diff options
| -rw-r--r-- | src/hello.zip | bin | 179 -> 330 bytes | |||
| -rw-r--r-- | src/main.zig | 400 | ||||
| -rw-r--r-- | src/spec.txt | 3798 |
3 files changed, 4032 insertions, 166 deletions
diff --git a/src/hello.zip b/src/hello.zip Binary files differindex d17d176..dc166b5 100644 --- a/src/hello.zip +++ b/src/hello.zip diff --git a/src/main.zig b/src/main.zig index ed52f53..653003b 100644 --- a/src/main.zig +++ b/src/main.zig @@ -1,9 +1,59 @@ const std = @import("std"); -const testing = std.testing; -// https://pkware.cachefly.net/webdocs/APPNOTE/APPNOTE-6.3.10.TXT +// ZIP file implementation +// See spec.txt. const ZipFile = struct { + allocator: std.mem.Allocator, + is_zip_64: bool = false, + end_of_central_directory_record: EndOfCentralDirectoryRecord, + central_directory_headers: []CentralDirectoryHeader, + fn from(allocator: std.mem.Allocator, file_or_stream: anytype) !ZipFile { + // Find the EndOfCentralDirectoryRecord. It must be in the last 64k of the file + const eocdr_search_width_max: usize = 64_000; + const epos = try file_or_stream.getEndPos(); + const eocdr_search_width: usize = @min(epos, eocdr_search_width_max); + const eocdr_seek_start: usize = epos - eocdr_search_width; + try file_or_stream.seekTo(eocdr_seek_start); + var reader = file_or_stream.reader(); + const needle = @byteSwap(EndOfCentralDirectoryRecord.SIG); + var window: u32 = try reader.readIntLittle(u32); + while (true) { + if (window == needle) { + try file_or_stream.seekBy(-4); + break; + } + const nb = try reader.readByte(); + window <<= 8; + window |= nb; + } else { + return error.EndOfCentralDirectoryRecordNotFound; + } + const eocdr = try EndOfCentralDirectoryRecord.read(allocator, file_or_stream); + errdefer eocdr.deinit(); + if (eocdr.disk_number_this != 0 or eocdr.disk_number_central_dir_start != 0) return error.SpansNotSupported; + if (eocdr.total_central_dir_entries != eocdr.total_central_dir_entries_on_this_disk) return error.SpansNotSupported; + + var central_directory_headers = try allocator.alloc(CentralDirectoryHeader, eocdr.total_central_dir_entries); + errdefer allocator.free(central_directory_headers); + try file_or_stream.seekTo(eocdr.central_dir_offset); + for (0..eocdr.total_central_dir_entries) |i| { + central_directory_headers[i] = try CentralDirectoryHeader.read(allocator, file_or_stream); + } + + return ZipFile{ + .allocator = allocator, + .end_of_central_directory_record = eocdr, + .central_directory_headers = central_directory_headers, + }; + } + fn deinit(self: *ZipFile) void { + self.end_of_central_directory_record.deinit(); + for (0..self.central_directory_headers.len) |i| { + self.central_directory_headers[i].deinit(); + } + self.allocator.free(self.central_directory_headers); + } // [local file header 1] // [encryption header 1] // [file data 1] @@ -27,201 +77,219 @@ const ZipFile = struct { // [end of central directory record] }; -const LocalFileHeader = packed struct { - const GPBF = packed struct(u16) { - encrypted: bool = false, - }; - const SIG: u32 = 0x04034b50; - sig: u32 = SIG, - // version needed to extract 2 bytes - general_purpose_bit_flag: GPBF, - // 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) -}; +// const LocalFileHeader = struct { +// const GPBF = packed struct(u16) { +// encrypted: bool = false, +// }; +// const SIG: [4]u8 = @bitCast(@as(u32, 0x04034b50)); +// sig: [4]u8 = SIG, +// // version needed to extract 2 bytes +// general_purpose_bit_flag: GPBF, +// // 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) +// }; -const DataDescriptor = struct { - const SIG: u32 = 0x08074b50; - sig: u32 = SIG, - // crc-32 4 bytes - // compressed size 4 bytes - // uncompressed size 4 bytes -}; +// const DataDescriptor = struct { +// const SIG: [4]u8 = @bitCast(@as(u32, 0x08074b50)); +// sig: [4]u8 = SIG, +// // crc-32 4 bytes +// // compressed size 4 bytes +// // uncompressed size 4 bytes +// }; -const ArchiveExtraDataRecord = struct { - const SIG: u32 = 0x08064b50; - sig: u32 = SIG, - // extra field length 4 bytes - // extra field data (variable size) +// const ArchiveExtraDataRecord = struct { +// const SIG: [4]u8 = @bitCast(@as(u32, 0x08064b50)); +// sig: [4]u8 = SIG, +// // extra field length 4 bytes +// // extra field data (variable size) -}; +// }; -const CentralDirectoryHeader = packed struct { - const SIG: u32 = 0x02014b50; - // central file header signature 4 bytes () - sig: u32 = SIG, - // version made by 2 bytes +const CentralDirectoryHeader = struct { + const SIG: u32 = @as(u32, 0x02014b50); + allocator: std.mem.Allocator, version_made_by: u16, - // version needed to extract 2 bytes version_needed_to_extract: u16, - // general purpose bit flag 2 bytes general_purpose_bit_flag: u16, - // compression method 2 bytes compression_method: u16, - // last mod file time 2 bytes last_mod_file_time: u16, - // last mod file date 2 bytes last_mod_file_date: u16, - // crc-32 4 bytes crc32: u32, - // compressed size 4 bytes compressed_size: u32, - // uncompressed size 4 bytes uncompressed_size: u32, - // file name length 2 bytes file_name_length: u16, - // extra field length 2 bytes extra_field_length: u16, - // file comment length 2 bytes file_comment_length: u16, - // disk number start 2 bytes disk_number_start: u16, - // internal file attributes 2 bytes internal_file_attributes: u16, - // external file attributes 4 bytes external_file_attributes: u32, - // relative offset of local header 4 bytes - relative_offset_of_local_header: u16, + relative_offset_of_local_header: u32, + file_name: []const u8, + extra_field: []const u8, + file_comment: []const u8, - // file name (variable size) - // extra field (variable size) - // file comment (variable size) -}; + fn read(allocator: std.mem.Allocator, stream_or_file: anytype) !CentralDirectoryHeader { + var reader = stream_or_file.reader(); + const sig = try reader.readIntLittle(u32); + if (sig != CentralDirectoryHeader.SIG) { + std.log.err("invalid signature expected {x} got {x}", .