Unicode

This document discusses subsets of the Unicode character repertoire for use in protocols and data formats and specifies three subsets recommended for use in IETF specifications.

This document describes the changes between Unicode 6.0.0 and Unicode 12.0.0 in the context of the current version of Internationalized Domain Names for Applications 2008 (IDNA2008). Some additions and changes have been made in the Unicode Standard that affect the values produced by the algorithm IDNA2008 specifies. IDNA2008 allows adding exceptions to the algorithm for backward compatibility; however, this document does not add any such exceptions. This document provides the necessary tables to IANA to make its database consistent with Unicode 12.0.0.

To improve understanding, this document describes systems that are being used as alternatives to those that conform to IDNA2008.

The standards for Internationalized Domain Names in Applications (IDNA) require a review of each new version of Unicode to determine whether incompatibilities with prior versions or other issues exist and, where appropriate, to allow the IETF to decide on the trade-offs between compatibility with prior IDNA versions and compatibility with Unicode going forward. That requirement, and its relationship to tables maintained by IANA, has caused significant confusion in the past. This document makes adjustments to the review procedure based on experience and updates IDNA, specifically RFC 5892, to reflect those changes and to clarify the various relationships involved. It also makes other minor adjustments to align that document with experience.

This document describes updated methods for handling Unicode strings representing usernames and passwords. The previous approach was known as SASLprep (RFC 4013) and was based on Stringprep (RFC 3454). The methods specified in this document provide a more sustainable approach to the handling of internationalized usernames and passwords. This document obsoletes RFC 7613.

This document defines UTF-8 representations for IP Flow Information Export (IPFIX) abstract data types (ADTs) to support interoperable usage of the IPFIX Information Elements with protocols based on textual encodings.

Internationalized Domain Names in Applications (IDNA) makes available to DNS zone administrators a very wide range of Unicode code points. Most operators of zones should probably not permit registration of U-labels using the entire range. This is especially true of zones that accept registrations across organizational boundaries, such as top-level domains and, most importantly, the root. It is unfortunately not possible to generate algorithms to determine whether permitting a code point presents a low risk. This memo presents a set of principles that can be used to guide the decision of whether a Unicode code point may be wisely included in the repertoire of permissible code points in a U-label in a zone.

This memo splits message submission from message relay, allowing each service to operate according to its own rules (for security, policy, etc.), and specifies what actions are to be taken by a submission server.

Message relay is unaffected, and continues to use SMTP over port 25.

When conforming to this document, message submission uses the protocol specified here, normally over port 587.

This separation of function offers a number of benefits, including the ability to apply specific security or policy requirements. [STANDARDS-TRACK]

This memo documents IETF consensus for Internationalized Domain Names for Applications (IDNA) derived character properties related to the three code points, existing in Unicode 5.2, that changed property values when version 6.0 was released. The consensus is that no update is needed to RFC 5892 based on the changes made in Unicode 6.0. [STANDARDS-TRACK]

This document explores issues with Internationalized Domain Names (IDNs) that result from the use of various encoding schemes such as UTF-8 and the ASCII-Compatible Encoding produced by the Punycode algorithm. It focuses on the importance of agreeing on a single encoding and how complicated the state of affairs ends up being as a result of using different encodings today.

This document specifies an Extension to BCP 47 that provides subtags that specify language and/or locale-based behavior or refinements to language tags, according to work done by the Unicode Consortium. This document is not an Internet Standards Track specification; it is published for informational purposes.

RFC 2482, "Language Tagging in Unicode Plain Text", describes a mechanism for using special Unicode language tag characters to identify languages when needed without more general markup such as that provided by XML. The Unicode Consortium has deprecated that facility and strongly recommends against its use. RFC 2482 has been moved to Historic status to reduce the possibility that Internet implementers would consider that system an appropriate mechanism for identifying languages. This document is not an Internet Standards Track specification; it is published for informational purposes.

