draft-ietf-precis-problem-statement-09.txt   rfc6885.txt 
Network Working Group M. Blanchet Internet Engineering Task Force (IETF) M. Blanchet
Internet-Draft Viagenie Request for Comments: 6885 Viagenie
Intended status: Informational A. Sullivan Category: Informational A. Sullivan
Expires: July 26, 2013 Dyn, Inc. ISSN: 2070-1721 Dyn, Inc.
January 22, 2013 March 2013
Stringprep Revision and PRECIS Problem Statement Stringprep Revision and Problem Statement
draft-ietf-precis-problem-statement-09.txt for the Preparation and Comparison of Internationalized Strings (PRECIS)
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 code points 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
Stringprep profiles need to be similarly updated or a replacement of Stringprep profiles need to be similarly updated, or a replacement of
Stringprep needs to be designed. This document outlines the issues Stringprep needs to be designed. This document outlines the issues
to be faced by those 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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provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering This document is not an Internet Standards Track specification; it is
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Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
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approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
This Internet-Draft will expire on July 26, 2013. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6885.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Stringprep Profiles Limitations . . . . . . . . . . . . . . . 6 4. Stringprep Profiles Limitations . . . . . . . . . . . . . . . 6
5. Major Topics for Consideration . . . . . . . . . . . . . . . . 7 5. Major Topics for Consideration . . . . . . . . . . . . . . . . 8
5.1. Comparison . . . . . . . . . . . . . . . . . . . . . . . . 7 5.1. Comparison . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1.1. Types of Identifiers . . . . . . . . . . . . . . . . . 7 5.1.1. Types of Identifiers . . . . . . . . . . . . . . . . . 8
5.1.2. Effect of comparison . . . . . . . . . . . . . . . . . 8 5.1.2. Effect of Comparison . . . . . . . . . . . . . . . . . 8
5.2. Dealing with characters . . . . . . . . . . . . . . . . . 8 5.2. Dealing with Characters . . . . . . . . . . . . . . . . . 9
5.2.1. Case folding, case sensitivity, and case 5.2.1. Case Folding, Case Sensitivity, and Case
preservation . . . . . . . . . . . . . . . . . . . . . 8 Preservation . . . . . . . . . . . . . . . . . . . . . 9
5.2.2. Stringprep and NFKC . . . . . . . . . . . . . . . . . 8 5.2.2. Stringprep and NFKC . . . . . . . . . . . . . . . . . 9
5.2.3. Character mapping . . . . . . . . . . . . . . . . . . 9 5.2.3. Character Mapping . . . . . . . . . . . . . . . . . . 10
5.2.4. Prohibited characters . . . . . . . . . . . . . . . . 9 5.2.4. Prohibited Characters . . . . . . . . . . . . . . . . 10
5.2.5. Internal structure, delimiters, and special 5.2.5. Internal Structure, Delimiters, and Special
characters . . . . . . . . . . . . . . . . . . . . . . 9 Characters . . . . . . . . . . . . . . . . . . . . . . 10
5.2.6. Restrictions because of glyph similarity . . . . . . . 10 5.2.6. Restrictions Because of Glyph Similarity . . . . . . . 11
5.3. Where the data comes from and where it goes . . . . . . . 10 5.3. Where the Data Comes from and Where It Goes . . . . . . . 11
5.3.1. User input and the source of protocol elements . . . . 10 5.3.1. User Input and the Source of Protocol Elements . . . . 11
5.3.2. User output . . . . . . . . . . . . . . . . . . . . . 11 5.3.2. User Output . . . . . . . . . . . . . . . . . . . . . 12
5.3.3. Operations . . . . . . . . . . . . . . . . . . . . . . 11 5.3.3. Operations . . . . . . . . . . . . . . . . . . . . . . 12
6. Considerations for Stringprep replacement . . . . . . . . . . 12 6. Considerations for Stringprep Replacement . . . . . . . . . . 13
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13 7. Security Considerations . . . . . . . . . . . . . . . . . . . 14
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
9. Discussion home for this draft . . . . . . . . . . . . . . . . 13 9. Informative References . . . . . . . . . . . . . . . . . . . . 15
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 Appendix A. Classification of Stringprep Profiles . . . . . . . . 19
11. Informative References . . . . . . . . . . . . . . . . . . . . 14 Appendix B. Evaluation of Stringprep Profiles . . . . . . . . . . 19
Appendix A. Classification of Stringprep Profiles . . . . . . . . 18 B.1. iSCSI Stringprep Profile: RFC 3720, RFC 3721, RFC 3722 . . 19
Appendix B. Evaluation of Stringprep Profiles . . . . . . . . . . 18 B.2. SMTP/POP3/ManageSieve Stringprep Profiles: RFC 4954,
B.1. iSCSI Stringprep Profile: RFC3722 (and RFC3721, RFC 5034, RFC 5804 . . . . . . . . . . . . . . . . . . . . 21
RFC3720) . . . . . . . . . . . . . . . . . . . . . . . . . 18 B.3. IMAP Stringprep Profiles for Usernames: RFC 4314, RFC
B.2. SMTP/POP3/ManageSieve Stringprep Profiles: 5738 . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
RFC4954,RFC5034,RFC 5804 . . . . . . . . . . . . . . . . . 20 B.4. IMAP Stringprep Profiles for Passwords: RFC 5738 . . . . . 26
B.3. IMAP Stringprep Profiles: RFC5738, RFC4314: Usernames . . 22 B.5. Anonymous SASL Stringprep Profiles: RFC 4505 . . . . . . . 28
B.4. IMAP Stringprep Profiles: RFC5738: Passwords . . . . . . . 23 B.6. XMPP Stringprep Profiles for Nodeprep: RFC 3920 . . . . . 30
B.5. Anonymous SASL Stringprep Profiles: RFC4505 . . . . . . . 24 B.7. XMPP Stringprep Profiles for Resourceprep: RFC 3920 . . . 31
B.6. XMPP Stringprep Profiles: RFC3920 Nodeprep . . . . . . . . 26 B.8. EAP Stringprep Profiles: RFC 3748 . . . . . . . . . . . . 33
B.7. XMPP Stringprep Profiles: RFC3920 Resourceprep . . . . . . 27
B.8. EAP Stringprep Profiles: RFC3748 . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28
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] and [RFC3454] describes a
mechanism for encoding Unicode labels making up Internationalized mechanism for encoding Unicode labels that make up the
Domain Names (IDNs) as standard DNS labels. The labels were Internationalized Domain Names (IDNs) as standard DNS labels. The
processed using a method called Nameprep [RFC3491] and Punycode labels were processed using a method called Nameprep [RFC3491] and
[RFC3492]. That method was specific to IDNA2003, but is generalized Punycode [RFC3492]. That method was specific to IDNA2003 but is
as Stringprep [RFC3454]. The general mechanism is used by other generalized as Stringprep [RFC3454]. The general mechanism is used
protocols with similar needs, but with different constraints than by other protocols with similar needs but with different constraints
IDNA2003. than IDNA2003.