{CentralDirectoryHeader.SIG, sig}); + return error.InvalidSignature; + } + const version_made_by = try reader.readIntLittle(u16); + const version_needed_to_extract = try reader.readIntLittle(u16); + const general_purpose_bit_flag = try reader.readIntLittle(u16); + const compression_method = try reader.readIntLittle(u16); + const last_mod_file_time = try reader.readIntLittle(u16); + const last_mod_file_date = try reader.readIntLittle(u16); + const crc32 = try reader.readIntLittle(u32); + const compressed_size = try reader.readIntLittle(u32); + const uncompressed_size = try reader.readIntLittle(u32); + const file_name_length = try reader.readIntLittle(u16); + const extra_field_length = try reader.readIntLittle(u16); + const file_comment_length = try reader.readIntLittle(u16); + const disk_number_start = try reader.readIntLittle(u16); + const internal_file_attributes = try reader.readIntLittle(u16); + const external_file_attributes = try reader.readIntLittle(u32); + const relative_offset_of_local_header = try reader.readIntLittle(u32); + const file_name = try allocator.alloc(u8, file_name_length); + errdefer allocator.free(file_name); + _ = try reader.readAll(file_name); + const extra_field = try allocator.alloc(u8, extra_field_length); + errdefer allocator.free(extra_field); + _ = try reader.readAll(extra_field); -const DigitalSignature = struct { - const SIG: u32 = 0x05054b50; - sig: u32 = SIG, - // size of data 2 bytes - // signature data (variable size) + const file_comment = try allocator.alloc(u8, file_comment_length); + errdefer allocator.free(file_comment); + _ = try reader.readAll(file_comment); + return CentralDirectoryHeader{ + .allocator = allocator, + .version_made_by = version_made_by, + .version_needed_to_extract = version_needed_to_extract, + .general_purpose_bit_flag = general_purpose_bit_flag, + .compression_method = compression_method, + .last_mod_file_time = last_mod_file_time, + .last_mod_file_date = last_mod_file_date, + .crc32 = crc32, + .compressed_size = compressed_size, + .uncompressed_size = uncompressed_size, + .file_name_length = file_name_length, + .extra_field_length = extra_field_length, + .file_comment_length = file_comment_length, + .disk_number_start = disk_number_start, + .internal_file_attributes = internal_file_attributes, + .external_file_attributes = external_file_attributes, + .relative_offset_of_local_header = relative_offset_of_local_header, + .file_name = file_name, + .extra_field = extra_field, + .file_comment = file_comment, + }; + } + fn deinit(self: *CentralDirectoryHeader) void { + self.allocator.free(self.file_name); + self.allocator.free(self.extra_field); + self.allocator.free(self.file_comment); + } }; -const Zip64EndOfCentralDirectoryRecord = struct { - const SIG: u32 = 0x06064b50; - sig: u32 = SIG, - // 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) -}; +// const DigitalSignature = struct { +// const SIG: [4]u8 = @bitCast(@as(u32, 0x05054b50)); +// sig: [4]u8 = SIG, +// // size of data 2 bytes +// // signature data (variable size) +// }; -const Zip64EndOfCentralDirectoryLocator = struct { - const SIG: u32 = 0x07064b50; - sig: u32 = SIG, - // 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 -}; +// const Zip64EndOfCentralDirectoryRecord = struct { +// const SIG: [4]u8 = @bitCast(@as(u32, 0x06064b50)); +// sig: [4]u8 = SIG, +// // 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) +// }; + +// const Zip64EndOfCentralDirectoryLocator = struct { +// const SIG: [4]u8 = @bitCast(@as(u32, 0x07064b50)); +// sig: [4]u8 = SIG, +// // 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 +// }; -const EndOfCentralDirectoryRecord = packed struct { - const SIG: u32 = 0x06054b50; - // // end of central dir signa SIG: u32 = 0x06054b50;ure 4 bytes (0x06054b50) - sig: u32 = SIG, // 504b0506 - // number of this disk 2 bytes - disk_number_this: u16, // 0000 - // number of the disk with the - // start of the central directory 2 bytes - disk_number_central_dir_start: u16, // 0000 - // total number of entries in the - // central directory on this disk 2 bytes - total_central_dir_entries_on_this_disk: u16, // 0100 - // total number of entries in - // the central directory 2 bytes - total_central_dir_entries: u16, // 0100 - // size of the central directory 4 bytes - size_of_central_dir: u32, // 4f000000 - // offset of start of central - // directory with respect to - // the starting disk number 4 bytes - central_dir_offset: u32, // 4e000000 - // .ZIP file comment length 2 bytes - comment_length: u16, // 0000 - // .ZIP file comment (variable size) - // comment: [*]u8, - - fn from(bytes: []const u8) !EndOfCentralDirectoryRecord { - var fbs = std.io.fixedBufferStream(bytes); - var rr = fbs.reader(); +const EndOfCentralDirectoryRecord = struct { + const SIG: u32 = @as(u32, 0x06054b50); + allocator: std.mem.Allocator, + disk_number_this: u16, + disk_number_central_dir_start: u16, + total_central_dir_entries_on_this_disk: u16, + total_central_dir_entries: u16, + size_of_central_dir: u32, + central_dir_offset: u32, + comment_length: u16, + comment: []const u8, + + fn read(allocator: std.mem.Allocator, file_or_stream: anytype) !EndOfCentralDirectoryRecord { + var reader = file_or_stream.reader(); + const sig = try reader.readIntLittle(u32); + if (sig != EndOfCentralDirectoryRecord.SIG) { + std.log.err("invalid signature expected {x} got {x}", .