In the original version of the Internationalized Domain Names in Applications (IDNA) protocol, any Unicode code points taken from user input were mapped into a set of Unicode code points that "made sense", and then encoded and passed to the domain name system (DNS). The IDNA2008 protocol (described in RFCs 5890, 5891, 5892, and 5893) presumes that the input to the protocol comes from a set of "permitted" code points, which it then encodes and passes to the DNS, but does not specify what to do with the result of user input. This document describes the actions that can be taken by an implementation between receiving user input and passing permitted code points to the new IDNA protocol. This document is not an Internet Standards Track specification; it is published for informational purposes.

This document specifies rules for deciding whether a code point, considered in isolation or in context, is a candidate for inclusion in an Internationalized Domain Name (IDN).

It is part of the specification of Internationalizing Domain Names in Applications 2008 (IDNA2008). [STANDARDS-TRACK]

The Internet today is in need of a standardized form for the transmission of internationalized "text" information, paralleling the specifications for the use of ASCII that date from the early days of the ARPANET. This document specifies that format, using UTF-8 with normalization and specific line-ending sequences. [STANDARDS-TRACK]

There are a number of circumstances in which an escape mechanism is needed in conjunction with a protocol to encode characters that cannot be represented or transmitted directly. With ASCII coding, the traditional escape has been either the decimal or hexadecimal numeric value of the character, written in a variety of different ways. The move to Unicode, where characters occupy two or more octets and may be coded in several different forms, has further complicated the question of escapes. This document discusses some options now in use and discusses considerations for selecting one for use in new IETF protocols, and protocols that are now being internationalized. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.

This document describes "i;unicode-casemap", a simple case-insensitive collation for Unicode strings. It provides equality, substring, and ordering operations. [STANDARDS-TRACK]

This memo describes various internal workings of the Unicode Consortium for the benefit of participants in the IETF. It is intended solely for informational purposes. Included are discussions of how the decision-making bodies of the Consortium work and their procedures, as well as information on public access to the character encoding & standardization processes.

ISO/IEC 10646-1 defines a large character set called the Universal Character Set (UCS) which encompasses most of the world's writing systems. The originally proposed encodings of the UCS, however, were not compatible with many current applications and protocols, and this has led to the development of UTF-8, the object of this memo. UTF-8 has the characteristic of preserving the full US-ASCII range, providing compatibility with file systems, parsers and other software that rely on US-ASCII values but are transparent to other values. This memo obsoletes and replaces RFC 2279.

Punycode is a simple and efficient transfer encoding syntax designed for use with Internationalized Domain Names in Applications (IDNA). It uniquely and reversibly transforms a Unicode string into an ASCII string. ASCII characters in the Unicode string are represented literally, and non-ASCII characters are represented by ASCII characters that are allowed in host name labels (letters, digits, and hyphens). This document defines a general algorithm called Bootstring that allows a string of basic code points to uniquely represent any string of code points drawn from a larger set. Punycode is an instance of Bootstring that uses particular parameter values specified by this document, appropriate for IDNA. [STANDARDS-TRACK]

This document reviews the original function and purpose of the domain name system (DNS). It contrasts that history with some of the purposes for which the DNS has recently been applied and some of the newer demands being placed upon it or suggested for it. A framework for an alternative to placing these additional stresses on the DNS is then outlined. This document and that framework are not a proposed solution, only a strong suggestion that the time has come to begin thinking more broadly about the problems we are encountering and possible approaches to solving them. This memo provides information for the Internet community.

This document describes the UTF-16 encoding of Unicode/ISO-10646, addresses the issues of serializing UTF-16 as an octet stream for transmission over the Internet, discusses MIME charset naming as described in [CHARSET-REG], and contains the registration for three MIME charset parameter values: UTF-16BE (big-endian), UTF-16LE (little- endian), and UTF-16. This memo provides information for the Internet community.

This document describes a transformation format of Unicode that contains only 7-bit ASCII octets and is intended to be readable by humans in the limiting case that the document consists of characters from the US-ASCII repertoire. It also specifies how this transformation format is used in the context of MIME and RFC 1641, "Using Unicode with MIME". This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind.

This document specifies the usage of Unicode within MIME. This memo defines an Experimental Protocol for the Internet community.