Stringprep defines a framework within which protocols define their Stringprep defines a framework within which protocols define their
Stringprep profiles. Some known IETF specifications using Stringprep Stringprep profiles. Some known IETF specifications using Stringprep
are listed below: are 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 IAX using Nameprep [RFC5456];
o The Inter-Asterisk eXchange (IAX) using Nameprep [RFC5456];
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
Systems Interface (iSCSI) Names; o The Internet Small Computer System Interface (iSCSI) profile
o EAP [RFC3748]; [RFC3722] for use in iSCSI names;
o The Nodeprep and Resourceprep profiles [RFC3920] for use in the
Extensible Messaging and Presence Protocol (XMPP), and the XMPP to o The Extensible Authentication Protocol (EAP) [RFC3748];
CPIM mapping [RFC3922] (the latter of these relies on the former);
o IRI and URI in XMPP [RFC5122]; o The Nodeprep and Resourceprep profiles [RFC3920] (which was
obsoleted by [RFC6120]) for use in the Extensible Messaging and
Presence Protocol (XMPP), and the XMPP to Common Presence and
Instant Messaging (CPIM) mapping [RFC3922] (the latter of these
relies on the former);
o The Internationalized Resource Identifier (IRI) and URI in XMPP
[RFC5122];
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 TLS [RFC4279];
o The LDAP profile [RFC4518] for use with LDAP [RFC4511] and its o Transport Layer Security (TLS) [RFC4279];
authentication methods [RFC4513];
o The Lightweight Directory Access Protocol (LDAP) profile [RFC4518]
for use with LDAP [RFC4511] and its authentication methods
[RFC4513];
o PKIX subject identification using LDAPprep [RFC4683]; o PKIX subject identification using LDAPprep [RFC4683];
o PKIX CRL using LDAPprep [RFC5280]; o PKIX Certificate Revocation List (CRL) using LDAPprep [RFC5280];
o The SASLprep profile [RFC4013] for use in the Simple
Authentication and Security Layer (SASL), and SASL itself o The Simple Authentication and Security Layer (SASL) [RFC4422] and
[RFC4422]; SASLprep profile [RFC4013] for use in SASL;
o Plain SASL using SASLprep [RFC4616]; o Plain SASL using SASLprep [RFC4616];
o SMTP Auth using SASLprep [RFC4954]; o SMTP Auth using SASLprep [RFC4954];
o POP3 Auth using SASLprep [RFC5034];
o TLS SRP using SASLprep [RFC5054]; o The Post Office Protocol (POP3) Auth using SASLprep [RFC5034];
o SASL SCRAM using SASLprep [RFC5802];
o TLS Secure Remote Password (SRP) using SASLprep [RFC5054];
o SASL Salted Challenge Response Authentication Mechanism (SCRAM)
using SASLprep [RFC5802];
o Remote management of Sieve using SASLprep [RFC5804]; o Remote management of Sieve using SASLprep [RFC5804];
o NNTP using SASLprep [RFC4643];
o The Network News Transfer Protocol (NNTP) using SASLprep
[RFC4643];
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 Internet Application Protocol Collation Registry [RFC4790]; o Internet Application Protocol Collation Registry [RFC4790];
o The unicode-casemap Unicode Collation [RFC5051]. o The unicode-casemap Unicode Collation [RFC5051].
However, a review (see [ietf78precis]) of these protocol However, a review (see [78PRECIS]) of these protocol specifications
specifications found that they are very similar and can be grouped found that they are very similar and can be grouped into a short
into a short number of classes. Moreover, many reuse the same number of classes. Moreover, many reuse the same Stringprep profile,
Stringprep profile, such as the SASL one. 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 code points is defined.
algorithm generates a stable and complete table of the supported That algorithm generates a stable and complete table of the supported
Unicode codepoints for each Unicode version. This algorithm uses an Unicode code points for each Unicode version. This algorithm uses an
inclusion-based approach, instead of the exclusion-based approach of inclusion-based approach, instead of the exclusion-based approach of
Stringprep/Nameprep. That is, IDNA2003 created an explicit list of Stringprep/Nameprep. That is, IDNA2003 created an explicit list of
excluded or mapped-away characters; anything in Unicode 3.2 that was excluded or mapped-away characters; anything in Unicode 3.2 that was
not so listed could be assumed to be allowed under the protocol. not so listed could be assumed to be allowed under the protocol.
IDNA2008 begins instead from the assumption that code points are IDNA2008 begins instead from the assumption that code points are
disallowed, and then relies on Unicode properties to derive whether a disallowed and then relies on Unicode properties to derive whether a
given code point actually is allowed in the protocol. 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. Keywords 2. Keywords
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
This document uses various internationalization terms, which are This document uses various internationalization terms, which are
defined and discussed in [RFC6365]. defined and discussed in [RFC6365].
Additionally, this document defines the following keyword: Additionally, this document defines the following keyword:
o PRECIS: Preparation and Comparison of Internationalized Strings
PRECIS: Preparation and Comparison of Internationalized Strings
3. Conventions 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],
A. Appendix A.
4. 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
requirement. For example, Stringprep normalization is based on requirement. For example, Stringprep normalization is based on
and profiles may use Unicode Normalization Form KC (NFKC) [UAX15], and profiles may use Unicode Normalization Form KC (NFKC) [UAX15],
while IDNA2008 mostly uses Unicode Normalization Form C (NFC) while IDNA2008 mostly uses Unicode Normalization Form C (NFC)
[UAX15]. [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 code points may be passed between SASL, XMPP,
LDAP and EAP. Therefore, common set of rules or classes of LDAP, and EAP. Therefore, a 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 Jabber Identifier (JID): a localpart, which is similar to
for authentication, a domainpart which is a domain name, and a a username and used for authentication; a domainpart, which is a
resource part which is less restrictive than the localpart. domain name; and a resourcepart, which is less restrictive than
the localpart.
o iSCSI uses a Stringprep profile for the names of protocol o iSCSI uses a Stringprep profile for the names of protocol
participants (called initiators and targets). The IQN format of participants (called initiators and targets). The iSCSI Qualified
iSCSI names contains a reversed DNS domain name. Name (IQN) format of iSCSI names contains a reversed DNS domain
o SASL and LDAP uses a Stringprep profile for usernames. name.
o SASL and LDAP use a Stringprep profile for usernames.
o LDAP uses a set of Stringprep profiles. o LDAP uses a set of Stringprep profiles.
The apparent judgement of the BOF attendees [NEWPREP] was that it The apparent judgement of the BOF attendees [NEWPREP] was that it
would be highly desirable to have a replacement of Stringprep, with would be highly desirable to have a replacement of Stringprep, with
similar characteristics to IDNA2008. That replacement should be similar characteristics to IDNA2008. That replacement should be
defined so that the protocols could use internationalized strings defined so that the protocols could use internationalized strings
without a lot of specialized internationalization work, since without a lot of specialized internationalization work, since
internationalization expertise is not available in the respective internationalization expertise is not available in the respective
protocols or working groups. Accordingly, the IESG formed the PRECIS protocols or working groups. Accordingly, the IESG formed the PRECIS
working group to undertake the task. working group to undertake the task.
skipping to change at page 7, line 29 skipping to change at page 8, line 19
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.
5.1. Comparison 5.1. Comparison
5.1.1. Types of Identifiers 5.1.1. Types of Identifiers
Following [I-D.iab-identifier-comparison], it is possible to organize Following [ID-COMP], it is possible to organize identifiers into
identifiers into three classes in respect of how they may be compared three classes in respect of how they may be compared with one
with one another: 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
algorithm on which all parties agree. Definite Identifiers: Identifiers that have a well-defined
Indefinite Identifiers Identifiers that have no single comparison comparison algorithm on which all parties agree.
Indefinite Identifiers: Identifiers that have no single comparison
algorithm on which all parties agree. algorithm on which all parties agree.
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 [ID-COMP].
The section on treating the existing known cases, Appendix A uses the The section on treating the existing known cases, Appendix A, uses
categories above. the categories above.
5.1.2. Effect of comparison 5.1.2. Effect of Comparison
The three classes of comparison style outlined in Section 5.1.1 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 or a false
effects are if a comparison results in a false negative, especially negative, especially in terms of the consequences to security and
in terms of the consequences to security and usability. usability.
5.2. 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, the ways in which IDNA2008 might be a good
might be a good analogy to other protocols, and ways in which it analogy to other protocols, and ways in which it might be a poor one.
might be a poor one.
5.2.1. 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 lowercase 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 uppercase 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 case be preserved, then the
preserved, then the analogy with IDNA2008 will break down. analogy with IDNA2008 will break down. Accordingly, existing
Accordingly, existing protocols are to be evaluated according to the 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?
5.2.2. 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 code points than NFC. For
things like the spelling of users' names, then, NFKC may not be the things like the spelling of users' names, NFKC may not be the best
best form to use. At the same time, one of the nice things about form to use. At the same time, one of the nice things about NFKC is
NFKC is that it deals with the width of characters that are otherwise 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.
5.2.3. Character mapping 5.2.3. Character Mapping
Along with the case mapping issues raised in Section 5.2.1, 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.
5.2.4. 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).
skipping to change at page 9, line 42 skipping to change at page 10, line 36
by the protocol"; this is unlike IDNA2003. While some code points by the protocol"; this is unlike IDNA2003. While some code points
are disallowed outright, some are allowed only in certain contexts. are disallowed outright, some are allowed only in certain contexts.
The reasons for the context-dependent rules have to do with the way The reasons for the context-dependent rules have to do with the way
some characters are used. For instance, the ZERO WIDTH JOINER and 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 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) rule (see [RFC0952]), 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.
5.2.5. 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 displayed 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.
