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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 Literal Shannon-Fano tree is present
- read and decode character using Literal Shannon-Fano tree.
- otherwise
- read 8 bits from input stream.
- copy character to the output stream.
- otherwise (encoded data is sliding dictionary match)
- if 8K dictionary size
- read 7 bits for offset Distance (lower 7 bits of offset).
- otherwise
- read 6 bits for offset Distance (lower 6 bits of offset).
- using the Distance Shannon-Fano tree, read and decode the
- upper 6 bits of the Distance value.
- using the Length Shannon-Fano tree, read and decode
- the Length value.
- Length <- Length + Minimum Match Length
- if Length = 63 + Minimum Match Length
- read 8 bits from the input stream,
- add this value to Length.
- move backwards Distance+1 bytes in the output stream, and
- copy Length characters from this position to 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).
- end loop
- 5.4 Tokenizing - Method 7
- -------------------------
- 5.4.1 This method is not used by PKZIP.
- 5.5 Deflating - Method 8
- ------------------------
- 5.5.1 The Deflate algorithm is similar to the Implode algorithm using
- a sliding dictionary of up to 32K with secondary compression
- from Huffman/Shannon-Fano codes.
- 5.5.2 The compressed data is stored in blocks with a header describing
- the block and the Huffman codes used in the data block. The header
- format is as follows:
- Bit 0: Last Block bit This bit is set to 1 if this is the last
- compressed block in the data.
- Bits 1-2: Block type
- 00 (0) - Block is stored - All stored data is byte aligned.
- Skip bits until next byte, then next word = block
- length, followed by the ones compliment of the block
- length word. Remaining data in block is the stored
- data.
- 01 (1) - Use fixed Huffman codes for literal and distance codes.
- Lit Code Bits Dist Code Bits
- --------- ---- --------- ----
- 0 - 143 8 0 - 31 5
- 144 - 255 9
- 256 - 279 7
- 280 - 287 8
- Literal codes 286-287 and distance codes 30-31 are
- never used but participate in the huffman construction.
- 10 (2) - Dynamic Huffman codes. (See expanding Huffman codes)
- 11 (3) - Reserved - Flag a "Error in compressed data" if seen.
- 5.5.3 Expanding Huffman Codes
- If the data block is stored with dynamic Huffman codes, the Huffman
- codes are sent in the following compressed format:
- 5 Bits: # of Literal codes sent - 256 (256 - 286)
- All other codes are never sent.
- 5 Bits: # of Dist codes - 1 (1 - 32)
- 4 Bits: # of Bit Length codes - 3 (3 - 19)
- The Huffman codes are sent as bit lengths and the codes are built as
- described in the implode algorithm. The bit lengths themselves are
- compressed with Huffman codes. There are 19 bit length codes:
- 0 - 15: Represent bit lengths of 0 - 15
- 16: Copy the previous bit length 3 - 6 times.
- The next 2 bits indicate repeat length (0 = 3, ... ,3 = 6)
- Example: Codes 8, 16 (+2 bits 11), 16 (+2 bits 10) will
- expand to 12 bit lengths of 8 (1 + 6 + 5)
- 17: Repeat a bit length of 0 for 3 - 10 times. (3 bits of length)
- 18: Repeat a bit length of 0 for 11 - 138 times (7 bits of length)
- The lengths of the bit length codes are sent packed 3 bits per value
- (0 - 7) in the following order:
- 16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15
- The Huffman codes should be built as described in the Implode algorithm
- except codes are assigned starting at the shortest bit length, i.e. the
- shortest code should be all 0's rather than all 1's. Also, codes with
- a bit length of zero do not participate in the tree construction. The
- codes are then used to decode the bit lengths for the literal and
- distance tables.
- The bit lengths for the literal tables are sent first with the number
- of entries sent described by the 5 bits sent earlier. There are up
- to 286 literal characters; the first 256 represent the respective 8
- bit character, code 256 represents the End-Of-Block code, the remaining
- 29 codes represent copy lengths of 3 thru 258. There are up to 30
- distance codes representing distances from 1 thru 32k as described
- below.
- Length Codes
- ------------
- Extra Extra Extra Extra
- Code Bits Length Code Bits Lengths Code Bits Lengths Code Bits Length(s)
- ---- ---- ------ ---- ---- ------- ---- ---- ------- ---- ---- ---------
- 257 0 3 265 1 11,12 273 3 35-42 281 5 131-162
- 258 0 4 266 1 13,14 274 3 43-50 282 5 163-194
- 259 0 5 267 1 15,16 275 3 51-58 283 5 195-226
- 260 0 6 268 1 17,18 276 3 59-66 284 5 227-257
- 261 0 7 269 2 19-22 277 4 67-82 285 0 258
- 262 0 8 270 2 23-26 278 4 83-98
- 263 0 9 271 2 27-30 279 4 99-114
- 264 0 10 272 2 31-34 280 4 115-130
- Distance Codes
- --------------
- Extra Extra Extra Extra
- Code Bits Dist Code Bits Dist Code Bits Distance Code Bits Distance
- ---- ---- ---- ---- ---- ------ ---- ---- -------- ---- ---- --------
- 0 0 1 8 3 17-24 16 7 257-384 24 11 4097-6144
- 1 0 2 9 3 25-32 17 7 385-512 25 11 6145-8192
- 2 0 3 10 4 33-48 18 8 513-768 26 12 8193-12288
- 3 0 4 11 4 49-64 19 8 769-1024 27 12 12289-16384
- 4 1 5,6 12 5 65-96 20 9 1025-1536 28 13 16385-24576
- 5 1 7,8 13 5 97-128 21 9 1537-2048 29 13 24577-32768
- 6 2 9-12 14 6 129-192 22 10 2049-3072
- 7 2 13-16 15 6 193-256 23 10 3073-4096
- 5.5.4 The compressed data stream begins immediately after the
- compressed header data. The compressed data stream can be
- interpreted as follows:
- do
- read header from input stream.
- if stored block
- skip bits until byte aligned
- read count and 1's compliment of count
- copy count bytes data block
- otherwise
- loop until end of block code sent
- decode literal character from input stream
- if literal < 256
- copy character to the output stream
- otherwise
- if literal = end of block
- break from loop
- otherwise
- decode distance from input stream
- move backwards distance bytes in the output stream, and
- copy length characters from this position to the output
- stream.
- end loop
- while not last block
- if data descriptor exists
- skip bits until byte aligned
- read crc and sizes
- endif
- 5.6 Enhanced Deflating - Method 9
- ---------------------------------
- 5.6.1 The Enhanced Deflating algorithm is similar to Deflate but uses
- a sliding dictionary of up to 64K. Deflate64(tm) is supported
- by the Deflate extractor.
- 5.7 BZIP2 - Method 12
- ---------------------
- 5.7.1 BZIP2 is an open-source data compression algorithm developed by
- Julian Seward. Information and source code for this algorithm
- can be found on the internet.
- 5.8 LZMA - Method 14
- ---------------------
- 5.8.1 LZMA is a block-oriented, general purpose data compression
- algorithm developed and maintained by Igor Pavlov. It is a derivative
- of LZ77 that utilizes Markov chains and a range coder. Information and
- source code for this algorithm can be found on the internet. Consult
- with the author of this algorithm for information on terms or
- restrictions on use.
