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rfc:rfc1505

Network Working Group A. Costanzo Request for Comments: 1505 AKC Consulting Obsoletes: 1154 D. Robinson

                                            Computervision Corporation
                                                            R. Ullmann
                                                           August 1993
            Encoding Header Field for Internet Messages

Status of this Memo

 This memo defines an Experimental Protocol for the Internet
 community.  It does not specify an Internet standard.  Discussion and
 suggestions for improvement are requested.  Please refer to the
 current edition of the "IAB Official Protocol Standards" for the
 standardization state and status of this protocol.  Distribution of
 this memo is unlimited.

IESG Note

 Note that a standards-track technology already exists in this area
 [11].

Abstract

 This document expands upon the elective experimental Encoding header
 field which permits the mailing of multi-part, multi-structured
 messages.  It replaces RFC 1154 [1].

Table of Contents

        1.      Introduction . . . . . . . . . . . . . . . . . . . . 3
        2.      The Encoding Field . . . . . . . . . . . . . . . . . 3
        2.1       Format of the Encoding Field . . . . . . . . . . . 3
        2.2       <count>  . . . . . . . . . . . . . . . . . . . . . 4
        2.3       <keyword>  . . . . . . . . . . . . . . . . . . . . 4
        2.3.1       Nested Keywords  . . . . . . . . . . . . . . . . 4
        2.4       Comments . . . . . . . . . . . . . . . . . . . . . 4
        3.      Encodings  . . . . . . . . . . . . . . . . . . . . . 5
        3.1       Text . . . . . . . . . . . . . . . . . . . . . . . 5
        3.2       Message  . . . . . . . . . . . . . . . . . . . . . 6
        3.3       Hex  . . . . . . . . . . . . . . . . . . . . . . . 6
        3.4       EVFU . . . . . . . . . . . . . . . . . . . . . . . 6
        3.5       EDI-X12 and EDIFACT  . . . . . . . . . . . . . . . 7
        3.6       FS   . . . . . . . . . . . . . . . . . . . . . . . 7
        3.7       LZJU90 . . . . . . . . . . . . . . . . . . . . . . 7
        3.8       LZW  . . . . . . . . . . . . . . . . . . . . . . . 7

Costanzo, Robinson & Ullmann [Page 1] RFC 1505 Encoding Header Field August 1993

        3.9       UUENCODE . . . . . . . . . . . . . . . . . . . . . 7
        3.10      PEM and PEM-Clear  . . . . . . . . . . . . . . . . 8
        3.11      PGP  . . . . . . . . . . . . . . . . . . . . . . . 8
        3.12      Signature  . . . . . . . . . . . . . . . . . . .  10
        3.13      TAR  . . . . . . . . . . . . . . . . . . . . . .  10
        3.14      PostScript . . . . . . . . . . . . . . . . . . .  10
        3.15      SHAR . . . . . . . . . . . . . . . . . . . . . .  10
        3.16      Uniform Resource Locator . . . . . . . . . . . .  10
        3.17      Registering New Keywords . . . . . . . . . . . .  11
        4.      FS (File System) Object Encoding . . . . . . . . .  11
        4.1       Sections . . . . . . . . . . . . . . . . . . . .  12
        4.1.1       Directory  . . . . . . . . . . . . . . . . . .  12
        4.1.2       Entry  . . . . . . . . . . . . . . . . . . . .  13
        4.1.3       File . . . . . . . . . . . . . . . . . . . . .  13
        4.1.4       Segment  . . . . . . . . . . . . . . . . . . .  13
        4.1.5       Data . . . . . . . . . . . . . . . . . . . . .  14
        4.2       Attributes . . . . . . . . . . . . . . . . . . .  14
        4.2.1       Display  . . . . . . . . . . . . . . . . . . .  14
        4.2.2       Comment  . . . . . . . . . . . . . . . . . . .  15
        4.2.3       Type . . . . . . . . . . . . . . . . . . . . .  15
        4.2.4       Created  . . . . . . . . . . . . . . . . . . .  15
        4.2.5       Modified . . . . . . . . . . . . . . . . . . .  15
        4.2.6       Accessed . . . . . . . . . . . . . . . . . . .  15
        4.2.7       Owner  . . . . . . . . . . . . . . . . . . . .  15
        4.2.8       Group  . . . . . . . . . . . . . . . . . . . .  16
        4.2.9       ACL  . . . . . . . . . . . . . . . . . . . . .  16
        4.2.10      Password . . . . . . . . . . . . . . . . . . .  16
        4.2.11      Block  . . . . . . . . . . . . . . . . . . . .  16
        4.2.12      Record . . . . . . . . . . . . . . . . . . . .  17
        4.2.13      Application  . . . . . . . . . . . . . . . . .  17
        4.3       Date Field . . . . . . . . . . . . . . . . . . .  17
        4.3.1       Syntax . . . . . . . . . . . . . . . . . . . .  17
        4.3.2       Semantics  . . . . . . . . . . . . . . . . . .  17
        5.      LZJU90: Compressed Encoding  . . . . . . . . . . .  18
        5.1       Overview . . . . . . . . . . . . . . . . . . . .  18
        5.2       Specification of the LZJU90 compression  . . . .  19
        5.3       The Decoder  . . . . . . . . . . . . . . . . . .  21
        5.3.1       An example of an Encoder . . . . . . . . . . .  27
        5.3.2       Example LZJU90 Compressed Object . . . . . . .  33
        6.      Alphabetical Listing of Defined Encodings  . . . .  34
        7.      Security Considerations  . . . . . . . . . . . . .  34
        8.      References . . . . . . . . . . . . . . . . . . . .  34
        9.      Acknowledgements . . . . . . . . . . . . . . . . .  35
        10.     Authors' Addresses . . . . . . . . . . . . . . . .  36

Costanzo, Robinson & Ullmann [Page 2] RFC 1505 Encoding Header Field August 1993

1. Introduction

 STD 11, RFC 822 [2] defines an electronic mail message to consist of
 two parts, the message header and the message body, separated by a
 blank line.
 The Encoding header field permits the message body itself to be
 further broken up into parts, each part also separated from the next
 by a blank line.  Thus, conceptually, a message has a header part,
 followed by one or more body parts, all separated by apparently blank
 lines.  Each body part has an encoding type.  The default (no
 Encoding field in the header) is a one part message body of type
 "Text".
 The purpose of Encoding is to be descriptive of the content of a mail
 message without placing constraints on the content or requiring
 additional structure to appear in the body of the message that will
 interfere with other processing.
 A similar message format is used in the network news facility, and
 posted articles are often transferred by gateways between news and
 mail.  The Encoding field is perhaps even more useful in news, where
 articles often are uuencoded or shar'd, and have a number of
 different nested encodings of graphics images and so forth.  In news
 in particular, the Encoding header keeps the structural information
 within the (usually concealed) article header, without affecting the
 visual presentation by simple news-reading software.

