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Posted to commits@commons.apache.org by bo...@apache.org on 2015/12/13 17:38:42 UTC
[3/7] commons-compress git commit: Added headers to recognize PKWARE
crypto headers.
http://git-wip-us.apache.org/repos/asf/commons-compress/blob/a433f625/doc/APPNOTE-6.3.4.TXT
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+File: APPNOTE.TXT - .ZIP File Format Specification
+Version: 6.3.4
+Status: Final - replaces version 6.3.3
+Revised: October 1, 2014
+Copyright (c) 1989 - 2014 PKWARE Inc., All Rights Reserved.
+
+1.0 Introduction
+---------------
+
+1.1 Purpose
+-----------
+
+ 1.1.1 This specification is intended to define a cross-platform,
+ interoperable file storage and transfer format. Since its
+ first publication in 1989, PKWARE, Inc. ("PKWARE") has remained
+ committed to ensuring the interoperability of the .ZIP file
+ format through periodic publication and maintenance of this
+ specification. We trust that all .ZIP compatible vendors and
+ application developers that use and benefit from this format
+ will share and support this commitment to interoperability.
+
+1.2 Scope
+---------
+
+ 1.2.1 ZIP is one of the most widely used compressed file formats. It is
+ universally used to aggregate, compress, and encrypt files into a single
+ interoperable container. No specific use or application need is
+ defined by this format and no specific implementation guidance is
+ provided. This document provides details on the storage format for
+ creating ZIP files. Information is provided on the records and
+ fields that describe what a ZIP file is.
+
+1.3 Trademarks
+--------------
+
+ 1.3.1 PKWARE, PKZIP, SecureZIP, and PKSFX are registered trademarks of
+ PKWARE, Inc. in the United States and elsewhere. PKPatchMaker,
+ Deflate64, and ZIP64 are trademarks of PKWARE, Inc. Other marks
+ referenced within this document appear for identification
+ purposes only and are the property of their respective owners.
+
+
+1.4 Permitted Use
+-----------------
+
+ 1.4.1 This document, "APPNOTE.TXT - .ZIP File Format Specification" is the
+ exclusive property of PKWARE. Use of the information contained in this
+ document is permitted solely for the purpose of creating products,
+ programs and processes that read and write files in the ZIP format
+ subject to the terms and conditions herein.
+
+ 1.4.2 Use of the content of this document within other publications is
+ permitted only through reference to this document. Any reproduction
+ or distribution of this document in whole or in part without prior
+ written permission from PKWARE is strictly prohibited.
+
+ 1.4.3 Certain technological components provided in this document are the
+ patented proprietary technology of PKWARE and as such require a
+ separate, executed license agreement from PKWARE. Applicable
+ components are marked with the following, or similar, statement:
+ 'Refer to the section in this document entitled "Incorporating
+ PKWARE Proprietary Technology into Your Product" for more information'.
+
+1.5 Contacting PKWARE
+---------------------
+
+ 1.5.1 If you have questions on this format, its use, or licensing, or if you
+ wish to report defects, request changes or additions, please contact:
+
+ PKWARE, Inc.
+ 201 E. Pittsburgh Avenue, Suite 400
+ Milwaukee, WI 53204
+ +1-414-289-9788
+ +1-414-289-9789 FAX
+ zipformat@pkware.com
+
+ 1.5.2 Information about this format and copies of this document are publicly
+ available at:
+
+ http://www.pkware.com/appnote
+
+1.6 Disclaimer
+--------------
+
+ 1.6.1 Although PKWARE will attempt to supply current and accurate
+ information relating to its file formats, algorithms, and the
+ subject programs, the possibility of error or omission cannot
+ be eliminated. PKWARE therefore expressly disclaims any warranty
+ that the information contained in the associated materials relating
+ to the subject programs and/or the format of the files created or
+ accessed by the subject programs and/or the algorithms used by
+ the subject programs, or any other matter, is current, correct or
+ accurate as delivered. Any risk of damage due to any possible
+ inaccurate information is assumed by the user of the information.
+ Furthermore, the information relating to the subject programs
+ and/or the file formats created or accessed by the subject
+ programs and/or the algorithms used by the subject programs is
+ subject to change without notice.
+
+2.0 Revisions
+--------------
+
+2.1 Document Status
+--------------------
+
+ 2.1.1 If the STATUS of this file is marked as DRAFT, the content
+ defines proposed revisions to this specification which may consist
+ of changes to the ZIP format itself, or that may consist of other
+ content changes to this document. Versions of this document and
+ the format in DRAFT form may be subject to modification prior to
+ publication STATUS of FINAL. DRAFT versions are published periodically
+ to provide notification to the ZIP community of pending changes and to
+ provide opportunity for review and comment.
+
+ 2.1.2 Versions of this document having a STATUS of FINAL are
+ considered to be in the final form for that version of the document
+ and are not subject to further change until a new, higher version
+ numbered document is published. Newer versions of this format
+ specification are intended to remain interoperable with with all prior
+ versions whenever technically possible.
+
+2.2 Change Log
+--------------
+
+ Version Change Description Date
+ ------- ------------------ ----------
+ 5.2 -Single Password Symmetric Encryption 07/16/2003
+ storage
+
+ 6.1.0 -Smartcard compatibility 01/20/2004
+ -Documentation on certificate storage
+
+ 6.2.0 -Introduction of Central Directory 04/26/2004
+ Encryption for encrypting metadata
+ -Added OS X to Version Made By values
+
+ 6.2.1 -Added Extra Field placeholder for 04/01/2005
+ POSZIP using ID 0x4690
+
+ -Clarified size field on
+ "zip64 end of central directory record"
+
+ 6.2.2 -Documented Final Feature Specification 01/06/2006
+ for Strong Encryption
+
+ -Clarifications and typographical
+ corrections
+
+ 6.3.0 -Added tape positioning storage 09/29/2006
+ parameters
+
+ -Expanded list of supported hash algorithms
+
+ -Expanded list of supported compression
+ algorithms
+
+ -Expanded list of supported encryption
+ algorithms
+
+ -Added option for Unicode filename
+ storage
+
+ -Clarifications for consistent use
+ of Data Descriptor records
+
+ -Added additional "Extra Field"
+ definitions
+
+ 6.3.1 -Corrected standard hash values for 04/11/2007
+ SHA-256/384/512
+
+ 6.3.2 -Added compression method 97 09/28/2007
+
+ -Documented InfoZIP "Extra Field"
+ values for UTF-8 file name and
+ file comment storage
+
+ 6.3.3 -Formatting changes to support 09/01/2012
+ easier referencing of this APPNOTE
+ from other documents and standards
+
+ 6.3.4 -Address change 10/01/2014
+
+
+3.0 Notations
+-------------
+
+ 3.1 Use of the term MUST or SHALL indicates a required element.
+
+ 3.2 MAY NOT or SHALL NOT indicates an element is prohibited from use.
+
+ 3.3 SHOULD indicates a RECOMMENDED element.
+
+ 3.4 SHOULD NOT indicates an element NOT RECOMMENDED for use.
+
+ 3.5 MAY indicates an OPTIONAL element.
+
+
+4.0 ZIP Files
+-------------
+
+4.1 What is a ZIP file
+----------------------
+
+ 4.1.1 ZIP files MAY be identified by the standard .ZIP file extension
+ although use of a file extension is not required. Use of the
+ extension .ZIPX is also recognized and MAY be used for ZIP files.
+ Other common file extensions using the ZIP format include .JAR, .WAR,
+ .DOCX, .XLXS, .PPTX, .ODT, .ODS, .ODP and others. Programs reading or
+ writing ZIP files SHOULD rely on internal record signatures described
+ in this document to identify files in this format.
+
+ 4.1.2 ZIP files SHOULD contain at least one file and MAY contain
+ multiple files.
+
+ 4.1.3 Data compression MAY be used to reduce the size of files
+ placed into a ZIP file, but is not required. This format supports the
+ use of multiple data compression algorithms. When compression is used,
+ one of the documented compression algorithms MUST be used. Implementors
+ are advised to experiment with their data to determine which of the
+ available algorithms provides the best compression for their needs.
+ Compression method 8 (Deflate) is the method used by default by most
+ ZIP compatible application programs.
+
+
+ 4.1.4 Data encryption MAY be used to protect files within a ZIP file.
+ Keying methods supported for encryption within this format include
+ passwords and public/private keys. Either MAY be used individually
+ or in combination. Encryption MAY be applied to individual files.
+ Additional security MAY be used through the encryption of ZIP file
+ metadata stored within the Central Directory. See the section on the
+ Strong Encryption Specification for information. Refer to the section
+ in this document entitled "Incorporating PKWARE Proprietary Technology
+ into Your Product" for more information.
+
+ 4.1.5 Data integrity MUST be provided for each file using CRC32.
+
+ 4.1.6 Additional data integrity MAY be included through the use of
+ digital signatures. Individual files MAY be signed with one or more
+ digital signatures. The Central Directory, if signed, MUST use a
+ single signature.
+
+ 4.1.7 Files MAY be placed within a ZIP file uncompressed or stored.
+ The term "stored" as used in the context of this document means the file
+ is copied into the ZIP file uncompressed.
+
+ 4.1.8 Each data file placed into a ZIP file MAY be compressed, stored,
+ encrypted or digitally signed independent of how other data files in the
+ same ZIP file are archived.
+
+ 4.1.9 ZIP files MAY be streamed, split into segments (on fixed or on
+ removable media) or "self-extracting". Self-extracting ZIP
+ files MUST include extraction code for a target platform within
+ the ZIP file.
+
+ 4.1.10 Extensibility is provided for platform or application specific
+ needs through extra data fields that MAY be defined for custom
+ purposes. Extra data definitions MUST NOT conflict with existing
+ documented record definitions.