- Support for LZMA within the ZIP format is defined as follows:
- 5.8.2 The Compression method field within the ZIP Local and Central
- Header records will be set to the value 14 to indicate data was
- compressed using LZMA.
- 5.8.3 The Version needed to extract field within the ZIP Local and
- Central Header records will be set to 6.3 to indicate the minimum
- ZIP format version supporting this feature.
- 5.8.4 File data compressed using the LZMA algorithm must be placed
- immediately following the Local Header for the file. If a standard
- ZIP encryption header is required, it will follow the Local Header
- and will precede the LZMA compressed file data segment. The location
- of LZMA compressed data segment within the ZIP format will be as shown:
- [local header file 1]
- [encryption header file 1]
- [LZMA compressed data segment for file 1]
- [data descriptor 1]
- [local header file 2]
- 5.8.5 The encryption header and data descriptor records may
- be conditionally present. The LZMA Compressed Data Segment
- will consist of an LZMA Properties Header followed by the
- LZMA Compressed Data as shown:
- [LZMA properties header for file 1]
- [LZMA compressed data for file 1]
- 5.8.6 The LZMA Compressed Data will be stored as provided by the
- LZMA compression library. Compressed size, uncompressed size and
- other file characteristics about the file being compressed must be
- stored in standard ZIP storage format.
- 5.8.7 The LZMA Properties Header will store specific data required
- to decompress the LZMA compressed Data. This data is set by the
- LZMA compression engine using the function WriteCoderProperties()
- as documented within the LZMA SDK.
- 5.8.8 Storage fields for the property information within the LZMA
- Properties Header are as follows:
- LZMA Version Information 2 bytes
- LZMA Properties Size 2 bytes
- LZMA Properties Data variable, defined by "LZMA Properties Size"
- 5.8.8.1 LZMA Version Information - this field identifies which version
- of the LZMA SDK was used to compress a file. The first byte will
- store the major version number of the LZMA SDK and the second
- byte will store the minor number.
- 5.8.8.2 LZMA Properties Size - this field defines the size of the
- remaining property data. Typically this size should be determined by
- the version of the SDK. This size field is included as a convenience
- and to help avoid any ambiguity should it arise in the future due
- to changes in this compression algorithm.
- 5.8.8.3 LZMA Property Data - this variable sized field records the
- required values for the decompressor as defined by the LZMA SDK.
- The data stored in this field should be obtained using the
- WriteCoderProperties() in the version of the SDK defined by
- the "LZMA Version Information" field.
- 5.8.8.4 The layout of the "LZMA Properties Data" field is a function of
- the LZMA compression algorithm. It is possible that this layout may be
- changed by the author over time. The data layout in version 4.3 of the
- LZMA SDK defines a 5 byte array that uses 4 bytes to store the dictionary
- size in little-endian order. This is preceded by a single packed byte as
- the first element of the array that contains the following fields:
- PosStateBits
- LiteralPosStateBits
- LiteralContextBits
- Refer to the LZMA documentation for a more detailed explanation of
- these fields.
- 5.8.9 Data compressed with method 14, LZMA, may include an end-of-stream
- (EOS) marker ending the compressed data stream. This marker is not
- required, but its use is highly recommended to facilitate processing
- and implementers should include the EOS marker whenever possible.
- When the EOS marker is used, general purpose bit 1 must be set. If
- general purpose bit 1 is not set, the EOS marker is not present.
- 5.9 WavPack - Method 97
- -----------------------
- 5.9.1 Information describing the use of compression method 97 is
- provided by WinZIP International, LLC. This method relies on the
- open source WavPack audio compression utility developed by David Bryant.
- Information on WavPack is available at www.wavpack.com. Please consult
- with the author of this algorithm for information on terms and
- restrictions on use.
- 5.9.2 WavPack data for a file begins immediately after the end of the
- local header data. This data is the output from WavPack compression
- routines. Within the ZIP file, the use of WavPack compression is
- indicated by setting the compression method field to a value of 97
- in both the local header and the central directory header. The Version
- needed to extract and version made by fields use the same values as are
- used for data compressed using the Deflate algorithm.
- 5.9.3 An implementation note for storing digital sample data when using
- WavPack compression within ZIP files is that all of the bytes of
- the sample data should be compressed. This includes any unused
- bits up to the byte boundary. An example is a 2 byte sample that
- uses only 12 bits for the sample data with 4 unused bits. If only
- 12 bits are passed as the sample size to the WavPack routines, the 4
- unused bits will be set to 0 on extraction regardless of their original
- state. To avoid this, the full 16 bits of the sample data size
- should be provided.
- 5.10 PPMd - Method 98
- ---------------------
- 5.10.1 PPMd is a data compression algorithm developed by Dmitry Shkarin
- which includes a carryless rangecoder developed by Dmitry Subbotin.
- This algorithm is based on predictive phrase matching on multiple
- order contexts. Information and source code for this algorithm
- can be found on the internet. Consult with the author of this
- algorithm for information on terms or restrictions on use.
- 5.10.2 Support for PPMd within the ZIP format currently is provided only
- for version I, revision 1 of the algorithm. Storage requirements
- for using this algorithm are as follows:
- 5.10.3 Parameters needed to control the algorithm are stored in the two
- bytes immediately preceding the compressed data. These bytes are
- used to store the following fields:
- Model order - sets the maximum model order, default is 8, possible
- values are from 2 to 16 inclusive
- Sub-allocator size - sets the size of sub-allocator in MB, default is 50,
- possible values are from 1MB to 256MB inclusive
- Model restoration method - sets the method used to restart context
- model at memory insufficiency, values are:
- 0 - restarts model from scratch - default
- 1 - cut off model - decreases performance by as much as 2x
- 2 - freeze context tree - not recommended
- 5.10.4 An example for packing these fields into the 2 byte storage field is
- illustrated below. These values are stored in Intel low-byte/high-byte
- order.
- wPPMd = (Model order - 1) +
- ((Sub-allocator size - 1) << 4) +
- (Model restoration method << 12)
- 6.0 Traditional PKWARE Encryption
- ----------------------------------
- 6.0.1 The following information discusses the decryption steps
- required to support traditional PKWARE encryption. This
- form of encryption is considered weak by today's standards
- and its use is recommended only for situations with
- low security needs or for compatibility with older .ZIP
- applications.
- 6.1 Traditional PKWARE Decryption
- ---------------------------------
- 6.1.1 PKWARE is grateful to Mr. Roger Schlafly for his expert
- contribution towards the development of PKWARE's traditional
- encryption.
- 6.1.2 PKZIP encrypts the compressed data stream. Encrypted files
- must be decrypted before they can be extracted to their original
- form.
- 6.1.3 Each encrypted file has an extra 12 bytes stored at the start
- of the data area defining the encryption header for that file. The
- encryption header is originally set to random values, and then
- itself encrypted, using three, 32-bit keys. The key values are
- initialized using the supplied encryption password. After each byte
- is encrypted, the keys are then updated using pseudo-random number
- generation techniques in combination with the same CRC-32 algorithm
- used in PKZIP and described elsewhere in this document.
- 6.1.4 The following are the basic steps required to decrypt a file:
- 1) Initialize the three 32-bit keys with the password.
