--- /dev/null
+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.
+
+
+
+
Code Review / src / app-framework-demo.git / blobdiff