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rfc:rfc4289

Network Working Group N. Freed Request for Comments: 4289 Sun Microsystems BCP: 13 J. Klensin Obsoletes: 2048 December 2005 Category: Best Current Practice

      Multipurpose Internet Mail Extensions (MIME) Part Four:
                      Registration Procedures

Status of This Memo

 This document specifies an Internet Best Current Practices for the
 Internet Community, and requests discussion and suggestions for
 improvements.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2005).

Abstract

 This document specifies IANA registration procedures for MIME
 external body access types and content-transfer-encodings.

Freed & Klensin Best Current Practice [Page 1] RFC 4289 MIME Registration December 2005

Table of Contents

 1. Introduction ....................................................2
 2. External Body Access Types ......................................3
    2.1. Registration Requirements ..................................3
       2.1.1. Naming Requirements ...................................3
       2.1.2. Mechanism Specification Requirements ..................3
       2.1.3. Publication Requirements ..............................4
       2.1.4. Security Requirements .................................4
    2.2. Registration Procedure .....................................4
       2.2.1. Present the Access Type to the Community ..............4
       2.2.2. Access Type Reviewer ..................................4
       2.2.3. IANA Registration .....................................5
    2.3. Location of Registered Access Type List ....................5
    2.4. IANA Procedures for Registering Access Types ...............5
 3. Transfer Encodings ..............................................5
    3.1. Transfer Encoding Requirements .............................6
       3.1.1. Naming Requirements ...................................6
       3.1.2. Algorithm Specification Requirements ..................6
       3.1.3. Input Domain Requirements .............................6
       3.1.4. Output Range Requirements .............................6
       3.1.5. Data Integrity and Generality Requirements ............7
       3.1.6. New Functionality Requirements ........................7
       3.1.7. Security Requirements .................................7
    3.2. Transfer Encoding Definition Procedure .....................7
    3.3. IANA Procedures for Transfer Encoding Registration .........8
    3.4. Location of Registered Transfer Encodings List .............8
 4. Security Considerations .........................................8
 5. IANA Considerations .............................................8
 6. Acknowledgements ................................................8
 7. References ......................................................9
 A.  Changes Since RFC 2048 .........................................9

1. Introduction

 Recent Internet protocols have been carefully designed to be easily
 extensible in certain areas.  In particular, MIME [RFC2045] is an
 open-ended framework and can accommodate additional object types,
 charsets, and access methods without any changes to the basic
 protocol.  A registration process is needed, however, to ensure that
 the set of such values is developed in an orderly, well-specified,
 and public manner.
 This document defines registration procedures that use the Internet
 Assigned Numbers Authority (IANA) as a central registry for these
 values.

Freed & Klensin Best Current Practice [Page 2] RFC 4289 MIME Registration December 2005

 Note:
    Registration of media types and charsets for use in MIME are
    specified in separate documents [RFC4288] [RFC2978] and are not
    addressed here.

1.1. Conventions Used in This Document

 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].

2. External Body Access Types

 [RFC2046] defines the message/external-body media type, whereby a
 MIME entity can act as pointer to the actual body data in lieu of
 including the data directly in the entity body.  Each
 message/external-body reference specifies an access type, which
 determines the mechanism used to retrieve the actual body data.  RFC
 2046 defines an initial set of access types but allows for the
 registration of additional access types to accommodate new retrieval
 mechanisms.

2.1. Registration Requirements

 New access type specifications MUST conform to the requirements
 described below.

2.1.1. Naming Requirements

 Each access type MUST have a unique name.  This name appears in the
 access-type parameter in the message/external-body content-type
 header field and MUST conform to MIME content type parameter syntax.

2.1.2. Mechanism Specification Requirements

 All of the protocols, transports, and procedures used by a given
 access type MUST be described, either in the specification of the
 access type itself or in some other publicly available specification,
 in sufficient detail for the access type to be implemented by any
 competent implementor.  Use of secret and/or proprietary methods in
 access types is expressly prohibited.  The restrictions imposed by
 [RFC2026] on the standardization of patented algorithms must be
 respected as well.

Freed & Klensin Best Current Practice [Page 3] RFC 4289 MIME Registration December 2005

2.1.3. Publication Requirements

 All access types MUST be described by an RFC.  The RFC may be
 informational rather than standards-track, although standards-track
 review and approval are encouraged for all access types.

2.1.4. Security Requirements

 Any known security issues that arise from the use of the access type
 MUST be completely and fully described.  It is not required that the
 access type be secure or that it be free from risks, but it is
 required that the known risks be identified.  Publication of a new
 access type does not require an exhaustive security review, and the
 security considerations section is subject to continuing evaluation.
 Additional security considerations SHOULD be addressed by publishing
 revised versions of the access type specification.

2.2. Registration Procedure

 Registration of a new access type starts with the publication of the
 specification as an Internet Draft.