Other protocols may include characters with similar special meaning Other protocols may include characters with similar special meaning
within the protocol. Common characters for these purposes include within the protocol. Common characters for these purposes include
FULL STOP, U+002E (.); COMMERCIAL AT, U+0040 (@); HYPHEN-MINUS, FULL STOP, U+002E (.); COMMERCIAL AT, U+0040 (@); HYPHEN-MINUS,
U+002D (-); SOLIDUS, U+002F (/); and LOW LINE, U+005F (_). The mere U+002D (-); SOLIDUS, U+002F (/); and LOW LINE, U+005F (_). The mere
inclusion of such a character in the protocol is not enough for it to inclusion of such a character in the protocol is not enough for it to
be considered similar to another protocol using the same character; be considered similar to another protocol using the same character;
instead, handling of the character must be taken into consideration instead, handling of the character must be taken into consideration
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 favor 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.
5.2.6. 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 code points. For DNS names, homoglyphs may enable
If a protocol requires some visual comparison by end-users, then the phishing. If a protocol requires some visual comparison by end-
issue of homoglyphs is to be considered. In the DNS context, theses users, then the issue of homoglyphs is to be considered. In the DNS
issues are documented in [RFC5894] and [RFC4690]. IDNA2008 does not, context, these issues are documented in [RFC5894] and [RFC4690].
however, have a mechanism to deal with them, trusting to DNS zone However, IDNA2008 does not have a mechanism to deal with them,
operators to enact sensible policies for the subset of Unicode they trusting DNS zone operators to enact sensible policies for the subset
wish to support, given their user community. A similar policy/ of Unicode they wish to support, given their user community. A
protocol split may not be desirable in every protocol. similar policy/protocol split may not be desirable in every protocol.
5.3. Where the data comes from and where it goes 5.3. Where the Data Comes from and Where It Goes
5.3.1. 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])
5.3.2. 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
skipping to change at page 11, line 30 skipping to change at page 12, line 28
5.3.3. 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).
5.3.3.1. 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.
5.3.3.2. Community Considerations 5.3.3.2. Community Considerations
skipping to change at page 12, line 18 skipping to change at page 13, line 12
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.
6. Considerations for Stringprep replacement 6. Considerations for Stringprep Replacement
The above suggests the following guidance: The above suggests the following guidance:
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.
by using codepoint properties instead of codepoint whitelisting) o The replacement should take an approach similar to IDNA2008 (e.g.,
in that it enables better Unicode agility. by using properties of code points instead of whitelisting of code
points), 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 5 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 to at least 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
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
skipping to change at page 13, line 19 skipping to change at page 14, line 19
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.
7. 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. Moreover, the Stringprep Security Considerations completed. Moreover, the Stringprep Security Considerations
[RFC3454] Section applies. See also the analysis in the subsections [RFC3454] Section applies. See also the analysis in the subsections
of Appendix B, below. of Appendix B, below.
8. IANA Considerations 8. Acknowledgements
This document has no actions for IANA.
9. Discussion home for this draft
Note: RFC-Editor, please remove this section before publication.
This document is intended to define the problem space discussed on
the precis@ietf.org mailing list.
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 5.1.1, 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, and
Thaler. Dave Thaler.
11. Informative References 9. Informative References
[I-D.iab-identifier-comparison] [78PRECIS] Blanchet, M., "PRECIS Framework", Proceedings of IETF
Thaler, D., "Issues in Identifier Comparison for Security 78, July 2010, <http://www.ietf.org/proceedings/78/
Purposes", draft-iab-identifier-comparison-07 (work in slides/precis-2.pdf>.
progress), August 2012.
[NEWPREP] "Newprep BoF Meeting Minutes", March 2010. [ID-COMP] Thaler, D., Ed., "Issues in Identifier Comparison for
Security Purposes", Work in Progress, March 2013.
[RFC0952] Harrenstien, K., Stahl, M., and E. Feinler, "DoD Internet [NEWPREP] "Newprep BoF Meeting Minutes", March 2010,
host table specification", RFC 952, October 1985. <http://www.ietf.org/proceedings/77/minutes/
newprep.txt>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC0952] Harrenstien, K., Stahl, M., and E. Feinler, "DoD
Requirement Levels", BCP 14, RFC 2119, March 1997. Internet host table specification", RFC 952,
October 1985.
[RFC3454] Hoffman, P. and M. Blanchet, "Preparation of [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Internationalized Strings ("stringprep")", RFC 3454, Requirement Levels", BCP 14, RFC 2119, March 1997.
December 2002.
[RFC3490] Faltstrom, P., Hoffman, P., and A. Costello, [RFC3454] Hoffman, P. and M. Blanchet, "Preparation of
"Internationalizing Domain Names in Applications (IDNA)", Internationalized Strings ("stringprep")", RFC 3454,
RFC 3490, March 2003. December 2002.
[RFC3491] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep [RFC3490] Faltstrom, P., Hoffman, P., and A. Costello,
Profile for Internationalized Domain Names (IDN)", "Internationalizing Domain Names in Applications
RFC 3491, March 2003. (IDNA)", RFC 3490, March 2003.
[RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode [RFC3491] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep
for Internationalized Domain Names in Applications Profile for Internationalized Domain Names (IDN)",
(IDNA)", RFC 3492, March 2003. RFC 3491, March 2003.
[RFC3530] Shepler, S., Callaghan, B., Robinson, D., Thurlow, R., [RFC3492] Costello, A., "Punycode: A Bootstring encoding of
Beame, C., Eisler, M., and D. Noveck, "Network File System Unicode for Internationalized Domain Names in
(NFS) version 4 Protocol", RFC 3530, April 2003. Applications (IDNA)", RFC 3492, March 2003.
[RFC3722] Bakke, M., "String Profile for Internet Small Computer [RFC3530] Shepler, S., Callaghan, B., Robinson, D., Thurlow, R.,
Systems Interface (iSCSI) Names", RFC 3722, April 2004. Beame, C., Eisler, M., and D. Noveck, "Network File
System (NFS) version 4 Protocol", RFC 3530, April 2003.
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. [RFC3722] Bakke, M., "String Profile for Internet Small Computer
Levkowetz, "Extensible Authentication Protocol (EAP)", Systems Interface (iSCSI) Names", RFC 3722, April 2004.
RFC 3748, June 2004.
[RFC3920] Saint-Andre, P., Ed., "Extensible Messaging and Presence [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and
Protocol (XMPP): Core", RFC 3920, October 2004. H. Levkowetz, "Extensible Authentication Protocol
(EAP)", RFC 3748, June 2004.
[RFC3922] Saint-Andre, P., "Mapping the Extensible Messaging and [RFC3920] Saint-Andre, P., Ed., "Extensible Messaging and Presence
Presence Protocol (XMPP) to Common Presence and Instant Protocol (XMPP): Core", RFC 3920, October 2004.
Messaging (CPIM)", RFC 3922, October 2004.
[RFC4011] Waldbusser, S., Saperia, J., and T. Hongal, "Policy Based [RFC3922] Saint-Andre, P., "Mapping the Extensible Messaging and
Management MIB", RFC 4011, March 2005. Presence Protocol (XMPP) to Common Presence and Instant
Messaging (CPIM)", RFC 3922, October 2004.
[RFC4013] Zeilenga, K., "SASLprep: Stringprep Profile for User Names [RFC4011] Waldbusser, S., Saperia, J., and T. Hongal, "Policy
and Passwords", RFC 4013, February 2005. Based Management MIB", RFC 4011, March 2005.
[RFC4279] Eronen, P. and H. Tschofenig, "Pre-Shared Key Ciphersuites [RFC4013] Zeilenga, K., "SASLprep: Stringprep Profile for User
for Transport Layer Security (TLS)", RFC 4279, Names and Passwords", RFC 4013, February 2005.
December 2005.
[RFC4314] Melnikov, A., "IMAP4 Access Control List (ACL) Extension", [RFC4279] Eronen, P. and H. Tschofenig, "Pre-Shared Key
RFC 4314, December 2005. Ciphersuites for Transport Layer Security (TLS)",
RFC 4279, December 2005.
[RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and [RFC4314] Melnikov, A., "IMAP4 Access Control List (ACL)
Security Layer (SASL)", RFC 4422, June 2006. Extension", RFC 4314, December 2005.
[RFC4505] Zeilenga, K., "Anonymous Simple Authentication and [RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and
Security Layer (SASL) Mechanism", RFC 4505, June 2006. Security Layer (SASL)", RFC 4422, June 2006.