- 2) Read and decrypt the 12-byte encryption header, further
- initializing the encryption keys.
- 3) Read and decrypt the compressed data stream using the
- encryption keys.
- 6.1.5 Initializing the encryption keys
- Key(0) <- 305419896
- Key(1) <- 591751049
- Key(2) <- 878082192
- loop for i <- 0 to length(password)-1
- update_keys(password(i))
- end loop
- Where update_keys() is defined as:
- update_keys(char):
- Key(0) <- crc32(key(0),char)
- Key(1) <- Key(1) + (Key(0) & 000000ffH)
- Key(1) <- Key(1) * 134775813 + 1
- Key(2) <- crc32(key(2),key(1) >> 24)
- end update_keys
- Where crc32(old_crc,char) is a routine that given a CRC value and a
- character, returns an updated CRC value after applying the CRC-32
- algorithm described elsewhere in this document.
- 6.1.6 Decrypting the encryption header
- The purpose of this step is to further initialize the encryption
- keys, based on random data, to render a plaintext attack on the
- data ineffective.
- Read the 12-byte encryption header into Buffer, in locations
- Buffer(0) thru Buffer(11).
- loop for i <- 0 to 11
- C <- buffer(i) ^ decrypt_byte()
- update_keys(C)
- buffer(i) <- C
- end loop
- Where decrypt_byte() is defined as:
- unsigned char decrypt_byte()
- local unsigned short temp
- temp <- Key(2) | 2
- decrypt_byte <- (temp * (temp ^ 1)) >> 8
- end decrypt_byte
- After the header is decrypted, the last 1 or 2 bytes in Buffer
- should be the high-order word/byte of the CRC for the file being
- decrypted, stored in Intel low-byte/high-byte order. Versions of
- PKZIP prior to 2.0 used a 2 byte CRC check; a 1 byte CRC check is
- used on versions after 2.0. This can be used to test if the password
- supplied is correct or not.
- 6.1.7 Decrypting the compressed data stream
- The compressed data stream can be decrypted as follows:
- loop until done
- read a character into C
- Temp <- C ^ decrypt_byte()
- update_keys(temp)
- output Temp
- end loop
- 7.0 Strong Encryption Specification
- -----------------------------------
- 7.0.1 Portions of the Strong Encryption technology defined in this
- specification are covered under patents and pending patent applications.
- Refer to the section in this document entitled "Incorporating
- PKWARE Proprietary Technology into Your Product" for more information.
- 7.1 Strong Encryption Overview
- ------------------------------
- 7.1.1 Version 5.x of this specification introduced support for strong
- encryption algorithms. These algorithms can be used with either
- a password or an X.509v3 digital certificate to encrypt each file.
- This format specification supports either password or certificate
- based encryption to meet the security needs of today, to enable
- interoperability between users within both PKI and non-PKI
- environments, and to ensure interoperability between different
- computing platforms that are running a ZIP program.
- 7.1.2 Password based encryption is the most common form of encryption
- people are familiar with. However, inherent weaknesses with
- passwords (e.g. susceptibility to dictionary/brute force attack)
- as well as password management and support issues make certificate
- based encryption a more secure and scalable option. Industry
- efforts and support are defining and moving towards more advanced
- security solutions built around X.509v3 digital certificates and
- Public Key Infrastructures(PKI) because of the greater scalability,
- administrative options, and more robust security over traditional
- password based encryption.
- 7.1.3 Most standard encryption algorithms are supported with this
- specification. Reference implementations for many of these
- algorithms are available from either commercial or open source
- distributors. Readily available cryptographic toolkits make
- implementation of the encryption features straight-forward.
- This document is not intended to provide a treatise on data
- encryption principles or theory. Its purpose is to document the
- data structures required for implementing interoperable data
- encryption within the .ZIP format. It is strongly recommended that
- you have a good understanding of data encryption before reading
- further.
- 7.1.4 The algorithms introduced in Version 5.0 of this specification
- include:
- RC2 40 bit, 64 bit, and 128 bit
- RC4 40 bit, 64 bit, and 128 bit
- DES
- 3DES 112 bit and 168 bit
- Version 5.1 adds support for the following:
- AES 128 bit, 192 bit, and 256 bit
- 7.1.5 Version 6.1 introduces encryption data changes to support
- interoperability with Smartcard and USB Token certificate storage
- methods which do not support the OAEP strengthening standard.
- 7.1.6 Version 6.2 introduces support for encrypting metadata by compressing
- and encrypting the central directory data structure to reduce information
- leakage. Information leakage can occur in legacy ZIP applications
- through exposure of information about a file even though that file is
- stored encrypted. The information exposed consists of file
- characteristics stored within the records and fields defined by this
- specification. This includes data such as a file's name, its original
- size, timestamp and CRC32 value.
- 7.1.7 Version 6.3 introduces support for encrypting data using the Blowfish
- and Twofish algorithms. These are symmetric block ciphers developed
- by Bruce Schneier. Blowfish supports using a variable length key from
- 32 to 448 bits. Block size is 64 bits. Implementations should use 16
- rounds and the only mode supported within ZIP files is CBC. Twofish
- supports key sizes 128, 192 and 256 bits. Block size is 128 bits.
- Implementations should use 16 rounds and the only mode supported within
- ZIP files is CBC. Information and source code for both Blowfish and
- Twofish algorithms can be found on the internet. Consult with the author
- of these algorithms for information on terms or restrictions on use.
- 7.1.8 Central Directory Encryption provides greater protection against
- information leakage by encrypting the Central Directory structure and
- by masking key values that are replicated in the unencrypted Local
- Header. ZIP compatible programs that cannot interpret an encrypted
- Central Directory structure cannot rely on the data in the corresponding
- Local Header for decompression information.
- 7.1.9 Extra Field records that may contain information about a file that should
- not be exposed should not be stored in the Local Header and should only
- be written to the Central Directory where they can be encrypted. This
- design currently does not support streaming. Information in the End of
- Central Directory record, the Zip64 End of Central Directory Locator,
- and the Zip64 End of Central Directory records are not encrypted. Access
- to view data on files within a ZIP file with an encrypted Central Directory
- requires the appropriate password or private key for decryption prior to
- viewing any files, or any information about the files, in the archive.
- 7.1.10 Older ZIP compatible programs not familiar with the Central Directory
- Encryption feature will no longer be able to recognize the Central
- Directory and may assume the ZIP file is corrupt. Programs that
- attempt streaming access using Local Headers will see invalid
- information for each file. Central Directory Encryption need not be
- used for every ZIP file. Its use is recommended for greater security.
- ZIP files not using Central Directory Encryption should operate as
- in the past.
- 7.1.11 This strong encryption feature specification is intended to provide for
- scalable, cross-platform encryption needs ranging from simple password
- encryption to authenticated public/private key encryption.
- 7.1.12 Encryption provides data confidentiality and privacy. It is
- recommended that you combine X.509 digital signing with encryption
- to add authentication and non-repudiation.
- 7.2 Single Password Symmetric Encryption Method
- -----------------------------------------------
- 7.2.1 The Single Password Symmetric Encryption Method using strong
- encryption algorithms operates similarly to the traditional
- PKWARE encryption defined in this format. Additional data
- structures are added to support the processing needs of the
- strong algorithms.