2. The Encoding Field

 The Encoding field consists of one or more subfields, separated by
 commas.  Each subfield corresponds to a part of the message, in the
 order of that part's appearance.  A subfield consists of a line count
 and a keyword or a series of nested keywords defining the encoding.
 The line count is optional in the last subfield.

2.1 Format of the Encoding Field

 The format of the Encoding field is:
      [  <count> <keyword> [ <keyword> ]* ,  ]*
              [ <count> ] <keyword> [ <keyword> ]*
      where:
      <count>    := a decimal integer
      <keyword>  := a single alphanumeric token starting with an alpha

Costanzo, Robinson & Ullmann [Page 3] RFC 1505 Encoding Header Field August 1993

2.2 <count>

 The line count is a decimal number specifying the number of text
 lines in the part.  Parts are separated by a blank line, which is not
 included in the count of either the preceding or following part.
 Blank lines consist only of CR/LF.  Count may be zero, it must be
 non-negative.
 It is always possible to determine if the count is present because a
 count always begins with a digit and a keyword always begins with a
 letter.
 The count is not required on the last or only part.  A multi-part
 message that consists of only one part is thus identical to a
 single-part message.

2.3 <keyword>

 Keyword defines the encoding type.  The keyword is a common single-
 word name for the encoding type and is not case-sensitive.
           Encoding: 107 Text

2.3.1 Nested Keywords

 Nested keywords are a series of keywords defining a multi-encoded
 message part.  The encoding keywords may either be an actual series
 of encoding steps the encoder used to generate the message part or
 may merely be used to more precisely identify the type of encoding
 (as in the use of the keyword "Signature").
 Nested keywords are parsed and generated from left to right.  The
 order is significant.  A decoding application would process the list
 from left to right, whereas, an encoder would process the Internet
 message and generate the nested keywords in the reverse order of the
 actual encoding process.
      Encoding: 458 uuencode LZW tar (Unix binary object)

2.4 Comments

 Comments enclosed in parentheses may be inserted anywhere in the
 encoding field.  Mail reading systems may pass the comments to their
 clients.  Comments must not be used by mail reading systems for
 content interpretation.  Other parameters defining the type of
 encoding must be contained within the body portion of the Internet
 message or be implied by a keyword in the encoding field.

Costanzo, Robinson & Ullmann [Page 4] RFC 1505 Encoding Header Field August 1993

3. Encodings

 This section describes some of the defined encodings used.  An
 alphabetical listing is provided in Section 6.
 As with the other keyword-defined parts of the header format
 standard, new keywords are expected and welcomed.  Several basic
 principles should be followed in adding encodings.  The keyword
 should be the most common single word name for the encoding,
 including acronyms if appropriate.  The intent is that different
 implementors will be likely to choose the same name for the same
 encoding.  Keywords should not be too general:  "binary" would have
 been a bad choice for the "hex" encoding.
 The encoding should be as free from unnecessary idiosyncracies as
 possible, except when conforming to an existing standard, in which
 case there is nothing that can be done.
 The encoding should, if possible, use only the 7 bit ASCII printing
 characters if it is a complete transformation of a source document
 (e.g., "hex" or "uuencode").  If it is essentially a text format, the
 full range may be used.  If there is an external standard, the
 character set may already be defined.  Keywords beginning with "X-"
 are permanently reserved to implementation-specific use.  No standard
 registered encoding keyword will ever begin with "X-".
 New encoding keywords which are not reserved for implementation-
 specific use must be registered with the Internet Assigned Numbers
 Authority (IANA).  Refer to section 3.17 for additional information.

3.1 Text

 This indicates that the message is in no particular encoded format,
 but is to be presented to the user as-is.
 The text is ISO-10646-UTF-1 [3].  As specified in STD 10, RFC 821
 [10], the message is expected to consist of lines of reasonable
 length (less than or equal to 1000 characters).
 On some older implementations of mail and news, only the 7 bit subset
 of ISO-10646-UTF-1 can be used.  This is identical to the ASCII 7 bit
 code.  On some mail transports that are not compliant with STD 10,
 RFC 821 [10], line length may be restricted by the service.
 Text may be followed by a nested keyword to define the encoded part
 further, e.g., "signature":
      Encoding: 496 Text, 8 Text Signature

Costanzo, Robinson & Ullmann [Page 5] RFC 1505 Encoding Header Field August 1993

 An automated file sending service may find this useful, for example,
 to differentiate between and ignore the signature area when parsing
 the body of a message for file requests.

3.2 Message

 This encoding indicates that the body part is itself in the format of
 an Internet message, with its own header part and body part(s).  A
 "message" body part's message header may be a full Internet message
 header or it may consist only of an Encoding field.
 Using the message encoding on returned mail makes it practical for a
 mail reading system to implement a reliable automatic resending
 function, if the mailer generates it when returning contents.  It is
 also useful in a "copy append" MUA (mail user agent) operation.
 MTAs (mail transfer agents) returning mail should generate an
 Encoding header.  Note that this does not require any parsing or
 transformation of the returned message; the message is simply
 appended un-modified; MTAs are prohibited from modifying the content
 of messages.
      Encoding: 7 Text (Return Reason), Message (Returned Mail)

3.3 Hex

 The encoding indicates that the body part contains binary data,
 encoded as 2 hexadecimal digits per byte, highest significant nibble
 first.
 Lines consist of an even number of hexadecimal digits.  Blank lines
 are not permitted.  The decode process must accept lines with between
 2 and 1000 characters, inclusive.
 The Hex encoding is provided as a simple way of providing a method of
 encoding small binary objects.

3.4 EVFU

 EVFU (electronic vertical format unit) specifies that each line
 begins with a one-character "channel selector".  The original purpose
 was to select a channel on a paper tape loop controlling the printer.
 This encoding is sometimes called "FORTRAN" format.  It is the
 default output format of FORTRAN programs on a number of computer
 systems.

Costanzo, Robinson & Ullmann [Page 6] RFC 1505 Encoding Header Field August 1993

 The legal characters are '0' to '9', '+', '-', and space.  These
 correspond to the 12 rows (and absence of a punch) on a printer
 control tape (used when the control unit was electromechanical).
 The channels that have generally agreed definitions are:
      1          advances to the first print line on the next page
      0          skip a line, i.e., double-space
      +          over-print the preceeding line
      -          skip 2 lines, i.e., triple-space
      (space)    print on the next line, single-space

3.5 EDI-X12 and EDIFACT

 The EDI-X12 and EDIFACT keywords indicate that the message or part is
 a EDI (Electronic Document Interchange) business document, formatted
 according to ANSI X12 or the EDIFACT standard.
 A message containing a note and 2 X12 purchase orders might have an
 encoding of:
      Encoding: 17 TEXT, 146 EDI-X12, 69 EDI-X12

3.6 FS

 The FS (File System) keyword specifies a section consisting of
 encoded file system objects.  This encoding method (defined in
 section 4) allows the moving of a structured set of files from one
 environment to another while preserving all common elements.

3.7 LZJU90

 The LZJU90 keyword specifies a section consisting of an encoded
 binary or text object.  The encoding (defined in section 5) provides
 both compression and representation in a text format.

