Network Working Group N. Freed Internet-Draft Sun Microsystems Obsoletes: 2048 (if approved) J. Klensin Expires: December 5, 2003 June 6, 2003 Multipurpose Internet Mail Extensions (MIME) Part Four: Registration Procedures draft-freed-mime-p4-01.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http:// www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on December 5, 2003. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract This document specifies various IANA registration procedures for the following MIME facilities: o media types, o external body access types, and o content-transfer-encodings. Registration of charsets for use in MIME is covered elsewhere and is Freed & Klensin Expires December 5, 2003 [Page 1] Internet-Draft MIME Registration Procedures June 2003 no longer addressed by this document. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 4 2. Conventions Used In This Document . . . . . . . . . . . . 5 3. Media Type Registration . . . . . . . . . . . . . . . . . 6 3.1 Registration Trees and Subtype Names . . . . . . . . . . . 6 3.1.1 Standards Tree . . . . . . . . . . . . . . . . . . . . . . 6 3.1.2 Vendor Tree . . . . . . . . . . . . . . . . . . . . . . . 6 3.1.3 Personal or Vanity Tree . . . . . . . . . . . . . . . . . 7 3.1.4 Special x. Tree . . . . . . . . . . . . . . . . . . . . . 7 3.1.5 Additional Registration Trees . . . . . . . . . . . . . . 8 3.2 Registration Requirements . . . . . . . . . . . . . . . . 8 3.2.1 Functionality Requirement . . . . . . . . . . . . . . . . 8 3.2.2 Naming Requirements . . . . . . . . . . . . . . . . . . . 8 3.2.3 Parameter Requirements . . . . . . . . . . . . . . . . . . 9 3.2.4 Canonicalization and Format Requirements . . . . . . . . . 9 3.2.5 Interchange Recommendations . . . . . . . . . . . . . . . 10 3.2.6 Security Requirements . . . . . . . . . . . . . . . . . . 10 3.2.7 Requirements specific to XML media types . . . . . . . . . 12 3.2.8 Usage and Implementation Non-requirements . . . . . . . . 12 3.2.9 Publication Requirements . . . . . . . . . . . . . . . . . 12 3.2.10 Additional Information . . . . . . . . . . . . . . . . . . 13 3.3 Registration Procedure . . . . . . . . . . . . . . . . . . 13 3.3.1 Preliminary Community Review . . . . . . . . . . . . . . . 14 3.3.2 IESG Approval . . . . . . . . . . . . . . . . . . . . . . 14 3.3.3 IANA Registration . . . . . . . . . . . . . . . . . . . . 14 3.3.4 Media Types Reviewer . . . . . . . . . . . . . . . . . . . 15 3.4 Comments on Media Type Registrations . . . . . . . . . . . 15 3.5 Location of Registered Media Type List . . . . . . . . . . 15 3.6 IANA Procedures for Registering Media Types . . . . . . . 15 3.7 Change Procedures . . . . . . . . . . . . . . . . . . . . 16 3.8 Registration Template . . . . . . . . . . . . . . . . . . 17 4. External Body Access Types . . . . . . . . . . . . . . . . 18 4.1 Registration Requirements . . . . . . . . . . . . . . . . 18 4.1.1 Naming Requirements . . . . . . . . . . . . . . . . . . . 18 4.1.2 Mechanism Specification Requirements . . . . . . . . . . . 18 4.1.3 Publication Requirements . . . . . . . . . . . . . . . . . 18 4.1.4 Security Requirements . . . . . . . . . . . . . . . . . . 18 4.2 Registration Procedure . . . . . . . . . . . . . . . . . . 19 4.2.1 Present the Access Type to the Community . . . . . . . . . 19 4.2.2 Access Type Reviewer . . . . . . . . . . . . . . . . . . . 19 4.2.3 IANA Registration . . . . . . . . . . . . . . . . . . . . 19 4.3 Location of Registered Access Type List . . . . . . . . . 19 4.4 IANA Procedures for Registering Access Types . . . . . . . 19 5. Transfer Encodings . . . . . . . . . . . . . . . . . . . . 21 5.1 Transfer Encoding Requirements . . . . . . . . . . . . . . 21 Freed & Klensin Expires December 5, 2003 [Page 2] Internet-Draft MIME Registration Procedures June 2003 5.1.1 Naming Requirements . . . . . . . . . . . . . . . . . . . 21 5.1.2 Algorithm Specification Requirements . . . . . . . . . . . 21 5.1.3 Input Domain Requirements . . . . . . . . . . . . . . . . 22 5.1.4 Output Range Requirements . . . . . . . . . . . . . . . . 22 5.1.5 Data Integrity and Generality Requirements . . . . . . . . 22 5.1.6 New Functionality Requirements . . . . . . . . . . . . . . 22 5.2 Transfer Encoding Definition Procedure . . . . . . . . . . 22 5.3 IANA Procedures for Transfer Encoding Registration . . . . 23 5.4 Location of Registered Transfer Encodings List . . . . . . 23 Normative References . . . . . . . . . . . . . . . . . . . 24 Informative References . . . . . . . . . . . . . . . . . . 25 Authors' Addresses . . . . . . . . . . . . . . . . . . . . 25 A. Grandfathered Media Types . . . . . . . . . . . . . . . . 26 B. Changes made since RFC 2048 . . . . . . . . . . . . . . . 27 Intellectual Property and Copyright Statements . . . . . . 28 Freed & Klensin Expires December 5, 2003 [Page 3] Internet-Draft MIME Registration Procedures June 2003 1. Introduction Recent Internet protocols have been carefully designed to be easily extensible in certain areas. In particular, MIME [1] 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 which use the Internet Assigned Numbers Authority (IANA) as a central registry for such values. Of particular interest is the registration procedure for media types described in Section 3.3. Historical Note The media types registration process was initially defined for the purpose of registering media types for use in the context of the asynchronous Internet mail environment. In this mail environment there is a need to limit the number of possible media types to increase the likelihood of interoperability when the capabilities of the remote mail system are not known. As media types are used in new environments, where the proliferation of media types is not a hindrance to interoperability, the original procedure was excessively restrictive and had to be generalized. Freed & Klensin Expires December 5, 2003 [Page 4] Internet-Draft MIME Registration Procedures June 2003 2. 