2.2.1. Present the Access Type to the Community

 A proposed access type specification is sent to the
 "ietf-types@iana.org" mailing list for a two-week review period.
 This mailing list has been established for the purpose of reviewing
 proposed access and media types.  Proposed access types are not
 formally registered and must not be used.
 The intent of the public posting is to solicit comments and feedback
 on the access type specification and a review of any security
 considerations.

2.2.2. Access Type Reviewer

 When the two-week period has passed, the access type reviewer, who is
 appointed by the IETF Applications Area Director(s), either forwards
 the request to iana@iana.org or rejects it because of significant
 objections raised on the list.
 Decisions made by the reviewer must be posted to the ietf-types
 mailing list within 14 days.  Decisions made by the reviewer may be
 appealed to the IESG as specified in [RFC2026].

Freed & Klensin Best Current Practice [Page 4] RFC 4289 MIME Registration December 2005

2.2.3. IANA Registration

 Provided that the access type either has passed review or has been
 successfully appealed to the IESG, the IANA will register the access
 type and make the registration available to the community.  The
 specification of the access type must also be published as an RFC.

2.3. Location of Registered Access Type List

 Access type registrations are listed by the IANA on the following web
 page:
   http://www.iana.org/assignments/access-types

2.4. IANA Procedures for Registering Access Types

 The identity of the access type reviewer is communicated to the IANA
 by the IESG.  The IANA then only acts either in response to access
 type definitions that are approved by the access type reviewer and
 forwarded to the IANA for registration, or in response to a
 communication from the IESG that an access type definition appeal has
 overturned the access type reviewer's ruling.

3. Transfer Encodings

 Transfer encodings are transformations applied to MIME media types
 after conversion to the media type's canonical form.  Transfer
 encodings are used for several purposes:
 o  Many transports, especially message transports, can only handle
    data consisting of relatively short lines of text.  There can be
    severe restrictions on what characters can be used in these lines
    of text.  Some transports are restricted to a small subset of US-
    ASCII, and others cannot handle certain character sequences.
    Transfer encodings are used to transform binary data into a
    textual form that can survive such transports.  Examples of this
    sort of transfer encoding include the base64 and quoted-printable
    transfer encodings defined in [RFC2045].
 o  Image, audio, video, and even application entities are sometimes
    quite large.  Compression algorithms are often effective in
    reducing the size of large entities.  Transfer encodings can be
    used to apply general-purpose non-lossy compression algorithms to
    MIME entities.
 o  Transport encodings can be defined as a means of representing
    existing encoding formats in a MIME context.

Freed & Klensin Best Current Practice [Page 5] RFC 4289 MIME Registration December 2005

 IMPORTANT:  The standardization of a large number of different
 transfer encodings is seen as a significant barrier to widespread
 interoperability and is expressly discouraged.  Nevertheless, the
 following procedure has been defined in order to provide a means of
 defining additional transfer encodings, should standardization
 actually be justified.

3.1. Transfer Encoding Requirements

 Transfer encoding specifications MUST conform to the requirements
 described below.

3.1.1. Naming Requirements

 Each transfer encoding MUST have a unique name.  This name appears in
 the Content-Transfer-Encoding header field and MUST conform to the
 syntax of that field.

3.1.2. Algorithm Specification Requirements

 All of the algorithms used in a transfer encoding (e.g., conversion
 to printable form, compression) MUST be described in their entirety
 in the transfer encoding specification.  Use of secret and/or
 proprietary algorithms in standardized transfer encodings is
 expressly prohibited.  The restrictions imposed by [RFC2026] on the
 standardization of patented algorithms MUST be respected as well.

3.1.3. Input Domain Requirements

 All transfer encodings MUST be applicable to an arbitrary sequence of
 octets of any length.  Dependence on particular input forms is not
 allowed.
 It should be noted that the 7bit and 8bit encodings do not conform to
 this requirement.  Aside from the undesirability of having
 specialized encodings, the intent here is to forbid the addition of
 additional encodings similar to, or redundant with, 7bit and 8bit.

3.1.4. Output Range Requirements

 There is no requirement that a particular transfer encoding produce a
 particular form of encoded output.  However, the output format for
 each transfer encoding MUST be fully and completely documented.  In
 particular, each specification MUST clearly state whether the output
 format always lies within the confines of 7bit or 8bit or is simply
 pure binary data.

Freed & Klensin Best Current Practice [Page 6] RFC 4289 MIME Registration December 2005

3.1.5. Data Integrity and Generality Requirements

 All transfer encodings MUST be fully invertible on any platform; it
 MUST be possible for anyone to recover the original data by
 performing the corresponding decoding operation.  Note that this
 requirement effectively excludes all forms of lossy compression as
 well as all forms of encryption from use as a transfer encoding.

3.1.6. New Functionality Requirements

 All transfer encodings MUST provide some sort of new functionality.
 Some degree of functionality overlap with previously defined transfer
 encodings is acceptable, but any new transfer encoding MUST also
 offer something no other transfer encoding provides.

3.1.7. Security Requirements

 To the greatest extent possible, transfer encodings SHOULD NOT
 contain known security issues.  Regardless, any known security issues
 that arise from the use of the transfer encoding MUST be completely
 and fully described.  If additional security issues come to light
 after initial publication and registration, they SHOULD be addressed
 by publishing revised versions of the transfer encoding
 specification.

