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diff --git a/afb-client/bower_components/jszip/docs/APPNOTE.TXT b/afb-client/bower_components/jszip/docs/APPNOTE.TXT new file mode 100644 index 0000000..1565e77 --- /dev/null +++ b/afb-client/bower_components/jszip/docs/APPNOTE.TXT @@ -0,0 +1,3217 @@ +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. + + + + |