Network Working Group P. Faltstrom
Request for Comments: 1741 Royal Institute of Technology
Category: Informational D. Crocker
 Brandenburg Consulting
 E. Fair
 Apple Computer Inc.
 December 1994
 MIME Content Type for BinHex Encoded Files
Status of this Memo
 This memo provides information for the Internet community. This memo
 does not specify an Internet standard of any kind. Distribution of
 this memo is unlimited.
Abstract
 This memo describes the format to use when sending BinHex4.0 files
 via MIME [BORE93]. The format is compatible with existing mechanisms
 for distributing Macintosh files. Only when available software
 and/or user practice dictates, should this method be employed. It is
 recommended to use application/applefile [FALT94] for maximum
 interoperability.
1. Introduction
 Files on the Macintosh consists of two parts, called forks:
 DATA FORK: The actual data included in the file. The Data
 fork is typically the only meaningful part of a
 Macintosh file on a non-Macintosh computer system.
 For example, if a Macintosh user wants to send a
 file of data to a user on an IBM-PC, she would only
 send the Data fork.
 RESOURCE FORK: Contains a collection of arbitrary attribute/value
 pairs, including program segments, icon bitmaps,
 and parametric values.
 Additional information regarding Macintosh files is stored by the
 Finder has in a hidden file, called the "Desktop Database".
 Because of the complications in storing different parts of a
 Macintosh file in a non-Macintosh filesystem that only handles
 consecutive data in one part, it is common to convert the Macintosh
 file into some other format before transferring it over the network.
 AppleDouble file format [APPL90], encoded in MIME as
 multipart/appledouble [FALT94] and application/applefile [FALT94] is
 the preferred format for a Macintosh file that is to be included in
 an Internet mail message, because it provides recipients with
 Macintosh computers the entire document, including Icons and other
 Macintosh specific information, while other users easily can extract
 the Data fork (the actual data).
 However, this specification provides for use of the currently popular
 BinHex4.0 encoding schemes, as a convinience to the installed base of
 users.
2. MIME format for BinHex4.0
 MIME-base Apple information is specified by:
 MIME type-name: APPLICATION
 MIME subtype name: MAC-BINHEX40
 Required parameters: none
 Optional parameters: NAME, which must be a "value" as
 defined in RFC-1521 [BORE93].
 Encoding considerations: none
 Security considerations: See separate section in the document
 Published specification: Appendix A
 Rationale: Permits MIME-based transmission of data
 with Apple Macintosh file system specific
 information using a currently popular,
 though platform specific, format.
 2a. Detail specific to MIME-based usage
 Macintosh documents do not always need to be sent in a special
 format. Those documents with well-known MIME types and non-
 existent or trivial resource forks can be sent as regular MIME
 body parts, without use of AppleSingle, AppleDouble or BinHex4.0.
 Documents which lack a data fork must be sent as AppleSingle
 according to RFC 1740 [FALT94].
 Unless there are strong reasons not to, all other documents should
 be sent as AppleDouble according to RFC 1740 [FALT94]. This
 includes documents with non-trivial resource forks, and documents
 without corresponding well-known MIME types.
 It may be valuable in some cases to allow the user to choose one
 format over another, either because he disagrees with the
 implementor's definition of "trivial" resource forks, or for
 reasons of his own.
 Only when available software and/or user practice dictates, should
 BinHex 4.0 be employed.
3. BinHex
 BinHex 4.0 is a propular means of encoding Macintosh files for
 archiving on non-Macintosh file systems and for transmission via
 Internet mail. (See Appendix A for a brief description of the BinHex
 4.0 format.)
 The content-type application/mac-binhex40 indicates that the body of
 the mail is a BinHex4.0 file. Even though the BinHex encoding
 consists of characters which are not the same as those used in Base64
 (those regarded as safe according to RFC-1521 [BORE93]) a
 transportation encoding should not be done.
 Even though a BinHex file includes the original Macintosh filename,
 it is recommended that a name parameter be included on the Content-
 Type header to give the recipient a hint as to what file is attached.