+
+ 4.1.11 Common uses for ZIP MAY also include the use of manifest files.
+ Manifest files store application specific information within a file stored
+ within the ZIP file. This manifest file SHOULD be the first file in the
+ ZIP file. This specification does not provide any information or guidance on
+ the use of manifest files within ZIP files. Refer to the application developer
+ for information on using manifest files and for any additional profile
+ information on using ZIP within an application.
+
+ 4.1.12 ZIP files MAY be placed within other ZIP files.
+
+4.2 ZIP Metadata
+----------------
+
+ 4.2.1 ZIP files are identified by metadata consisting of defined record types
+ containing the storage information necessary for maintaining the files
+ placed into a ZIP file. Each record type MUST be identified using a header
+ signature that identifies the record type. Signature values begin with the
+ two byte constant marker of 0x4b50, representing the characters "PK".
+
+
+4.3 General Format of a .ZIP file
+---------------------------------
+
+ 4.3.1 A ZIP file MUST contain an "end of central directory record". A ZIP
+ file containing only an "end of central directory record" is considered an
+ empty ZIP file. Files may be added or replaced within a ZIP file, or deleted.
+ A ZIP file MUST have only one "end of central directory record". Other
+ records defined in this specification MAY be used as needed to support
+ storage requirements for individual ZIP files.
+
+ 4.3.2 Each file placed into a ZIP file MUST be preceeded by a "local
+ file header" record for that file. Each "local file header" MUST be
+ accompanied by a corresponding "central directory header" record within
+ the central directory section of the ZIP file.
+
+ 4.3.3 Files MAY be stored in arbitrary order within a ZIP file. A ZIP
+ file MAY span multiple volumes or it MAY be split into user-defined
+ segment sizes. All values MUST be stored in little-endian byte order unless
+ otherwise specified in this document for a specific data element.
+
+ 4.3.4 Compression MUST NOT be applied to a "local file header", an "encryption
+ header", or an "end of central directory record". Individual "central
+ directory records" must not be compressed, but the aggregate of all central
+ directory records MAY be compressed.
+
+ 4.3.5 File data MAY be followed by a "data descriptor" for the file. Data
+ descriptors are used to facilitate ZIP file streaming.
+
+
+ 4.3.6 Overall .ZIP file format:
+
+ [local file header 1]
+ [encryption header 1]
+ [file data 1]
+ [data descriptor 1]
+ .
+ .
+ .
+ [local file header n]
+ [encryption header n]
+ [file data n]
+ [data descriptor n]
+ [archive decryption header]
+ [archive extra data record]
+ [central directory header 1]
+ .
+ .
+ .
+ [central directory header n]
+ [zip64 end of central directory record]
+ [zip64 end of central directory locator]
+ [end of central directory record]
+
+
+ 4.3.7 Local file header:
+
+ local file header signature 4 bytes (0x04034b50)
+ version needed to extract 2 bytes
+ general purpose bit flag 2 bytes
+ compression method 2 bytes
+ last mod file time 2 bytes
+ last mod file date 2 bytes
+ crc-32 4 bytes
+ compressed size 4 bytes
+ uncompressed size 4 bytes
+ file name length 2 bytes
+ extra field length 2 bytes
+
+ file name (variable size)
+ extra field (variable size)
+
+ 4.3.8 File data
+
+ Immediately following the local header for a file
+ SHOULD be placed the compressed or stored data for the file.
+ If the file is encrypted, the encryption header for the file
+ SHOULD be placed after the local header and before the file
+ data. The series of [local file header][encryption header]
+ [file data][data descriptor] repeats for each file in the
+ .ZIP archive.
+
+ Zero-byte files, directories, and other file types that
+ contain no content MUST not include file data.
+
+ 4.3.9 Data descriptor:
+
+ crc-32 4 bytes
+ compressed size 4 bytes
+ uncompressed size 4 bytes
+
+ 4.3.9.1 This descriptor MUST exist if bit 3 of the general
+ purpose bit flag is set (see below). It is byte aligned
+ and immediately follows the last byte of compressed data.
+ This descriptor SHOULD be used only when it was not possible to
+ seek in the output .ZIP file, e.g., when the output .ZIP file
+ was standard output or a non-seekable device. For ZIP64(tm) format
+ archives, the compressed and uncompressed sizes are 8 bytes each.
+
+ 4.3.9.2 When compressing files, compressed and uncompressed sizes
+ should be stored in ZIP64 format (as 8 byte values) when a
+ file's size exceeds 0xFFFFFFFF. However ZIP64 format may be
+ used regardless of the size of a file. When extracting, if
+ the zip64 extended information extra field is present for
+ the file the compressed and uncompressed sizes will be 8
+ byte values.
+
+ 4.3.9.3 Although not originally assigned a signature, the value
+ 0x08074b50 has commonly been adopted as a signature value
+ for the data descriptor record. Implementers should be
+ aware that ZIP files may be encountered with or without this
+ signature marking data descriptors and SHOULD account for
+ either case when reading ZIP files to ensure compatibility.
+
+ 4.3.9.4 When writing ZIP files, implementors SHOULD include the
+ signature value marking the data descriptor record. When
+ the signature is used, the fields currently defined for
+ the data descriptor record will immediately follow the
+ signature.
+
+ 4.3.9.5 An extensible data descriptor will be released in a
+ future version of this APPNOTE. This new record is intended to
+ resolve conflicts with the use of this record going forward,
+ and to provide better support for streamed file processing.
+
+ 4.3.9.6 When the Central Directory Encryption method is used,
+ the data descriptor record is not required, but MAY be used.
+ If present, and bit 3 of the general purpose bit field is set to
+ indicate its presence, the values in fields of the data descriptor
+ record MUST be set to binary zeros. See the section on the Strong
+ Encryption Specification for information. Refer to the section in
+ this document entitled "Incorporating PKWARE Proprietary Technology
+ into Your Product" for more information.
+
+
+ 4.3.10 Archive decryption header:
+
+ 4.3.10.1 The Archive Decryption Header is introduced in version 6.2
+ of the ZIP format specification. This record exists in support
+ of the Central Directory Encryption Feature implemented as part of
+ the Strong Encryption Specification as described in this document.
+ When the Central Directory Structure is encrypted, this decryption
+ header MUST precede the encrypted data segment.
+
+ 4.3.10.2 The encrypted data segment SHALL consist of the Archive
+ extra data record (if present) and the encrypted Central Directory
+ Structure data. The format of this data record is identical to the
+ Decryption header record preceding compressed file data. If the
+ central directory structure is encrypted, the location of the start of
+ this data record is determined using the Start of Central Directory
+ field in the Zip64 End of Central Directory record. See the
+ section on the Strong Encryption Specification for information
+ on the fields used in the Archive Decryption Header record.
+ Refer to the section in this document entitled "Incorporating
+ PKWARE Proprietary Technology into Your Product" for more information.
+
+
+ 4.3.11 Archive extra data record:
+
+ archive extra data signature 4 bytes (0x08064b50)
+ extra field length 4 bytes
+ extra field data (variable size)
+
+ 4.3.11.1 The Archive Extra Data Record is introduced in version 6.2
+ of the ZIP format specification. This record MAY be used in support
+ of the Central Directory Encryption Feature implemented as part of
+ the Strong Encryption Specification as described in this document.
+ When present, this record MUST immediately precede the central
+ directory data structure.
+
+ 4.3.11.2 The size of this data record SHALL be included in the
+ Size of the Central Directory field in the End of Central
+ Directory record. If the central directory structure is compressed,
+ but not encrypted, the location of the start of this data record is
+ determined using the Start of Central Directory field in the Zip64
+ End of Central Directory record. Refer to the section in this document
+ entitled "Incorporating PKWARE Proprietary Technology into Your
+ Product" for more information.
+
+ 4.3.12 Central directory structure:
+
+ [central directory header 1]
+ .
+ .
+ .
+ [central directory header n]
+ [digital signature]
+
+ File header:
+
+ central file header signature 4 bytes (0x02014b50)
+ version made by 2 bytes
+ version needed to extract 2 bytes
+ general purpose bit flag 2 bytes
+ compression method 2 bytes
+ last mod file time 2 bytes
+ last mod file date 2 bytes
+ crc-32 4 bytes
+ compressed size 4 bytes
+ uncompressed size 4 bytes
+ file name length 2 bytes
+ extra field length 2 bytes
+ file comment length 2 bytes
+ disk number start 2 bytes
+ internal file attributes 2 bytes
+ external file attributes 4 bytes
+ relative offset of local header 4 bytes
+
+ file name (variable size)
+ extra field (variable size)
+ file comment (variable size)
+
+ 4.3.13 Digital signature:
+
+ header signature 4 bytes (0x05054b50)
+ size of data 2 bytes
+ signature data (variable size)
+
+ With the introduction of the Central Directory Encryption
+ feature in version 6.2 of this specification, the Central
+ Directory Structure MAY be stored both compressed and encrypted.
+ Although not required, it is assumed when encrypting the
+ Central Directory Structure, that it will be compressed
+ for greater storage efficiency. Information on the
+ Central Directory Encryption feature can be found in the section
+ describing the Strong Encryption Specification. The Digital
+ Signature record will be neither compressed nor encrypted.