3.8 LZW

 The LZW keyword specifies a section consisting of the data produced
 by the Unix compress program.

3.9 UUENCODE

 The uuencode keyword specifies a section consisting of the output of
 the uuencode program supplied as part of uucp.

Costanzo, Robinson & Ullmann [Page 7] RFC 1505 Encoding Header Field August 1993

3.10 PEM and PEM-Clear

 The PEM and PEM-Clear keywords indicate that the section is encrypted
 with the methods specified in RFCs 1421-1424 [4,5,6,7] or uses the
 MIC-Clear encapsulation specified therein.
 A simple text object encrypted with PEM has the header:
           Encoding: PEM Text
 Note that while this indicates that the text resulting from the PEM
 decryption is ISO-10646-UTF-1 text, the present version of PEM
 further restricts this to only the 7 bit subset.  A future version of
 PEM may lift this restriction.
 If the object resulting from the decryption starts with Internet
 message header(s), the encoding is:
           Encoding: PEM Message
 This is useful to conceal both the encoding within and the headers
 not needed to deliver the message (such as Subject:).
 PEM does not provide detached signatures, but rather provides the
 MIC-Clear mode to send messages with integrity checks that are not
 encrypted.  In this mode, the keyword PEM-Clear is used:
           Encoding: PEM-Clear EDIFACT
 The example being a non-encrypted EDIFACT transaction with a digital
 signature.  With the proper selection of PEM parameters and
 environment, this can also provide non-repudiation, but it does not
 provide confidentiality.
 Decoders that are capable of decrypting PEM treat the two keywords in
 the same way, using the contained PEM headers to distinguish the
 mode.  Decoders that do not understand PEM can use the PEM-Clear
 keyword as a hint that it may be useful to treat the section as text,
 or even continue the decode sequence after removing the PEM headers.
 When Encoding is used for PEM, the RFC934 [9] encapsulation specified
 in RFC1421 is not used.

3.11 PGP

 The PGP keyword indicates that the section is encrypted using the
 Pretty Good Privacy specification, or is a public key block, keyring,
 or detached signature meaningful to the PGP program.  (These objects

Costanzo, Robinson & Ullmann [Page 8] RFC 1505 Encoding Header Field August 1993

 are distinguished by internal information.)
 The keyword actually implies 3 different transforms:  a compression
 step, the encryption, and an ASCII encoding.  These transforms are
 internal to the PGP encoder/decoder.  A simple text message encrypted
 with PGP is specified by:
      Encoding: PGP Text
 An EDI transaction using ANSI X12 might be:
      Encoding: 176 PGP EDI-X12
 Since an evesdropper can still "see" the nested type (Text or EDI in
 these examples), thus making information available to traffic
 analysis which is undesirable in some applications, the sender may
 prefer to use:
      Encoding: PGP Message
 As discussed in the description of the Message keyword, the enclosed
 object may have a complete header or consist only of an Encoding:
 header describing its content.
 When PGP is used to transmit an encoded key or keyring, with no
 object significant to the mail user agent as a result of the decoding
 (e.g., text to display), the keyword is used by itself.
 Another case of the PGP keyword occurs in "clear-signing" a message.
 That is, sending an un-encrypted message with a digital signature
 providing authentication and (in some environments) non-deniability.
      Encoding: 201 Text, 8 PGP Signature, 4 Text Signature
 This example indicates a 201 line message, followed by an 8 line (in
 its encoded form) PGP detached signature.  The processing of the PGP
 section is expected (in this example) to result in a text object that
 is to be treated by the receiver as a signature, possibly something
 like:
      [PGP signed Ariel@Process.COM Robert L Ullmann  VALID/TRUSTED]
 Note that the PGP signature algorithm is applied to the encoded form
 of the clear-text section, not the object(s) before encoding.  (Which
 would be quite difficult for encodings like tar or FS).  Continuing
 the example, the PGP signature is then followed by a 4 line
 "ordinary" signature section.

Costanzo, Robinson & Ullmann [Page 9] RFC 1505 Encoding Header Field August 1993

3.12 Signature

 The signature keyword indicates that the section contains an Internet
 message signature.  An Internet message signature is an area of an
 Internet message (usually located at the end) which contains a single
 line or multiple lines of characters.  The signature may comprise the
 sender's name or a saying the sender is fond of.  It is normally
 inserted automatically in all outgoing message bodies.  The encoding
 keyword "Signature" must always be nested and follow another keyword.
      Encoding: 14 Text, 3 Text Signature
 A usenet news posting program should generate an encoding showing
 which is the text and which is the signature area of the posted
 message.

3.13 TAR

 The tar keyword specifies a section consisting of the output of the
 tar program supplied as part of Unix.

3.14 PostScript

 The PostScript keyword specifies a section formatted according to the
 PostScript [8] computer program language definition.  PostScript is a
 registered trademark of Adobe Systems Inc.

3.15 SHAR

 The SHAR keyword specifies a section encoded in shell archive format.
 Use of shar, although supported, is not recommended.
 WARNING:  Because the shell archive may contain commands you may not
 want executed, the decoder should not automatically execute decoded
 shell archived statements.  This warning also applies to any future
 types that include commands to be executed by the receiver.

3.16 Uniform Resource Locator

 The URL keyword indicates that the section consists of zero or more
 references to resources of some type.  URL provides a facility to
 include by reference arbitrary external resources from various
 sources in the Internet.  The specification of URL is a work in
 progress in the URI working group of the IETF.

Costanzo, Robinson & Ullmann [Page 10] RFC 1505 Encoding Header Field August 1993

3.17 Registering New Keywords

 New encoding keywords which are not reserved for implementation-
 specific use must be registered with the Internet Assigned Numbers
 Authority (IANA).  IANA acts as a central registry for these values.
 IANA may reject or modify the keyword registration request if it does
 not meet the criteria as specified in section 3.  Keywords beginning
 with "X-" are permanently reserved to implementation-specific use.
 IANA will not register an encoding keyword that begins with "X-".
 Registration requests should be sent via electronic mail to IANA as
 follows:
           To:  IANA@isi.edu
           Subject:  Registration of a new EHF-MAIL Keyword
 The mail message must specify the keyword for the encoding and
 acronyms if appropriate.  Documentation defining the keyword and its
 proposed purpose must be included.  The documentation must either
 reference an external non-Internet standards document or an existing
 or soon to be RFC.  If applicable, the documentation should contain a
 draft version of the future RFC.  The draft must be submitted as a
 RFC according to the normal procedure within a reasonable amount of
 time after the keyword's registration has been approved.

4. FS (File System) Object Encoding

 The file system encoding provides a standard, transportable encoding
 of file system objects from many different operating systems.  The
 intent is to allow the moving of a structured set of files from one
 environment to another while preserving common elements.  At the same
 time, files can be moved within a single environment while preserving
 all attributes.
 The representations consist of a series of nested sections, with
 attributes defined at the appropriate levels.  Each section begins
 with an open bracket "[" followed by a directive keyword and ends
 with a close bracket "]".  Attributes are lines, beginning with a
 keyword.  Lines which begin with a LWSP (linear white space)
 character are continuation lines.
 Any string-type directive or attribute may be a simple string not
 starting with a quotation mark ( " ) and not containing special
 characters (e.g.  newline) or LWSP (space and tab).  The string name
 begins with the first non-LWSP character on the line following the
 attribute or directive keyword and ends with the last non-LWSP
 character.