[RFC4511] Sermersheim, J., "Lightweight Directory Access Protocol [RFC4505] Zeilenga, K., "Anonymous Simple Authentication and
(LDAP): The Protocol", RFC 4511, June 2006. Security Layer (SASL) Mechanism", RFC 4505, June 2006.
[RFC4513] Harrison, R., "Lightweight Directory Access Protocol [RFC4511] Sermersheim, J., "Lightweight Directory Access Protocol
(LDAP): Authentication Methods and Security Mechanisms", (LDAP): The Protocol", RFC 4511, June 2006.
RFC 4513, June 2006.
[RFC4518] Zeilenga, K., "Lightweight Directory Access Protocol [RFC4513] Harrison, R., "Lightweight Directory Access Protocol
(LDAP): Internationalized String Preparation", RFC 4518, (LDAP): Authentication Methods and Security Mechanisms",
June 2006. RFC 4513, June 2006.
[RFC4616] Zeilenga, K., "The PLAIN Simple Authentication and [RFC4518] Zeilenga, K., "Lightweight Directory Access Protocol
Security Layer (SASL) Mechanism", RFC 4616, August 2006. (LDAP): Internationalized String Preparation", RFC 4518,
June 2006.
[RFC4643] Vinocur, J. and K. Murchison, "Network News Transfer [RFC4616] Zeilenga, K., "The PLAIN Simple Authentication and
Protocol (NNTP) Extension for Authentication", RFC 4643, Security Layer (SASL) Mechanism", RFC 4616, August 2006.
October 2006.
[RFC4683] Park, J., Lee, J., Lee, H., Park, S., and T. Polk, [RFC4643] Vinocur, J. and K. Murchison, "Network News Transfer
"Internet X.509 Public Key Infrastructure Subject Protocol (NNTP) Extension for Authentication", RFC 4643,
Identification Method (SIM)", RFC 4683, October 2006. October 2006.
[RFC4690] Klensin, J., Faltstrom, P., Karp, C., and IAB, "Review and [RFC4683] Park, J., Lee, J., Lee, H., Park, S., and T. Polk,
Recommendations for Internationalized Domain Names "Internet X.509 Public Key Infrastructure Subject
(IDNs)", RFC 4690, September 2006. Identification Method (SIM)", RFC 4683, October 2006.
[RFC4790] Newman, C., Duerst, M., and A. Gulbrandsen, "Internet [RFC4690] Klensin, J., Faltstrom, P., Karp, C., and IAB, "Review
Application Protocol Collation Registry", RFC 4790, and Recommendations for Internationalized Domain Names
March 2007. (IDNs)", RFC 4690, September 2006.
[RFC4954] Siemborski, R. and A. Melnikov, "SMTP Service Extension [RFC4790] Newman, C., Duerst, M., and A. Gulbrandsen, "Internet
for Authentication", RFC 4954, July 2007. Application Protocol Collation Registry", RFC 4790,
March 2007.
[RFC5034] Siemborski, R. and A. Menon-Sen, "The Post Office Protocol [RFC4954] Siemborski, R. and A. Melnikov, "SMTP Service Extension
(POP3) Simple Authentication and Security Layer (SASL) for Authentication", RFC 4954, July 2007.
Authentication Mechanism", RFC 5034, July 2007.
[RFC5051] Crispin, M., "i;unicode-casemap - Simple Unicode Collation [RFC5034] Siemborski, R. and A. Menon-Sen, "The Post Office
Algorithm", RFC 5051, October 2007. Protocol (POP3) Simple Authentication and Security Layer
(SASL) Authentication Mechanism", RFC 5034, July 2007.
[RFC5054] Taylor, D., Wu, T., Mavrogiannopoulos, N., and T. Perrin, [RFC5051] Crispin, M., "i;unicode-casemap - Simple Unicode
"Using the Secure Remote Password (SRP) Protocol for TLS Collation Algorithm", RFC 5051, October 2007.
Authentication", RFC 5054, November 2007.
[RFC5122] Saint-Andre, P., "Internationalized Resource Identifiers [RFC5054] Taylor, D., Wu, T., Mavrogiannopoulos, N., and T.
(IRIs) and Uniform Resource Identifiers (URIs) for the Perrin, "Using the Secure Remote Password (SRP) Protocol
Extensible Messaging and Presence Protocol (XMPP)", for TLS Authentication", RFC 5054, November 2007.
RFC 5122, February 2008.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., [RFC5122] Saint-Andre, P., "Internationalized Resource Identifiers
Housley, R., and W. Polk, "Internet X.509 Public Key (IRIs) and Uniform Resource Identifiers (URIs) for the
Infrastructure Certificate and Certificate Revocation List Extensible Messaging and Presence Protocol (XMPP)",
(CRL) Profile", RFC 5280, May 2008. RFC 5122, February 2008.
[RFC5456] Spencer, M., Capouch, B., Guy, E., Miller, F., and K. [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Shumard, "IAX: Inter-Asterisk eXchange Version 2", Housley, R., and W. Polk, "Internet X.509 Public Key
RFC 5456, February 2010. Infrastructure Certificate and Certificate Revocation
List (CRL) Profile", RFC 5280, May 2008.
[RFC5661] Shepler, S., Eisler, M., and D. Noveck, "Network File [RFC5456] Spencer, M., Capouch, B., Guy, E., Miller, F., and K.
System (NFS) Version 4 Minor Version 1 Protocol", Shumard, "IAX: Inter-Asterisk eXchange Version 2",
RFC 5661, January 2010. RFC 5456, February 2010.
[RFC5802] Newman, C., Menon-Sen, A., Melnikov, A., and N. Williams, [RFC5661] Shepler, S., Eisler, M., and D. Noveck, "Network File
"Salted Challenge Response Authentication Mechanism System (NFS) Version 4 Minor Version 1 Protocol",
(SCRAM) SASL and GSS-API Mechanisms", RFC 5802, July 2010. RFC 5661, January 2010.
[RFC5804] Melnikov, A. and T. Martin, "A Protocol for Remotely [RFC5802] Newman, C., Menon-Sen, A., Melnikov, A., and N.
Managing Sieve Scripts", RFC 5804, July 2010. Williams, "Salted Challenge Response Authentication
Mechanism (SCRAM) SASL and GSS-API Mechanisms",
RFC 5802, July 2010.
[RFC5890] Klensin, J., "Internationalized Domain Names for [RFC5804] Melnikov, A. and T. Martin, "A Protocol for Remotely
Applications (IDNA): Definitions and Document Framework", Managing Sieve Scripts", RFC 5804, July 2010.
RFC 5890, August 2010.
[RFC5891] Klensin, J., "Internationalized Domain Names in [RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Protocol", RFC 5891, August 2010. Applications (IDNA): Definitions and Document
Framework", RFC 5890, August 2010.
[RFC5892] Faltstrom, P., "The Unicode Code Points and [RFC5891] Klensin, J., "Internationalized Domain Names in
Internationalized Domain Names for Applications (IDNA)", Applications (IDNA): Protocol", RFC 5891, August 2010.
RFC 5892, August 2010.
[RFC5893] Alvestrand, H. and C. Karp, "Right-to-Left Scripts for [RFC5892] Faltstrom, P., "The Unicode Code Points and
Internationalized Domain Names for Applications (IDNA)", Internationalized Domain Names for Applications (IDNA)",
RFC 5893, August 2010. RFC 5892, August 2010.
[RFC5894] Klensin, J., "Internationalized Domain Names for [RFC5893] Alvestrand, H. and C. Karp, "Right-to-Left Scripts for
Applications (IDNA): Background, Explanation, and Internationalized Domain Names for Applications (IDNA)",
Rationale", RFC 5894, August 2010. RFC 5893, August 2010.
[RFC5895] Resnick, P. and P. Hoffman, "Mapping Characters for [RFC5894] Klensin, J., "Internationalized Domain Names for
Internationalized Domain Names in Applications (IDNA) Applications (IDNA): Background, Explanation, and
2008", RFC 5895, September 2010. Rationale", RFC 5894, August 2010.
[RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in [RFC5895] Resnick, P. and P. Hoffman, "Mapping Characters for
Internationalization in the IETF", BCP 166, RFC 6365, Internationalized Domain Names in Applications (IDNA)
September 2011. 2008", RFC 5895, September 2010.
[RFC6452] Faltstrom, P. and P. Hoffman, "The Unicode Code Points and [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
Internationalized Domain Names for Applications (IDNA) - Protocol (XMPP): Core", RFC 6120, March 2011.