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 RFC 2119 [3]. Freed & Klensin Expires December 5, 2003 [Page 5] Internet-Draft MIME Registration Procedures June 2003 3. Media Type Registration Registration of a new media type or types starts with the construction of a registration proposal. Registration may occur in several different registration trees, which have different requirements as discussed below. In general, the new registration proposal is circulated and reviewed in a fashion appropriate to the tree involved. The media type is then registered if the proposal is acceptable. The following sections describe the requirements and procedures used for each of the different registration trees. 3.1 Registration Trees and Subtype Names In order to increase the efficiency and flexibility of the registration process, different structures of subtype names may be registered to accomodate the different natural requirements for, e.g., a subtype that will be recommended for wide support and implementation by the Internet Community or a subtype that is used to move files associated with proprietary software. The following subsections define registration "trees", distinguished by the use of faceted names (e.g., names of the form "tree.subtree...subtype"). Note that some media types defined prior to this document do not conform to the naming conventions described below. See Appendix A for a discussion of them. 3.1.1 Standards Tree The standards tree is intended for types of general interest to the Internet Community. Registrations in the standards tree MUST be approved by the IESG and MUST correspond to a formal publication by a recognized standards body. In the case of registrations for the IETF itself, the registration MUST be published as an RFC. Media types in the standards tree are normally denoted by names that are not explicitly faceted, i.e., do not contain period (".", full stop) characters. The "owner" of a media type registration in the standards tree is assumed to be the standards body itself. Modification or alteration of the specification requires the same level of processing (e.g., standards track) required for the initial registration. 3.1.2 Vendor Tree The vendor tree is used for media types associated with commercially available products. "Vendor" or "producer" are construed as equivalent and very broadly in this context. Freed & Klensin Expires December 5, 2003 [Page 6] Internet-Draft MIME Registration Procedures June 2003 A registration may be placed in the vendor tree by anyone who has need to interchange files associated with the particular product. However, the registration formally belongs to the vendor or organization producing the software or file format. Changes to the specification will be made at their request, as discussed in subsequent sections. Registrations in the vendor tree will be distinguished by the leading facet "vnd.". That may be followed, at the discretion of the registration, by either a media subtype name from a well-known producer (e.g., "vnd.mudpie") or by an IANA-approved designation of the producer's name which is then followed by a media type or product designation (e.g., vnd.bigcompany.funnypictures). While public exposure and review of media types to be registered in the vendor tree is not required, using the ietf-types list for review is strongly encouraged to improve the quality of those specifications. Registrations in the vendor tree may be submitted directly to the IANA. 3.1.3 Personal or Vanity Tree Registrations for media types created experimentally or as part of products that are not distributed commercially may be registered in the personal or vanity tree. The registrations are distinguished by the leading facet "prs.". The owner of "personal" registrations and associated specifications is the person or entity making the registration, or one to whom responsibility has been transferred as described below. While public exposure and review of media types to be registered in the personal tree is not required, using the ietf-types list for review is strongly encouraged to improve the quality of those specifications. Registrations in the personal tree may be submitted directly to the IANA. 3.1.4 Special x. Tree For convenience and symmetry with this registration scheme, subtype names with "x." as the first facet may be used for the same purposes for which names starting in "x-" are normally used. These types are unregistered, experimental, and should be used only with the active agreement of the parties exchanging them. However, with the simplified registration procedures described above for vendor and personal trees, it should rarely, if ever, be necessary to use unregistered experimental types, and as such use of Freed & Klensin Expires December 5, 2003 [Page 7] Internet-Draft MIME Registration Procedures June 2003 both "x-" and "x." forms is discouraged. Types in this tree MUST NOT be registered. 