+
+ 4.3.14 Zip64 end of central directory record
+
+ zip64 end of central dir
+ signature 4 bytes (0x06064b50)
+ size of zip64 end of central
+ directory record 8 bytes
+ version made by 2 bytes
+ version needed to extract 2 bytes
+ number of this disk 4 bytes
+ number of the disk with the
+ start of the central directory 4 bytes
+ total number of entries in the
+ central directory on this disk 8 bytes
+ total number of entries in the
+ central directory 8 bytes
+ size of the central directory 8 bytes
+ offset of start of central
+ directory with respect to
+ the starting disk number 8 bytes
+ zip64 extensible data sector (variable size)
+
+ 4.3.14.1 The value stored into the "size of zip64 end of central
+ directory record" should be the size of the remaining
+ record and should not include the leading 12 bytes.
+
+ Size = SizeOfFixedFields + SizeOfVariableData - 12.
+
+ 4.3.14.2 The above record structure defines Version 1 of the
+ zip64 end of central directory record. Version 1 was
+ implemented in versions of this specification preceding
+ 6.2 in support of the ZIP64 large file feature. The
+ introduction of the Central Directory Encryption feature
+ implemented in version 6.2 as part of the Strong Encryption
+ Specification defines Version 2 of this record structure.
+ Refer to the section describing the Strong Encryption
+ Specification for details on the version 2 format for
+ this record. Refer to the section in this document entitled
+ "Incorporating PKWARE Proprietary Technology into Your Product"
+ for more information applicable to use of Version 2 of this
+ record.
+
+ 4.3.14.3 Special purpose data MAY reside in the zip64 extensible
+ data sector field following either a V1 or V2 version of this
+ record. To ensure identification of this special purpose data
+ it must include an identifying header block consisting of the
+ following:
+
+ Header ID - 2 bytes
+ Data Size - 4 bytes
+
+ The Header ID field indicates the type of data that is in the
+ data block that follows.
+
+ Data Size identifies the number of bytes that follow for this
+ data block type.
+
+ 4.3.14.4 Multiple special purpose data blocks MAY be present.
+ Each MUST be preceded by a Header ID and Data Size field. Current
+ mappings of Header ID values supported in this field are as
+ defined in APPENDIX C.
+
+ 4.3.15 Zip64 end of central directory locator
+
+ zip64 end of central dir locator
+ signature 4 bytes (0x07064b50)
+ number of the disk with the
+ start of the zip64 end of
+ central directory 4 bytes
+ relative offset of the zip64
+ end of central directory record 8 bytes
+ total number of disks 4 bytes
+
+ 4.3.16 End of central directory record:
+
+ end of central dir signature 4 bytes (0x06054b50)
+ number of this disk 2 bytes
+ number of the disk with the
+ start of the central directory 2 bytes
+ total number of entries in the
+ central directory on this disk 2 bytes
+ total number of entries in
+ the central directory 2 bytes
+ size of the central directory 4 bytes
+ offset of start of central
+ directory with respect to
+ the starting disk number 4 bytes
+ .ZIP file comment length 2 bytes
+ .ZIP file comment (variable size)
+
+4.4 Explanation of fields
+--------------------------
+
+ 4.4.1 General notes on fields
+
+ 4.4.1.1 All fields unless otherwise noted are unsigned and stored
+ in Intel low-byte:high-byte, low-word:high-word order.
+
+ 4.4.1.2 String fields are not null terminated, since the length
+ is given explicitly.
+
+ 4.4.1.3 The entries in the central directory may not necessarily
+ be in the same order that files appear in the .ZIP file.
+
+ 4.4.1.4 If one of the fields in the end of central directory
+ record is too small to hold required data, the field should be
+ set to -1 (0xFFFF or 0xFFFFFFFF) and the ZIP64 format record
+ should be created.
+
+ 4.4.1.5 The end of central directory record and the Zip64 end
+ of central directory locator record MUST reside on the same
+ disk when splitting or spanning an archive.
+
+ 4.4.2 version made by (2 bytes)
+
+ 4.4.2.1 The upper byte indicates the compatibility of the file
+ attribute information. If the external file attributes
+ are compatible with MS-DOS and can be read by PKZIP for
+ DOS version 2.04g then this value will be zero. If these
+ attributes are not compatible, then this value will
+ identify the host system on which the attributes are
+ compatible. Software can use this information to determine
+ the line record format for text files etc.
+
+ 4.4.2.2 The current mappings are:
+
+ 0 - MS-DOS and OS/2 (FAT / VFAT / FAT32 file systems)
+ 1 - Amiga 2 - OpenVMS
+ 3 - UNIX 4 - VM/CMS
+ 5 - Atari ST 6 - OS/2 H.P.F.S.
+ 7 - Macintosh 8 - Z-System
+ 9 - CP/M 10 - Windows NTFS
+ 11 - MVS (OS/390 - Z/OS) 12 - VSE
+ 13 - Acorn Risc 14 - VFAT
+ 15 - alternate MVS 16 - BeOS
+ 17 - Tandem 18 - OS/400
+ 19 - OS X (Darwin) 20 thru 255 - unused
+
+ 4.4.2.3 The lower byte indicates the ZIP specification version
+ (the version of this document) supported by the software
+ used to encode the file. The value/10 indicates the major
+ version number, and the value mod 10 is the minor version
+ number.
+
+ 4.4.3 version needed to extract (2 bytes)
+
+ 4.4.3.1 The minimum supported ZIP specification version needed
+ to extract the file, mapped as above. This value is based on
+ the specific format features a ZIP program MUST support to
+ be able to extract the file. If multiple features are
+ applied to a file, the minimum version MUST be set to the
+ feature having the highest value. New features or feature
+ changes affecting the published format specification will be
+ implemented using higher version numbers than the last
+ published value to avoid conflict.
+
+ 4.4.3.2 Current minimum feature versions are as defined below:
+
+ 1.0 - Default value
+ 1.1 - File is a volume label
+ 2.0 - File is a folder (directory)
+ 2.0 - File is compressed using Deflate compression
+ 2.0 - File is encrypted using traditional PKWARE encryption
+ 2.1 - File is compressed using Deflate64(tm)
+ 2.5 - File is compressed using PKWARE DCL Implode
+ 2.7 - File is a patch data set
+ 4.5 - File uses ZIP64 format extensions
+ 4.6 - File is compressed using BZIP2 compression*
+ 5.0 - File is encrypted using DES
+ 5.0 - File is encrypted using 3DES
+ 5.0 - File is encrypted using original RC2 encryption
+ 5.0 - File is encrypted using RC4 encryption
+ 5.1 - File is encrypted using AES encryption
+ 5.1 - File is encrypted using corrected RC2 encryption**
+ 5.2 - File is encrypted using corrected RC2-64 encryption**
+ 6.1 - File is encrypted using non-OAEP key wrapping***
+ 6.2 - Central directory encryption
+ 6.3 - File is compressed using LZMA
+ 6.3 - File is compressed using PPMd+
+ 6.3 - File is encrypted using Blowfish
+ 6.3 - File is encrypted using Twofish
+
+ 4.4.3.3 Notes on version needed to extract
+
+ * Early 7.x (pre-7.2) versions of PKZIP incorrectly set the
+ version needed to extract for BZIP2 compression to be 50
+ when it should have been 46.
+
+ ** Refer to the section on Strong Encryption Specification
+ for additional information regarding RC2 corrections.
+
+ *** Certificate encryption using non-OAEP key wrapping is the
+ intended mode of operation for all versions beginning with 6.1.
+ Support for OAEP key wrapping MUST only be used for
+ backward compatibility when sending ZIP files to be opened by
+ versions of PKZIP older than 6.1 (5.0 or 6.0).
+
+ + Files compressed using PPMd MUST set the version
+ needed to extract field to 6.3, however, not all ZIP
+ programs enforce this and may be unable to decompress
+ data files compressed using PPMd if this value is set.
+
+ When using ZIP64 extensions, the corresponding value in the
+ zip64 end of central directory record MUST also be set.
+ This field should be set appropriately to indicate whether
+ Version 1 or Version 2 format is in use.
+
+
+ 4.4.4 general purpose bit flag: (2 bytes)
+
+ Bit 0: If set, indicates that the file is encrypted.
+
+ (For Method 6 - Imploding)
+ Bit 1: If the compression method used was type 6,
+ Imploding, then this bit, if set, indicates
+ an 8K sliding dictionary was used. If clear,
+ then a 4K sliding dictionary was used.
+
+ Bit 2: If the compression method used was type 6,
+ Imploding, then this bit, if set, indicates
+ 3 Shannon-Fano trees were used to encode the
+ sliding dictionary output. If clear, then 2
+ Shannon-Fano trees were used.
+
+ (For Methods 8 and 9 - Deflating)
+ Bit 2 Bit 1
+ 0 0 Normal (-en) compression option was used.
+ 0 1 Maximum (-exx/-ex) compression option was used.
+ 1 0 Fast (-ef) compression option was used.
+ 1 1 Super Fast (-es) compression option was used.
+
+ (For Method 14 - LZMA)
+ Bit 1: If the compression method used was type 14,
+ LZMA, then this bit, if set, indicates
+ an end-of-stream (EOS) marker is used to
+ mark the end of the compressed data stream.
+ If clear, then an EOS marker is not present
+ and the compressed data size must be known
+ to extract.
+
+ Note: Bits 1 and 2 are undefined if the compression
+ method is any other.
+
+ Bit 3: If this bit is set, the fields crc-32, compressed
+ size and uncompressed size are set to zero in the
+ local header. The correct values are put in the
+ data descriptor immediately following the compressed
+ data. (Note: PKZIP version 2.04g for DOS only
+ recognizes this bit for method 8 compression, newer
+ versions of PKZIP recognize this bit for any
+ compression method.)
+
+ Bit 4: Reserved for use with method 8, for enhanced
+ deflating.
