File:    APPNOTE.TXT - .ZIP File Format Specification


Version: 6.3.2 


Revised: September 28, 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


     +1-414-289-9788


     +1-414-289-9789 FAX


     zipformat@pkware.com





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





6.3.2         -Added compression method 97             09/28/2007





              -Documented InfoZIP "Extra Field"


               values for UTF-8 file name and


               file comment storage





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


        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)


         97 - WavPack compressed data


         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


          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. 





      compressed size: (4 bytes)


      uncompressed size: (4 bytes)





          The size of the file compressed and uncompressed,


          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. 





      file name length: (2 bytes)


      extra field length: (2 bytes)


      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.  





      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.





      internal file attributes: (2 bytes)





          Bits 1 and 2 are reserved for use by PKWARE.





          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.





          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.





      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.





      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.





      file name: (Variable)





          The name of the file, with optional relative path.


          The path stored should not contain a drive or


          device letter, or a leading slash.  All slashes


          should 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.  If encrypting


          the central directory 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. 





      extra field: (Variable)





          This is for expansion.  If additional information


          needs to be stored for special needs or for specific 


          platforms, it should be stored here.  Earlier versions 


          of the software can then safely skip this file, and 


          find the next file or header.  This field will be 0 


          length in version 1.0.





          In order to allow different programs and different types


          of information to be stored in the 'extra' field in .ZIP


          files, the following structure should 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 ID's of 0 thru 31 are reserved for use by PKWARE.


          The remaining ID's can be used by third party vendors for


          proprietary usage.





          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) 





          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.





          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.





          In case two different programs should appropriate the same


          Header ID value, it is strongly recommended that each


          program 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.





         -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 will


          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.








         -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 it's entirety within this 


          structure.  There will only ever be one "block" of data in 


          VarFields[].





         -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





         -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





          Rules:





          1. There will be one or more of 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.





          2. No word alignment or padding is performed.





          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.





         -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.


          


         -PATCH Descriptor Extra Field (0x000f):





          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 





          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





          Actions





          Action       Value


          ------       ----- 


          none         0


          add          1


          delete       2


          patch        3





          Reactions


 


          Reaction     Value


          --------     -----


          ask          0


          skip         1


          ignore       2


          fail         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, patching, or extended tape operations requires


          a license from PKWARE.  Please contact PKWARE with regard to 


          acquiring a license. 





         -PKCS#7 Store for X.509 Certificates (0x0014):





          This field contains 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








         -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





         -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





         -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)








         -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








         -PKCS#7 Encryption Recipient Certificate List (0x0019): 





          This field contains 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 aide 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








         -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)








         -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)








          Third-party Mappings:


          


         -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








         -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








         -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;








         -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."








         -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.








         -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.


 





        -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








      file comment: (Variable)





          The comment for this file.





      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.








      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.





      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.





      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.





      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.





      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.





      .ZIP file comment length: (2 bytes)





          The length of the comment for this .ZIP file.





      .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.





      zip64 extensible data sector    (variable size)





          (currently reserved for use by PKWARE)








  K.  Splitting and Spanning ZIP files





          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. 





          File splitting is a newer derivative 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...





          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.





          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.





          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





          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.





          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.





          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


          


          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.





          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.  





          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.





          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.  





  L.  General notes:





      1)  All fields unless otherwise noted are unsigned and stored


          in Intel low-byte:high-byte, low-word:high-word order.





      2)  String fields are not null terminated, since the


          length is given explicitly.





      3)  The entries in the central directory may not necessarily


          be in the same order that files appear in the .ZIP file.





      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.





      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.





VI. Explanation of compression methods


--------------------------------------





UnShrinking - Method 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:





1)  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.





2)  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.





Expanding - Methods 2-5


-----------------------





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.





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.





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.





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.





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.





Imploding - Method 6


--------------------





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.





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.





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.





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.





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.





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.





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)





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.





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





Tokenizing - Method 7


---------------------





This method is not used by PKZIP.





Deflating - Method 8


--------------------





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.





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.





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





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





Enhanced Deflating - Method 9


-----------------------------





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. 





BZIP2 - Method 12


-----------------





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.





LZMA - Method 14 (EFS)


----------------------





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:   





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. 





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.





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]





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]





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.





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. 


 


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"





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.  





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. 





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.  





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 4.32 


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.  





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.





WavPack - Method 97


-------------------





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.





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.





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. 





PPMd - Method 98


----------------





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.