3.1.5 Additional Registration Trees From time to time and as required by the community, the IANA may, by and with the advice and consent of the IESG, create new top-level registration trees. It is explicitly assumed that these trees may be created for external registration and management by well-known permanent bodies, such as scientific societies for media types specific to the sciences they cover. In general, the quality of review of specifications for one of these additional registration trees is expected to be equivalent to registrations in the standards tree. Establishment of these new trees will be announced through RFC publication approved by the IESG. 3.2 Registration Requirements Media type registration proposals are all expected to conform to various requirements laid out in the following sections. Note that requirement specifics sometimes vary depending on the registration tree, again as detailed in the following sections. 3.2.1 Functionality Requirement Media types MUST function as an actual media format: Registration of things that are better thought of as a transfer encoding, as a charset, or as a collection of separate entities of another type, is not allowed. For example, although applications exist to decode the base64 transfer encoding [1], base64 cannot be registered as a media type. This requirement applies regardless of the registration tree involved. 3.2.2 Naming Requirements All registered media types MUST be assigned MIME type and subtype names. The combination of these names then serves to uniquely identify the media type and the format of the subtype name identifies the registration tree. Type and subtype names beginning with "X-" are reserved for experimental use and MUST NOT be registered. The choice of top-level type name MUST take the nature of media type involved into account. For example, media normally used for Freed & Klensin Expires December 5, 2003 [Page 8] Internet-Draft MIME Registration Procedures June 2003 representing still images should be a subtype of the image content type, whereas media capable of representing audio information should be under the audio content type. See RFC 2046 [2] for additional information on the basic set of top-level types and their characteristics. New subtypes of top-level types MUST conform to the restrictions of the top-level type, if any. For example, all subtypes of the multipart content type MUST use the same encapsulation syntax. In some cases a new media type may not "fit" under any currently defined top-level content type. Such cases are expected to be quite rare. However, if such a case arises a new top-level type can be defined to accommodate it. Such a definition MUST be done via standards-track RFC; no other mechanism can be used to define additional top-level content types. In accordance with the rules specified in RFC 3023 [5], media subtypes that do not represent XML MIME entities MUST NOT be given a name that ends with the "+xml" suffix. These requirements apply regardless of the registration tree involved. 3.2.3 Parameter Requirements Media types MAY elect to use one or more MIME content type parameters, or some parameters may be automatically made available to the media type by virtue of being a subtype of a content type that defines a set of parameters applicable to any of its subtypes. In either case, the names, values, and meanings of any parameters MUST be fully specified when a media type is registered in the standards tree, and SHOULD be specified as completely as possible when media types are registered in the vendor or personal trees. New parameters SHOULD NOT be defined as a way to introduce new functionality in types registered in the standards tree, although new parameters MAY be added to convey additional information that does not otherwise change existing functionality. An example of this would be a "revision" parameter to indicate a revision level of an external specification such as JPEG. Similar behavior is encouraged for media types registered in the vendor or personal trees but is not required. 3.2.4 Canonicalization and Format Requirements All registered media types MUST employ a single, canonical data format, regardless of registration tree. Freed & Klensin Expires December 5, 2003 [Page 9] Internet-Draft MIME Registration Procedures June 2003 A precise and openly available specification of the format of each media type MUST exist for all types registered in the standards tree and MUST at a minimum be referenced by, if it isn't actually included in, the media type registration proposal itself. The specifications of format and processing particulars may or may not be publically available for media types registered in the vendor tree, and such registration proposals are explicitly permitted to include only a specification of which software and version produce or process such media types. References to or inclusion of format specifications in registration proposals is encouraged but not required. Format specifications are still required for registration in the personal tree, but may be either published as RFCs or otherwise deposited with the IANA. The deposited specifications will meet the same criteria as those required to register a well-known TCP port and, in particular, need not be made public. Some media types involve the use of patented technology. The registration of media types involving patented technology is specifically permitted. However, the restrictions set forth in RFC 2026 [6] on the use of patented technology in IETF standards-track protocols must be respected when the specification of a media type is part of a standards-track protocol. In addition, other standards bodies making use of the standards tree may have their own rules regarding intellectual property that must be observed in their registrations. 