Costanzo, Robinson & Ullmann [Page 11] RFC 1505 Encoding Header Field August 1993

 Otherwise, the character string name is enclosed in quotes.  The
 string itself contains characters in ISO-10646-UTF-1 but is quoted
 and escaped at octet level (as elsewhere in RFC822 [2]).  The strings
 begin and end with a quotation mark ( " ).  Octets equal to quote in
 the string are escaped, as are octets equal to the escape characters
 (\" and \\).  The escaped octets may be part of a UTF multi-octet
 character.  Octets that are not printable are escaped with \nnn octal
 representation.  When an escape (\) occurs at the end of a line, the
 escape, the end of the line, and the first character of the next
 line, which must be one of the LWSP characters, are removed
 (ignored).
  [ file Simple-File.Name
  [ file "   Long file name starting with spaces and having a couple\
    [sic] of nasties in it like this newline\012near the end."
 Note that in the above example, there is one space (not two) between
 "couple" and "[sic]".  The encoder may choose to use the nnn sequence
 for any character that might cause trouble.  Refer to section 5.1 for
 line length recommendations.

4.1 Sections

 A section starts with an open bracket, followed by a keyword that
 defines the type of section.
 The section keywords are:
           directory
           entry
           file
           segment
           data
 The encoding may start with either a file, directory or entry.  A
 directory section may contain zero or more file, entry, and directory
 sections.  A file section contains a data section or zero or more
 segment sections.  A segment section contains a data section or zero
 or more segment sections.

4.1.1 Directory

 This indicates the start of a directory.  There is one parameter, the
 entry name of the directory:

Costanzo, Robinson & Ullmann [Page 12] RFC 1505 Encoding Header Field August 1993

           [ directory foo
           ...
           ]

4.1.2 Entry

 The entry keyword represents an entry in a directory that is not a
 file or a sub-directory.  Examples of entries are soft links in Unix,
 or access categories in Primos.  A Primos access category might look
 like this:
           [ entry SYS.ACAT
           type ACAT
           created 27 Jan 1987 15:31:04.00
           acl SYADMIN:* ARIEL:DALURWX $REST:
           ]

4.1.3 File

 The file keyword is followed by the entry name of the file.  The
 section then continues with attributes, possibly segments, and then
 data.
           [ file MY.FILE
           created 27 Feb 1987 12:10:20.07
           modified 27 Mar 1987 16:17:03.02
           type DAM
           [ data LZJU90
           * LZJU90
           ...
           ]]

4.1.4 Segment

 This is used to define segments of a file.  It should only be used
 when encoding files that are actually segmented.  The optional
 parameter is the number or name of the segment.
 When encoding Macintosh files, the two forks of the file are treated
 as segments:

Costanzo, Robinson & Ullmann [Page 13] RFC 1505 Encoding Header Field August 1993

           [ file A.MAC.FILE
           display "A Mac File"
           type MAC
           comment "I created this myself"
           ...
           [ segment resource
           [ data ...
           ...
           ]]
           [ segment data
           [ data ...
           ...
           ]]]

4.1.5 Data

 The data section contains the encoded data of the file.  The encoding
 method is defined in section 5.  The data section must be last within
 the containing section.

4.2 Attributes

 Attributes may occur within file, entry, directory, and segment
 sections.  Attributes must occur before sub-sections.
 The attribute directives are:
           display
           type
           created
           modified
           accessed
           owner
           group
           acl
           password
           block
           record
           application

4.2.1 Display

 This indicates the display name of the object.  Some systems, such as
 the Macintosh, use a different form of the name for matching or
 uniqueness.

Costanzo, Robinson & Ullmann [Page 14] RFC 1505 Encoding Header Field August 1993

4.2.2 Comment

 This contains an arbitrary comment on the object.  The Macintosh
 stores this attribute with the file.

4.2.3 Type

 The type of an object is usually of interest only to the operating
 system that the object was created on.
 Types are:
        ACAT       access category (Primos)
        CAM        contiguous access method (Primos)
        DAM        direct access method (Primos)
        FIXED      fixed length records (VMS)
        FLAT       `flat file', sequence of bytes (Unix, DOS, default)
        ISAM       indexed-sequential access method (VMS)
        LINK       soft link (Unix)
        MAC        Macintosh file
        SAM        sequential access method (Primos)
        SEGSAM     segmented direct access method (Primos)
        SEGDAM     segmented sequential access method (Primos)
        TEXT       lines of ISO-10646-UTF-1 text ending with CR/LF
        VAR        variable length records (VMS)

4.2.4 Created

 Indicates the creation date of the file.  Dates are in the format
 defined in section 4.3.

4.2.5 Modified

 Indicates the date and time the file was last modified or closed
 after being open for write.

4.2.6 Accessed

 Indicates the date and time the file was last accessed on the
 original file system.

4.2.7 Owner

 The owner directive gives the name or numerical ID of the owner or
 creator of the file.

Costanzo, Robinson & Ullmann [Page 15] RFC 1505 Encoding Header Field August 1993

4.2.8 Group

 The group directive gives the name(s) or numerical IDs of the group
 or groups to which the file belongs.

4.2.9 ACL

 This directive specifies the access control list attribute of an
 object (the ACL attribute may occur more than once within an object).
 The list consist of a series of pairs of IDs and access codes in the
 format:
              user-ID:access-list
 There are four reserved IDs:
              $OWNER  the owner or creator
              $GROUP  a member of the group or groups
              $SYSTEM a system administrator
              $REST   everyone else
 The access list is zero or more single letters:
              A    add (create file)
              D    delete
              L    list (read directory)
              P    change protection
              R    read
              U    use
              W    write
              X    execute
              *    all possible access

4.2.10 Password

 The password attribute gives the access password for this object.
 Since the content of the object follows (being the raison d'etre of
 the encoding), the appearance of the password in plain text is not
 considered a security problem.  If the password is actually set by
 the decoder on a created object, the security (or lack) is the
 responsibility of the application domain controlling the decoder as
 is true of ACL and other protections.

4.2.11 Block

 The block attribute gives the block size of the file as a decimal
 number of bytes.

Costanzo, Robinson & Ullmann [Page 16] RFC 1505 Encoding Header Field August 1993

4.2.12 Record

 The record attribute gives the record size of the file as a decimal
 number of bytes.

4.2.13 Application

 This specifies the application that the file was created with or
 belongs to.  This is of particular interest for Macintosh files.

4.3 Date Field

 Various attributes have a date and time subsequent to and associated
 with them.