+
+ Bit 5: If this bit is set, this indicates that the file is
+ compressed patched data. (Note: Requires PKZIP
+ version 2.70 or greater)
+
+ Bit 6: Strong encryption. If this bit is set, you MUST
+ set the version needed to extract value to at least
+ 50 and you MUST also set bit 0. If AES encryption
+ is used, the version needed to extract value MUST
+ be at least 51. See the section describing the Strong
+ Encryption Specification for details. Refer to the
+ section in this document entitled "Incorporating PKWARE
+ Proprietary Technology into Your Product" for more
+ information.
+
+ Bit 7: Currently unused.
+
+ Bit 8: Currently unused.
+
+ Bit 9: Currently unused.
+
+ Bit 10: Currently unused.
+
+ Bit 11: Language encoding flag (EFS). If this bit is set,
+ the filename and comment fields for this file
+ MUST be encoded using UTF-8. (see APPENDIX D)
+
+ Bit 12: Reserved by PKWARE for enhanced compression.
+
+ Bit 13: Set when encrypting the Central Directory to indicate
+ selected data values in the Local Header are masked to
+ hide their actual values. See the section describing
+ the Strong Encryption Specification for details. Refer
+ to the section in this document entitled "Incorporating
+ PKWARE Proprietary Technology into Your Product" for
+ more information.
+
+ Bit 14: Reserved by PKWARE.
+
+ Bit 15: Reserved by PKWARE.
+
+ 4.4.5 compression method: (2 bytes)
+
+ 0 - The file is stored (no compression)
+ 1 - The file is Shrunk
+ 2 - The file is Reduced with compression factor 1
+ 3 - The file is Reduced with compression factor 2
+ 4 - The file is Reduced with compression factor 3
+ 5 - The file is Reduced with compression factor 4
+ 6 - The file is Imploded
+ 7 - Reserved for Tokenizing compression algorithm
+ 8 - The file is Deflated
+ 9 - Enhanced Deflating using Deflate64(tm)
+ 10 - PKWARE Data Compression Library Imploding (old IBM TERSE)
+ 11 - Reserved by PKWARE
+ 12 - File is compressed using BZIP2 algorithm
+ 13 - Reserved by PKWARE
+ 14 - LZMA (EFS)
+ 15 - Reserved by PKWARE
+ 16 - Reserved by PKWARE
+ 17 - Reserved by PKWARE
+ 18 - File is compressed using IBM TERSE (new)
+ 19 - IBM LZ77 z Architecture (PFS)
+ 97 - WavPack compressed data
+ 98 - PPMd version I, Rev 1
+
+
+ 4.4.6 date and time fields: (2 bytes each)
+
+ The date and time are encoded in standard MS-DOS format.
+ If input came from standard input, the date and time are
+ those at which compression was started for this data.
+ If encrypting the central directory and general purpose bit
+ flag 13 is set indicating masking, the value stored in the
+ Local Header will be zero.
+
+ 4.4.7 CRC-32: (4 bytes)
+
+ The CRC-32 algorithm was generously contributed by
+ David Schwaderer and can be found in his excellent
+ book "C Programmers Guide to NetBIOS" published by
+ Howard W. Sams & Co. Inc. The 'magic number' for
+ the CRC is 0xdebb20e3. The proper CRC pre and post
+ conditioning is used, meaning that the CRC register
+ is pre-conditioned with all ones (a starting value
+ of 0xffffffff) and the value is post-conditioned by
+ taking the one's complement of the CRC residual.
+ If bit 3 of the general purpose flag is set, this
+ field is set to zero in the local header and the correct
+ value is put in the data descriptor and in the central
+ directory. When encrypting the central directory, if the
+ local header is not in ZIP64 format and general purpose
+ bit flag 13 is set indicating masking, the value stored
+ in the Local Header will be zero.
+
+ 4.4.8 compressed size: (4 bytes)
+ 4.4.9 uncompressed size: (4 bytes)
+
+ The size of the file compressed (4.4.8) and uncompressed,
+ (4.4.9) respectively. When a decryption header is present it
+ will be placed in front of the file data and the value of the
+ compressed file size will include the bytes of the decryption
+ header. If bit 3 of the general purpose bit flag is set,
+ these fields are set to zero in the local header and the
+ correct values are put in the data descriptor and
+ in the central directory. If an archive is in ZIP64 format
+ and the value in this field is 0xFFFFFFFF, the size will be
+ in the corresponding 8 byte ZIP64 extended information
+ extra field. When encrypting the central directory, if the
+ local header is not in ZIP64 format and general purpose bit
+ flag 13 is set indicating masking, the value stored for the
+ uncompressed size in the Local Header will be zero.
+
+ 4.4.10 file name length: (2 bytes)
+ 4.4.11 extra field length: (2 bytes)
+ 4.4.12 file comment length: (2 bytes)
+
+ The length of the file name, extra field, and comment
+ fields respectively. The combined length of any
+ directory record and these three fields should not
+ generally exceed 65,535 bytes. If input came from standard
+ input, the file name length is set to zero.
+
+
+ 4.4.13 disk number start: (2 bytes)
+
+ The number of the disk on which this file begins. If an
+ archive is in ZIP64 format and the value in this field is
+ 0xFFFF, the size will be in the corresponding 4 byte zip64
+ extended information extra field.
+
+ 4.4.14 internal file attributes: (2 bytes)
+
+ Bits 1 and 2 are reserved for use by PKWARE.
+
+ 4.4.14.1 The lowest bit of this field indicates, if set,
+ that the file is apparently an ASCII or text file. If not
+ set, that the file apparently contains binary data.
+ The remaining bits are unused in version 1.0.
+
+ 4.4.14.2 The 0x0002 bit of this field indicates, if set, that
+ a 4 byte variable record length control field precedes each
+ logical record indicating the length of the record. The
+ record length control field is stored in little-endian byte
+ order. This flag is independent of text control characters,
+ and if used in conjunction with text data, includes any
+ control characters in the total length of the record. This
+ value is provided for mainframe data transfer support.
+
+ 4.4.15 external file attributes: (4 bytes)
+
+ The mapping of the external attributes is
+ host-system dependent (see 'version made by'). For
+ MS-DOS, the low order byte is the MS-DOS directory
+ attribute byte. If input came from standard input, this
+ field is set to zero.
+
+ 4.4.16 relative offset of local header: (4 bytes)
+
+ This is the offset from the start of the first disk on
+ which this file appears, to where the local header should
+ be found. If an archive is in ZIP64 format and the value
+ in this field is 0xFFFFFFFF, the size will be in the
+ corresponding 8 byte zip64 extended information extra field.
+
+ 4.4.17 file name: (Variable)
+
+ 4.4.17.1 The name of the file, with optional relative path.
+ The path stored MUST not contain a drive or
+ device letter, or a leading slash. All slashes
+ MUST be forward slashes '/' as opposed to
+ backwards slashes '\' for compatibility with Amiga
+ and UNIX file systems etc. If input came from standard
+ input, there is no file name field.
+
+ 4.4.17.2 If using the Central Directory Encryption Feature and
+ general purpose bit flag 13 is set indicating masking, the file
+ name stored in the Local Header will not be the actual file name.
+ A masking value consisting of a unique hexadecimal value will
+ be stored. This value will be sequentially incremented for each
+ file in the archive. See the section on the Strong Encryption
+ Specification for details on retrieving the encrypted file name.
+ Refer to the section in this document entitled "Incorporating PKWARE
+ Proprietary Technology into Your Product" for more information.
+
+
+ 4.4.18 file comment: (Variable)
+
+ The comment for this file.
+
+ 4.4.19 number of this disk: (2 bytes)
+
+ The number of this disk, which contains central
+ directory end record. If an archive is in ZIP64 format
+ and the value in this field is 0xFFFF, the size will
+ be in the corresponding 4 byte zip64 end of central
+ directory field.
+
+
+ 4.4.20 number of the disk with the start of the central
+ directory: (2 bytes)
+
+ The number of the disk on which the central
+ directory starts. If an archive is in ZIP64 format
+ and the value in this field is 0xFFFF, the size will
+ be in the corresponding 4 byte zip64 end of central
+ directory field.
+
+ 4.4.21 total number of entries in the central dir on
+ this disk: (2 bytes)
+
+ The number of central directory entries on this disk.
+ If an archive is in ZIP64 format and the value in
+ this field is 0xFFFF, the size will be in the
+ corresponding 8 byte zip64 end of central
+ directory field.
+
+ 4.4.22 total number of entries in the central dir: (2 bytes)
+
+ The total number of files in the .ZIP file. If an
+ archive is in ZIP64 format and the value in this field
+ is 0xFFFF, the size will be in the corresponding 8 byte
+ zip64 end of central directory field.
+
+ 4.4.23 size of the central directory: (4 bytes)
+
+ The size (in bytes) of the entire central directory.
+ If an archive is in ZIP64 format and the value in
+ this field is 0xFFFFFFFF, the size will be in the
+ corresponding 8 byte zip64 end of central
+ directory field.
+
+ 4.4.24 offset of start of central directory with respect to
+ the starting disk number: (4 bytes)
+
+ Offset of the start of the central directory on the
+ disk on which the central directory starts. If an
+ archive is in ZIP64 format and the value in this
+ field is 0xFFFFFFFF, the size will be in the
+ corresponding 8 byte zip64 end of central
+ directory field.
+
+ 4.4.25 .ZIP file comment length: (2 bytes)
+
+ The length of the comment for this .ZIP file.
+
+ 4.4.26 .ZIP file comment: (Variable)
+
+ The comment for this .ZIP file. ZIP file comment data
+ is stored unsecured. No encryption or data authentication
+ is applied to this area at this time. Confidential information
+ should not be stored in this section.