3.2.5 Interchange Recommendations Media types SHOULD interoperate across as many systems and applications as possible. However, some media types will inevitably have problems interoperating across different platforms. Problems with different versions, byte ordering, and specifics of gateway handling can and will arise. Universal interoperability of media types is not required, but known interoperability issues SHOULD be identified whenever possible. Publication of a media type does not require an exhaustive review of interoperability, and the interoperability considerations section is subject to continuing evaluation. These recommendations apply regardless of the registration tree involved. 3.2.6 Security Requirements Freed & Klensin Expires December 5, 2003 [Page 10] Internet-Draft MIME Registration Procedures June 2003 An analysis of security issues MUST be done for all types registered in the standards Tree. A similar analysis for media types registered in the vendor or personal trees is encouraged but not required. However, regardless of what security analysis has or has not been done, all descriptions of security issues MUST be as accurate as possible regardless of registration tree. In particular, a statement that there are "no security issues associated with this type" MUST NOT be confused with "the security issues associates with this type have not been assessed". There is absolutely no requirement that media types registered in any tree be secure or completely free from risks. Nevertheless, all known security risks MUST be identified in the registration of a media type, again regardless of registration tree. The security considerations section of all registrations is subject to continuing evaluation and modification, and in particular MAY be extended by use of the "comments on media types" mechanism described in Section 3.4 below. Some of the issues that should be looked at in a security analysis of a media type are: o Complex media types may include provisions for directives that institute actions on a recipient's files or other resources. In many cases provision is made for originators to specify arbitrary actions in an unrestricted fashion which may then have devastating effects. See the registration of the application/postscript media type in RFC 2046 [2] for an example of such directives and how they should be described in a media type registration. o All registrations MUST state whether or not they employ such "active content", and if they do, they MUST state what steps have been taken to protect users of the media type from harm. o Complex media types may include provisions for directives that institute actions which, while not directly harmful to the recipient, may result in disclosure of information that either facilitates a subsequent attack or else violates a recipient's privacy in some way. Again, the registration of the application/ postscript media type illustrates how such directives can be handled. o A media type which employs compression may provide an opportunity for sending a small amount of data which, when received and evaluated, expands enormously to consume all of the recipient's resources. All media types SHOULD state whether or not they employ compression, and if they do they should discuss what steps Freed & Klensin Expires December 5, 2003 [Page 11] Internet-Draft MIME Registration Procedures June 2003 need to be taken to avoid such attacks. o A media type might be targeted for applications that require some sort of security assurance but not provide the necessary security mechanisms themselves. For example, a media type could be defined for storage of confidential medical information which in turn requires an external confidentiality service, or which is designed for use only within a secure environment. 3.2.7 Requirements specific to XML media types There are a number of additional requirements specific to the registration of XML media types. These requirements are specified in RFC 3023 [5]. 3.2.8 Usage and Implementation Non-requirements In the asynchronous mail environment, where information on the capabilities of the remote mail agent is frequently not available to the sender, maximum interoperability is attained by restricting the number of media types used to those "common" formats expected to be widely implemented. This was asserted in the past as a reason to limit the number of possible media types and resulted in a registration process with a significant hurdle and delay for those registering media types. However, the need for "common" media types does not require limiting the registration of new media types. If a limited set of media types is recommended for a particular application, that should be asserted by a separate applicability statement specific for the application and/or environment. As such, universal support and implementation of a media type is NOT a requirement for registration. If, however, a media type is explicitly intended for limited use, this SHOULD be noted in its registration. 3.2.9 Publication Requirements Proposals for media types registered in the standards tree by the IETF itself MUST be published as RFCs. RFC publication of vendor and personal media type proposals is encouraged but not required. In all cases the IANA will retain copies of all media type proposals and "publish" them as part of the media types registration tree itself. As stated previously, standards tree registrations for media types defined in documents produced by other standards bodies MUST be Freed & Klensin Expires December 5, 2003 [Page 12] Internet-Draft MIME Registration Procedures June 2003 described by a formal standards specification produced by that body. Other than IETF registrations in the standards tree, the registration of a data type does not imply endorsement, approval, or recommendation by the IANA or the IETF or even certification that the specification is adequate. To become Internet Standards, protocol, data objects, or whatever must go through the IETF standards process. This is too difficult and too lengthy a process for the convenient registration of media types. The stanards tree exists for media types that do require require a substantive review and approval process in a recognized standards body. The vendor and personal trees exist for those media types that do not require such a process. It is expected that applicability statements for particular applications will be published from time to time in the IETF that recommend implementation of, and support for, media types that have proven particularly useful in those contexts. As discussed above, registration of a top-level type requires standards-track processing in the IETF and, hence, RFC publication. 