- The Strong Encryption data structures are:
- 7.2.2 General Purpose Bits - Bits 0 and 6 of the General Purpose bit
- flag in both local and central header records. Both bits set
- indicates strong encryption. Bit 13, when set indicates the Central
- Directory is encrypted and that selected fields in the Local Header
- are masked to hide their actual value.
- 7.2.3 Extra Field 0x0017 in central header only.
- Fields to consider in this record are:
- 7.2.3.1 Format - the data format identifier for this record. The only
- value allowed at this time is the integer value 2.
- 7.2.3.2 AlgId - integer identifier of the encryption algorithm from the
- following range
- 0x6601 - DES
- 0x6602 - RC2 (version needed to extract < 5.2)
- 0x6603 - 3DES 168
- 0x6609 - 3DES 112
- 0x660E - AES 128
- 0x660F - AES 192
- 0x6610 - AES 256
- 0x6702 - RC2 (version needed to extract >= 5.2)
- 0x6720 - Blowfish
- 0x6721 - Twofish
- 0x6801 - RC4
- 0xFFFF - Unknown algorithm
- 7.2.3.3 Bitlen - Explicit bit length of key
- 32 - 448 bits
- 7.2.3.4 Flags - Processing flags needed for decryption
- 0x0001 - Password is required to decrypt
- 0x0002 - Certificates only
- 0x0003 - Password or certificate required to decrypt
- Values > 0x0003 reserved for certificate processing
- 7.2.4 Decryption header record preceding compressed file data.
- -Decryption Header:
- Value Size Description
- ----- ---- -----------
- IVSize 2 bytes Size of initialization vector (IV)
- IVData IVSize Initialization vector for this file
- Size 4 bytes Size of remaining decryption header data
- 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
- ErdSize 2 bytes Size of Encrypted Random Data
- ErdData ErdSize Encrypted Random Data
- Reserved1 4 bytes Reserved certificate processing data
- Reserved2 (var) Reserved for certificate processing data
- VSize 2 bytes Size of password validation data
- VData VSize-4 Password validation data
- VCRC32 4 bytes Standard ZIP CRC32 of password validation data
- 7.2.4.1 IVData - The size of the IV should match the algorithm block size.
- The IVData can be completely random data. If the size of
- the randomly generated data does not match the block size
- it should be complemented with zero's or truncated as
- necessary. If IVSize is 0,then IV = CRC32 + Uncompressed
- File Size (as a 64 bit little-endian, unsigned integer value).
- 7.2.4.2 Format - the data format identifier for this record. The only
- value allowed at this time is the integer value 3.
- 7.2.4.3 AlgId - integer identifier of the encryption algorithm from the
- following range
- 0x6601 - DES
- 0x6602 - RC2 (version needed to extract < 5.2)
- 0x6603 - 3DES 168
- 0x6609 - 3DES 112
- 0x660E - AES 128
- 0x660F - AES 192
- 0x6610 - AES 256
- 0x6702 - RC2 (version needed to extract >= 5.2)
- 0x6720 - Blowfish
- 0x6721 - Twofish
- 0x6801 - RC4
- 0xFFFF - Unknown algorithm
- 7.2.4.4 Bitlen - Explicit bit length of key
- 32 - 448 bits
- 7.2.4.5 Flags - Processing flags needed for decryption
- 0x0001 - Password is required to decrypt
- 0x0002 - Certificates only
- 0x0003 - Password or certificate required to decrypt
- Values > 0x0003 reserved for certificate processing
- 7.2.4.6 ErdData - Encrypted random data is used to store random data that
- is used to generate a file session key for encrypting
- each file. SHA1 is used to calculate hash data used to
- derive keys. File session keys are derived from a master
- session key generated from the user-supplied password.
- If the Flags field in the decryption header contains
- the value 0x4000, then the ErdData field must be
- decrypted using 3DES. If the value 0x4000 is not set,
- then the ErdData field must be decrypted using AlgId.
- 7.2.4.7 Reserved1 - Reserved for certificate processing, if value is
- zero, then Reserved2 data is absent. See the explanation
- under the Certificate Processing Method for details on
- this data structure.
- 7.2.4.8 Reserved2 - If present, the size of the Reserved2 data structure
- is located by skipping the first 4 bytes of this field
- and using the next 2 bytes as the remaining size. See
- the explanation under the Certificate Processing Method
- for details on this data structure.
- 7.2.4.9 VSize - This size value will always include the 4 bytes of the
- VCRC32 data and will be greater than 4 bytes.
- 7.2.4.10 VData - Random data for password validation. This data is VSize
- in length and VSize must be a multiple of the encryption
- block size. VCRC32 is a checksum value of VData.
- VData and VCRC32 are stored encrypted and start the
- stream of encrypted data for a file.
- 7.2.5 Useful Tips
- 7.2.5.1 Strong Encryption is always applied to a file after compression. The
- block oriented algorithms all operate in Cypher Block Chaining (CBC)
- mode. The block size used for AES encryption is 16. All other block
- algorithms use a block size of 8. Two IDs are defined for RC2 to
- account for a discrepancy found in the implementation of the RC2
- algorithm in the cryptographic library on Windows XP SP1 and all
- earlier versions of Windows. It is recommended that zero length files
- not be encrypted, however programs should be prepared to extract them
- if they are found within a ZIP file.
- 7.2.5.2 A pseudo-code representation of the encryption process is as follows:
- Password = GetUserPassword()
- MasterSessionKey = DeriveKey(SHA1(Password))
- RD = CryptographicStrengthRandomData()
- For Each File
- IV = CryptographicStrengthRandomData()
- VData = CryptographicStrengthRandomData()
- VCRC32 = CRC32(VData)
- FileSessionKey = DeriveKey(SHA1(IV + RD)
- ErdData = Encrypt(RD,MasterSessionKey,IV)
- Encrypt(VData + VCRC32 + FileData, FileSessionKey,IV)
- Done
- 7.2.5.3 The function names and parameter requirements will depend on
- the choice of the cryptographic toolkit selected. Almost any
- toolkit supporting the reference implementations for each
- algorithm can be used. The RSA BSAFE(r), OpenSSL, and Microsoft
- CryptoAPI libraries are all known to work well.
- 7.3 Single Password - Central Directory Encryption
- --------------------------------------------------
- 7.3.1 Central Directory Encryption is achieved within the .ZIP format by
- encrypting the Central Directory structure. This encapsulates the metadata
- most often used for processing .ZIP files. Additional metadata is stored for
- redundancy in the Local Header for each file. The process of concealing
- metadata by encrypting the Central Directory does not protect the data within
- the Local Header. To avoid information leakage from the exposed metadata
- in the Local Header, the fields containing information about a file are masked.
- 7.3.2 Local Header
- Masking replaces the true content of the fields for a file in the Local
- Header with false information. When masked, the Local Header is not
- suitable for streaming access and the options for data recovery of damaged
- archives is reduced. Extra Data fields that may contain confidential
- data should not be stored within the Local Header. The value set into
- the Version needed to extract field should be the correct value needed to
- extract the file without regard to Central Directory Encryption. The fields
- within the Local Header targeted for masking when the Central Directory is
- encrypted are:
- Field Name Mask Value
- ------------------ ---------------------------
- compression method 0
- last mod file time 0
- last mod file date 0
- crc-32 0
- compressed size 0
- uncompressed size 0
- file name (variable size) Base 16 value from the
- range 1 - 0xFFFFFFFFFFFFFFFF
- represented as a string whose
- size will be set into the
- file name length field
- The Base 16 value assigned as a masked file name is simply a sequentially
- incremented value for each file starting with 1 for the first file.