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:





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





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)








VII. Traditional PKWARE Encryption


----------------------------------





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.





Decryption


----------





PKWARE is grateful to Mr. Roger Schlafly for his expert contribution 


towards the development of PKWARE's traditional encryption.





PKZIP encrypts the compressed data stream.  Encrypted files must


be decrypted before they can be extracted.





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.





The following is 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.





Step 1 - 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.





Step 2 - 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.





Step 3 - 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








VIII. Strong Encryption Specification


-------------------------------------





The Strong Encryption technology defined in this specification is 


covered under a pending patent application. The use or implementation


in a product of certain technological aspects set forth in the current


APPNOTE, including those with regard to strong encryption, patching, 


or extended tape operations requires a license from PKWARE. Portions


of this Strong Encryption technology are available for use at no charge.


Contact PKWARE for licensing terms and conditions. Refer to section II


of this APPNOTE (Contacting PKWARE) for information on how to 


contact PKWARE. 





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.  





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. 





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.





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








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.





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 files name, its original 


size, timestamp and CRC32 value. 





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.





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.  





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.  





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. 





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.  





Encryption provides data confidentiality and privacy.  It is 


recommended that you combine X.509 digital signing with encryption 


to add authentication and non-repudiation.








Single Password Symmetric Encryption Method:


-------------------------------------------





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:





1. 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.








2. Extra Field 0x0017 in central header only.





     Fields to consider in this record are:





     Format - the data format identifier for this record.  The only


     value allowed at this time is the integer value 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





     Bitlen - Explicit bit length of key





         32 - 448 bits


   


     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








3. 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





     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).





     Format - the data format identifier for this record.  The only


     value allowed at this time is the integer value 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





     Bitlen - Explicit bit length of key





         32 - 448 bits


   


     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





     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.








     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.





     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.





     VSize - This size value will always include the 4 bytes of the


             VCRC32 data and will be greater than 4 bytes.





     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.








4. Useful Tips





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 ID's 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.





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





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.  








Single Password - Central Directory Encryption:


-----------------------------------------------





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.  





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.  





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.  





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





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.





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.





Decrypting and decompressing the Central Directory is accomplished


in the same manner as decrypting and decompressing a file.





Certificate Processing Method:


-----------------------------





The Certificate Processing Method of for ZIP file encryption 


defines the following additional data fields:





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








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.








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.








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.





Certificate Processing - Central Directory Encryption:


------------------------------------------------------





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.





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. 





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.





Certificate Processing Differences:





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.





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.





OAEP Processing with Certificate-based Encryption:





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.  





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. 





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.





IX. Change Process


------------------





In order for the .ZIP file format to remain a viable definition, 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.  If your application requires new definitions to the


extensible sections in this format, or if you would like to 


submit new data structures, 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.  Periodic revisions


to this specification will be published to ensure interoperability. 


We encourage comments and feedback that may help improve clarity 


or content.





X. Incorporating PKWARE Proprietary Technology into Your Product


----------------------------------------------------------------





PKWARE is committed to the interoperability and advancement of the


.ZIP format.  PKWARE offers a free license for certain technological


aspects described above under certain restrictions and conditions.


However, the use or implementation in a product of certain technological


aspects set forth in the current APPNOTE, including those with regard to


strong encryption, patching, or extended tape operations requires a 


license from PKWARE.  Please contact PKWARE with regard to acquiring


a license.





XI. Acknowledgements


---------------------





In addition to the above mentioned contributors to PKZIP and PKUNZIP,


I would like to extend special thanks to Robert Mahoney for suggesting


the extension .ZIP for this software.





XII. 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


--------------------------------------------------------------





Field Definition Structure:





   a. field length including length             2 bytes


   b. field code                                2 bytes


   c. data                                      x bytes





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


------------------------------------------------------------





Field Definition Structure:





   a. field length including length             2 bytes


   b. field code                                2 bytes


   c. data                                      x bytes





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 (EFS)


--------------------------------------------------------





          -Z390   Extra Field:





          The following is the general layout of the attributes for the 


          ZIP 64 "extra" block for extended tape operations. Portions of 


          this extended tape processing technology is covered under a 


          pending patent application. The use or implementation in a 


          product of certain technological aspects set forth in the 


          current APPNOTE, including those with regard to strong encryption,


          patching or extended tape operations, requires a license from


          PKWARE.  Please contact PKWARE with regard to acquiring a license. 


 





          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)


------------------------------------





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. 





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). 





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.





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.





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.





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.





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).





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.





 