 The value of the name parameter must be a "value" as defined by RFC-
 1521 [BORE93]. Note that this restricts the value to seven-bit US-
 ASCII characters.
 3a. BinHex example
 Content-Type: application/mac-binhex40; name="car.hqx"
 [The BinHex4.0 file goes here]
4. References
 APPL90 AppleSingle/AppleDouble Formats for Foreign Files
 Developer's Note, Apple Computer, Inc., 1990.
 FALT94 Faltstrom P., Crocker, D., and E. Fair, "MIME
 Encapsulation of Macintosh Files - MacMIME", RFC 1740,
 KTH, Brandenburg Consulting, Apple Computer Inc.,
 December 1994.
 BORE93 Borenstein N., and N. Freed, "MIME (Multipurpose Internet
 Mail Extensions): Mechanisms for Specifying and Describing
 the Format of Internet Message Bodies", RFC 1521, Bellcore,
 Innosoft, September 1993.
5. Security Considerations
 To the extent that application/mac-binhex40 facilitates the
 transmission of operating-system sensitive data, it may open a door
 for easier relaxation of security rules than is intended either by
 the sender of the administrator of the sender's system.
6. Acknowledgements
 Thanks to all of the people on the ietf-822 list who have provided
 much meaningful input for this document. Some of them must though be
 remembered by name, because they have almost crushed my mailbox the
 last weeks with a very nice and interesting debate:
 Johan Berglund, Steve Dorner, David Gelhar, David Herron, Raymond
 Lau, Jamey Maze, John B. Melby, Jan Michael Rynning, Rens Troost,
 and Peter Svanberg.
7. Authors' Addresses
 Patrik Faltstrom
 Department of Numerical Analysis and Computing Science
 Royal Institute of Technology
 S-100 44 Stockholm
 Sweden
 EMail: paf@nada.kth.se
 Dave Crocker
 Brandenburg Consulting
 675 Spruce Dr.
 Sunnyvale, CA 94086
 EMail: dcrocker@mordor.stanford.edu
 Erik E. Fair
 Engineering Computer Operations
 Apple Computer Inc.
 EMail: fair@apple.com
Appendix A. The BinHex format
 Here is a description of the Hqx7 (7 bit format as implemented in
 BinHex 4.0) formats for Macintosh Application and File transfers.
 The main features of the format are:
 1) Error checking even using ASCII download
 2) Compression of repetitive characters
 3) 7 bit encoding for ASCII download
 The format is processed at three different levels:
 1) 8 bit encoding of the file:
 Byte: Length of FileName (1->63)
 Bytes: FileName ("Length" bytes)
 Byte: Version
 Long: Type
 Long: Creator
 Word: Flags (And $F800)
 Long: Length of Data Fork
 Long: Length of Resource Fork
 Word: CRC
 Bytes: Data Fork ("Data Length" bytes)
 Word: CRC
 Bytes: Resource Fork ("Rsrc Length" bytes)
 Word: CRC
 2) Compression of repetitive characters.
 (90ドル is the marker, encoding is made for 3->255 characters)
 00 11 22 33 44 55 66 77 -> 00 11 22 33 44 55 66 77
 11 22 22 22 22 22 22 33 -> 11 22 90 06 33
 11 22 90 33 44 -> 11 22 90 00 33 44
 The whole file is considered as a stream of bits. This stream will
 be divided in blocks of 6 bits and then converted to one of 64
 characters contained in a table. The characters in this table have
 been chosen for maximum noise protection. The format will start
 with a ":" (first character on a line) and end with a ":".
 There will be a maximum of 64 characters on a line. It must be
 preceded, by this comment, starting in column 1 (it does not start
 in column 1 in this document):
 (This file must be converted with BinHex 4.0)
 Any text before this comment is to be ignored.
 The characters used is:
 !"#$%&'()*+,- 012345689@ABCDEFGHIJKLMNPQRSTUVXYZ[`abcdefhijklmpqr