- Modifications to a ZIP file may cause different values to be stored for
- each file. For compatibility, the file name field in the Local Header
- should never be left blank. As of Version 6.2 of this specification,
- the Compression Method and Compressed Size fields are not yet masked.
- Fields having a value of 0xFFFF or 0xFFFFFFFF for the ZIP64 format
- should not be masked.
- 7.3.3 Encrypting the Central Directory
- Encryption of the Central Directory does not include encryption of the
- Central Directory Signature data, the Zip64 End of Central Directory
- record, the Zip64 End of Central Directory Locator, or the End
- of Central Directory record. The ZIP file comment data is never
- encrypted.
- Before encrypting the Central Directory, it may optionally be compressed.
- Compression is not required, but for storage efficiency it is assumed
- this structure will be compressed before encrypting. Similarly, this
- specification supports compressing the Central Directory without
- requiring that it also be encrypted. Early implementations of this
- feature will assume the encryption method applied to files matches the
- encryption applied to the Central Directory.
- Encryption of the Central Directory is done in a manner similar to
- that of file encryption. The encrypted data is preceded by a
- decryption header. The decryption header is known as the Archive
- Decryption Header. The fields of this record are identical to
- the decryption header preceding each encrypted file. The location
- of the Archive Decryption Header is determined by the value in the
- Start of the Central Directory field in the Zip64 End of Central
- Directory record. When the Central Directory is encrypted, the
- Zip64 End of Central Directory record will always be present.
- The layout of the Zip64 End of Central Directory record for all
- versions starting with 6.2 of this specification will follow the
- Version 2 format. The Version 2 format is as follows:
- The leading fixed size fields within the Version 1 format for this
- record remain unchanged. The record signature for both Version 1
- and Version 2 will be 0x06064b50. Immediately following the last
- byte of the field known as the Offset of Start of Central
- Directory With Respect to the Starting Disk Number will begin the
- new fields defining Version 2 of this record.
- 7.3.4 New fields for Version 2
- Note: all fields stored in Intel low-byte/high-byte order.
- Value Size Description
- ----- ---- -----------
- Compression Method 2 bytes Method used to compress the
- Central Directory
- Compressed Size 8 bytes Size of the compressed data
- Original Size 8 bytes Original uncompressed size
- AlgId 2 bytes Encryption algorithm ID
- BitLen 2 bytes Encryption key length
- Flags 2 bytes Encryption flags
- HashID 2 bytes Hash algorithm identifier
- Hash Length 2 bytes Length of hash data
- Hash Data (variable) Hash data
- The Compression Method accepts the same range of values as the
- corresponding field in the Central Header.
- The Compressed Size and Original Size values will not include the
- data of the Central Directory Signature which is compressed or
- encrypted.
- The AlgId, BitLen, and Flags fields accept the same range of values
- the corresponding fields within the 0x0017 record.
- Hash ID identifies the algorithm used to hash the Central Directory
- data. This data does not have to be hashed, in which case the
- values for both the HashID and Hash Length will be 0. Possible
- values for HashID are:
- Value Algorithm
- ------ ---------
- 0x0000 none
- 0x0001 CRC32
- 0x8003 MD5
- 0x8004 SHA1
- 0x8007 RIPEMD160
- 0x800C SHA256
- 0x800D SHA384
- 0x800E SHA512
- 7.3.5 When the Central Directory data is signed, the same hash algorithm
- used to hash the Central Directory for signing should be used.
- This is recommended for processing efficiency, however, it is
- permissible for any of the above algorithms to be used independent
- of the signing process.
- The Hash Data will contain the hash data for the Central Directory.
- The length of this data will vary depending on the algorithm used.
- The Version Needed to Extract should be set to 62.
- The value for the Total Number of Entries on the Current Disk will
- be 0. These records will no longer support random access when
- encrypting the Central Directory.
- 7.3.6 When the Central Directory is compressed and/or encrypted, the
- End of Central Directory record will store the value 0xFFFFFFFF
- as the value for the Total Number of Entries in the Central
- Directory. The value stored in the Total Number of Entries in
- the Central Directory on this Disk field will be 0. The actual
- values will be stored in the equivalent fields of the Zip64
- End of Central Directory record.
- 7.3.7 Decrypting and decompressing the Central Directory is accomplished
- in the same manner as decrypting and decompressing a file.
- 7.4 Certificate Processing Method
- ---------------------------------
- The Certificate Processing Method for ZIP file encryption
- defines the following additional data fields:
- 7.4.1 Certificate Flag Values
- Additional processing flags that can be present in the Flags field of both
- the 0x0017 field of the central directory Extra Field and the Decryption
- header record preceding compressed file data are:
- 0x0007 - reserved for future use
- 0x000F - reserved for future use
- 0x0100 - Indicates non-OAEP key wrapping was used. If this
- this field is set, the version needed to extract must
- be at least 61. This means OAEP key wrapping is not
- used when generating a Master Session Key using
- ErdData.
- 0x4000 - ErdData must be decrypted using 3DES-168, otherwise use the
- same algorithm used for encrypting the file contents.
- 0x8000 - reserved for future use
- 7.4.2 CertData - Extra Field 0x0017 record certificate data structure
- The data structure used to store certificate data within the section
- of the Extra Field defined by the CertData field of the 0x0017
- record are as shown:
- Value Size Description
- ----- ---- -----------
- RCount 4 bytes Number of recipients.
- HashAlg 2 bytes Hash algorithm identifier
- HSize 2 bytes Hash size
- SRList (var) Simple list of recipients hashed public keys
- RCount This defines the number intended recipients whose
- public keys were used for encryption. This identifies
- the number of elements in the SRList.
- HashAlg This defines the hash algorithm used to calculate
- the public key hash of each public key used
- for encryption. This field currently supports
- only the following value for SHA-1
- 0x8004 - SHA1
- HSize This defines the size of a hashed public key.
- SRList This is a variable length list of the hashed
- public keys for each intended recipient. Each
- element in this list is HSize. The total size of
- SRList is determined using RCount * HSize.
- 7.4.3 Reserved1 - Certificate Decryption Header Reserved1 Data
- Value Size Description
- ----- ---- -----------
- RCount 4 bytes Number of recipients.
- RCount This defines the number intended recipients whose
- public keys were used for encryption. This defines
- the number of elements in the REList field defined below.
- 7.4.4 Reserved2 - Certificate Decryption Header Reserved2 Data Structures
- Value Size Description
- ----- ---- -----------
- HashAlg 2 bytes Hash algorithm identifier
- HSize 2 bytes Hash size
- REList (var) List of recipient data elements
- HashAlg This defines the hash algorithm used to calculate
- the public key hash of each public key used
- for encryption. This field currently supports
- only the following value for SHA-1
- 0x8004 - SHA1
- HSize This defines the size of a hashed public key
- defined in REHData.