4.3.1 Syntax

 The syntax of the date field is a combination of date, time, and
 timezone:
     DD Mon YYYY HH:MM:SS.FFFFFF [+-]HHMMSS
     Date :=  DD Mon YYYY      1 or 2 Digits " " 3 Alpha " " 4 Digits
     DD   :=  Day              e.g. "08", " 8", "8"
     Mon  :=  Month            "Jan" | "Feb" | "Mar" | "Apr" |
                               "May" | "Jun" | "Jul" | "Aug" |
                               "Sep" | "Oct" | "Nov" | "Dec"
     YYYY :=  Year
     Time :=  HH:MM:SS.FFFFFF  2 Digits ":" 2 Digits [ ":" 2 Digits
                               ["." 1 to 6 Digits ] ]
                               e.g. 00:00:00, 23:59:59.999999
     HH   :=  Hours            00 to 23
     MM   :=  Minutes          00 to 59
     SS   :=  Seconds          00 to 60 (60 only during a leap second)
     FFFFF:=  Fraction
     Zone :=  [+-]HHMMSS       "+" | "-" 2 Digits [ 2 Digits
                               [ 2 Digits ] ]
     HH   :=  Local Hour Offset
     MM   :=  Local Minutes Offset
     SS   :=  Local Seconds Offset

4.3.2 Semantics

 The date information is that which the file system has stored in
 regard to the file system object.  Date information is stored
 differently and with varying degrees of precision by different
 computer file systems.  An encoder must include as much date
 information as it has available concerning the file system object.  A

Costanzo, Robinson & Ullmann [Page 17] RFC 1505 Encoding Header Field August 1993

 decoder which receives an object encoded with a date field containing
 greater precision than its own must disregard the excessive
 information.  Zone is Co-ordinated Universal Time "UTC" (formerly
 called "Greenwich Mean Time").  The field specifies the time zone of
 the file system object as an offset from Universal Time.  It is
 expressed as a signed [+-] two, four or six digit number.
 A file that was created April 15, 1993 at 8:05 p.m.  in Roselle Park,
 New Jersey, U.S.A.  might have a date field which looks like:
 15 Apr 1993 20:05:22.12 -0500

5. LZJU90: Compressed Encoding

 LZJU90 is an encoding for a binary or text object to be sent in an
 Internet mail message.  The encoding provides both compression and
 representation in a text format that will successfully survive
 transmission through the many different mailers and gateways that
 comprise the Internet and connected mail networks.

5.1 Overview

 The encoding first compresses the binary object, using a modified
 LZ77 algorithm, called LZJU90.  It then encodes each 6 bits of the
 output of the compression as a text character, using a character set
 chosen to survive any translations between codes, such as ASCII to
 EBCDIC.  The 64 six-bit strings 000000 through 111111 are represented
 by the characters "+", "-", "0" to "9", "A" to "Z", and "a" to "z".
 The output text begins with a line identifying the encoding.  This is
 for visual reference only, the "Encoding:" field in the header
 identifies the section to the user program.  It also names the object
 that was encoded, usually by a file name.
 The format of this line is:
  • LZJU90 <name>
 where <name> is optional.  For example:
  • LZJU90 vmunix
 This is followed by the compressed and encoded data, broken into
 lines where convenient.  It is recommended that lines be broken every
 78 characters to survive mailers than incorrectly restrict line
 length.  The decoder must accept lines with 1 to 1000 characters on
 each line.  After this, there is one final line that gives the number
 of bytes in the original data and a CRC of the original data.  This

Costanzo, Robinson & Ullmann [Page 18] RFC 1505 Encoding Header Field August 1993

 should match the byte count and CRC found during decompression.
 This line has the format:
  • <count> <CRC>
 where <count> is a decimal number, and CRC is 8 hexadecimal digits.
 For example:
  • 4128076 5AC2D50E
 The count used in the Encoding:  field in the message header is the
 total number of lines, including the start and end lines that begin
 with *.  A complete example is given in section 5.3.2.

5.2 Specification of the LZJU90 compression

 The Lempel-Ziv-Storer-Szymanski model of mixing pointers and literal
 characters is used in the compression algorithm.  Repeat occurrences
 of strings of octets are replaced by pointers to the earlier
 occurrence.
 The data compression is defined by the decoding algorithm.  Any
 encoder that emits symbols which cause the decoder to produce the
 original input is defined to be valid.
 There are many possible strategies for the maximal-string matching
 that the encoder does, section 5.3.1 gives the code for one such
 algorithm.  Regardless of which algorithm is used, and what tradeoffs
 are made between compression ratio and execution speed or space, the
 result can always be decoded by the simple decoder.
 The compressed data consists of a mixture of unencoded literal
 characters and copy pointers which point to an earlier occurrence of
 the string to be encoded.
 Compressed data contains two types of codewords:
 LITERAL pass the literal directly to the uncompressed output.
 COPY    length, offset
         go back offset characters in the output and copy length
         characters forward to the current position.
 To distinguish between codewords, the copy length is used.  A copy
 length of zero indicates that the following codeword is a literal
 codeword.  A copy length greater than zero indicates that the

Costanzo, Robinson & Ullmann [Page 19] RFC 1505 Encoding Header Field August 1993

 following codeword is a copy codeword.
 To improve copy length encoding, a threshold value of 2 has been
 subtracted from the original copy length for copy codewords, because
 the minimum copy length is 3 in this compression scheme.
 The maximum offset value is set at 32255.  Larger offsets offer
 extremely low improvements in compression (less than 1 percent,
 typically).
 No special encoding is done on the LITERAL characters.  However,
 unary encoding is used for the copy length and copy offset values to
 improve compression.  A start-step-stop unary code is used.
 A (start, step, stop) unary code of the integers is defined as
 follows:  The Nth codeword has N ones followed by a zero followed by
 a field of size START + (N * STEP).  If the field width is equal to
 STOP then the preceding zero can be omitted.  The integers are laid
 out sequentially through these codewords.  For example, (0, 1, 4)
 would look like:
           Codeword      Range
           0             0
           10x           1-2
           110xx         3-6
           1110xxx       7-14
           1111xxxx      15-30
 Following are the actual values used for copy length and copy offset:
 The copy length is encoded with a (0, 1, 7) code leading to a maximum
 copy length of 256 by including the THRESHOLD value of 2.
           Codeword       Range
           0              0
           10x            3-4
           110xx          5-8
           1110xxx        9-16
           11110xxxx      17-32
           111110xxxxx    33-64
           1111110xxxxxx  65-128
           1111111xxxxxxx 129-256
 The copy offset is encoded with a (9, 1, 14) code leading to a
 maximum copy offset of 32255.  Offset 0 is reserved as an end of
 compressed data flag.