Unicode 6.0", RFC 6452, November 2011.
[UAX15] "Unicode Standard Annex #15: Unicode Normalization Forms", [RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in
UAX 15, September 2009. Internationalization in the IETF", BCP 166, RFC 6365,
September 2011.
[Unicode61] [RFC6452] Faltstrom, P. and P. Hoffman, "The Unicode Code Points
The Unicode Consortium. The Unicode Standard, Version and Internationalized Domain Names for Applications
6.1, defined by:, "The Unicode Standard -- Version 6.1", (IDNA) - Unicode 6.0", RFC 6452, November 2011.
(Mountain View, CA: The Unicode Consortium, 2012. ISBN
978-1-936213-02-3), September 2009,
<http://www.unicode.org/versions/Unicode6.1.0/>.
[ietf78precis] [UAX15] "Unicode Standard Annex #15: Unicode Normalization
Blanchet, M., "PRECIS Framework", Proceedings of the Forms", UAX 15, September 2009.
Seventy-Eighth Internet Engineering Task
Force https://www.ietf.org/proceedings/78/, July 2010, [Unicode61] The Unicode Consortium. The Unicode Standard, Version
<http://www.ietf.org/proceedings/78/slides/precis-2.pdf>. 6.1.0, (Mountain View, CA: The Unicode Consortium, 2012.
ISBN 978-1-936213-02-3).
<http://www.unicode.org/versions/Unicode6.1.0/>.
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 5.1.1), using the called out in the ID type column (from Section 5.1.1) using the short
short forms "a" for Absolute, "d" for Definite, and "i" for forms "a" for Absolute, "d" for Definite, and "i" for Indefinite.
Indefinite. Next, there is a column that contains an "i" if the Next, there is a column that contains an "i" if the protocol string
protocol string comes from user input, an "o" if the protocol string comes from user input, an "o" if the protocol string becomes user-
becomes user-facing output, "b" if both are true, and "n" if neither 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 |
| 3748 | - | - | | 3748 | - | - |
| 3920 | a,d | b | | 3920 | a,d | b |
| 4505 | a | i | | 4505 | a | i |
| 4314 | a,d | b | | 4314 | a,d | b |
| 4954 | a,d | b | | 4954 | a,d | b |
skipping to change at page 18, line 40 skipping to change at page 19, line 39
Table 1 Table 1
Appendix B. Evaluation of Stringprep Profiles Appendix B. Evaluation of Stringprep Profiles
This section is a summary of evaluation of Stringprep profiles that This section is a summary of evaluation of Stringprep profiles that
was done to get a good understanding of the usage of Stringprep. was done to get a good understanding of the usage of Stringprep.
This summary is by no means normative nor the actual evaluations This summary is by no means normative nor the actual evaluations
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: RFC 3720, RFC 3721, RFC 3722
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
units (storage volumes), although both are unusual in practice. (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 internationalization protocol? The iSCSI protocol requires that all
string preparation occur in the user interface. The iSCSI internationalization string preparation occur in the user
protocol treats iSCSI names as opaque identifiers that are interface. The iSCSI protocol treats iSCSI names as opaque
compared byte-by-byte for equality. iSCSI names are generally not identifiers that are compared byte-by-byte for equality. iSCSI
checked for correct formatting by the protocol. names are generally not 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
Case Folding, Sensitivity, Preservation Case folding is required for Comparison: Byte-by-byte.
the code blocks specified in RFC 3454, Table B.2. The overall
Case Folding, Sensitivity, Preservation: Case folding is required
for 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.
access to the wrong storage, an authentication failure is the
probable result. - If the initiator has access to the wrong - If the initiator has no access to the wrong storage, an
storage, the resulting mis-identification could result in use of authentication failure is the probable result.
the wrong data and possible corruption of stored data.
- If the initiator has access to the wrong storage, the resulting
misidentification could result in use of 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 may be used as the What are the security impacts? iSCSI names may be 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.
Mapping Yes, as specified by table B.1 in RFC 3454 Normalization: NFKC, as specified by RFC 3454.
Disallowed Characters Only the following characters are allowed: -
ASCII dash, dot, colon - ASCII lower case letters and digits - Mapping: Yes, as specified by Table B.1 in RFC 3454.
Unicode lower case characters as specified by RFC 3454 All other
characters are disallowed. Disallowed Characters: Only the following characters are allowed:
Which other strings or identifiers are these most similar to? None - - ASCII dash, dot, colon
iSCSI names are unique to iSCSI. - ASCII lowercase letters and digits
- Unicode lowercase characters as specified by RFC 3454.
All other characters are disallowed.
Which other strings or identifiers are these most similar to?
None -- 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 Good tolerance; the community would prefer that
internationalization experts solve internationalization 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: RFC 4954, RFC 5034,
5804 RFC 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.
How It's Used: Used for proxy authorization, e.g. to [lawfully]
impersonate a particular user after a privileged authentication How It's Used: Used for proxy authorization, e.g., to [lawfully]
Who Generates It: Typically generated by email system administrators impersonate a particular user after a privileged authentication.
using some tools/conventions, sometimes from some backend
database. - In some setups human users can register own usernames Who Generates It:
(e.g. webmail self registration) - Typically generated by email system administrators using some
User Input Methods: - Typed by user / selected from a list - Copy- tools/conventions, sometimes from some backend database.
and-paste - Perhaps voice input - Can also be specified in - In some setups, human users can register their own usernames
configuration files or on a command line (e.g., webmail self-registration).
Enforcement: - Rules enforced by server / add-on service (e.g.,
gateway service) on registration of account User Input Methods:
Comparison Method: "Type 1" (byte-for-byte) or "type 2" (compare by - typing or selecting from a list
- copy and paste
- voice input
- in configuration files or on the command line
Enforcement: Rules enforced by server / add-on service (e.g.,
gateway service) on registration of account.
Comparison Method: "Type 1" (byte-for-byte) or "Type 2" (compare by
a common algorithm that everyone agrees on (e.g., normalize and a common algorithm that everyone agrees on (e.g., normalize and
then compare the result byte-by-byte)) then compare the result byte-by-byte).
Case Folding, Sensitivity, Preservation: Most likely case sensitive.
Case Folding, Sensitivity, Preservation: Most likely case-sensitive.
Exact requirements on case-sensitivity/case-preservation depend on Exact requirements on case-sensitivity/case-preservation depend on
a specific implementation, e.g. an implementation might treat all a specific implementation, e.g., an implementation might treat all
user identifiers as case insensitive (or case insensitive for US- user identifiers as case-insensitive (or case-insensitive for
ASCII subset only). US-ASCII subset only).
Impact of Comparison: False positives: - an unauthorized user is Impact of Comparison: False positives: an unauthorized user is
allowed email service access (login) False negatives: - an allowed email service access (login). False negatives: an
authorized user is denied email service access authorized user is denied email service access.
Normalization: NFKC (as per RFC 4013)
Mapping: (see Section 2 of RFC 4013 for the full list): Non ASCII Normalization: NFKC (as per RFC 4013).
Mapping: (see Section 2 of RFC 4013 for the full list) Non-ASCII
spaces are mapped to space, etc. spaces are mapped to space, etc.
Disallowed Characters: (see Section 2 of RFC 4013 for the full
list): Unicode Control characters, etc. Disallowed Characters: (see Section 2 of RFC 4013 for the full list)
String Classes: - simple username. See Section 2 of RFC 4013 for Unicode Control characters, etc.
String Classes: Simple username. See Section 2 of RFC 4013 for
details on restrictions. Note that some implementations allow details on restrictions. Note that some implementations allow
spaces in these. While implementations are not required to use a spaces in these. While implementations are not required to use a
specific format, an authorization identity frequently has the same specific format, an authorization identity frequently has the same
format as an email address (and EAI email address in the future), format as an email address (and Email Address Internationalization
or as a left hand side of an email address. Note: whatever is (EAI) email address in the future), or as a left hand side of an
recommended for SMTP/POP/ManageSieve authorization identity should email address. Note: whatever is recommended for SMTP/POP/
also be used for IMAP authorization identities, as IMAP/POP3/SMTP/ ManageSieve authorization identity should also be used for IMAP
ManageSieve are frequently implemented together. authorization identities, as IMAP/POP3/SMTP/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. as an email address.
