appnote.txt

SharpZipLib之前叫做NZipLib

File:    APPNOTE.TXT - .ZIP File Format Specification
Version: 6.3.1 
Revised: April 11, 2007
Copyright (c) 1989 - 2007 PKWARE Inc., All Rights Reserved.

The use of certain technological aspects disclosed in the current
APPNOTE is available pursuant to the below section entitled
"Incorporating PKWARE Proprietary Technology into Your Product".

I. Purpose
----------

This specification is intended to define a cross-platform,
interoperable file storage and transfer format.  Since its 
first publication in 1989, PKWARE has remained committed to 
ensuring the interoperability of the .ZIP file format through 
publication and maintenance of this specification.  We trust that 
all .ZIP compatible vendors and application developers that have 
adopted and benefited from this format will share and support 
this commitment to interoperability.

II. Contacting PKWARE
---------------------

     PKWARE, Inc.
     648 N. Plankinton Avenue, Suite 220
     Milwaukee, WI 53203
     [phone]
     [phone] FAX
     [e-mail]

III. Disclaimer
---------------

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.

If the version of this file is marked as a NOTIFICATION OF CHANGE,
the content defines an Early Feature Specification (EFS) change 
to the .ZIP file format that may be subject to modification prior 
to publication of the Final Feature Specification (FFS).  This
document may also contain information on Planned Feature 
Specifications (PFS) defining recognized future extensions.

IV. Change Log
--------------

Version       Change Description                        Date
-------       ------------------                       ----------
5.2           -Single Password Symmetric Encryption    06/02/2003
               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


V. General Format of a .ZIP file
--------------------------------

  Files stored in arbitrary order.  Large .ZIP files can span multiple
  volumes or be split into user-defined segment sizes. All values
  are stored in little-endian byte order unless otherwise specified. 

  Overall .ZIP file format:

    [local file header 1]
    [file data 1]
    [data descriptor 1]
    . 
    .
    .
    [local file header n]
    [file data n]
    [data descriptor n]
    [archive decryption header] 
    [archive extra data record] 
    [central directory]
    [zip64 end of central directory record]
    [zip64 end of central directory locator] 
    [end of central directory record]


  A.  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)

  B.  File data

      Immediately following the local header for a file
      is the compressed or stored data for the file. 
      The series of [local file header][file data][data
      descriptor] repeats for each file in the .ZIP archive. 

  C.  Data descriptor:

        crc-32                          4 bytes
        compressed size                 4 bytes
        uncompressed size               4 bytes

      This descriptor exists only 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 is 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.

      When compressing files, compressed and uncompressed sizes 
      should be stored in ZIP64 format (as 8 byte values) when a 
      files 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.  

      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.
      When writing ZIP files, it is recommended to 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.

      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.

      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 should be set to binary zeros.

  D.  Archive decryption header:  

      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 will precede the encrypted data segment.  The encrypted
      data segment will 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.  Refer to the 
      section on the Strong Encryption Specification for information
      on the fields used in the Archive Decryption Header record.


  E.  Archive extra data record: 

        archive extra data signature    4 bytes  (0x08064b50)
        extra field length              4 bytes
        extra field data                (variable size)

      The Archive Extra Data Record 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 present, this record immediately precedes the central 
      directory data structure.  The size of this data record will 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.  


  F.  Central directory structure:

      [file header 1]
      .
      .
      . 
      [file 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)

      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.

  G.  Zip64 end of central directory record

        zip64 end of central dir 
        signature                       4 bytes  (0x06064b50)
        size of zip64 end of central