3.2.10 Additional Information Various sorts of optional information SHOULD be included in the specification of a media type if it is available: o Magic number(s) (length, octet values). Magic numbers are byte sequences that are always present and thus can be used to identify entities as being of a given media type. o File extension(s) commonly used on one or more platforms to indicate that some file containing a given type of media. o Macintosh File Type code(s) (4 octets) used to label files containing a given type of media. o Information about how fragment/anchor identifiers RFC 2396 [4] are constructed for use in conjunction with this media type. In the case of a registration in the standards tree this additional information MAY be provided in the formal specification of the media type. It is suggested that this be done by incorporating the IANA media type registration form into the specification itself. 3.3 Registration Procedure The following procedure has been implemented by the IANA for review and approval of new media types. This is not a formal standards Freed & Klensin Expires December 5, 2003 [Page 13] Internet-Draft MIME Registration Procedures June 2003 process, but rather an administrative procedure intended to allow community comment and sanity checking without excessive time delay. The normal IETF processes should be followed for all IETF registrations in the standards tree, with the posting of an internet-draft being a necessary first step. Proposed registrations in the standards tree by other standards bodies should be communicated to the IESG (at iesg@ietf.org). Registrations in the vendor and personal tree should be submitted directly to the IANA. 3.3.1 Preliminary Community Review In all cases notice of a potential media type registration MAY be sent to the "ietf-types@iana.org" mailing list for review. This mailing list has been established for the purpose of reviewing proposed media and access types. The intent of the public posting is to solicit comments and feedback on the choice of type/subtype name, the unambiguity of the references with respect to versions and external profiling information, and a review of any interoperability or security considerations. The submitter may submit a revised registration, or abandon the registration completely, at any time. 3.3.2 IESG Approval Media types registered in the standards tree MUST be approved by the IESG prior to registration. 3.3.3 IANA Registration Provided that the media type meets all of the relevant requirements and has obtained whateveer approval is necessary, the author may submit the registration request to the IANA. Registration requests can be sent to iana@iana.org. A web form for registration requests is also available: http://www.iana.org/cgi-bin/mediatypes.pl Sending to ietf-types@iana.org does not constitute submitting the registration to the IANA. When the registration is part of an RFC publication request, close coordination between the IANA and the IESG means IESG approval in effect submits the registration to the IANA. There is no need for an Freed & Klensin Expires December 5, 2003 [Page 14] Internet-Draft MIME Registration Procedures June 2003 additional registration request in such cases. 3.3.4 Media Types Reviewer Registrations submitted to the IANA will be passed on to the media types reviewer. The media types reviewer, who is appointed by the IETF Applications Area Director(s), will review the registration to make sure it meets the requirements set forth in this document. Registrations which do not meet these requirements will be returned to the submitter for revision. Decisions made by the media types reviewer may be appealed to the IESG. Once a media type registration has passed review the IANA will register the media type and make the media type registration available to the community. 3.4 Comments on Media Type Registrations Comments on registered media types may be submitted by members of the community to the IANA. These comments will be reviewed by the media types reviewer and then passed on to the "owner" of the media type if possible. Submitters of comments may request that their comment be attached to the media type registration itself, and if the IANA approves of this the comment will be made accessible in conjunction with the type registration itself. 