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.



 