Costanzo, Robinson & Ullmann [Page 20] RFC 1505 Encoding Header Field August 1993

           Codeword       Range
           0xxxxxxxxx                0-511
           10xxxxxxxxxx            512-1535
           110xxxxxxxxxxx         1536-3583
           1110xxxxxxxxxxxx       3485-7679
           11110xxxxxxxxxxxxx     7680-15871
           11111xxxxxxxxxxxxxx   15872-32255
 The 0 has been chosen to signal the start of the field for ease of
 encoding.  (The bit generator can simply encode one more bit than is
 significant in the binary representation of the excess.)
 The stop values are useful in the encoding to prevent out of range
 values for the lengths and offsets, as well as shortening some codes
 by one bit.
 The worst case compression using this scheme is a 1/8 increase in
 size of the encoded data.  (One zero bit followed by 8 character
 bits).  After the character encoding, the worst case ratio is 3/2 to
 the original data.
 The minimum copy length of 3 has been chosen because the worst case
 copy length and offset is 3 bits (3) and 19 bits (32255) for a total
 of 22 bits to encode a 3 character string (24 bits).

5.3 The Decoder

 As mentioned previously, the compression is defined by the decoder.
 Any encoder that produced output that is correctly decoded is by
 definition correct.
 The following is an implementation of the decoder, written more for
 clarity and as much portability as possible, rather than for maximum
 speed.
 When optimized for a specific environment, it will run significantly
 faster.
  /* LZJU 90 Decoding program */
  /* Written By Robert Jung and Robert Ullmann, 1990 and 1991. */
  /* This code is NOT COPYRIGHT, not protected. It is in the true
     Public Domain. */
  #include <stdio.h>
  #include <string.h>

Costanzo, Robinson & Ullmann [Page 21] RFC 1505 Encoding Header Field August 1993

  typedef unsigned char uchar;
  typedef unsigned int  uint;
  #define N          32255
  #define THRESHOLD      3
  #define STRTP          9
  #define STEPP          1
  #define STOPP         14
  #define STRTL          0
  #define STEPL          1
  #define STOPL          7
  static FILE *in;
  static FILE *out;
  static int   getbuf;
  static int   getlen;
  static long  in_count;
  static long  out_count;
  static long  crc;
  static long  crctable[256];
  static uchar xxcodes[] =
  "+-0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ\
  abcdefghijklmnopqrstuvwxyz";
  static uchar ddcodes[256];
  static uchar text[N];
  #define CRCPOLY         0xEDB88320
  #define CRC_MASK        0xFFFFFFFF
  #define UPDATE_CRC(crc, c)  \
          crc = crctable[((uchar)(crc) ^ (uchar)(c)) & 0xFF] \
                ^ (crc >> 8)
  #define START_RECD      "* LZJU90"
  void MakeCrctable()     /* Initialize CRC-32 table */
  {
  uint i, j;
  long r;
      for (i = 0; i <= 255; i++) {
          r = i;
          for (j = 8; j > 0; j--) {
              if (r & 1)
                  r = (r >> 1) ^ CRCPOLY;
              else

Costanzo, Robinson & Ullmann [Page 22] RFC 1505 Encoding Header Field August 1993

                  r >>= 1;
              }
          crctable[i] = r;
          }
  }
  int GetXX()             /* Get xxcode and translate */
  {
  int c;
      do {
          if ((c = fgetc(in)) == EOF)
              c = 0;
          } while (c == '\n');
      in_count++;
      return ddcodes[c];
  }
  int GetBit()            /* Get one bit from input buffer */
  {
  int c;
      while (getlen <= 0) {
          c = GetXX();
          getbuf |= c << (10-getlen);
          getlen += 6;
          }
      c = (getbuf & 0x8000) != 0;
      getbuf <<= 1;
      getbuf &= 0xFFFF;
      getlen--;
      return(c);
  }
  int GetBits(int len)        /* Get len bits */
  {
  int c;
      while (getlen <= 10) {
          c = GetXX();
          getbuf |= c << (10-getlen);
          getlen += 6;
          }
      if (getlen < len) {
          c = (uint)getbuf >> (16-len);

Costanzo, Robinson & Ullmann [Page 23] RFC 1505 Encoding Header Field August 1993

          getbuf = GetXX();
          c |= getbuf >> (6+getlen-len);
          getbuf <<= (10+len-getlen);
          getbuf &= 0xFFFF;
          getlen -= len - 6;
          }
      else {
          c = (uint)getbuf >> (16-len);
          getbuf <<= len;
          getbuf &= 0xFFFF;
          getlen -= len;
          }
      return(c);
  }
  int DecodePosition()    /* Decode offset position pointer */
  {
  int c;
  int width;
  int plus;
  int pwr;
      plus = 0;
      pwr = 1 << STRTP;
      for (width = STRTP; width < STOPP; width += STEPP) {
          c = GetBit();
          if (c == 0)
              break;
          plus += pwr;
          pwr <<= 1;
          }
      if (width != 0)
          c = GetBits(width);
      c += plus;
      return(c);
  }
  int DecodeLength()      /* Decode code length */
  {
  int c;
  int width;
  int plus;
  int pwr;
      plus = 0;
      pwr = 1 << STRTL;

Costanzo, Robinson & Ullmann [Page 24] RFC 1505 Encoding Header Field August 1993

      for (width = STRTL; width < STOPL; width += STEPL) {
          c = GetBit();
          if (c == 0)
              break;
          plus += pwr;
          pwr <<= 1;
          }
      if (width != 0)
          c = GetBits(width);
      c += plus;
  return(c);
  }
  void InitCodes()        /* Initialize decode table */
  {
  int i;
      for (i = 0; i < 256; i++) ddcodes[i] = 0;
      for (i = 0; i < 64; i++) ddcodes[xxcodes[i]] = i;
  return;
  }
  main(int ac, char **av)            /* main program */
  {
  int r;
  int j, k;
  int c;
  int pos;
  char buf[80];
  char name[3];
  long num, bytes;
      if (ac < 3) {
          fprintf(stderr, "usage: judecode in out\n");
          return(1);
          }
      in = fopen(av[1], "r");
      if (!in){
          fprintf(stderr, "Can't open %s\n", av[1]);
          return(1);
          }
      out = fopen(av[2], "wb");
      if (!out) {
          fprintf(stderr, "Can't open %s\n", av[2]);
          fclose(in);

Costanzo, Robinson & Ullmann [Page 25] RFC 1505 Encoding Header Field August 1993

      return(1);
          }
      while (1) {
          if (fgets(buf, sizeof(buf), in) == NULL) {
              fprintf(stderr, "Unexpected EOF\n");
          return(1);
              }
          if (strncmp(buf, START_RECD, strlen(START_RECD)) == 0)
              break;
          }
      in_count = 0;
      out_count = 0;
      getbuf = 0;
      getlen = 0;
      InitCodes();
      MakeCrctable();
      crc = CRC_MASK;
      r = 0;
      while (feof(in) == 0) {
          c = DecodeLength();
          if (c == 0) {
              c = GetBits(8);
              UPDATE_CRC(crc, c);
              out_count++;
              text[r] = c;
              fputc(c, out);
              if (++r >= N)
                  r = 0;
              }
          else {
              pos = DecodePosition();
              if (pos == 0)
                  break;
              pos--;
              j = c + THRESHOLD - 1;
              pos = r - pos - 1;
              if (pos < 0)
                  pos += N;
              for (k = 0; k < j; k++) {
                  c = text[pos];
                  text[r] = c;
                  UPDATE_CRC(crc, c);