Operations: - Sometimes concatenated with other data and then used
as input to a cryptographic hash function Operations: Sometimes concatenated with other data and then used 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
command: The authorization identity generated by the SASL exchange
is a simple username, and SHOULD use the SASLprep profile (see
RFC4013) of the StringPrep algorithm (see RFC3454) to prepare
these names for matching. If preparation of the authorization
identity fails or results in an empty string (unless it was
transmitted as the empty string), the server MUST fail the
authentication. In RFC 4954, when describing the SMTP AUTH
command: The authorization identity generated by this SASL
exchange is a "simple username" (in the sense defined in
SASLprep), and both client and server SHOULD (*) use the SASLprep
profile of the StringPrep algorithm to prepare these names for
transmission or comparison. If preparation of the authorization
identity fails or results in an empty string (unless it was
transmitted as the empty string), the server MUST fail the
authentication. (*) Note: Future revision of this specification
may change this requirement to MUST. Currently, the SHOULD is
used in order to avoid breaking the majority of existing
implementations. In RFC 5804, when describing the ManageSieve
AUTHENTICATE command: The authorization identity generated by this
SASL exchange is a "simple username" (in the sense defined in
SASLprep), and both client and server MUST use the SASLprep
profile of the StringPrep algorithm to prepare these names for
transmission or comparison. If preparation of the authorization
identity fails or results in an empty string (unless it was
transmitted as the empty string), the server MUST fail the
authentication.
B.3. IMAP Stringprep Profiles: RFC5738, RFC4314: Usernames Background Information:
In RFC 5034, when describing the POP3 AUTH command:
Evaluation Note These documents have 2 types of strings (usernames The authorization identity generated by the SASL exchange is a
simple username, and SHOULD use the SASLprep profile (see
[RFC4013]) of the StringPrep algorithm (see [RFC3454]) to
prepare these names for matching. If preparation of the
authorization identity fails or results in an empty string
(unless it was transmitted as the empty string), the server
MUST fail the authentication.
In RFC 4954, when describing the SMTP AUTH command:
The authorization identity generated by this [SASL] exchange is
a "simple username" (in the sense defined in [SASLprep]), and
both client and server SHOULD (*) use the [SASLprep] profile of
the [StringPrep] algorithm to prepare these names for
transmission or comparison. If preparation of the
authorization identity fails or results in an empty string
(unless it was transmitted as the empty string), the server
MUST fail the authentication.
(*) Note: Future revision of this specification may change this
requirement to MUST. Currently, the SHOULD is used in order to
avoid breaking the majority of existing implementations.
In RFC 5804, when describing the ManageSieve AUTHENTICATE command:
The authorization identity generated by this [SASL] exchange is
a "simple username" (in the sense defined in [SASLprep]), and
both client and server MUST use the [SASLprep] profile of the
[StringPrep] algorithm to prepare these names for transmission
or comparison. If preparation of the authorization identity
fails or results in an empty string (unless it was transmitted
as the empty string), the server MUST fail the authentication.
B.3. IMAP Stringprep Profiles for Usernames: RFC 4314, RFC 5738
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,
identifiers in IMAP ACL commands. Note that any valid username is identifiers in IMAP Access Control List (ACL) commands. Note that
also an IMAP ACL identifier, but IMAP ACL identifiers can include any valid username is also an IMAP ACL identifier, but IMAP ACL
other things like name of group of users. identifiers can include other things like the name of a group of
users.
How It's Used: Used for authentication (Usernames), or in IMAP How It's Used: Used for authentication (Usernames), or in IMAP
Access Control Lists (Usernames or Group names) Access Control Lists (Usernames or Group names).
Who Generates It: - Typically generated by email system
administrators using some tools/conventions, sometimes from some Who Generates It:
backend database. - In some setups human users can register own - Typically generated by email system administrators using some
usernames (e.g. webmail self registration) tools/conventions, sometimes from some backend database.
User Input Methods: - Typed by user / selected from a list - Copy- - In some setups, human users can register own usernames (e.g.,
and-paste - Perhaps voice input - Can also be specified in webmail self-registration).
configuration files or on a command line
Enforcement: - Rules enforced by server / add-on service (e.g., User Input Methods:
gateway service) on registration of account - typing or selecting from a list
Comparison Method: Type 1" (byte-for-byte) or "type 2" (compare by a - copy and paste
common algorithm that everyone agrees on (e.g., normalize and then - voice input
compare the result byte-by-byte)) - in configuration files or on the command line
Case Folding, Sensitivity, Preservation: - Most likely case
sensitive. Exact requirements on case-sensitivity/ Enforcement: Rules enforced by server / add-on service (e.g.,
case-preservation depend on a specific implementation, e.g. an gateway service) on registration of account.
implementation might treat all user identifiers as case
insensitive (or case insensitive for US-ASCII subset only). Comparison Method: "Type 1" (byte-for-byte) or "Type 2" (compare by
Impact of Comparison: False positives: - an unauthorized user is a common algorithm that everyone agrees on (e.g., normalize and
allowed IMAP access (login) - improperly grant privileges (e.g., then compare the result byte-by-byte).
Case Folding, Sensitivity, Preservation: Most likely case-sensitive.
Exact requirements on case-sensitivity/case-preservation depend on
a specific implementation, e.g., an implementation might treat all
user identifiers as case-insensitive (or case-insensitive for
US-ASCII subset only).
Impact of Comparison: False positives: an unauthorized user is
allowed IMAP access (login), privileges improperly granted (e.g.,
access to a specific mailbox, ability to manage ACLs for a access to a specific mailbox, ability to manage ACLs for a
mailbox) False negatives: - an authorized user is denied IMAP mailbox). False negatives: an authorized user is denied IMAP
access - unable to use granted privileges (e.g., access to a access, unable to use granted privileges (e.g., access to a
specific mailbox, ability to manage ACLs for a mailbox) specific mailbox, ability to manage ACLs for a mailbox).
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
spaces are mapped to space Mapping: (see Section 2 of RFC 4013 for the full list) Non-ASCII
Disallowed Characters: (see Section 2 of RFC 4013 for the full spaces are mapped to space.
list): Unicode Control characters, etc.
String Classes: - simple username. See Section 2 of RFC 4013 for Disallowed Characters: (see Section 2 of RFC 4013 for the full list)
Unicode Control characters, etc.
String Classes: Simple username. See Section 2 of RFC 4013 for
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 the IMAP username should also be used for
POP3 and SMTP authorization identities, as IMAP/POP3/SMTP/ ManageSieve, POP3 and SMTP authorization identities, as IMAP/POP3/
ManageSieve are frequently implemented together. SMTP/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 shows up as mailbox names
(under Other Users IMAP namespace) (under Other Users IMAP namespace).
Operations: - Sometimes concatenated with other data and then used
as input to a cryptographic hash function Operations: Sometimes concatenated with other data and then used 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 for Passwords: RFC 5738
Description: "Password" parameter to the IMAP LOGIN command.
How It's Used: Used for authentication (Passwords).
Description: "Password" parameter to the IMAP LOGIN command
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
input - Can also be specified in configuration files or on a User Input Methods:
command line - typing or selecting from a list
- copy and paste
- voice input
- in configuration files or on the 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 database) on registration of account.
Comparison Method: "Type 1" (byte-for-byte)
Case Folding, Sensitivity, Preservation: Most likely case sensitive. Comparison Method: "Type 1" (byte-for-byte).
Impact of Comparison: False positives: - an unauthorized user is
allowed IMAP access (login) False negatives: - an authorized user Case Folding, Sensitivity, Preservation: Most likely case-sensitive.
is denied IMAP access
Normalization: NFKC (as per RFC 4013) Impact of Comparison: False positives: an unauthorized user is
Mapping: (see Section 2 of RFC 4013 for the full list): non ASCII allowed IMAP access (login). False negatives: an authorized user
spaces are mapped to space is denied IMAP access.
Disallowed Characters: (see Section 2 of RFC 4013 for the full
list): Unicode Control characters, etc. Normalization: NFKC (as per RFC 4013).
Mapping: (see Section 2 of RFC 4013 for the full list) Non-ASCII
spaces are mapped to space.
Disallowed Characters: (see Section 2 of RFC 4013 for the full 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, and etc.
Internal Structure: None applications.
User Output: - text of email messages (e.g. in "you forgot your
password" email messages) - web page / directory - side of the bus Internal Structure: None.
/ in ads -- possible
User Output: Text of email messages (e.g. in "you forgot your
password" email messages), web page / directory, side of the bus /
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.