{EndOfCentralDirectoryRecord.SIG, sig}); + return error.InvalidSignature; + } + const disk_number_this = try reader.readIntLittle(u16); + const disk_number_central_dir_start = try reader.readIntLittle(u16); + const total_central_dir_entries_on_this_disk = try reader.readIntLittle(u16); + const total_central_dir_entries = try reader.readIntLittle(u16); + const size_of_central_dir = try reader.readIntLittle(u32); + const central_dir_offset = try reader.readIntLittle(u32); + const comment_length = try reader.readIntLittle(u16); + var comment = try allocator.alloc(u8, comment_length); + _ = try reader.readAll(comment); return EndOfCentralDirectoryRecord{ - .sig = try rr.readIntLittle(u32), - .disk_number_this = try rr.readIntLittle(u16), - .disk_number_central_dir_start = try rr.readIntLittle(u16), - .total_central_dir_entries_on_this_disk = try rr.readIntLittle(u16), - .total_central_dir_entries = try rr.readIntLittle(u16), - .size_of_central_dir = try rr.readIntLittle(u32), - .central_dir_offset = try rr.readIntLittle(u32), - .comment_length = try rr.readIntLittle(u16), - // .comment = rr.read() + .allocator = allocator, + .disk_number_this = disk_number_this, + .disk_number_central_dir_start = disk_number_central_dir_start, + .total_central_dir_entries_on_this_disk = total_central_dir_entries_on_this_disk, + .total_central_dir_entries = total_central_dir_entries, + .size_of_central_dir = size_of_central_dir, + .central_dir_offset = central_dir_offset, + .comment_length = comment_length, + .comment = comment, }; } + + fn deinit(self: *EndOfCentralDirectoryRecord) void { + self.allocator.free(self.comment); + } }; test "foo" { const test_zip = @embedFile("hello.zip"); var fbs = std.io.fixedBufferStream(test_zip); - - const eocdr_search_width_max: usize = 64_000; - var eocdr_search_buf: [eocdr_search_width_max]u8 = undefined; - - const epos = try fbs.getEndPos(); - const eocdr_search_width: usize = @min(epos, eocdr_search_width_max); - const eocdr_seek_start: usize = epos - eocdr_search_width; - - std.log.err("epos {}", .{epos}); - std.log.err("eocdr_search_width {}", .{eocdr_search_width}); - std.log.err("eocdr_seek_start {}", .{eocdr_seek_start}); - - try fbs.seekTo(eocdr_seek_start); - const eocdr_did_read = try fbs.read(&eocdr_search_buf); - std.log.err("eocdr_did_read {}", .{eocdr_did_read}); - const needle: [4]u8 = @bitCast(EndOfCentralDirectoryRecord.SIG); - const eocdr_start = std.mem.indexOf(u8, eocdr_search_buf[0..eocdr_search_width], &needle) orelse return error.NoEndOfCentralDirectoryRecord; - std.log.err("eocdr_start {}", .{eocdr_start}); - try fbs.seekTo(eocdr_start); - const eocdr_pos = try fbs.getPos(); - std.log.err("eocdr_pos {}", .{eocdr_pos}); - - // const eocdr = try fbs.reader().readStruct(EndOfCentralDirectoryRecord); - // _ = eocdr; - // _ = eocdr; - var rr = fbs.reader(); - const eocdrb = try rr.readAllAlloc(std.testing.allocator, 10_000_000); - defer std.testing.allocator.free(eocdrb); - const eocdr = try EndOfCentralDirectoryRecord.from(eocdrb); - _ = eocdr; - // const comment = try rr.readAllAlloc(std.testing.allocator, eocdr.comment_length); - // defer std.testing.allocator.free(comment); - std.log.err("eocdrb {} len {}", .{ std.fmt.fmtSliceHexLower(eocdrb), eocdrb.len }); - std.log.err("sz {}", .{@sizeOf(EndOfCentralDirectoryRecord)}); + var zf = try ZipFile.from(std.testing.allocator, &fbs); + defer zf.deinit(); + try std.testing.expectEqual(zf.central_directory_headers.len, 2); + try std.testing.expectEqualStrings(zf.central_directory_headers[0].file_name, "hello.txt"); + try std.testing.expectEqualStrings(zf.central_directory_headers[1].file_name, "foo.txt"); } diff --git a/src/spec.txt b/src/spec.txt new file mode 100644 index 0000000..efc0da9 --- /dev/null +++ b/src/spec.txt @@ -0,0 +1,3798 @@ +File: APPNOTE.TXT - .ZIP File Format Specification +Version: 6.3.10 +Status: FINAL - replaces version 6.3.9 +Revised: Nov 01, 2022 +Copyright (c) 1989 - 2014, 2018, 2019, 2020, 2022 PKWARE Inc., All Rights Reserved. + +1.0 Introduction +--------------- + +1.1 Purpose +----------- + + 1.1.1 This specification is intended to define a cross-platform, + interoperable file storage and transfer format. Since its + first publication in 1989, PKWARE, Inc. ("PKWARE") has remained + committed to ensuring the interoperability of the .ZIP file + format through periodic publication and maintenance of this + specification. We trust that all .ZIP compatible vendors and + application developers that use and benefit from this format + will share and support this commitment to interoperability. + +1.2 Scope +--------- + + 1.2.1 ZIP is one of the most widely used compressed file formats. It is + universally used to aggregate, compress, and encrypt files into a single + interoperable container. No specific use or application need is + defined by this format and no specific implementation guidance is + provided. This document provides details on the storage format for + creating ZIP files. Information is provided on the records and + fields that describe what a ZIP file is. + +1.3 Trademarks +-------------- + + 1.3.1 PKWARE, PKZIP, Smartcrypt, SecureZIP, and PKSFX are registered + trademarks of PKWARE, Inc. in the United States and elsewhere. + PKPatchMaker, Deflate64, and ZIP64 are trademarks of PKWARE, Inc. + Other marks referenced within this document appear for identification + purposes only and are the property of their respective owners. + + +1.4 Permitted Use +----------------- + + 1.4.1 This document, "APPNOTE.TXT - .ZIP File Format Specification" is the + exclusive property of PKWARE. Use of the information contained in this + document is permitted solely for the purpose of creating products, + programs and processes that read and write files in the ZIP format + subject to the terms and conditions herein. + + 1.4.2 Use of the content of this document within other publications is + permitted only through reference to this document. Any reproduction + or distribution of this document in whole or in part without prior + written permission from PKWARE is strictly prohibited. + + 1.4.3 Certain technological components provided in this document are the + patented proprietary technology of PKWARE and as such require a + separate, executed license agreement from PKWARE. Applicable + components are marked with the following, or similar, statement: + 'Refer to the section in this document entitled "Incorporating + PKWARE Proprietary Technology into Your Product" for more information'. + +1.5 Contacting PKWARE +--------------------- + + 1.5.1 If you have questions on this format, its use, or licensing, or if you + wish to report defects, request changes or additions, please contact: + + PKWARE, Inc. + 201 E. Pittsburgh Avenue, Suite 400 + Milwaukee, WI 53204 + +1-414-289-9788 + +1-414-289-9789 FAX + zipformat@pkware.com + + 1.5.2 Information about this format and a reference copy of this document + is publicly available at: + + http://www.pkware.com/appnote + +1.6 Disclaimer +-------------- + + 1.6.1 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. + +2.0 Revisions +-------------- + +2.1 Document Status +-------------------- + + 2.1.1 If the STATUS of this file is marked as DRAFT, the content + defines proposed revisions to this specification which may consist + of changes to the ZIP format itself, or that may consist of other + content changes to this document. Versions of this document and + the format in DRAFT form may be subject to modification prior to + publication STATUS of FINAL. DRAFT versions are published periodically + to provide notification to the ZIP community of pending changes and to + provide opportunity for review and comment. + + 2.1.2 Versions of this document having a STATUS of FINAL are + considered to be in the final form for that version of the document + and are not subject to further change until a new, higher version + numbered document is published. Newer versions of this format + specification are intended to remain interoperable with all prior + versions whenever technically possible. + +2.2 Change Log +-------------- + + Version Change Description Date + ------- ------------------ ---------- + 5.2 -Single Password Symmetric Encryption 07/16/2003 + 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 + + 6.3.3 -Formatting changes to support 09/01/2012 + easier referencing of this APPNOTE + from other documents and standards + + 6.3.4 -Address change 10/01/2014 + + 6.3.5 -Documented compression methods 16 11/31/2018 + and 99 (4.4.5, 4.6.1, 5.11, 5.17, + APPENDIX E) + + -Corrected several typographical + errors (2.1.2, 3.2, 4.1.1, 10.2) + + -Marked legacy algorithms as no + longer suitable for use (4.4.5.1) + + -Added clarity on MS DOS time format + (4.4.6) + + -Assign extrafield ID for Timestamps + (4.5.2) + + -Field code description correction (A.2) + + -More consistent use of MAY/SHOULD/MUST + + -Expanded 0x0065 record attribute codes (B.2) + + -Initial information on 0x0022 Extra Data + + 6.3.6 -Corrected typographical error 04/26/2019 + (4.4.1.3) + + 6.3.7 -Added Zstandard compression method ID + (4.4.5) + + -Corrected several reported typos + + -Marked intended use for general purpose bit 14 + + -Added Data Stream Alignment Extra Data info + (4.6.11) + + 6.3.8 -Resolved Zstandard compression method ID conflict + (4.4.5) + + -Added additional compression method ID values in use + + 6.3.9 -Corrected a typo in Data Stream Alignment description + (4.6.11) + + 6.3.10 -Added several z/OS attribute values for APPENDIX B + + -Added several additional 3rd party Extra Field mappings + (thanks to Armijn Hemel @tjaldur.nl for forwarding info + on several of the Header ID's) + + + +3.0 Notations +------------- + + 3.1 Use of the term MUST or SHALL indicates a required element. + + 3.2 MUST NOT or SHALL NOT indicates an element is prohibited from use. + + 3.3 SHOULD indicates a RECOMMENDED element. + + 3.4 SHOULD NOT indicates an element NOT RECOMMENDED for use. + + 3.5 MAY indicates an OPTIONAL element. + + +4.0 ZIP Files +------------- + +4.1 What is a ZIP file +---------------------- + + 4.1.1 ZIP files MAY be identified by the standard .ZIP file extension + although use of a file extension is not required. Use of the + extension .ZIPX is also recognized and MAY be used for ZIP files. + Other common file extensions using the ZIP format include .JAR, .WAR, + .DOCX, .XLSX, .PPTX, .ODT, .ODS, .ODP and others. Programs reading or + writing ZIP files SHOULD rely on internal record signatures described + in this document to identify files in this format. + + 4.1.2 ZIP files SHOULD contain at least one file and MAY contain + multiple files. + + 4.1.3 Data compression MAY be used to reduce the size of files + placed into a ZIP file, but is not required. This format supports the + use of multiple data compression algorithms. When compression is used, + one of the documented compression algorithms MUST be used. Implementors + are advised to experiment with their data to determine which of the + available algorithms provides the best compression for their needs. + Compression method 8 (Deflate) is the method used by default by most + ZIP compatible application programs. + + + 4.1.4 Data encryption MAY be used to protect files within a ZIP file. + Keying methods supported for encryption within this format include + passwords and public/private keys. Either MAY be used individually + or in combination. Encryption MAY be applied to individual files. + Additional security MAY be used through the encryption of ZIP file + metadata stored within the Central Directory. See the section on the + Strong Encryption Specification for information. Refer to the section + in this document entitled "Incorporating PKWARE Proprietary Technology + into Your Product" for more information. + + 4.1.5 Data integrity MUST be provided for each file using CRC32. + + 4.1.6 Additional data integrity MAY be included through the use of + digital signatures. Individual files MAY be signed with one or more + digital signatures. The Central Directory, if signed, MUST use a + single signature. + + 4.1.7 Files MAY be placed within a ZIP file uncompressed or stored. + The term "stored" as used in the context of this document means the file + is copied into the ZIP file uncompressed. + + 4.1.8 Each data file placed into a ZIP file MAY be compressed, stored, + encrypted or digitally signed independent of how other data files in the + same ZIP file are archived. + + 4.1.9 ZIP files MAY be streamed, split into segments (on fixed or on + removable media) or "self-extracting". Self-extracting ZIP + files MUST include extraction code for a target platform within + the ZIP file. + + 4.1.10 Extensibility is provided for platform or application specific + needs through extra data fields that MAY be defined for custom + purposes. Extra data definitions MUST NOT conflict with existing + documented record definitions. + + 4.1.11 Common uses for ZIP MAY also include the use of manifest files. + Manifest files store application specific information within a file stored + within the ZIP file. This manifest file SHOULD be the first file in the + ZIP file. This specification does not provide any information or guidance on + the use of manifest files within ZIP files. Refer to the application developer + for information on using manifest files and for any additional profile + information on using ZIP within an application. + + 4.1.12 ZIP files MAY be placed within other ZIP files. + +4.2 ZIP Metadata +---------------- + + 4.2.1 ZIP files are identified by metadata consisting of defined record types + containing the storage information necessary for maintaining the files + placed into a ZIP file. Each record type MUST be identified using a header + signature that identifies the record type. Signature values begin with the + two byte constant marker of 0x4b50, representing the characters "PK". + + +4.3 General Format of a .ZIP file +--------------------------------- + + 4.3.1 A ZIP file MUST contain an "end of central directory record". A ZIP + file containing only an "end of central directory record" is considered an + empty ZIP file. Files MAY be added or replaced within a ZIP file, or deleted. + A ZIP file MUST have only one "end of central directory record". Other + records defined in this specification MAY be used as needed to support + storage requirements for individual ZIP files. + + 4.3.2 Each file placed into a ZIP file MUST be preceded by a "local + file header" record for that file. Each "local file header" MUST be + accompanied by a corresponding "central directory header" record within + the central directory section of the ZIP file. + + 4.3.3 Files MAY be stored in arbitrary order within a ZIP file. A ZIP + file MAY span multiple volumes or it MAY be split into user-defined + segment sizes. All values MUST be stored in little-endian byte order unless + otherwise specified in this document for a specific data element. + + 4.3.4 Compression MUST NOT be applied to a "local file header", an "encryption + header", or an "end of central directory record". Individual "central + directory records" MUST NOT be compressed, but the aggregate of all central + directory records MAY be compressed. + + 4.3.5 File data MAY be followed by a "data descriptor" for the file. Data + descriptors are used to facilitate ZIP file streaming. + + + 4.3.6 Overall .ZIP file format: + + [local file header 1] + [encryption header 1] + [file data 1] + [data descriptor 1] + . + . + . + [local file header n] + [encryption header n] + [file data n] + [data descriptor n] + [archive decryption header] + [archive extra data record] + [central directory header 1] + . + . + . + [central directory header n] + [zip64 end of central directory record] + [zip64 end of central directory locator] + [end of central directory record] + + + 4.3.7 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) + + 4.3.8 File data + + Immediately following the local header for a file + SHOULD be placed the compressed or stored data for the file. + If the file is encrypted, the encryption header for the file + SHOULD be placed after the local header and before the file + data. The series of [local file header][encryption header] + [file data][data descriptor] repeats for each file in the + .ZIP archive. + + Zero-byte files, directories, and other file types that + contain no content MUST NOT include file data. + + 4.3.9 Data descriptor: + + crc-32 4 bytes + compressed size 4 bytes + uncompressed