- REList This is a variable length of list of recipient data.
- Each element in this list consists of a Recipient
- Element data structure as follows:
- Recipient Element (REList) Data Structure:
- Value Size Description
- ----- ---- -----------
- RESize 2 bytes Size of REHData + REKData
- REHData HSize Hash of recipients public key
- REKData (var) Simple key blob
- RESize This defines the size of an individual REList
- element. This value is the combined size of the
- REHData field + REKData field. REHData is defined by
- HSize. REKData is variable and can be calculated
- for each REList element using RESize and HSize.
- REHData Hashed public key for this recipient.
- REKData Simple Key Blob. The format of this data structure
- is identical to that defined in the Microsoft
- CryptoAPI and generated using the CryptExportKey()
- function. The version of the Simple Key Blob
- supported at this time is 0x02 as defined by
- Microsoft.
- 7.5 Certificate Processing - Central Directory Encryption
- ---------------------------------------------------------
- 7.5.1 Central Directory Encryption using Digital Certificates will
- operate in a manner similar to that of Single Password Central
- Directory Encryption. This record will only be present when there
- is data to place into it. Currently, data is placed into this
- record when digital certificates are used for either encrypting
- or signing the files within a ZIP file. When only password
- encryption is used with no certificate encryption or digital
- signing, this record is not currently needed. When present, this
- record will appear before the start of the actual Central Directory
- data structure and will be located immediately after the Archive
- Decryption Header if the Central Directory is encrypted.
- 7.5.2 The Archive Extra Data record will be used to store the following
- information. Additional data may be added in future versions.
- Extra Data Fields:
- 0x0014 - PKCS#7 Store for X.509 Certificates
- 0x0016 - X.509 Certificate ID and Signature for central directory
- 0x0019 - PKCS#7 Encryption Recipient Certificate List
- The 0x0014 and 0x0016 Extra Data records that otherwise would be
- located in the first record of the Central Directory for digital
- certificate processing. When encrypting or compressing the Central
- Directory, the 0x0014 and 0x0016 records must be located in the
- Archive Extra Data record and they should not remain in the first
- Central Directory record. The Archive Extra Data record will also
- be used to store the 0x0019 data.
- 7.5.3 When present, the size of the Archive Extra Data record will be
- included in the size of the Central Directory. The data of the
- Archive Extra Data record will also be compressed and encrypted
- along with the Central Directory data structure.
- 7.6 Certificate Processing Differences
- --------------------------------------
- 7.6.1 The Certificate Processing Method of encryption differs from the
- Single Password Symmetric Encryption Method as follows. Instead
- of using a user-defined password to generate a master session key,
- cryptographically random data is used. The key material is then
- wrapped using standard key-wrapping techniques. This key material
- is wrapped using the public key of each recipient that will need
- to decrypt the file using their corresponding private key.
- 7.6.2 This specification currently assumes digital certificates will follow
- the X.509 V3 format for 1024 bit and higher RSA format digital
- certificates. Implementation of this Certificate Processing Method
- requires supporting logic for key access and management. This logic
- is outside the scope of this specification.
- 7.7 OAEP Processing with Certificate-based Encryption
- -----------------------------------------------------
- 7.7.1 OAEP stands for Optimal Asymmetric Encryption Padding. It is a
- strengthening technique used for small encoded items such as decryption
- keys. This is commonly applied in cryptographic key-wrapping techniques
- and is supported by PKCS #1. Versions 5.0 and 6.0 of this specification
- were designed to support OAEP key-wrapping for certificate-based
- decryption keys for additional security.
- 7.7.2 Support for private keys stored on Smartcards or Tokens introduced
- a conflict with this OAEP logic. Most card and token products do
- not support the additional strengthening applied to OAEP key-wrapped
- data. In order to resolve this conflict, versions 6.1 and above of this
- specification will no longer support OAEP when encrypting using
- digital certificates.
- 7.7.3 Versions of PKZIP available during initial development of the
- certificate processing method set a value of 61 into the
- version needed to extract field for a file. This indicates that
- non-OAEP key wrapping is used. This affects certificate encryption
- only, and password encryption functions should not be affected by
- this value. This means values of 61 may be found on files encrypted
- with certificates only, or on files encrypted with both password
- encryption and certificate encryption. Files encrypted with both
- methods can safely be decrypted using the password methods documented.
- 8.0 Splitting and Spanning ZIP files
- -------------------------------------
- 8.1 Spanned ZIP files
- 8.1.1 Spanning is the process of segmenting a ZIP file across
- multiple removable media. This support has typically only
- been provided for DOS formatted floppy diskettes.
- 8.2 Split ZIP files
- 8.2.1 File splitting is a newer derivation of spanning.
- Splitting follows the same segmentation process as
- spanning, however, it does not require writing each
- segment to a unique removable medium and instead supports
- placing all pieces onto local or non-removable locations
- such as file systems, local drives, folders, etc.
- 8.3 File Naming Differences
- 8.3.1 A key difference between spanned and split ZIP files is
- that all pieces of a spanned ZIP file have the same name.
- Since each piece is written to a separate volume, no name
- collisions occur and each segment can reuse the original
- .ZIP file name given to the archive.
- 8.3.2 Sequence ordering for DOS spanned archives uses the DOS
- volume label to determine segment numbers. Volume labels
- for each segment are written using the form PKBACK#xxx,
- where xxx is the segment number written as a decimal
- value from 001 - nnn.
- 8.3.3 Split ZIP files are typically written to the same location
- and are subject to name collisions if the spanned name
- format is used since each segment will reside on the same
- drive. To avoid name collisions, split archives are named
- as follows.
- Segment 1 = filename.z01
- Segment n-1 = filename.z(n-1)
- Segment n = filename.zip
- 8.3.4 The .ZIP extension is used on the last segment to support
- quickly reading the central directory. The segment number
- n should be a decimal value.
- 8.4 Spanned Self-extracting ZIP Files
- 8.4.1 Spanned ZIP files may be PKSFX Self-extracting ZIP files.
- PKSFX files may also be split, however, in this case
- the first segment must be named filename.exe. The first
- segment of a split PKSFX archive must be large enough to
- include the entire executable program.
- 8.5 Capacities and Markers
- 8.5.1 Capacities for split archives are as follows:
- Maximum number of segments = 4,294,967,295 - 1
- Maximum .ZIP segment size = 4,294,967,295 bytes
- Minimum segment size = 64K
- Maximum PKSFX segment size = 2,147,483,647 bytes
- 8.5.2 Segment sizes may be different however by convention, all
- segment sizes should be the same with the exception of the
- last, which may be smaller. Local and central directory
- header records must never be split across a segment boundary.
- When writing a header record, if the number of bytes remaining
- within a segment is less than the size of the header record,
- end the current segment and write the header at the start
- of the next segment. The central directory may span segment
- boundaries, but no single record in the central directory
- should be split across segments.
- 8.5.3 Spanned/Split archives created using PKZIP for Windows
- (V2.50 or greater), PKZIP Command Line (V2.50 or greater),
- or PKZIP Explorer will include a special spanning
- signature as the first 4 bytes of the first segment of
- the archive. This signature (0x08074b50) will be
- followed immediately by the local header signature for
- the first file in the archive.