3.5 Location of Registered Media Type List Media type registrations are listed by the IANA at: http://www.iana.org/assignments/media-types/index.html 3.6 IANA Procedures for Registering Media Types The IANA will only register media types in the standards tree in response to a communication from the IESG stating that a given registration has been approved. Vendor and personal types will be registered by the IANA automatically and without any formal review as long as the following minimal conditions are met: o Media types MUST function as an actual media format. In particular, charsets and transfer encodings MUST NOT be registered as media types. o All media types MUST have properly formed type and subtype names. Freed & Klensin Expires December 5, 2003 [Page 15] Internet-Draft MIME Registration Procedures June 2003 All type names MUST be defined by a standards-track RFC. All subtype names MUST be unique, must conform to the MIME grammar for such names, and MUST contain the proper tree prefix. o Types registered in the personal tree MUST either provide a format specification or a pointer to one. o All media types MUST have a reasonable security considerations section. (It is neither possible nor necessary for the IANA to conduct a comprehensive security review of media type registrations. Nevertheless, the IANA has the authority to identify obviously incompetent material and exclude it.) o Registrations in the standards tree MUST satisfy the additional requirement that they originate from another standards body recognized as such by the IETF. 3.7 Change Procedures Once a content type has been published by the IANA, the owner may request a change to its definition. The descriptions of the different registration trees above designate the "owners" of each type of registration. The same procedure as would be appropriate for the original registration request is used to process a change request. Changes should be requested only when there are serious omissions or errors in the published specification. When review is required, a change request may be denied if it renders entities that were valid under the previous definition invalid under the new definition. The owner of a content type may pass responsibility for the content type to another person or agency by informing the IANA and the ietf-types list; this can be done without discussion or review. The IESG may reassign responsibility for a media type. The most common case of this will be to enable changes to be made to types where the author of the registration has died, moved out of contact or is otherwise unable to make changes that are important to the community. Media type registrations may not be deleted; media types which are no longer believed appropriate for use can be declared OBSOLETE by a change to their "intended use" field; such media types will be clearly marked in the lists published by the IANA. 3.8 Registration Template Freed & Klensin Expires December 5, 2003 [Page 16] Internet-Draft MIME Registration Procedures June 2003 To: ietf-types@iana.org Subject: Registration of MIME media type XXX/YYY MIME media type name: MIME subtype name: Required parameters: Optional parameters: Encoding considerations: Security considerations: Interoperability considerations: Published specification: Applications which use this media type: Additional information: Magic number(s): File extension(s): Macintosh File Type Code(s): Person & email address to contact for further information: Intended usage: (One of COMMON, LIMITED USE or OBSOLETE) Author/Change controller: (Any other information that the author deems interesting may be added below this line.) Freed & Klensin Expires December 5, 2003 [Page 17] Internet-Draft MIME Registration Procedures June 2003 4. External Body Access Types RFC 2046 [2] 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. 4.1 Registration Requirements New access type specifications MUST conform to a number of requirements as described below. 4.1.1 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. 4.1.2 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 are expressly prohibited. The restrictions imposed by RFC 2026 [6] on the standardization of patented algorithms must be respected as well. 4.1.3 Publication Requirements All access types MUST be described by an RFC. The RFC may be informational rather than standards-track, although standard-track review and approval are encouraged for all access types. 4.1.4 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 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 Freed & Klensin Expires December 5, 2003 [Page 18] Internet-Draft MIME Registration Procedures June 2003 revised versions of the access type specification. 4.2 Registration Procedure Registration of a new access type starts with the the publication of the specification as an internet-draft. 4.2.1 Present the Access Type to the Community Send a proposed access type specification 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. 4.2.2 Access Type Reviewer When the two week period has passed, the access type reviewer, who is appointed by the IETF Applications Area Director, either forwards the request to iana@isi.edu, 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. 4.2.3 IANA Registration Provided that the access type has either 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. 4.3 Location of Registered Access Type List Access type registrations are listed by the IANA on the web page: http://www.iana.org/assignments/access-types 4.4 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 in response to access type Freed & Klensin Expires December 5, 2003 [Page 19] Internet-Draft MIME Registration Procedures June 2003 definitions that either are approved by the access type reviewer and forwarded by the reviewer 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. Freed & Klensin Expires December 5, 2003 [Page 20] Internet-Draft MIME Registration Procedures June 2003 5. Transfer Encodings Transfer encodings are tranformations 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 also 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 textual form that can survive such transports. Examples of this sort of transfer encoding include the base64 and quoted-printable transfer encodings defined in RFC 2045 [1]. o Image, audio, video, and even application entities are sometimes quite large. Compression algorithms are often quite 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. IMPORTANT: The standardization of a large numbers of different transfer encodings is seen as a significant barrier to widespread interoperability and is expressely discouraged. Nevertheless, the following procedure has been defined to provide a means of defining additional transfer encodings, should standardization actually be justified. 