3.2. Transfer Encoding Definition Procedure

 Definition of a new transfer encoding starts with the publication of
 the specification as an Internet Draft.  The draft MUST define the
 transfer encoding precisely and completely, and it MUST also provide
 substantial justification for defining and standardizing a new
 transfer encoding.  This specification MUST then be presented to the
 IESG for consideration.  The IESG can:
 o  reject the specification outright as being inappropriate for
    standardization,
 o  assign the specification to an existing IETF working group for
    further work,
 o  approve the formation of an IETF working group to work on the
    specification in accordance with IETF procedures, or
 o  accept the specification as-is for processing as an individual
    standards-track submission.
 Transfer encoding specifications on the standards track follow normal
 IETF rules for standards-track documents.  A transfer encoding is

Freed & Klensin Best Current Practice [Page 7] RFC 4289 MIME Registration December 2005

 considered to be defined and available for use once it is on the
 standards track.

3.3. IANA Procedures for Transfer Encoding Registration

 There is no need for a special procedure for registering Transfer
 Encodings with the IANA.  All legitimate transfer encoding
 registrations MUST appear as a standards-track RFC, so it is the
 IESG's responsibility to notify the IANA when a new transfer encoding
 has been approved.

3.4. Location of Registered Transfer Encodings List

 The list of transfer encoding registrations can be found at:
   http://www.iana.org/assignments/transfer-encodings

4. Security Considerations

 Security requirements for access types are discussed in Section
 2.1.4.  Security requirements for transfer encodings are discussed in
 Section 3.1.7.

5. IANA Considerations

 The sole purpose of this document is to define IANA registries for
 access types and transfer encodings.  The IANA procedures for these
 registries are specified in Section 2.4 and Section 3.3 respectively.

6. Acknowledgements

 The current authors would like to acknowledge their debt to the late
 Dr. Jon Postel, whose general model of IANA registration procedures
 and specific contributions shaped the predecessors of this document
 [RFC2048].  We hope that the current version is one with which he
 would have agreed but, as it is impossible to verify that agreement,
 we have regretfully removed his name as a co-author.

Freed & Klensin Best Current Practice [Page 8] RFC 4289 MIME Registration December 2005

7. References

7.1. Normative References

 [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
            Extensions (MIME) Part One: Format of Internet Message
            Bodies", RFC 2045, November 1996.
 [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
            Extensions (MIME) Part Two: Media Types", RFC 2046,
            November 1996.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC4288]  Freed, N. and J. Klensin, "Media Type Specifications and
            Registration Procedures", BCP 13, RFC 4288, December 2005.

7.2. Informative References

 [RFC2026]  Bradner, S., "The Internet Standards Process -- Revision
            3", BCP 9, RFC 2026, October 1996.
 [RFC2048]  Freed, N., Klensin, J., and J. Postel, "Multipurpose
            Internet Mail Extensions (MIME) Part Four: Registration
            Procedures", BCP 13, RFC 2048, November 1996.
 [RFC2978]  Freed, N. and J. Postel, "IANA Charset Registration
            Procedures", BCP 19, RFC 2978, October 2000.

Freed & Klensin Best Current Practice [Page 9] RFC 4289 MIME Registration December 2005

Appendix A. Changes Since RFC 2048

 o  Media type registration procedures are now described in a separate
    document [RFC4288].
 o  The various URLs and addresses in this document have been changed
    so they all refer to iana.org rather than isi.edu.  Additionally,
    many of the URLs have been changed to use HTTP; formerly they used
    FTP.
 o  Much of the document has been clarified in the light of
    operational experience with these procedures.
 o  Several of the references in this document have been updated to
    refer to current versions of the relevant specifications.
 o  The option of assigning the task of working on a new transfer
    encoding to an existing working group has been added to the list
    of possible actions the IESG can take.
 o  Security considerations and IANA considerations sections have been
    added.
 o  Registration of charsets for use in MIME is specified in [RFC2978]
    and is no longer addressed by this document.

Authors' Addresses

 Ned Freed
 Sun Microsystems
 3401 Centrelake Drive, Suite 410
 Ontario, CA  92761-1205
 USA
 Phone: +1 909 457 4293
 EMail: ned.freed@mrochek.com
 John C. Klensin
 1770 Massachusetts Ave, #322
 Cambridge, MA  02140
 EMail: klensin+ietf@jck.com

Freed & Klensin Best Current Practice [Page 10] RFC 4289 MIME Registration December 2005

Full Copyright Statement

 Copyright (C) The Internet Society (2005).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
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 attempt made to obtain a general license or permission for the use of
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 specification can be obtained from the IETF on-line IPR repository at
 http://www.ietf.org/ipr.
 The IETF invites any interested party to bring to its attention any
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 rights that may cover technology that may be required to implement
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 ipr@ietf.org.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Freed & Klensin Best Current Practice [Page 11]

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