UTF8=USER Capability If the "UTF8=USER" capability is advertised,
that indicates the server accepts UTF-8 user names and passwords
and applies SASLprep RFC4013 to both arguments of the LOGIN
command. The server MUST reject UTF-8 that fails to comply with
the formal syntax in RFC 3629 RFC3629 or if it encounters Unicode
characters listed in Section 2.3 of SASLprep RFC 4013 RFC4013.
RFC 4314 (IMAP4 Access Control List (ACL) Extension): 3. Access
control management commands and responses Servers, when processing
a command that has an identifier as a parameter (i.e., any of
SETACL, DELETEACL, and LISTRIGHTS commands), SHOULD first prepare
the received identifier using "SASLprep" profile SASLprep of the
"Stringprep" algorithm Stringprep. If the preparation of the
identifier fails or results in an empty string, the server MUST
refuse to perform the command with a BAD response. Note that
Section 6 recommends additional identifier's verification steps.
and in Section 6: This document relies on SASLprep to describe
steps required to perform identifier canonicalization
(preparation). The preparation algorithm in SASLprep was
specifically designed such that its output is canonical, and it is
well-formed. However, due to an anomaly PR29 in the specification
of Unicode normalization, canonical equivalence is not guaranteed
for a select few character sequences. Identifiers prepared with
SASLprep can be stored and returned by an ACL server. The anomaly
affects ACL manipulation and evaluation of identifiers containing
the selected character sequences. These sequences, however, do
not appear in well-formed text. In order to address this problem,
an ACL server MAY reject identifiers containing sequences
described in PR29 by sending the tagged BAD response. This is in
addition to the requirement to reject identifiers that fail
SASLprep preparation as described in Section 3.
B.5. Anonymous SASL Stringprep Profiles: RFC4505 Background Information:
RFC 5738, Section 5 ("UTF8=USER Capability"):
If the "UTF8=USER" capability is advertised, that indicates the
server accepts UTF-8 user names and passwords and applies
SASLprep [RFC4013] to both arguments of the LOGIN command. The
server MUST reject UTF-8 that fails to comply with the formal
syntax in RFC 3629 [RFC3629] or if it encounters Unicode
characters listed in Section 2.3 of SASLprep RFC 4013
[RFC4013].
RFC 4314, Section 3 ("Access control management commands and
responses"):
Servers, when processing a command that has an identifier as a
parameter (i.e., any of SETACL, DELETEACL, and LISTRIGHTS
commands), SHOULD first prepare the received identifier using
"SASLprep" profile [SASLprep] of the "stringprep" algorithm
[Stringprep]. If the preparation of the identifier fails or
results in an empty string, the server MUST refuse to perform
the command with a BAD response. Note that Section 6
recommends additional identifier's verification steps.
RFC 4314, Section 6 ("Security Considerations"):
This document relies on [SASLprep] to describe steps required
to perform identifier canonicalization (preparation). The
preparation algorithm in SASLprep was specifically designed
such that its output is canonical, and it is well-formed.
However, due to an anomaly [PR29] in the specification of
Unicode normalization, canonical equivalence is not guaranteed
for a select few character sequences. Identifiers prepared
with SASLprep can be stored and returned by an ACL server. The
anomaly affects ACL manipulation and evaluation of identifiers
containing the selected character sequences. These sequences,
however, do not appear in well-formed text. In order to
address this problem, an ACL server MAY reject identifiers
containing sequences described in [PR29] by sending the tagged
BAD response. This is in addition to the requirement to reject
identifiers that fail SASLprep preparation as described in
Section 3.
B.5. Anonymous SASL Stringprep Profiles: RFC 4505
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
sensitive Case folding; case-sensitivity, preserve case: No case folding/
case-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
Disallowed Characters Control characters are disallowed. (See Normalization: None.
Section 3 of RFC 4505)
Which other strings or identifiers are these most similar to? RFC Disallowed Characters: Control characters are disallowed. (See
4505 says that the trace "should take one of two forms: an Section 3 of RFC 4505).
Which other strings or identifiers are these most similar to?
RFC 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 free-form text, so it belongs to a different class from
address" or "username". "email 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
use the same credentials database for authentication as an email sometimes use the same credentials database for authentication as
system)? Yes: see above. However there is no strong need to keep an email system)? Yes: see above. However, there is no strong
them consistent in the future. need to keep 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
user can be confused with another user. False negative: two Impacts of false positives and false negatives:
distinct users are treated as the same user. But note that the False positive: a user can be confused with another user.
trace field is not authenticated, so it can be easily falsified. False negative: two distinct users are treated as the same user.
Tolerance of changes in the community The community would be But note that the trace field is not authenticated, so it can be
easily falsified.
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
consists of a single message from the client to the server. The
client may include in this message trace information in the form
of a string of UTF-8-encoded Unicode characters prepared in
accordance with StringPrep and the "trace" Stringprep profile
defined in Section 3 of this document. The trace information,
which has no semantical value, should take one of two forms: an
Internet email address, or an opaque string that does not contain
the '@' (U+0040) character and that can be interpreted by the
system administrator of the client's domain. For privacy reasons,
an Internet email address or other information identifying the
user should only be used with permission from the user. 3. The
"trace" Profile of "Stringprep" This section defines the "trace"
profile of StringPrep. This profile is designed for use with the
SASL ANONYMOUS Mechanism. Specifically, the client is to prepare
the message production in accordance with this profile. The
character repertoire of this profile is Unicode 3.2. No mapping
is required by this profile. No Unicode normalization is required
by this profile. The list of unassigned code points for this
profile is that provided in Appendix A of StringPrep. Unassigned
code points are not prohibited. Characters from the following
tables of StringPrep are prohibited: - C.2.1 (ASCII control
characters) - C.2.2 (Non-ASCII control characters) - C.3 (Private
use characters) - C.4 (Non-character code points) - C.5 (Surrogate
codes) - C.6 (Inappropriate for plain text) - C.8 (Change display
properties are deprecated) - C.9 (Tagging characters) No
additional characters are prohibited. This profile requires
bidirectional character checking per Section 6 of StringPrep.
B.6. XMPP Stringprep Profiles: RFC3920 Nodeprep Background Information:
RFC 4505, Section 2 ("The Anonymous Mechanism"):
The mechanism consists of a single message from the client to the
server. The client may include in this message trace information
in the form of a string of [UTF-8]-encoded [Unicode] characters
prepared in accordance with [StringPrep] and the "trace"
stringprep profile defined in Section 3 of this document. The
trace information, which has no semantical value, should take one
of two forms: an Internet email address, or an opaque string that
does not contain the '@' (U+0040) character and that can be
interpreted by the system administrator of the client's domain.
For privacy reasons, an Internet email address or other
information identifying the user should only be used with
permission from the user.
RFC 4505, Section 3 ('The "trace" Profile of "Stringprep"'):
This section defines the "trace" profile of [StringPrep]. This
profile is designed for use with the SASL ANONYMOUS Mechanism.
Specifically, the client is to prepare the <message> production in
accordance with this profile.
The character repertoire of this profile is Unicode 3.2 [Unicode].
No mapping is required by this profile.
No Unicode normalization is required by this profile.
The list of unassigned code points for this profile is that
provided in Appendix A of [StringPrep]. Unassigned code points
are not prohibited.
Characters from the following tables of [StringPrep] are
prohibited:
- C.2.1 (ASCII control characters)
- C.2.2 (Non-ASCII control characters)
- C.3 (Private use characters)
- C.4 (Non-character code points)
- C.5 (Surrogate codes)
- C.6 (Inappropriate for plain text)
- C.8 (Change display properties are deprecated)
- C.9 (Tagging characters)
No additional characters are prohibited.
This profile requires bidirectional character checking per Section 6
of [StringPrep].
B.6. XMPP Stringprep Profiles for Nodeprep: RFC 3920
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
names (e.g., precis@jabber.ietf.org) - Publish-subscribe nodes - How It's Used:
Bot names - Usernames (e.g., stpeter@jabber.org)
Who Generates It: - Typically, end users via an XMPP client - - Chatroom names (e.g., precis@jabber.ietf.org)
Sometimes created in an automated fashion - Publish-subscribe nodes
User Input Methods: - Typed by user - Copy-and-paste - Perhaps voice - Bot names
input - Clicking a URI/IRI
Enforcement: - Rules enforced by server / add-on service (e.g., Who Generates It:
- Typically, end users via an XMPP client
- Sometimes created in an automated fashion
User Input Methods:
- typing
- copy and paste
- voice input
- clicking a URI/IRI
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.