+
+ 4.4.27 zip64 extensible data sector (variable size)
+
+ (currently reserved for use by PKWARE)
+
+
+ 4.4.28 extra field: (Variable)
+
+ This SHOULD be used for storage expansion. If additional
+ information needs to be stored within a ZIP file for special
+ application or platform needs, it SHOULD be stored here.
+ Programs supporting earlier versions of this specification can
+ then safely skip the file, and find the next file or header.
+ This field will be 0 length in version 1.0.
+
+ Existing extra fields are defined in the section
+ Extensible data fields that follows.
+
+4.5 Extensible data fields
+--------------------------
+
+ 4.5.1 In order to allow different programs and different types
+ of information to be stored in the 'extra' field in .ZIP
+ files, the following structure MUST be used for all
+ programs storing data in this field:
+
+ header1+data1 + header2+data2 . . .
+
+ Each header should consist of:
+
+ Header ID - 2 bytes
+ Data Size - 2 bytes
+
+ Note: all fields stored in Intel low-byte/high-byte order.
+
+ The Header ID field indicates the type of data that is in
+ the following data block.
+
+ Header IDs of 0 thru 31 are reserved for use by PKWARE.
+ The remaining IDs can be used by third party vendors for
+ proprietary usage.
+
+ 4.5.2 The current Header ID mappings defined by PKWARE are:
+
+ 0x0001 Zip64 extended information extra field
+ 0x0007 AV Info
+ 0x0008 Reserved for extended language encoding data (PFS)
+ (see APPENDIX D)
+ 0x0009 OS/2
+ 0x000a NTFS
+ 0x000c OpenVMS
+ 0x000d UNIX
+ 0x000e Reserved for file stream and fork descriptors
+ 0x000f Patch Descriptor
+ 0x0014 PKCS#7 Store for X.509 Certificates
+ 0x0015 X.509 Certificate ID and Signature for
+ individual file
+ 0x0016 X.509 Certificate ID for Central Directory
+ 0x0017 Strong Encryption Header
+ 0x0018 Record Management Controls
+ 0x0019 PKCS#7 Encryption Recipient Certificate List
+ 0x0065 IBM S/390 (Z390), AS/400 (I400) attributes
+ - uncompressed
+ 0x0066 Reserved for IBM S/390 (Z390), AS/400 (I400)
+ attributes - compressed
+ 0x4690 POSZIP 4690 (reserved)
+
+
+ 4.5.3 -Zip64 Extended Information Extra Field (0x0001):
+
+ The following is the layout of the zip64 extended
+ information "extra" block. If one of the size or
+ offset fields in the Local or Central directory
+ record is too small to hold the required data,
+ a Zip64 extended information record is created.
+ The order of the fields in the zip64 extended
+ information record is fixed, but the fields MUST
+ only appear if the corresponding Local or Central
+ directory record field is set to 0xFFFF or 0xFFFFFFFF.
+
+ Note: all fields stored in Intel low-byte/high-byte order.
+
+ Value Size Description
+ ----- ---- -----------
+(ZIP64) 0x0001 2 bytes Tag for this "extra" block type
+ Size 2 bytes Size of this "extra" block
+ Original
+ Size 8 bytes Original uncompressed file size
+ Compressed
+ Size 8 bytes Size of compressed data
+ Relative Header
+ Offset 8 bytes Offset of local header record
+ Disk Start
+ Number 4 bytes Number of the disk on which
+ this file starts
+
+ This entry in the Local header MUST include BOTH original
+ and compressed file size fields. If encrypting the
+ central directory and bit 13 of the general purpose bit
+ flag is set indicating masking, the value stored in the
+ Local Header for the original file size will be zero.
+
+
+ 4.5.4 -OS/2 Extra Field (0x0009):
+
+ The following is the layout of the OS/2 attributes "extra"
+ block. (Last Revision 09/05/95)
+
+ Note: all fields stored in Intel low-byte/high-byte order.
+
+ Value Size Description
+ ----- ---- -----------
+(OS/2) 0x0009 2 bytes Tag for this "extra" block type
+ TSize 2 bytes Size for the following data block
+ BSize 4 bytes Uncompressed Block Size
+ CType 2 bytes Compression type
+ EACRC 4 bytes CRC value for uncompress block
+ (var) variable Compressed block
+
+ The OS/2 extended attribute structure (FEA2LIST) is
+ compressed and then stored in its entirety within this
+ structure. There will only ever be one "block" of data in
+ VarFields[].
+
+ 4.5.5 -NTFS Extra Field (0x000a):
+
+ The following is the layout of the NTFS attributes
+ "extra" block. (Note: At this time the Mtime, Atime
+ and Ctime values MAY be used on any WIN32 system.)
+
+ Note: all fields stored in Intel low-byte/high-byte order.
+
+ Value Size Description
+ ----- ---- -----------
+(NTFS) 0x000a 2 bytes Tag for this "extra" block type
+ TSize 2 bytes Size of the total "extra" block
+ Reserved 4 bytes Reserved for future use
+ Tag1 2 bytes NTFS attribute tag value #1
+ Size1 2 bytes Size of attribute #1, in bytes
+ (var) Size1 Attribute #1 data
+ .
+ .
+ .
+ TagN 2 bytes NTFS attribute tag value #N
+ SizeN 2 bytes Size of attribute #N, in bytes
+ (var) SizeN Attribute #N data
+
+ For NTFS, values for Tag1 through TagN are as follows:
+ (currently only one set of attributes is defined for NTFS)
+
+ Tag Size Description
+ ----- ---- -----------
+ 0x0001 2 bytes Tag for attribute #1
+ Size1 2 bytes Size of attribute #1, in bytes
+ Mtime 8 bytes File last modification time
+ Atime 8 bytes File last access time
+ Ctime 8 bytes File creation time
+
+ 4.5.6 -OpenVMS Extra Field (0x000c):
+
+ The following is the layout of the OpenVMS attributes
+ "extra" block.
+
+ Note: all fields stored in Intel low-byte/high-byte order.
+
+ Value Size Description
+ ----- ---- -----------
+ (VMS) 0x000c 2 bytes Tag for this "extra" block type
+ TSize 2 bytes Size of the total "extra" block
+ CRC 4 bytes 32-bit CRC for remainder of the block
+ Tag1 2 bytes OpenVMS attribute tag value #1
+ Size1 2 bytes Size of attribute #1, in bytes
+ (var) Size1 Attribute #1 data
+ .
+ .
+ .
+ TagN 2 bytes OpenVMS attribute tag value #N
+ SizeN 2 bytes Size of attribute #N, in bytes
+ (var) SizeN Attribute #N data
+
+ OpenVMS Extra Field Rules:
+
+ 4.5.6.1. There will be one or more attributes present, which
+ will each be preceded by the above TagX & SizeX values.
+ These values are identical to the ATR$C_XXXX and ATR$S_XXXX
+ constants which are defined in ATR.H under OpenVMS C. Neither
+ of these values will ever be zero.
+
+ 4.5.6.2. No word alignment or padding is performed.
+
+ 4.5.6.3. A well-behaved PKZIP/OpenVMS program should never produce
+ more than one sub-block with the same TagX value. Also, there will
+ never be more than one "extra" block of type 0x000c in a particular
+ directory record.
+
+ 4.5.7 -UNIX Extra Field (0x000d):
+
+ The following is the layout of the UNIX "extra" block.
+ Note: all fields are stored in Intel low-byte/high-byte
+ order.
+
+ Value Size Description
+ ----- ---- -----------
+(UNIX) 0x000d 2 bytes Tag for this "extra" block type
+ TSize 2 bytes Size for the following data block
+ Atime 4 bytes File last access time
+ Mtime 4 bytes File last modification time
+ Uid 2 bytes File user ID
+ Gid 2 bytes File group ID
+ (var) variable Variable length data field
+
+ The variable length data field will contain file type
+ specific data. Currently the only values allowed are
+ the original "linked to" file names for hard or symbolic
+ links, and the major and minor device node numbers for
+ character and block device nodes. Since device nodes
+ cannot be either symbolic or hard links, only one set of
+ variable length data is stored. Link files will have the
+ name of the original file stored. This name is NOT NULL
+ terminated. Its size can be determined by checking TSize -
+ 12. Device entries will have eight bytes stored as two 4
+ byte entries (in little endian format). The first entry
+ will be the major device number, and the second the minor
+ device number.
+
+ 4.5.8 -PATCH Descriptor Extra Field (0x000f):
+
+ 4.5.8.1 The following is the layout of the Patch Descriptor
+ "extra" block.
+
+ Note: all fields stored in Intel low-byte/high-byte order.
+
+ Value Size Description
+ ----- ---- -----------
+(Patch) 0x000f 2 bytes Tag for this "extra" block type
+ TSize 2 bytes Size of the total "extra" block
+ Version 2 bytes Version of the descriptor
+ Flags 4 bytes Actions and reactions (see below)
+ OldSize 4 bytes Size of the file about to be patched
+ OldCRC 4 bytes 32-bit CRC of the file to be patched
+ NewSize 4 bytes Size of the resulting file
+ NewCRC 4 bytes 32-bit CRC of the resulting file
+
+ 4.5.8.2 Actions and reactions
+
+ Bits Description
+ ---- ----------------
+ 0 Use for auto detection
+ 1 Treat as a self-patch
+ 2-3 RESERVED
+ 4-5 Action (see below)
+ 6-7 RESERVED
+ 8-9 Reaction (see below) to absent file
+ 10-11 Reaction (see below) to newer file
+ 12-13 Reaction (see below) to unknown file
+ 14-15 RESERVED
+ 16-31 RESERVED
+
+ 4.5.8.2.1 Actions
+
+ Action Value
+ ------ -----
+ none 0
+ add 1
+ delete 2
+ patch 3
+
+ 4.5.8.2.2 Reactions
+
+ Reaction Value
+ -------- -----
+ ask 0
+ skip 1
+ ignore 2
+ fail 3
+
+ 4.5.8.3 Patch support is provided by PKPatchMaker(tm) technology
+ and is covered under U.S. Patents and Patents Pending. The use or
+ implementation in a product of certain technological aspects set
+ forth in the current APPNOTE, including those with regard to
+ strong encryption or patching requires a license from PKWARE.