Costanzo, Robinson & Ullmann [Page 26] RFC 1505 Encoding Header Field August 1993

                  out_count++;
                  fputc(c, out);
                  if (++r >= N)
                      r = 0;
                  if (++pos >= N)
                      pos = 0;
                  }
              }
          }
      fgetc(in); /* skip newline */
      if (fscanf(in, "* %ld %lX", &bytes, &num) != 2) {
          fprintf(stderr, "CRC record not found\n");
          return(1);
          }
      else if (crc != num) {
          fprintf(stderr,
               "CRC error, expected %lX, found %lX\n",
               crc, num);
          return(1);
          }
      else if (bytes != out_count) {
          fprintf(stderr,
               "File size error, expected %lu, found %lu\n",
               bytes, out_count);
      return(1);
          }
      else
          fprintf(stderr,
               "File decoded to %lu bytes correctly\n",
               out_count);
      fclose(in);
      fclose(out);
  return(0);
  }

5.3.1 An example of an Encoder

 Many algorithms are possible for the encoder, with different
 tradeoffs between speed, size, and complexity.  The following is a
 simple example program which is fairly efficient; more sophisticated
 implementations will run much faster, and in some cases produce

Costanzo, Robinson & Ullmann [Page 27] RFC 1505 Encoding Header Field August 1993

 somewhat better compression.
 This example also shows that the encoder need not use the entire
 window available.  Not using the full window costs a small amount of
 compression, but can greatly increase the speed of some algorithms.
  /* LZJU 90 Encoding program */
  /* Written By Robert Jung and Robert Ullmann, 1990 and 1991. */
  /* This code is NOT COPYRIGHT, not protected. It is in the true
     Public Domain. */
  #include <stdio.h>
  typedef unsigned char uchar;
  typedef unsigned int  uint;
  #define N          24000    /* Size of window buffer */
  #define F            256   /* Size of look-ahead buffer */
  #define THRESHOLD      3
  #define K          16384    /* Size of hash table */
  #define STRTP          9
  #define STEPP          1
  #define STOPP         14
  #define STRTL          0
  #define STEPL          1
  #define STOPL          7
  #define CHARSLINE     78
  static FILE *in;
  static FILE *out;
  static int   putlen;
  static int   putbuf;
  static int   char_ct;
  static long  in_count;
  static long  out_count;
  static long  crc;
  static long  crctable[256];
  static uchar xxcodes[] =
  "+-0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ\
  abcdefghijklmnopqrstuvwxyz";
  uchar window_text[N + F + 1];

Costanzo, Robinson & Ullmann [Page 28] RFC 1505 Encoding Header Field August 1993

  /* text contains window, plus 1st F of window again
     (for comparisons) */
  uint hash_table[K];
  /* table of pointers into the text */
  #define CRCPOLY         0xEDB88320
  #define CRC_MASK        0xFFFFFFFF
  #define UPDATE_CRC(crc, c)  \
    crc = crctable[((uchar)(crc) ^ (uchar)(c)) & 0xFF] \
    ^ (crc >> 8)
  void MakeCrctable()     /* Initialize CRC-32 table */
  {
  uint i, j;
  long r;
      for (i = 0; i <= 255; i++) {
          r = i;
          for (j = 8; j > 0; j--) {
              if (r & 1)
                  r = (r >> 1) ^ CRCPOLY;
              else
                  r >>= 1;
          }
          crctable[i] = r;
      }
  }
  void PutXX(int c)           /* Translate and put xxcode */
  {
      c = xxcodes[c & 0x3F];
      if (++char_ct > CHARSLINE) {
          char_ct = 1;
          fputc('\n', out);
      }
      fputc(c, out);
      out_count++;
  }
  void PutBits(int c, int len)  /* Put rightmost "len" bits of "c" */
  {
      c <<= 16 - len;
      c &= 0xFFFF;
      putbuf |= (uint) c >> putlen;

Costanzo, Robinson & Ullmann [Page 29] RFC 1505 Encoding Header Field August 1993

      c <<= 16 - putlen;
      c &= 0xFFFF;
      putlen += len;
      while (putlen >= 6) {
          PutXX(putbuf >> 10);
          putlen -= 6;
          putbuf <<= 6;
          putbuf &= 0xFFFF;
          putbuf |= (uint) c >> 10;
          c = 0;
          }
  }
  void EncodePosition(int ch) /* Encode offset position pointer */
  {
  int width;
  int prefix;
  int pwr;
      pwr = 1 << STRTP;
      for (width = STRTP; ch >= pwr; width += STEPP, pwr <<= 1)
          ch -= pwr;
      if ((prefix = width - STRTP) != 0)
          PutBits(0xffff, prefix);
      if (width < STOPP)
          width++;
      /* else if (width > STOPP)
      abort(); do nothing */
      PutBits(ch, width);
  }
  void EncodeLength(int ch)   /* Encode code length */
  {
  int width;
  int prefix;
  int pwr;
      pwr = 1 << STRTL;
      for (width = STRTL; ch >= pwr; width += STEPL, pwr <<= 1)
          ch -= pwr;
      if ((prefix = width - STRTL) != 0)
          PutBits(0xffff, prefix);
      if (width < STOPL)
          width++;
      /* else if (width > STOPL)
      abort(); do nothing */
      PutBits(ch, width);
  }

Costanzo, Robinson & Ullmann [Page 30] RFC 1505 Encoding Header Field August 1993

  main(int ac, char **av)            /* main program */
  {
  uint r, s, i, c;
  uchar *p, *rp;
  int match_position;
  int match_length;
  int len;
  uint hash, h;
      if (ac < 3) {
          fprintf(stderr, "usage: juencode in out\n");
      return(1);
          }
      in = fopen(av[1], "rb");
      if (!in) {
          fprintf(stderr, "Can't open %s\n", av[1]);
      return(1);
          }
      out = fopen(av[2], "w");
      if (!out) {
          fprintf(stderr, "Can't open %s\n", av[2]);
          fclose(in);
      return(1);
          }
      char_ct = 0;
      in_count = 0;
      out_count = 0;
      putbuf = 0;
      putlen = 0;
      hash = 0;
      MakeCrctable();
      crc = CRC_MASK;
      fprintf(out, "* LZJU90 %s\n", av[1]);
      /* The hash table inititialization is somewhat arbitrary */
      for (i = 0; i < K; i++) hash_table[i] = i % N;
      r = 0;
      s = 0;
      /* Fill lookahead buffer */
      for (len = 0; len < F && (c = fgetc(in)) != EOF; len++) {

Costanzo, Robinson & Ullmann [Page 31] RFC 1505 Encoding Header Field August 1993

