An X-IDNA Profile for Network News Group Names
draft-teint-xidna-newsgroup-00

Abstract

Traditional Network News (Netnews) systems handle only ASCII characters in newsgroup names used in NNTP commands and message headers.

This memo defines an extension to allow Internationalised Newsgroup Names, the characters of which can be drawn from the large Unicode repertoire, based on the Extending IDNA to Other Protocols (X-IDNA) base specification.

Status of this Memo

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Table of Contents

1.  Introduction
2.  The X-IDNA Profile for Network News Group Names
    2.1.  Applicability
    2.2.  Normalisation
    2.3.  Validation
3.  Submitting Messages to Moderators
4.  IANA Considerations
5.  Security Considerations
    5.1.  Visually Similar Characters
    5.2.  Other Issues
6.  References
    6.1.  Normative References
    6.2.  Informative References
Appendix A.  Examples
§  Author's Address

1.  Introduction

The X-IDNA base specification ([I‑D.teint‑xidna‑base] (Teint, N., “Extending IDNA to Other Protocols (X-IDNA),” February 2010.)) provides a generic framework for internationalisation of addresses, based on IDNA. This memo defines an X-IDNA Profile for use with Netnews newsgroup names.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).

2.  The X-IDNA Profile for Network News Group Names

2.1.  Applicability

This X-IDNA Profile ([I‑D.teint‑xidna‑base] (Teint, N., “Extending IDNA to Other Protocols (X-IDNA),” February 2010.)) applies to newsgroup names defined in [RFC3977] (Feather, C., “Network News Transfer Protocol (NNTP),” October 2006.) and [RFC5536] (Murchison, K., Lindsey, C., and D. Kohn, “Netnews Article Format,” November 2009.), i.e. to the following syntax elements:

• the <newsgroup-name> and <wildmat> syntax elements defined in Section 9.8 of [RFC3977] (Feather, C., “Network News Transfer Protocol (NNTP),” October 2006.) (includes the "group" and "wildmat" parameters to the "GROUP", "LISTGROUP", "NEWNEWS" and "LIST" commands).
• the <newsgroup-name> defined in Section 3.1.4 of [RFC5536] (Murchison, K., Lindsey, C., and D. Kohn, “Netnews Article Format,” November 2009.)

It also applies to other specifications based on these definitions (or their precedessors) if the elements are to be used as newsgroup names.

2.2.  Normalisation

Newsgroup names do not require normalisation.

2.3.  Validation

Validation of internationalised newsgroup names is the responsibility of whoever creates a newsgroup:

• for distributed newsgroups, the person sending out the "newgroup" and "checkgroup" control messages (Sections 5.2.1 and 5.2.3 of [RFC5537] (Allbery, R. and C. Lindsey, “Netnews Architecture and Protocols,” November 2009.))
• for local newsgroups, the person creating the newsgroup on the server

The following types newsgroup names SHOULD not be created:

• newsgroup names containing R-LDH-Labels and fake A-Labels
• newsgroup names containing uppercase ASCII characters and extended characters

3.  Submitting Messages to Moderators

This section is non-normative.

A common method for deriving the email address of the moderator of a group, which is described in a NOTE in section 3.5.1 of [RFC5537] (Allbery, R. and C. Lindsey, “Netnews Architecture and Protocols,” November 2009.), is forming the submission address for a moderated group by replacing each "." in the newsgroup name with "-" and then using that value as the <local-part> of a <mailbox> formed by appending a set domain.

When a forwarding service supports newsgroups the name of which is internationalised, they ought to provide two different addresses to accomodate both X-IDNA-aware and X-IDNA-unaware users:

• the result of replacing "." with "-" in the U-Address form of the newsgroup name
• the result of replacing "." with "-" in the A-Address form of the newsgroup name, which will usually result in fake A-Labels

NOTE: This method not only produces fake labels, which are discouraged in [I‑D.teint‑xidna‑email] (Teint, N., “An X-IDNA Profile for Electronic Mail Addresses,” February 2010.), but can also produce clashes where newsgroup names only differ in "-" and "." characters.

4.  IANA Considerations

This memo includes no request to IANA.

5.  Security Considerations

5.1.  Visually Similar Characters

By using visually similar characters, an attacker can create newsgroup names that are confusingly similar to other newsgroup names and newsgroup hierarchies that are confusingly similar to other hierarchies.

This may not only create a denial of service situation, where communication fails because users are tricked into posting into different groups, but may also create a leak for information where the distribution of the "fake" newsgroup is wider than that of the indented group.

This issue most prominently occurs if a single newsgroup servers carries multiple confusingly similar addresses. However, it can also occur if a user agent combines newsgroup lists from multiple servers, such as a private intranet NNTP server and a public, less trusted server, into a single list. Furthermore, even if the user agent clearly identifies the server carrying the group, users might still confuse the newsgroups when they see the familiar name and don't pay attention to the server identification.

It is suggested that Netnews server operators take care not to carry hierarchies that exploit confusingly similar newsgroup names.

In addition, user agent implementations ought to provide visual indications where a domain name contains multiple scripts, especially when the scripts contain characters that are easily confused visually, such as an omicron in Greek mixed with Latin text.

See Section 4.4 of [I‑D.ietf‑idnabis‑defs] (Klensin, J., “Internationalized Domain Names for Applications (IDNA): Definitions and Document Framework,” January 2010.) for further information on visually similar characters.

5.2.  Other Issues

See the Security Considerations of [I‑D.ietf‑idnabis‑defs] (Klensin, J., “Internationalized Domain Names for Applications (IDNA): Definitions and Document Framework,” January 2010.) and [I‑D.ietf‑idnabis‑bidi] (Alvestrand, H. and C. Karp, “Right-to-left scripts for IDNA,” January 2010.) for information on other issues.

6.  References

6.1. Normative References

6.2. Informative References

Appendix A.  Examples

In the plain text version of this memo, the sequence "&#nnnn;" denotes the literal Unicode character number nnnn (decimal).

Unicode:

alt.αλφα-βῆτα-γάμμα@example.com

Normalised:

alt.αλφα-βῆτα-γάμμα@example.com

Extracted:

L: "alt" S:"." L:"αλφα-βῆτα-γάμμα"

Converted:

L: "alt" S:"." L:"xn-----x8brabcel8esaa2hya7368h"

Re-Assembled:

alt.xn-----x8brabcel8esaa2hya7368h

Author's Address