+ Refer to the section in this document entitled "Incorporating
+ PKWARE Proprietary Technology into Your Product" for more
+ information.
+
+ 4.5.9 -PKCS#7 Store for X.509 Certificates (0x0014):
+
+ This field MUST contain information about each of the certificates
+ files may be signed with. When the Central Directory Encryption
+ feature is enabled for a ZIP file, this record will appear in
+ the Archive Extra Data Record, otherwise it will appear in the
+ first central directory record and will be ignored in any
+ other record.
+
+
+ Note: all fields stored in Intel low-byte/high-byte order.
+
+ Value Size Description
+ ----- ---- -----------
+(Store) 0x0014 2 bytes Tag for this "extra" block type
+ TSize 2 bytes Size of the store data
+ TData TSize Data about the store
+
+
+ 4.5.10 -X.509 Certificate ID and Signature for individual file (0x0015):
+
+ This field contains the information about which certificate in
+ the PKCS#7 store was used to sign a particular file. It also
+ contains the signature data. This field can appear multiple
+ times, but can only appear once per certificate.
+
+ Note: all fields stored in Intel low-byte/high-byte order.
+
+ Value Size Description
+ ----- ---- -----------
+(CID) 0x0015 2 bytes Tag for this "extra" block type
+ TSize 2 bytes Size of data that follows
+ TData TSize Signature Data
+
+ 4.5.11 -X.509 Certificate ID and Signature for central directory (0x0016):
+
+ This field contains the information about which certificate in
+ the PKCS#7 store was used to sign the central directory structure.
+ When the Central Directory Encryption feature is enabled for a
+ ZIP file, this record will appear in the Archive Extra Data Record,
+ otherwise it will appear in the first central directory record.
+
+ Note: all fields stored in Intel low-byte/high-byte order.
+
+ Value Size Description
+ ----- ---- -----------
+(CDID) 0x0016 2 bytes Tag for this "extra" block type
+ TSize 2 bytes Size of data that follows
+ TData TSize Data
+
+ 4.5.12 -Strong Encryption Header (0x0017):
+
+ Value Size Description
+ ----- ---- -----------
+ 0x0017 2 bytes Tag for this "extra" block type
+ TSize 2 bytes Size of data that follows
+ Format 2 bytes Format definition for this record
+ AlgID 2 bytes Encryption algorithm identifier
+ Bitlen 2 bytes Bit length of encryption key
+ Flags 2 bytes Processing flags
+ CertData TSize-8 Certificate decryption extra field data
+ (refer to the explanation for CertData
+ in the section describing the
+ Certificate Processing Method under
+ the Strong Encryption Specification)
+
+ See the section describing the Strong Encryption Specification
+ for details. Refer to the section in this document entitled
+ "Incorporating PKWARE Proprietary Technology into Your Product"
+ for more information.
+
+ 4.5.13 -Record Management Controls (0x0018):
+
+ Value Size Description
+ ----- ---- -----------
+(Rec-CTL) 0x0018 2 bytes Tag for this "extra" block type
+ CSize 2 bytes Size of total extra block data
+ Tag1 2 bytes Record control attribute 1
+ Size1 2 bytes Size of attribute 1, in bytes
+ Data1 Size1 Attribute 1 data
+ .
+ .
+ .
+ TagN 2 bytes Record control attribute N
+ SizeN 2 bytes Size of attribute N, in bytes
+ DataN SizeN Attribute N data
+
+
+ 4.5.14 -PKCS#7 Encryption Recipient Certificate List (0x0019):
+
+ This field MAY contain information about each of the certificates
+ used in encryption processing and it can be used to identify who is
+ allowed to decrypt encrypted files. This field should only appear
+ in the archive extra data record. This field is not required and
+ serves only to aid archive modifications by preserving public
+ encryption key data. Individual security requirements may dictate
+ that this data be omitted to deter information exposure.
+
+ Note: all fields stored in Intel low-byte/high-byte order.
+
+ Value Size Description
+ ----- ---- -----------
+(CStore) 0x0019 2 bytes Tag for this "extra" block type
+ TSize 2 bytes Size of the store data
+ TData TSize Data about the store
+
+ TData:
+
+ Value Size Description
+ ----- ---- -----------
+ Version 2 bytes Format version number - must 0x0001 at this time
+ CStore (var) PKCS#7 data blob
+
+ See the section describing the Strong Encryption Specification
+ for details. Refer to the section in this document entitled
+ "Incorporating PKWARE Proprietary Technology into Your Product"
+ for more information.
+
+ 4.5.15 -MVS Extra Field (0x0065):
+
+ The following is the layout of the MVS "extra" block.
+ Note: Some fields are stored in Big Endian format.
+ All text is in EBCDIC format unless otherwise specified.
+
+ Value Size Description
+ ----- ---- -----------
+(MVS) 0x0065 2 bytes Tag for this "extra" block type
+ TSize 2 bytes Size for the following data block
+ ID 4 bytes EBCDIC "Z390" 0xE9F3F9F0 or
+ "T4MV" for TargetFour
+ (var) TSize-4 Attribute data (see APPENDIX B)
+
+
+ 4.5.16 -OS/400 Extra Field (0x0065):
+
+ The following is the layout of the OS/400 "extra" block.
+ Note: Some fields are stored in Big Endian format.
+ All text is in EBCDIC format unless otherwise specified.
+
+ Value Size Description
+ ----- ---- -----------
+(OS400) 0x0065 2 bytes Tag for this "extra" block type
+ TSize 2 bytes Size for the following data block
+ ID 4 bytes EBCDIC "I400" 0xC9F4F0F0 or
+ "T4MV" for TargetFour
+ (var) TSize-4 Attribute data (see APPENDIX A)
+
+4.6 Third Party Mappings
+------------------------
+
+ 4.6.1 Third party mappings commonly used are:
+
+ 0x07c8 Macintosh
+ 0x2605 ZipIt Macintosh
+ 0x2705 ZipIt Macintosh 1.3.5+
+ 0x2805 ZipIt Macintosh 1.3.5+
+ 0x334d Info-ZIP Macintosh
+ 0x4341 Acorn/SparkFS
+ 0x4453 Windows NT security descriptor (binary ACL)
+ 0x4704 VM/CMS
+ 0x470f MVS
+ 0x4b46 FWKCS MD5 (see below)
+ 0x4c41 OS/2 access control list (text ACL)
+ 0x4d49 Info-ZIP OpenVMS
+ 0x4f4c Xceed original location extra field
+ 0x5356 AOS/VS (ACL)
+ 0x5455 extended timestamp
+ 0x554e Xceed unicode extra field
+ 0x5855 Info-ZIP UNIX (original, also OS/2, NT, etc)
+ 0x6375 Info-ZIP Unicode Comment Extra Field
+ 0x6542 BeOS/BeBox
+ 0x7075 Info-ZIP Unicode Path Extra Field
+ 0x756e ASi UNIX
+ 0x7855 Info-ZIP UNIX (new)
+ 0xa220 Microsoft Open Packaging Growth Hint
+ 0xfd4a SMS/QDOS
+
+ Detailed descriptions of Extra Fields defined by third
+ party mappings will be documented as information on
+ these data structures is made available to PKWARE.
+ PKWARE does not guarantee the accuracy of any published
+ third party data.
+
+ 4.6.2 Third-party Extra Fields must include a Header ID using
+ the format defined in the section of this document
+ titled Extensible Data Fields (section 4.5).
+
+ The Data Size field indicates the size of the following
+ data block. Programs can use this value to skip to the
+ next header block, passing over any data blocks that are
+ not of interest.
+
+ Note: As stated above, the size of the entire .ZIP file
+ header, including the file name, comment, and extra
+ field should not exceed 64K in size.
+
+ 4.6.3 In case two different programs should appropriate the same
+ Header ID value, it is strongly recommended that each
+ program SHOULD place a unique signature of at least two bytes in
+ size (and preferably 4 bytes or bigger) at the start of
+ each data area. Every program SHOULD verify that its
+ unique signature is present, in addition to the Header ID
+ value being correct, before assuming that it is a block of
+ known type.
+
+ Third-party Mappings:
+
+ 4.6.4 -ZipIt Macintosh Extra Field (long) (0x2605):
+
+ The following is the layout of the ZipIt extra block
+ for Macintosh. The local-header and central-header versions
+ are identical. This block must be present if the file is
+ stored MacBinary-encoded and it should not be used if the file
+ is not stored MacBinary-encoded.
+
+ Value Size Description
+ ----- ---- -----------
+ (Mac2) 0x2605 Short tag for this extra block type
+ TSize Short total data size for this block
+ "ZPIT" beLong extra-field signature
+ FnLen Byte length of FileName
+ FileName variable full Macintosh filename
+ FileType Byte[4] four-byte Mac file type string
+ Creator Byte[4] four-byte Mac creator string
+
+
+ 4.6.5 -ZipIt Macintosh Extra Field (short, for files) (0x2705):
+
+ The following is the layout of a shortened variant of the
+ ZipIt extra block for Macintosh (without "full name" entry).
+ This variant is used by ZipIt 1.3.5 and newer for entries of
+ files (not directories) that do not have a MacBinary encoded
+ file. The local-header and central-header versions are identical.