- 8.5.4 A special spanning marker may also appear in spanned/split
- archives if the spanning or splitting process starts but
- only requires one segment. In this case the 0x08074b50
- signature will be replaced with the temporary spanning
- marker signature of 0x30304b50. Split archives can
- only be uncompressed by other versions of PKZIP that
- know how to create a split archive.
- 8.5.5 The signature value 0x08074b50 is also used by some
- ZIP implementations as a marker for the Data Descriptor
- record. Conflict in this alternate assignment can be
- avoided by ensuring the position of the signature
- within the ZIP file to determine the use for which it
- is intended.
- 9.0 Change Process
- ------------------
- 9.1 In order for the .ZIP file format to remain a viable technology, this
- specification should be considered as open for periodic review and
- revision. Although this format was originally designed with a
- certain level of extensibility, not all changes in technology
- (present or future) were or will be necessarily considered in its
- design.
- 9.2 If your application requires new definitions to the
- extensible sections in this format, or if you would like to
- submit new data structures or new capabilities, please forward
- your request to zipformat@pkware.com. All submissions will be
- reviewed by the ZIP File Specification Committee for possible
- inclusion into future versions of this specification.
- 9.3 Periodic revisions to this specification will be published as
- DRAFT or as FINAL status to ensure interoperability. We encourage
- comments and feedback that may help improve clarity or content.
- 10.0 Incorporating PKWARE Proprietary Technology into Your Product
- ------------------------------------------------------------------
- 10.1 The Use or Implementation in a product of APPNOTE technological
- components pertaining to either strong encryption or patching requires
- a separate, executed license agreement from PKWARE. Please contact
- PKWARE at zipformat@pkware.com or +1-414-289-9788 with regard to
- acquiring such a license.
- 10.2 Additional information regarding PKWARE proprietray technology is
- available at http://www.pkware.com/appnote.
- 11.0 Acknowledgements
- ---------------------
- In addition to the above mentioned contributors to PKZIP and PKUNZIP,
- PKWARE would like to extend special thanks to Robert Mahoney for
- suggesting the extension .ZIP for this software.
- 12.0 References
- ---------------
- Fiala, Edward R., and Greene, Daniel H., "Data compression with
- finite windows", Communications of the ACM, Volume 32, Number 4,
- April 1989, pages 490-505.
- Held, Gilbert, "Data Compression, Techniques and Applications,
- Hardware and Software Considerations", John Wiley & Sons, 1987.
- Huffman, D.A., "A method for the construction of minimum-redundancy
- codes", Proceedings of the IRE, Volume 40, Number 9, September 1952,
- pages 1098-1101.
- Nelson, Mark, "LZW Data Compression", Dr. Dobbs Journal, Volume 14,
- Number 10, October 1989, pages 29-37.
- Nelson, Mark, "The Data Compression Book", M&T Books, 1991.
- Storer, James A., "Data Compression, Methods and Theory",
- Computer Science Press, 1988
- Welch, Terry, "A Technique for High-Performance Data Compression",
- IEEE Computer, Volume 17, Number 6, June 1984, pages 8-19.
- Ziv, J. and Lempel, A., "A universal algorithm for sequential data
- compression", Communications of the ACM, Volume 30, Number 6,
- June 1987, pages 520-540.
- Ziv, J. and Lempel, A., "Compression of individual sequences via
- variable-rate coding", IEEE Transactions on Information Theory,
- Volume 24, Number 5, September 1978, pages 530-536.
- APPENDIX A - AS/400 Extra Field (0x0065) Attribute Definitions
- --------------------------------------------------------------
- A.1 Field Definition Structure:
- a. field length including length 2 bytes
- b. field code 2 bytes
- c. data x bytes
- A.2 Field Code Description
- 4001 Source type i.e. CLP etc
- 4002 The text description of the library
- 4003 The text description of the file
- 4004 The text description of the member
- 4005 x'F0' or 0 is PF-DTA, x'F1' or 1 is PF_SRC
- 4007 Database Type Code 1 byte
- 4008 Database file and fields definition
- 4009 GZIP file type 2 bytes
- 400B IFS code page 2 bytes
- 400C IFS Creation Time 4 bytes
- 400D IFS Access Time 4 bytes
- 400E IFS Modification time 4 bytes
- 005C Length of the records in the file 2 bytes
- 0068 GZIP two words 8 bytes
- APPENDIX B - z/OS Extra Field (0x0065) Attribute Definitions
- ------------------------------------------------------------
- B.1 Field Definition Structure:
- a. field length including length 2 bytes
- b. field code 2 bytes
- c. data x bytes
- B.2 Field Code Description
- 0001 File Type 2 bytes
- 0002 NonVSAM Record Format 1 byte
- 0003 Reserved
- 0004 NonVSAM Block Size 2 bytes Big Endian
- 0005 Primary Space Allocation 3 bytes Big Endian
- 0006 Secondary Space Allocation 3 bytes Big Endian
- 0007 Space Allocation Type1 byte flag
- 0008 Modification Date Retired with PKZIP 5.0 +
- 0009 Expiration Date Retired with PKZIP 5.0 +
- 000A PDS Directory Block Allocation 3 bytes Big Endian binary value
- 000B NonVSAM Volume List variable
- 000C UNIT Reference Retired with PKZIP 5.0 +
- 000D DF/SMS Management Class 8 bytes EBCDIC Text Value
- 000E DF/SMS Storage Class 8 bytes EBCDIC Text Value
- 000F DF/SMS Data Class 8 bytes EBCDIC Text Value
- 0010 PDS/PDSE Member Info. 30 bytes
- 0011 VSAM sub-filetype 2 bytes
- 0012 VSAM LRECL 13 bytes EBCDIC "(num_avg num_max)"
- 0013 VSAM Cluster Name Retired with PKZIP 5.0 +
- 0014 VSAM KSDS Key Information 13 bytes EBCDIC "(num_length num_position)"
- 0015 VSAM Average LRECL 5 bytes EBCDIC num_value padded with blanks
- 0016 VSAM Maximum LRECL 5 bytes EBCDIC num_value padded with blanks
- 0017 VSAM KSDS Key Length 5 bytes EBCDIC num_value padded with blanks
- 0018 VSAM KSDS Key Position 5 bytes EBCDIC num_value padded with blanks
- 0019 VSAM Data Name 1-44 bytes EBCDIC text string
- 001A VSAM KSDS Index Name 1-44 bytes EBCDIC text string
- 001B VSAM Catalog Name 1-44 bytes EBCDIC text string
- 001C VSAM Data Space Type 9 bytes EBCDIC text string
- 001D VSAM Data Space Primary 9 bytes EBCDIC num_value left-justified
- 001E VSAM Data Space Secondary 9 bytes EBCDIC num_value left-justified
- 001F VSAM Data Volume List variable EBCDIC text list of 6-character Volume IDs
- 0020 VSAM Data Buffer Space 8 bytes EBCDIC num_value left-justified
- 0021 VSAM Data CISIZE 5 bytes EBCDIC num_value left-justified
- 0022 VSAM Erase Flag 1 byte flag
- 0023 VSAM Free CI % 3 bytes EBCDIC num_value left-justified
- 0024 VSAM Free CA % 3 bytes EBCDIC num_value left-justified
