appnote.txt

SharpZipLib之前叫做NZipLib

        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)

        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.

        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.

        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.

        Multiple special purpose data blocks may be present, but 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.

  H.  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
        
  I.  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)

  J.  Explanation of fields:

      version made by (2 bytes)

          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.  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

          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.  

      version needed to extract (2 bytes)

          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 should 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.

          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


          * 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 should 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 should 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 should also be set.  
          This field should be set appropriately to indicate whether 
          Version 1 or Version 2 format is in use. 

      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 should
                 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.

          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: Used 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.

          Bit 14: Reserved by PKWARE.

          Bit 15: Reserved by PKWARE.

      compression method: (2 bytes)

          (see accompanying documentation for algorithm
          descriptions)

          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)
         98 - PPMd version I, Rev 1

      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. 

      CRC-32: (4 bytes)

          The CRC-32 algorithm was generously contributed by
          David Schwaderer and can be found in his excellent