+
+ Value Size Description
+ ----- ---- -----------
+ (Mac2b) 0x2705 Short tag for this extra block type
+ TSize Short total data size for this block (12)
+ "ZPIT" beLong extra-field signature
+ FileType Byte[4] four-byte Mac file type string
+ Creator Byte[4] four-byte Mac creator string
+ fdFlags beShort attributes from FInfo.frFlags,
+ may be omitted
+ 0x0000 beShort reserved, may be omitted
+
+
+ 4.6.6 -ZipIt Macintosh Extra Field (short, for directories) (0x2805):
+
+ The following is the layout of a shortened variant of the
+ ZipIt extra block for Macintosh used only for directory
+ entries. This variant is used by ZipIt 1.3.5 and newer to
+ save some optional Mac-specific information about directories.
+ The local-header and central-header versions are identical.
+
+ Value Size Description
+ ----- ---- -----------
+ (Mac2c) 0x2805 Short tag for this extra block type
+ TSize Short total data size for this block (12)
+ "ZPIT" beLong extra-field signature
+ frFlags beShort attributes from DInfo.frFlags, may
+ be omitted
+ View beShort ZipIt view flag, may be omitted
+
+
+ The View field specifies ZipIt-internal settings as follows:
+
+ Bits of the Flags:
+ bit 0 if set, the folder is shown expanded (open)
+ when the archive contents are viewed in ZipIt.
+ bits 1-15 reserved, zero;
+
+
+ 4.6.7 -FWKCS MD5 Extra Field (0x4b46):
+
+ The FWKCS Contents_Signature System, used in
+ automatically identifying files independent of file name,
+ optionally adds and uses an extra field to support the
+ rapid creation of an enhanced contents_signature:
+
+ Header ID = 0x4b46
+ Data Size = 0x0013
+ Preface = 'M','D','5'
+ followed by 16 bytes containing the uncompressed file's
+ 128_bit MD5 hash(1), low byte first.
+
+ When FWKCS revises a .ZIP file central directory to add
+ this extra field for a file, it also replaces the
+ central directory entry for that file's uncompressed
+ file length with a measured value.
+
+ FWKCS provides an option to strip this extra field, if
+ present, from a .ZIP file central directory. In adding
+ this extra field, FWKCS preserves .ZIP file Authenticity
+ Verification; if stripping this extra field, FWKCS
+ preserves all versions of AV through PKZIP version 2.04g.
+
+ FWKCS, and FWKCS Contents_Signature System, are
+ trademarks of Frederick W. Kantor.
+
+ (1) R. Rivest, RFC1321.TXT, MIT Laboratory for Computer
+ Science and RSA Data Security, Inc., April 1992.
+ ll.76-77: "The MD5 algorithm is being placed in the
+ public domain for review and possible adoption as a
+ standard."
+
+
+ 4.6.8 -Info-ZIP Unicode Comment Extra Field (0x6375):
+
+ Stores the UTF-8 version of the file comment as stored in the
+ central directory header. (Last Revision 20070912)
+
+ Value Size Description
+ ----- ---- -----------
+ (UCom) 0x6375 Short tag for this extra block type ("uc")
+ TSize Short total data size for this block
+ Version 1 byte version of this extra field, currently 1
+ ComCRC32 4 bytes Comment Field CRC32 Checksum
+ UnicodeCom Variable UTF-8 version of the entry comment
+
+ Currently Version is set to the number 1. If there is a need
+ to change this field, the version will be incremented. Changes
+ may not be backward compatible so this extra field should not be
+ used if the version is not recognized.
+
+ The ComCRC32 is the standard zip CRC32 checksum of the File Comment
+ field in the central directory header. This is used to verify that
+ the comment field has not changed since the Unicode Comment extra field
+ was created. This can happen if a utility changes the File Comment
+ field but does not update the UTF-8 Comment extra field. If the CRC
+ check fails, this Unicode Comment extra field should be ignored and
+ the File Comment field in the header should be used instead.
+
+ The UnicodeCom field is the UTF-8 version of the File Comment field
+ in the header. As UnicodeCom is defined to be UTF-8, no UTF-8 byte
+ order mark (BOM) is used. The length of this field is determined by
+ subtracting the size of the previous fields from TSize. If both the
+ File Name and Comment fields are UTF-8, the new General Purpose Bit
+ Flag, bit 11 (Language encoding flag (EFS)), can be used to indicate
+ both the header File Name and Comment fields are UTF-8 and, in this
+ case, the Unicode Path and Unicode Comment extra fields are not
+ needed and should not be created. Note that, for backward
+ compatibility, bit 11 should only be used if the native character set
+ of the paths and comments being zipped up are already in UTF-8. It is
+ expected that the same file comment storage method, either general
+ purpose bit 11 or extra fields, be used in both the Local and Central
+ Directory Header for a file.
+
+
+ 4.6.9 -Info-ZIP Unicode Path Extra Field (0x7075):
+
+ Stores the UTF-8 version of the file name field as stored in the
+ local header and central directory header. (Last Revision 20070912)
+
+ Value Size Description
+ ----- ---- -----------
+ (UPath) 0x7075 Short tag for this extra block type ("up")
+ TSize Short total data size for this block
+ Version 1 byte version of this extra field, currently 1
+ NameCRC32 4 bytes File Name Field CRC32 Checksum
+ UnicodeName Variable UTF-8 version of the entry File Name
+
+ Currently Version is set to the number 1. If there is a need
+ to change this field, the version will be incremented. Changes
+ may not be backward compatible so this extra field should not be
+ used if the version is not recognized.
+
+ The NameCRC32 is the standard zip CRC32 checksum of the File Name
+ field in the header. This is used to verify that the header
+ File Name field has not changed since the Unicode Path extra field
+ was created. This can happen if a utility renames the File Name but
+ does not update the UTF-8 path extra field. If the CRC check fails,
+ this UTF-8 Path Extra Field should be ignored and the File Name field
+ in the header should be used instead.
+
+ The UnicodeName is the UTF-8 version of the contents of the File Name
+ field in the header. As UnicodeName is defined to be UTF-8, no UTF-8
+ byte order mark (BOM) is used. The length of this field is determined
+ by subtracting the size of the previous fields from TSize. If both
+ the File Name and Comment fields are UTF-8, the new General Purpose
+ Bit Flag, bit 11 (Language encoding flag (EFS)), can be used to
+ indicate that both the header File Name and Comment fields are UTF-8
+ and, in this case, the Unicode Path and Unicode Comment extra fields
+ are not needed and should not be created. Note that, for backward
+ compatibility, bit 11 should only be used if the native character set
+ of the paths and comments being zipped up are already in UTF-8. It is
+ expected that the same file name storage method, either general
+ purpose bit 11 or extra fields, be used in both the Local and Central
+ Directory Header for a file.
+
+
+ 4.6.10 -Microsoft Open Packaging Growth Hint (0xa220):
+
+ Value Size Description
+ ----- ---- -----------
+ 0xa220 Short tag for this extra block type
+ TSize Short size of Sig + PadVal + Padding
+ Sig Short verification signature (A028)
+ PadVal Short Initial padding value
+ Padding variable filled with NULL characters
+
+4.7 Manifest Files
+------------------
+
+ 4.7.1 Applications using ZIP files may have a need for additional
+ information that must be included with the files placed into
+ a ZIP file. Application specific information that cannot be
+ stored using the defined ZIP storage records SHOULD be stored
+ using the extensible Extra Field convention defined in this
+ document. However, some applications may use a manifest
+ file as a means for storing additional information. One
+ example is the META-INF/MANIFEST.MF file used in ZIP formatted
+ files having the .JAR extension (JAR files).
+
+ 4.7.2 A manifest file is a file created for the application process
+ that requires this information. A manifest file MAY be of any
+ file type required by the defining application process. It is
+ placed within the same ZIP file as files to which this information
+ applies. By convention, this file is typically the first file placed
+ into the ZIP file and it may include a defined directory path.
+
+ 4.7.3 Manifest files may be compressed or encrypted as needed for
+ application processing of the files inside the ZIP files.
+
+ Manifest files are outside of the scope of this specification.
+
+
+5.0 Explanation of compression methods
+--------------------------------------
+
+
+5.1 UnShrinking - Method 1
+--------------------------
+
+ 5.1.1 Shrinking is a Dynamic Ziv-Lempel-Welch compression algorithm
+ with partial clearing. The initial code size is 9 bits, and the
+ maximum code size is 13 bits. Shrinking differs from conventional
+ Dynamic Ziv-Lempel-Welch implementations in several respects:
+
+ 5.1.2 The code size is controlled by the compressor, and is
+ not automatically increased when codes larger than the current
+ code size are created (but not necessarily used). When
+ the decompressor encounters the code sequence 256
+ (decimal) followed by 1, it should increase the code size
+ read from the input stream to the next bit size. No
+ blocking of the codes is performed, so the next code at
+ the increased size should be read from the input stream
+ immediately after where the previous code at the smaller
+ bit size was read. Again, the decompressor should not
+ increase the code size used until the sequence 256,1 is
+ encountered.
+
+ 5.1.3 When the table becomes full, total clearing is not
+ performed. Rather, when the compressor emits the code
+ sequence 256,2 (decimal), the decompressor should clear
+ all leaf nodes from the Ziv-Lempel tree, and continue to
+ use the current code size. The nodes that are cleared
+ from the Ziv-Lempel tree are then re-used, with the lowest
+ code value re-used first, and the highest code value
+ re-used last. The compressor can emit the sequence 256,2
+ at any time.
+
+5.2 Expanding - Methods 2-5
+---------------------------
+
+ 5.2.1 The Reducing algorithm is actually a combination of two
+ distinct algorithms. The first algorithm compresses repeated
+ byte sequences, and the second algorithm takes the compressed
+ stream from the first algorithm and applies a probabilistic
+ compression method.