Comparison Method: "Type 2" (common algorithm) Comparison Method: "Type 2" (common algorithm)
Case Folding, Sensitivity, Preservation: - Strings are always folded
to lowercase - Case is not preserved Case Folding, Sensitivity, Preservation:
Impact of Comparison: False positives: - unable to authenticate at - Strings are always folded to lowercase
server (or authenticate to wrong account) - add wrong person to - Case is not preserved
buddy list - join the wrong chatroom - improperly grant privileges
(e.g., chatroom admin) - subscribe to wrong pubsub node - interact Impact of Comparison:
with wrong bot - allow communication with blocked entity False False positives:
negatives: - unable to authenticate - unable to add someone to - unable to authenticate at server (or authenticate to wrong
buddy list - unable to join desired chatroom - unable to use account)
granted privileges (e.g., chatroom admin) - unable to subscribe to - add wrong person to buddy list
desired pubsub node - unable to interact with desired bot - - join the wrong chatroom
disallow communication with unblocked entity - improperly grant privileges (e.g., chatroom admin)
- subscribe to wrong pubsub node
- interact with wrong bot
- allow communication with blocked entity
False negatives:
- unable to authenticate
- unable to add someone to buddy list
- unable to join desired chatroom
- unable to use granted privileges (e.g., chatroom admin)
- unable to subscribe to desired pubsub node
- unable to interact with desired bot
- disallow communication with unblocked entity
Normalization: NFKC Normalization: NFKC
Mapping: Spaces are mapped to nothing Mapping: Spaces are mapped to nothing
Disallowed Characters: ",&,',/,:,<,>,@ Disallowed Characters: ",&,',/,:,<,>,@
String Classes: - Often similar to generic username - Often similar
to localpart of email address - Sometimes same as localpart of String Classes:
email address - Often similar to generic username
- Often similar to localpart of email address
- Sometimes same as localpart of email address
Internal Structure: None Internal Structure: None
User Output: - vCard - email signature - web page / directory - text
of message (e.g., in a chatroom)
Operations: - Sometimes concatenated with other data and then used
as input to a cryptographic hash function
B.7. XMPP Stringprep Profiles: RFC3920 Resourceprep User Output:
- vCard
- email signature
- web page / directory
- text of message (e.g., in a chatroom)
Description: - Resourcepart of JabberID ("JID"), as in: Operations: Sometimes concatenated with other data and then used as
localpart@domainpart/resourcepart - Typically free-form text input to a cryptographic hash function
How It's Used: - Device / session names (e.g.,
stpeter@jabber.org/Home) - Nicknames (e.g., B.7. XMPP Stringprep Profiles for Resourceprep: RFC 3920
precis@jabber.ietf.org/StPeter)
Who Generates It: - Often human users via an XMPP client - Often Description:
generated in an automated fashion by client or server - Resourcepart of JabberID ("JID"), as in:
User Input Methods: - Typed by user - Copy-and-paste - Perhaps voice localpart@domainpart/resourcepart
input - Clicking a URI/IRI - Typically free-form text
Enforcement: - Rules enforced by server / add-on service (e.g.,
How It's Used:
- Device / session names (e.g., stpeter@jabber.org/Home)
- Nicknames (e.g., precis@jabber.ietf.org/StPeter)
Who Generates It:
- Often human users via an XMPP client
- Often generated in an automated fashion by client or server
User Input Methods:
- typing
- copy and paste
- voice input
- clicking a URI/IRI
Enforcement: Rules enforced by server / add-on service (e.g.,
chatroom service) on account login, joining a chatroom, etc. chatroom service) on account login, joining a chatroom, etc.
Comparison Method: "Type 2" (byte-for-byte) Comparison Method: "Type 2" (byte-for-byte)
Case Folding, Sensitivity, Preservation: - Strings are never folded
- Case is preserved Case Folding, Sensitivity, Preservation:
Impact of Comparison: False positives: - interact with wrong device - Strings are never folded
(e.g., for file transfer or voice call) - interact with wrong - Case is preserved
chatroom participant - improperly grant privileges (e.g., chatroom
moderator) - allow communication with blocked entity False Impact of Comparison:
negatives: - unable to choose desired chatroom nick - unable to False positives:
use granted privileges (e.g., chatroom moderator) - disallow - interact with wrong device (e.g., for file transfer or voice
communication with unblocked entity call)
- interact with wrong chatroom participant
- improperly grant privileges (e.g., chatroom moderator)
- allow communication with blocked entity
False negatives:
- unable to choose desired chatroom nickname
- unable to use granted privileges (e.g., chatroom moderator)
- disallow communication with unblocked entity
Normalization: NFKC Normalization: NFKC
Mapping: Spaces are mapped to nothing Mapping: Spaces are mapped to nothing
Disallowed Characters: None Disallowed Characters: None
String Classes: Basically a free-form identifier String Classes: Basically a free-form identifier
Internal Structure: None Internal Structure: None
User Output: - text of message (e.g., in a chatroom) - device names
often not exposed to human users User Output:
- text of message (e.g., in a chatroom)
- device names often not exposed to human users
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 input to a cryptographic hash function
B.8. EAP Stringprep Profiles: RFC3748 B.8. EAP Stringprep Profiles: RFC 3748
Description: RFC 3748 section 5 references Stringprep, but the WG Description: RFC 3748, Section 5, references Stringprep, but the WG
did not agree with the text (was added by IESG) and there are no did not agree with the text (was added by IESG) and there are no
known implementations that use Stringprep. The main problem with known implementations that use Stringprep. The main problem with
that text is that the use of strings is a per-method concept, not that text is that the use of strings is a per-method concept, not
a generic EAP concept and so RFC 3748 itself does not really use a generic EAP concept and so RFC 3748 itself does not really use
Stringprep, but individual EAP methods could. As such, the Stringprep, but individual EAP methods could. As such, the
answers to the template questions are mostly not applicable, but a answers to the template questions are mostly not applicable, but a
few answers are universal across methods. The list of IANA few answers are universal across methods. The list of IANA
registered EAP methods is at http://www.iana.org/assignments/ registered EAP methods is at
eap-numbers/eap-numbers.xml#eap-numbers-3 <http://www.iana.org/assignments/eap-numbers/eap-numbers.xml>.
Comparison Methods: n/a (per-method) Comparison Methods: n/a (per-method)
Case Folding, Case Sensitivity, Case Preservation: n/a (per-method)
Case Folding, Case-Sensitivity, Case Preservation: n/a (per-method)
Impact of comparison: A false positive results in unauthorized Impact of comparison: A false positive results in unauthorized
network access (and possibly theft of service if some else is network access (and possibly theft of service if some else is
billed). A false negative results in lack of authorized network billed). A false negative results in lack of authorized network
access (no connectivity). access (no connectivity).
User input: n/a (per-method) User input: n/a (per-method)
Normalization: n/a (per-method) Normalization: n/a (per-method)
Mapping: n/a (per-method) Mapping: n/a (per-method)
Disallowed characters: n/a (per-method) Disallowed characters: n/a (per-method)
String classes: Although some EAP methods may use a syntax similar String classes: Although some EAP methods may use a syntax similar
to other types of identifiers, EAP mandates that the actual values to other types of identifiers, EAP mandates that the actual values
must not be assumed to be identifiers usable with anything else. must not be assumed to be identifiers usable with anything else.
Internal structure: n/a (per-method) Internal structure: n/a (per-method)
User output: Identifiers are never human displayed except perhaps as User output: Identifiers are never human displayed except perhaps as
they're typed by a human. they're typed by a human.
Operations: n/a (per-method) Operations: n/a (per-method)
Community considerations: There is no resistance to change for the Community considerations: There is no resistance to change for the
base EAP protocol (as noted, the WG didn't want the existing base EAP protocol (as noted, the WG didn't want the existing
text). However actual use of Stringprep, if any, within specific text). However, actual use of Stringprep, if any, within specific
EAP methods may have resistance. It is currently unknown whether EAP methods may have resistance. It is currently unknown whether
any EAP methods use Stringprep. any EAP methods use Stringprep.
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
Andrew Sullivan Andrew Sullivan
Dyn, Inc. Dyn, Inc.
150 Dow St 150 Dow St
Manchester, NH 03101 Manchester, NH 03101
U.S.A. U.S.A.
Email: asullivan@dyn.com EMail: asullivan@dyn.com
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