors' Addresses
Marc Blanchet Marc Blanchet
Viagenie Viagenie
246 Aberdeen 246 Aberdeen
Quebec, QC G1R 2E1 Quebec, QC G1R 2E1
Canada Canada
Email: Marc.Blanchet@viagenie.ca Email: Marc.Blanchet@viagenie.ca
URI: http://viagenie.ca URI: http://viagenie.ca
 End of changes. 121 change blocks. 
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