+
+ 5.2.2 The probabilistic compression stores an array of 'follower
+ sets' S(j), for j=0 to 255, corresponding to each possible
+ ASCII character. Each set contains between 0 and 32
+ characters, to be denoted as S(j)[0],...,S(j)[m], where m<32.
+ The sets are stored at the beginning of the data area for a
+ Reduced file, in reverse order, with S(255) first, and S(0)
+ last.
+
+ 5.2.3 The sets are encoded as { N(j), S(j)[0],...,S(j)[N(j)-1] },
+ where N(j) is the size of set S(j). N(j) can be 0, in which
+ case the follower set for S(j) is empty. Each N(j) value is
+ encoded in 6 bits, followed by N(j) eight bit character values
+ corresponding to S(j)[0] to S(j)[N(j)-1] respectively. If
+ N(j) is 0, then no values for S(j) are stored, and the value
+ for N(j-1) immediately follows.
+
+ 5.2.4 Immediately after the follower sets, is the compressed data
+ stream. The compressed data stream can be interpreted for the
+ probabilistic decompression as follows:
+
+ let Last-Character <- 0.
+ loop until done
+ if the follower set S(Last-Character) is empty then
+ read 8 bits from the input stream, and copy this
+ value to the output stream.
+ otherwise if the follower set S(Last-Character) is non-empty then
+ read 1 bit from the input stream.
+ if this bit is not zero then
+ read 8 bits from the input stream, and copy this
+ value to the output stream.
+ otherwise if this bit is zero then
+ read B(N(Last-Character)) bits from the input
+ stream, and assign this value to I.
+ Copy the value of S(Last-Character)[I] to the
+ output stream.
+
+ assign the last value placed on the output stream to
+ Last-Character.
+ end loop
+
+ B(N(j)) is defined as the minimal number of bits required to
+ encode the value N(j)-1.
+
+ 5.2.5 The decompressed stream from above can then be expanded to
+ re-create the original file as follows:
+
+ let State <- 0.
+
+ loop until done
+ read 8 bits from the input stream into C.
+ case State of
+ 0: if C is not equal to DLE (144 decimal) then
+ copy C to the output stream.
+ otherwise if C is equal to DLE then
+ let State <- 1.
+
+ 1: if C is non-zero then
+ let V <- C.
+ let Len <- L(V)
+ let State <- F(Len).
+ otherwise if C is zero then
+ copy the value 144 (decimal) to the output stream.
+ let State <- 0
+
+ 2: let Len <- Len + C
+ let State <- 3.
+
+ 3: move backwards D(V,C) bytes in the output stream
+ (if this position is before the start of the output
+ stream, then assume that all the data before the
+ start of the output stream is filled with zeros).
+ copy Len+3 bytes from this position to the output stream.
+ let State <- 0.
+ end case
+ end loop
+
+ The functions F,L, and D are dependent on the 'compression
+ factor', 1 through 4, and are defined as follows:
+
+ For compression factor 1:
+ L(X) equals the lower 7 bits of X.
+ F(X) equals 2 if X equals 127 otherwise F(X) equals 3.
+ D(X,Y) equals the (upper 1 bit of X) * 256 + Y + 1.
+ For compression factor 2:
+ L(X) equals the lower 6 bits of X.
+ F(X) equals 2 if X equals 63 otherwise F(X) equals 3.
+ D(X,Y) equals the (upper 2 bits of X) * 256 + Y + 1.
+ For compression factor 3:
+ L(X) equals the lower 5 bits of X.
+ F(X) equals 2 if X equals 31 otherwise F(X) equals 3.
+ D(X,Y) equals the (upper 3 bits of X) * 256 + Y + 1.
+ For compression factor 4:
+ L(X) equals the lower 4 bits of X.
+ F(X) equals 2 if X equals 15 otherwise F(X) equals 3.
+ D(X,Y) equals the (upper 4 bits of X) * 256 + Y + 1.
+
+5.3 Imploding - Method 6
+------------------------
+
+ 5.3.1 The Imploding algorithm is actually a combination of two
+ distinct algorithms. The first algorithm compresses repeated byte
+ sequences using a sliding dictionary. The second algorithm is
+ used to compress the encoding of the sliding dictionary output,
+ using multiple Shannon-Fano trees.
+
+ 5.3.2 The Imploding algorithm can use a 4K or 8K sliding dictionary
+ size. The dictionary size used can be determined by bit 1 in the
+ general purpose flag word; a 0 bit indicates a 4K dictionary
+ while a 1 bit indicates an 8K dictionary.
+
+ 5.3.3 The Shannon-Fano trees are stored at the start of the
+ compressed file. The number of trees stored is defined by bit 2 in
+ the general purpose flag word; a 0 bit indicates two trees stored,
+ a 1 bit indicates three trees are stored. If 3 trees are stored,
+ the first Shannon-Fano tree represents the encoding of the
+ Literal characters, the second tree represents the encoding of
+ the Length information, the third represents the encoding of the
+ Distance information. When 2 Shannon-Fano trees are stored, the
+ Length tree is stored first, followed by the Distance tree.
+
+ 5.3.4 The Literal Shannon-Fano tree, if present is used to represent
+ the entire ASCII character set, and contains 256 values. This
+ tree is used to compress any data not compressed by the sliding
+ dictionary algorithm. When this tree is present, the Minimum
+ Match Length for the sliding dictionary is 3. If this tree is
+ not present, the Minimum Match Length is 2.
+
+ 5.3.5 The Length Shannon-Fano tree is used to compress the Length
+ part of the (length,distance) pairs from the sliding dictionary
+ output. The Length tree contains 64 values, ranging from the
+ Minimum Match Length, to 63 plus the Minimum Match Length.
+
+ 5.3.6 The Distance Shannon-Fano tree is used to compress the Distance
+ part of the (length,distance) pairs from the sliding dictionary
+ output. The Distance tree contains 64 values, ranging from 0 to
+ 63, representing the upper 6 bits of the distance value. The
+ distance values themselves will be between 0 and the sliding
+ dictionary size, either 4K or 8K.
+
+ 5.3.7 The Shannon-Fano trees themselves are stored in a compressed
+ format. The first byte of the tree data represents the number of
+ bytes of data representing the (compressed) Shannon-Fano tree
+ minus 1. The remaining bytes represent the Shannon-Fano tree
+ data encoded as:
+
+ High 4 bits: Number of values at this bit length + 1. (1 - 16)
+ Low 4 bits: Bit Length needed to represent value + 1. (1 - 16)
+
+ 5.3.8 The Shannon-Fano codes can be constructed from the bit lengths
+ using the following algorithm:
+
+ 1) Sort the Bit Lengths in ascending order, while retaining the
+ order of the original lengths stored in the file.
+
+ 2) Generate the Shannon-Fano trees:
+
+ Code <- 0
+ CodeIncrement <- 0
+ LastBitLength <- 0
+ i <- number of Shannon-Fano codes - 1 (either 255 or 63)
+
+ loop while i >= 0
+ Code = Code + CodeIncrement
+ if BitLength(i) <> LastBitLength then
+ LastBitLength=BitLength(i)
+ CodeIncrement = 1 shifted left (16 - LastBitLength)
+ ShannonCode(i) = Code
+ i <- i - 1
+ end loop
+
+ 3) Reverse the order of all the bits in the above ShannonCode()
+ vector, so that the most significant bit becomes the least
+ significant bit. For example, the value 0x1234 (hex) would
+ become 0x2C48 (hex).
+
+ 4) Restore the order of Shannon-Fano codes as originally stored
+ within the file.
+
+ Example:
+
+ This example will show the encoding of a Shannon-Fano tree
+ of size 8. Notice that the actual Shannon-Fano trees used
+ for Imploding are either 64 or 256 entries in size.
+
+ Example: 0x02, 0x42, 0x01, 0x13
+
+ The first byte indicates 3 values in this table. Decoding the
+ bytes:
+ 0x42 = 5 codes of 3 bits long
+ 0x01 = 1 code of 2 bits long
+ 0x13 = 2 codes of 4 bits long
+
+ This would generate the original bit length array of:
+ (3, 3, 3, 3, 3, 2, 4, 4)
+
+ There are 8 codes in this table for the values 0 thru 7. Using
+ the algorithm to obtain the Shannon-Fano codes produces:
+
+ Reversed Order Original
+ Val Sorted Constructed Code Value Restored Length
+ --- ------ ----------------- -------- -------- ------
+ 0: 2 1100000000000000 11 101 3
+ 1: 3 1010000000000000 101 001 3
+ 2: 3 1000000000000000 001 110 3
+ 3: 3 0110000000000000 110 010 3
+ 4: 3 0100000000000000 010 100 3
+ 5: 3 0010000000000000 100 11 2
+ 6: 4 0001000000000000 1000 1000 4
+ 7: 4 0000000000000000 0000 0000 4
+
+ The values in the Val, Order Restored and Original Length columns
+ now represent the Shannon-Fano encoding tree that can be used for
+ decoding the Shannon-Fano encoded data. How to parse the
+ variable length Shannon-Fano values from the data stream is beyond
+ the scope of this document. (See the references listed at the end of
+ this document for more information.) However, traditional decoding
+ schemes used for Huffman variable length decoding, such as the
+ Greenlaw algorithm, can be successfully applied.
+
+ 5.3.9 The compressed data stream begins immediately after the
+ compressed Shannon-Fano data. The compressed data stream can be
+ interpreted as follows:
+
+ loop until done
+ read 1 bit from input stream.
+
+ if this bit is non-zero then (encoded data is literal data)
+ if Liter
<TRUNCATED>