- 0025 VSAM Index Volume List variable EBCDIC text list of 6-character Volume IDs
- 0026 VSAM Ordered Flag 1 byte flag
- 0027 VSAM REUSE Flag 1 byte flag
- 0028 VSAM SPANNED Flag 1 byte flag
- 0029 VSAM Recovery Flag 1 byte flag
- 002A VSAM WRITECHK Flag 1 byte flag
- 002B VSAM Cluster/Data SHROPTS 3 bytes EBCDIC "n,y"
- 002C VSAM Index SHROPTS 3 bytes EBCDIC "n,y"
- 002D VSAM Index Space Type 9 bytes EBCDIC text string
- 002E VSAM Index Space Primary 9 bytes EBCDIC num_value left-justified
- 002F VSAM Index Space Secondary 9 bytes EBCDIC num_value left-justified
- 0030 VSAM Index CISIZE 5 bytes EBCDIC num_value left-justified
- 0031 VSAM Index IMBED 1 byte flag
- 0032 VSAM Index Ordered Flag 1 byte flag
- 0033 VSAM REPLICATE Flag 1 byte flag
- 0034 VSAM Index REUSE Flag 1 byte flag
- 0035 VSAM Index WRITECHK Flag 1 byte flag Retired with PKZIP 5.0 +
- 0036 VSAM Owner 8 bytes EBCDIC text string
- 0037 VSAM Index Owner 8 bytes EBCDIC text string
- 0038 Reserved
- 0039 Reserved
- 003A Reserved
- 003B Reserved
- 003C Reserved
- 003D Reserved
- 003E Reserved
- 003F Reserved
- 0040 Reserved
- 0041 Reserved
- 0042 Reserved
- 0043 Reserved
- 0044 Reserved
- 0045 Reserved
- 0046 Reserved
- 0047 Reserved
- 0048 Reserved
- 0049 Reserved
- 004A Reserved
- 004B Reserved
- 004C Reserved
- 004D Reserved
- 004E Reserved
- 004F Reserved
- 0050 Reserved
- 0051 Reserved
- 0052 Reserved
- 0053 Reserved
- 0054 Reserved
- 0055 Reserved
- 0056 Reserved
- 0057 Reserved
- 0058 PDS/PDSE Member TTR Info. 6 bytes Big Endian
- 0059 PDS 1st LMOD Text TTR 3 bytes Big Endian
- 005A PDS LMOD EP Rec # 4 bytes Big Endian
- 005B Reserved
- 005C Max Length of records 2 bytes Big Endian
- 005D PDSE Flag 1 byte flag
- 005E Reserved
- 005F Reserved
- 0060 Reserved
- 0061 Reserved
- 0062 Reserved
- 0063 Reserved
- 0064 Reserved
- 0065 Last Date Referenced 4 bytes Packed Hex "yyyymmdd"
- 0066 Date Created 4 bytes Packed Hex "yyyymmdd"
- 0068 GZIP two words 8 bytes
- 0071 Extended NOTE Location 12 bytes Big Endian
- 0072 Archive device UNIT 6 bytes EBCDIC
- 0073 Archive 1st Volume 6 bytes EBCDIC
- 0074 Archive 1st VOL File Seq# 2 bytes Binary
- APPENDIX C - Zip64 Extensible Data Sector Mappings
- ---------------------------------------------------
- -Z390 Extra Field:
- The following is the general layout of the attributes for the
- ZIP 64 "extra" block for extended tape operations.
- Note: some fields stored in Big Endian format. All text is
- in EBCDIC format unless otherwise specified.
- Value Size Description
- ----- ---- -----------
- (Z390) 0x0065 2 bytes Tag for this "extra" block type
- Size 4 bytes Size for the following data block
- Tag 4 bytes EBCDIC "Z390"
- Length71 2 bytes Big Endian
- Subcode71 2 bytes Enote type code
- FMEPos 1 byte
- Length72 2 bytes Big Endian
- Subcode72 2 bytes Unit type code
- Unit 1 byte Unit
- Length73 2 bytes Big Endian
- Subcode73 2 bytes Volume1 type code
- FirstVol 1 byte Volume
- Length74 2 bytes Big Endian
- Subcode74 2 bytes FirstVol file sequence
- FileSeq 2 bytes Sequence
- APPENDIX D - Language Encoding (EFS)
- ------------------------------------
- D.1 The ZIP format has historically supported only the original IBM PC character
- encoding set, commonly referred to as IBM Code Page 437. This limits storing
- file name characters to only those within the original MS-DOS range of values
- and does not properly support file names in other character encodings, or
- languages. To address this limitation, this specification will support the
- following change.
- D.2 If general purpose bit 11 is unset, the file name and comment should conform
- to the original ZIP character encoding. If general purpose bit 11 is set, the
- filename and comment must support The Unicode Standard, Version 4.1.0 or
- greater using the character encoding form defined by the UTF-8 storage
- specification. The Unicode Standard is published by the The Unicode
- Consortium (www.unicode.org). UTF-8 encoded data stored within ZIP files
- is expected to not include a byte order mark (BOM).
- D.3 Applications may choose to supplement this file name storage through the use
- of the 0x0008 Extra Field. Storage for this optional field is currently
- undefined, however it will be used to allow storing extended information
- on source or target encoding that may further assist applications with file
- name, or file content encoding tasks. Please contact PKWARE with any
- requirements on how this field should be used.
- D.4 The 0x0008 Extra Field storage may be used with either setting for general
- purpose bit 11. Examples of the intended usage for this field is to store
- whether "modified-UTF-8" (JAVA) is used, or UTF-8-MAC. Similarly, other
- commonly used character encoding (code page) designations can be indicated
- through this field. Formalized values for use of the 0x0008 record remain
- undefined at this time. The definition for the layout of the 0x0008 field
- will be published when available. Use of the 0x0008 Extra Field provides
- for storing data within a ZIP file in an encoding other than IBM Code
- Page 437 or UTF-8.
- D.5 General purpose bit 11 will not imply any encoding of file content or
- password. Values defining character encoding for file content or
- password must be stored within the 0x0008 Extended Language Encoding
- Extra Field.
- D.6 Ed Gordon of the Info-ZIP group has defined a pair of "extra field" records
- that can be used to store UTF-8 file name and file comment fields. These
- records can be used for cases when the general purpose bit 11 method
- for storing UTF-8 data in the standard file name and comment fields is
- not desirable. A common case for this alternate method is if backward
- compatibility with older programs is required.
- D.7 Definitions for the record structure of these fields are included above
- in the section on 3rd party mappings for "extra field" records. These
- records are identified by Header ID's 0x6375 (Info-ZIP Unicode Comment
- Extra Field) and 0x7075 (Info-ZIP Unicode Path Extra Field).
- D.8 The choice of which storage method to use when writing a ZIP file is left
- to the implementation. Developers should expect that a ZIP file may
- contain either method and should provide support for reading data in
- either format. Use of general purpose bit 11 reduces storage requirements
- for file name data by not requiring additional "extra field" data for
- each file, but can result in older ZIP programs not being able to extract
- files. Use of the 0x6375 and 0x7075 records will result in a ZIP file
- that should always be readable by older ZIP programs, but requires more
- storage per file to write file name and/or file comment fields.
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