5.1 Transfer Encoding Requirements Transfer encoding specifications MUST conform to a number of requirements as described below. 5.1.1 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. 5.1.2 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 Freed & Klensin Expires December 5, 2003 [Page 21] Internet-Draft MIME Registration Procedures June 2003 proprietary algorithms in standardized transfer encodings are expressly prohibited. The restrictions imposed by RFC 2026 [6] on the standardization of patented algorithms MUST be respected as well. 5.1.3 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 undesireability of having specialized encodings, the intent here is to forbid the addition of additional encodings along the lines of 7bit and 8bit. 5.1.4 Output Range Requirements There is no requirement that a particular tranfer 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 data, 8bit data, or is simply pure binary data. 5.1.5 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. 5.1.6 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. 5.2 Transfer Encoding Definition Procedure Definition of a new transfer encoding starts with the the publication of the specification as an internet-draft. The draft MUST define the transfer encoding precisely and completely, and 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 Freed & Klensin Expires December 5, 2003 [Page 22] Internet-Draft MIME Registration Procedures June 2003 o reject the specification outright as being inappropriate for standardization, 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 and put it directly on the standards track. Transfer encoding specifications on the standards track follow normal IETF rules for standards track documents. A transfer encoding is considered to be defined and available for use once it is on the standards track. 5.3 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. 5.4 Location of Registered Transfer Encodings List The list of transfer encoding registrations can be found at: http://www.iana.org/assignments/transfer-encodings Freed & Klensin Expires December 5, 2003 [Page 23] Internet-Draft MIME Registration Procedures June 2003 Normative References [1] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996. [2] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, November 1996. [3] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [4] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifiers (URI): Generic Syntax", RFC 2396, August 1998. [5] Murata, M., St. Laurent, S. and D. Kohn, "XML Media Types", RFC 3023, January 2001. Freed & Klensin Expires December 5, 2003 [Page 24] Internet-Draft MIME Registration Procedures June 2003 Informative References [6] Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. [7] Freed, N., Klensin, J. and J. Postel, "Multipurpose Internet Mail Extensions (MIME) Part Four: Registration Procedures", BCP 13, RFC 2048, November 1996. Authors' Addresses Ned Freed Sun Microsystems 1050 Lakes Drive West Covina, CA 91790 USA Phone: +1 626 850 4350 EMail: ned.freed@mrochek.com John C Klensin 1770 Massachusetts Ave, #322 Cambridge, MA 02140 EMail: klensin@jck.com Freed & Klensin Expires December 5, 2003 [Page 25] Internet-Draft MIME Registration Procedures June 2003 Appendix A. Grandfathered Media Types A number of media types, registered prior to 1996, would, if registered under the guidelines in this document, be placed into either the vendor or personal trees. Reregistration of those types to reflect the appropriate trees is encouraged, but not required. Ownership and change control principles outlined in this document apply to those types as if they had been registered in the trees described above. Freed & Klensin Expires December 5, 2003 [Page 26] Internet-Draft MIME Registration Procedures June 2003 Appendix B. Changes made since RFC 2048 o Much of the document has been clarified in the light of operational experience with these procedures. o The unfaceted IETF tree is now called the standards tree and the registration rules for this tree have been relaxed to allow use by other standards bodies. o The text describing the media type registration procedure has clarified. o The rules and requirements for constructing security considerations sections have been extended and clarified. o RFC 3023 is now referenced as the source of additional information concerning the registration of XML media types. o Several of the references in this document have been updated. Freed & Klensin Expires December 5, 2003 [Page 27] Internet-Draft MIME Registration Procedures June 2003 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property 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; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors or users of this specification can be obtained from the IETF Secretariat. 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This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION Freed & Klensin Expires December 5, 2003 [Page 28] Internet-Draft MIME Registration Procedures June 2003 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Freed & Klensin Expires December 5, 2003 [Page 29]