          UPDATE_CRC(crc, c);
      in_count++;
      window_text[s++] = c;
      }
      while (len > 0) {
      /* look for match in window at hash position */
      h = ((((window_text[r] << 5) ^ window_text[r+1])
              << 5) ^ window_text[r+2]);
      p = window_text + hash_table[h % K];
      rp = window_text + r;
      for (i = 0, match_length = 0; i < F; i++) {
              if (*p++ != *rp++) break;
              match_length++;
              }
      match_position = r - hash_table[h % K];
      if (match_position <= 0) match_position += N;
      if (match_position > N - F - 2) match_length = 0;
      if (match_position > in_count - len - 2)
          match_length = 0; /* ! :-) */
      if (match_length > len)
          match_length = len;
      if (match_length < THRESHOLD) {
          EncodeLength(0);
          PutBits(window_text[r], 8);
          match_length = 1;
          }
      else {
          EncodeLength(match_length - THRESHOLD + 1);
          EncodePosition(match_position);
          }
      for (i = 0; i < match_length &&
                      (c = fgetc(in)) != EOF; i++) {
              UPDATE_CRC(crc, c);
              in_count++;
          window_text[s] = c;
              if (s < F - 1)
              window_text
              [s + N] = c;
          if (++s > N - 1) s = 0;
          hash = ((hash << 5) ^ window_text[r]);
          if (r > 1) hash_table[hash % K] = r - 2;
          if (++r > N - 1) r = 0;
          }

Costanzo, Robinson & Ullmann [Page 32] RFC 1505 Encoding Header Field August 1993

      while (i++ < match_length) {
          if (++s > N - 1) s = 0;
          hash = ((hash << 5) ^ window_text[r]);
          if (r > 1) hash_table[hash % K] = r - 2;
          if (++r > N - 1 ) r = 0;
          len--;
              }
      }
      /* end compression indicator */
      EncodeLength(1);
      EncodePosition(0);
      PutBits(0, 7);
      fprintf(out, "\n* %lu %08lX\n", in_count, crc);
      fprintf(stderr, "Encoded %lu bytes to %lu symbols\n",
              in_count, out_count);
      fclose(in);
      fclose(out);
  return(0);
  }

5.3.2 Example LZJU90 Compressed Object

 The following is an example of an LZJU90 compressed object.  Using
 this as source for the program in section 5.3 will reveal what it is.
    Encoding: 7 LZJU90 Text
  • LZJU90 example

8-mBtWA7WBVZ3dEBtnCNdU2WkE4owW+l4kkaApW+o4Ir0k33Ao4IE4kk

    bYtk1XY618NnCQl+OHQ61d+J8FZBVVCVdClZ2-LUI0v+I4EraItasHbG
    VVg7c8tdk2lCBtr3U86FZANVCdnAcUCNcAcbCMUCdicx0+u4wEETHcRM
    7tZ2-6Btr268-Eh3cUAlmBth2-IUo3As42laIE2Ao4Yq4G-cHHT-wCEU
    6tjBtnAci-I++
    * 190 081E2601

Costanzo, Robinson & Ullmann [Page 33] RFC 1505 Encoding Header Field August 1993

6. Alphabetical Listing of Defined Encodings

      Keyword         Description             Section  Reference(s)
      _______         ___________             _______  ____________
      EDIFACT         EDIFACT format          3.5
      EDI-X12         EDI X12 format          3.5      ANSI X12
      EVFU            FORTRAN format          3.4
      FS              File System format      3.6, 4
      Hex             Hex binary format       3.3
      LZJU90          LZJU90 format           3.7, 5
      LZW             LZW format              3.8
      Message         Encapsulated Message    3.2      STD 11, RFC 822
      PEM, PEM-Clear  Privacy Enhanced Mail   3.10     RFC 1421-1424
      PGP             Pretty Good Privacy     3.11
      Postscript      Postscript format       3.14     [8]
      Shar            Shell Archive format    3.15
      Signature       Signature               3.12
      Tar             Tar format              3.13
      Text            Text                    3.1      IS 10646
      uuencode        uuencode format         3.9
      URL             external URL-reference  3.16

7. Security Considerations

 Security of content and the receiving (decoding) system is discussed
 in sections 3.10, 3.11, 3.15, and 4.2.10.  The considerations
 mentioned also apply to other encodings and attributes with similar
 functions.

8. References

 [1] Robinson, D. and R. Ullmann, "Encoding Header Field for Internet
     Messages", RFC 1154, Prime Computer, Inc., April 1990.
 [2] Crocker, D., "Standard for the Format of ARPA Internet Text
     Messages", STD 11, RFC 822, University of Delaware, August 1982.
 [3] International Organization for Standardization, Information
     Technology -- Universal Coded Character Set (UCS).  ISO/IEC
     10646-1:1993, June 1993.
 [4] Linn, J., "Privacy Enhancement for Internet Electronic Mail: Part
     I: Message Encryption and Authentication Procedures" RFC 1421,
     IAB IRTF PSRG, IETF PEM WG, February 1993.

Costanzo, Robinson & Ullmann [Page 34] RFC 1505 Encoding Header Field August 1993

 [5] Kent, S., "Privacy Enhancement for Internet Electronic Mail: Part
     II: Certificate-Based Key Management", RFC 1422, IAB IRTF PSRG,
     IETF PEM, BBN, February 1993.
 [6] Balenson, D., "Privacy Enhancement for Internet Electronic Mail:
     Part III: Algorithms, Modes, and Identifiers", RFC 1423, IAB IRTF
     PSRG, IETF PEM WG, TIS, February 1993.
 [7] Kaliski, B., "Privacy Enhancement for Internet Electronic Mail:
     Part IV: Key Certification and Related Services", RFC 1424, RSR
     Laboratories, February 1993.
 [8] Adobe Systems Inc., PostScript Language Reference Manual.  2nd
     Edition, 2nd Printing, January 1991.
 [9] Rose, M. and E. Steffererud, "Proposed Standard for Message
     Encapsulation", RFC 934, Delaware and NMA, January 1985.
[10] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821,
     USC/Information Sciences Institute, August 1982.
[11] Borenstein, N., and N. Freed, "MIME (Multipurpose Internet Mail
     Extensions): Mechanisms for Specifying and Describing the Format
     of Internet Message Bodies", RFC 1341, Bellcore, Innosoft, June
     1992.
[12] Borenstein, N., and M. Linimon, "Extension of MIME Content-Types
     to a New Medium", RFC 1437, 1 April 1993.

9. Acknowledgements

 The authors would like to thank Robert Jung for his contributions to
 this work, in particular the public domain sample code for LZJU90.

Costanzo, Robinson & Ullmann [Page 35] RFC 1505 Encoding Header Field August 1993

10. Authors' Addresses

 Albert K. Costanzo
 AKC Consulting Inc.
 P.O. Box 4031
 Roselle Park, NJ  07204-0531
 Phone: +1 908 298 9000
 Email: AL@AKC.COM
 David Robinson
 Computervision Corporation
 100 Crosby Drive
 Bedford, MA  01730
 Phone: +1 617 275 1800 x2774
 Email: DRB@Relay.CV.COM
 Robert Ullmann
 Phone: +1 617 247 7959
 Email: ariel@world.std.com

Costanzo, Robinson & Ullmann [Page 36]

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