size 4 bytes + + 4.3.9.1 This descriptor MUST exist 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 SHOULD be 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. + + 4.3.9.2 When compressing files, compressed and uncompressed sizes + SHOULD be stored in ZIP64 format (as 8 byte values) when a + file's 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. + + 4.3.9.3 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. + + 4.3.9.4 When writing ZIP files, implementors SHOULD 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. + + 4.3.9.5 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. + + 4.3.9.6 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 MUST be set to binary zeros. See the section on the Strong + Encryption Specification for information. Refer to the section in + this document entitled "Incorporating PKWARE Proprietary Technology + into Your Product" for more information. + + + 4.3.10 Archive decryption header: + + 4.3.10.1 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 MUST precede the encrypted data segment. + + 4.3.10.2 The encrypted data segment SHALL 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. See the + section on the Strong Encryption Specification for information + on the fields used in the Archive Decryption Header record. + Refer to the section in this document entitled "Incorporating + PKWARE Proprietary Technology into Your Product" for more information. + + + 4.3.11 Archive extra data record: + + archive extra data signature 4 bytes (0x08064b50) + extra field length 4 bytes + extra field data (variable size) + + 4.3.11.1 The Archive Extra Data Record is introduced in version 6.2 + of the ZIP format specification. This record MAY be used 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 MUST immediately precede the central + directory data structure. + + 4.3.11.2 The size of this data record SHALL 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. Refer to the section in this document + entitled "Incorporating PKWARE Proprietary Technology into Your + Product" for more information. + + 4.3.12 Central directory structure: + + [central directory header 1] + . + . + . + [central directory 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) + + 4.3.13 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. + + 4.3.14 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) + + 4.3.14.1 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. + + 4.3.14.2 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. Refer to the section in this document entitled + "Incorporating PKWARE Proprietary Technology into Your Product" + for more information applicable to use of Version 2 of this + record. + + 4.3.14.3 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. + + 4.3.14.4 Multiple special purpose data blocks MAY be present. + 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. + + 4.3.15 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 + + 4.3.16 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) + +4.4 Explanation of fields +-------------------------- + + 4.4.1 General notes on fields + + 4.4.1.1 All fields unless otherwise noted are unsigned and stored + in Intel low-byte:high-byte, low-word:high-word order. + + 4.4.1.2 String fields are not null terminated, since the length + is given explicitly. + + 4.4.1.3 The entries in the central directory MAY NOT necessarily + be in the same order that files appear in the .ZIP file. + + 4.4.1.4 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. + + 4.4.1.5 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. + + 4.4.2 version made by (2 bytes) + + 4.4.2.1 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. + + 4.4.2.2 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 + + 4.4.2.3 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. + + 4.4.3 version needed to extract (2 bytes) + + 4.4.3.1 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 MUST 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. + + 4.4.3.2 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 + + 4.4.3.3 Notes on version needed to extract + + * 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 MUST 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 MUST 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 MUST also be set. + This field SHOULD be set appropriately to indicate whether + Version 1 or Version 2 format is in use. + + + 4.4.4 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 MUST + 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. See the section describing the Strong + Encryption Specification for details. Refer to the + section in this document entitled "Incorporating PKWARE + Proprietary Technology into Your Product" for more + information. + + 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: Set 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. Refer + to the section in this document entitled "Incorporating + PKWARE Proprietary Technology into Your Product" for + more information. + + Bit 14: Reserved by PKWARE for alternate streams. + + Bit 15: Reserved by PKWARE. + + 4.4.5 compression method: (2 bytes) + + 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 + 15 - Reserved by PKWARE + 16 - IBM z/OS CMPSC Compression + 17 - Reserved by PKWARE + 18 - File is compressed using IBM TERSE (new) + 19 - IBM LZ77 z Architecture + 20 - deprecated (use method 93 for zstd) + 93 - Zstandard (zstd) Compression + 94 - MP3 Compression + 95 - XZ Compression + 96 - JPEG variant + 97 - WavPack compressed data + 98 - PPMd version I, Rev 1 + 99 - AE-x encryption marker (see APPENDIX E) + + 4.4.5.1 Methods 1-6 are legacy algorithms and are no longer + recommended for use when compressing files. + + 4.4.6 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. MS-DOS time format is different + from more commonly used computer time formats such as + UTC. For example, MS-DOS uses year values relative to 1980 + and 2 second precision. + + 4.4.7 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. + + 4.4.8 compressed size: (4 bytes) + 4.4.9 uncompressed size: (4 bytes) + + The size of the file compressed (4.4.8) and uncompressed, + (4.4.9) 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. + + 4.4.10 file name length: (2 bytes) + 4.4.11 extra field length: (2 bytes) + 4.4.12 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. + + + 4.4.13 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. + + 4.4.14 internal file attributes: (2 bytes) + + Bits 1 and 2 are reserved for use by PKWARE. + + 4.4.14.1 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. + + 4.4.14.2 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. + + 4.4.15 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. + + 4.4.16 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. + + 4.4.17 file name: (Variable) + + 4.4.17.1 The name of the file, with optional relative path. + The path stored MUST NOT contain a drive or + device letter, or a leading slash. All slashes + MUST 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. + + 4.4.17.2 If using the Central Directory Encryption Feature 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. + Refer to the section in this document entitled "Incorporating PKWARE + Proprietary Technology into Your Product" for more information. + + + 4.4.18 file comment: (Variable) + + The comment for this file. + + 4.4.19 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. + + + 4.4.20 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. + + 4.4.21 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. + + 4.4.22 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. + + 4.4.23 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. + + 4.4.24 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. + + 4.4.25 .ZIP file comment length: (2 bytes) + + The length of the comment for this .ZIP file. + + 4.4.26 .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. + + 4.4.27 zip64 extensible data sector (variable size) + + (currently reserved for use by PKWARE) + + + 4.4.28 extra field: (Variable) + + This SHOULD be used for storage expansion. If additional + information needs to be stored within a ZIP file for special + application or platform needs, it SHOULD be stored here. + Programs supporting earlier versions of this specification can + then safely skip the file, and find the next file or header. + This field will be 0 length in version 1.0. + + Existing extra fields are defined in the section + Extensible data fields that follows. + +4.5 Extensible data fields +-------------------------- + + 4.5.1 In order to allow different programs and different types + of information to be stored in the 'extra' field in .ZIP + files, the following structure MUST be used for all + programs storing data in this field: + + header1+data1 + header2+data2 . . . + + Each header MUST 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 IDs of 0 thru 31 are reserved for use by PKWARE. + The remaining IDs can be used by third party vendors for + proprietary usage. + + 4.5.2 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 + 0x0020 Reserved for Timestamp record + 0x0021 Policy Decryption Key Record + 0x0022 Smartcrypt Key Provider Record + 0x0023 Smartcrypt Policy Key Data Record + 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) + + + 4.5.3 -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 MUST + 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. + + + 4.5.4 -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 its entirety within this + structure. There will only ever be one "block" of data in + VarFields[]. + + 4.5.5 -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 + + 4.5.6 -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 + + OpenVMS Extra Field Rules: + + 4.5.6.1. There will be one or more 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. + + 4.5.6.2. No word alignment or padding is performed. + + 4.5.6.3. A well-behaved PKZIP/OpenVMS program SHOULD NOT produce + more than one sub-block with the same TagX value. Also, there MUST + NOT be more than one "extra" block of type 0x000c in a particular + directory record. + + 4.5.7 -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. + + 4.5.8 -PATCH Descriptor Extra Field (0x000f): + + 4.5.8.1 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 + + 4.5.8.2 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 + + 4.5.8.2.1 Actions + + Action Value + ------ ----- + none 0 + add 1 + delete 2 + patch 3 + + 4.5.8.2.2 Reactions + + Reaction Value + -------- ----- + ask 0 + skip 1 + ignore 2 + fail 3 + + 4.5.8.3 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 or patching requires a license from PKWARE. + Refer to the section in this document entitled "Incorporating + PKWARE Proprietary Technology into Your Product" for more + information. + + 4.5.9 -PKCS#7 Store for X.509 Certificates (0x0014): + + This field MUST contain 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 + + + 4.5.10 -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 + + 4.5.11 -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 + + 4.5.12 -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) + + See the section describing the Strong Encryption Specification + for details. Refer to the section in this document entitled + "Incorporating PKWARE Proprietary Technology into Your Product" + for more information. + + 4.5.13 -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 + + + 4.5.14 -PKCS#7 Encryption Recipient Certificate List (0x0019): + + This field MAY contain 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 aid 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 be 0x0001 at this time + CStore (var) PKCS#7 data blob + + See the section describing the Strong Encryption Specification + for details. Refer to the section in this document entitled + "Incorporating PKWARE Proprietary Technology into Your Product" + for more information. + + 4.5.15 -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) + + + 4.5.16 -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) + + 4.5.17 -Policy Decryption Key Record Extra Field (0x0021): + + The following is the layout of the Policy Decryption Key "extra" block. + TData is a variable length, variable content field. It holds + information about encryptions and/or encryption key sources. + Contact PKWARE for information on current TData structures. + Information in this "extra" block may aternatively be placed + within comment fields. Refer to the section in this document + entitled "Incorporating PKWARE Proprietary Technology into Your + Product" for more information. + + Value Size Description + ----- ---- ----------- + 0x0021 2 bytes Tag for this "extra" block type + TSize 2 bytes Size for the following data block + TData TSize Data about the key + + 4.5.18 -Key Provider Record Extra Field (0x0022): + + The following is the layout of the Key Provider "extra" block. + TData is a variable length, variable content field. It holds + information about encryptions and/or encryption key sources. + Contact PKWARE for information on current TData structures. + Information in this "extra" block may aternatively be placed + within comment fields. Refer to the section in this document + entitled "Incorporating PKWARE Proprietary Technology into Your + Product" for more information. + + Value Size Description + ----- ---- ----------- + 0x0022 2 bytes Tag for this "extra" block type + TSize 2 bytes Size for the following data block + TData TSize Data about the key + + 4.5.19 -Policy Key Data Record Record Extra Field (0x0023): + + The following is the layout of the Policy Key Data "extra" block. + TData is a variable length, variable content field. It holds + information about encryptions and/or encryption key sources. + Contact PKWARE for information on current TData structures. + Information in this "extra" block may aternatively be placed + within comment fields. Refer to the section in this document + entitled "Incorporating PKWARE Proprietary Technology into Your + Product" for more information. + + Value Size Description + ----- ---- ----------- + 0x0023 2 bytes Tag for this "extra" block type + TSize 2 bytes Size for the following data block + TData TSize Data about the key + +4.6 Third Party Mappings +------------------------ + + 4.6.1 Third party mappings commonly used are: + + 0x07c8 Macintosh + 0x1986 Pixar USD header ID + 0x2605 ZipIt Macintosh + 0x2705 ZipIt Macintosh 1.3.5+ + 0x2805 ZipIt Macintosh 1.3.5+ + 0x334d Info-ZIP Macintosh + 0x4154 Tandem + 0x4341 Acorn/SparkFS + 0x4453 Windows NT security descriptor (binary ACL) + 0x4704 VM/CMS + 0x470f MVS + 0x4854 THEOS (old?) + 0x4b46 FWKCS MD5 (see below) + 0x4c41 OS/2 access control list (text ACL) + 0x4d49 Info-ZIP OpenVMS + 0x4d63 Macintosh Smartzip (??) + 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 + 0x6854 THEOS + 0x7075 Info-ZIP Unicode Path Extra Field + 0x7441 AtheOS/Syllable + 0x756e ASi UNIX + 0x7855 Info-ZIP UNIX (new) + 0x7875 Info-ZIP UNIX (newer UID/GID) + 0xa11e Data Stream Alignment (Apache Commons-Compress) + 0xa220 Microsoft Open Packaging Growth Hint + 0xcafe Java JAR file Extra Field Header ID + 0xd935 Android ZIP Alignment Extra Field + 0xe57a Korean ZIP code page info + 0xfd4a SMS/QDOS + 0x9901 AE-x encryption structure (see APPENDIX E) + 0x9902 unknown + + + 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. + + 4.6.2 Third-party Extra Fields MUST include a Header ID using + the format defined in the section of this document + titled Extensible Data Fields (section 4.5). + + 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. + + 4.6.3 In case two different programs appropriate the same + Header ID value, it is strongly recommended that each + program SHOULD 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. + + Third-party Mappings: + Not all third-party extra field mappings are documented here. + + 4.6.4 -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 + + + 4.6.5 -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 + + + 4.6.6 -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; + + + 4.6.7 -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." + + + 4.6.8 -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. + + + 4.6.9 -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. + + + 4.6.10 -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 + + 4.6.11 -Data Stream Alignment (Apache Commons-Compress) (0xa11e): + + (per Zbynek Vyskovsky) Defines alignment of data stream of this + entry within the zip archive. Additionally, indicates whether the + compression method should be kept when re-compressing the zip file. + + The purpose of this extra field is to align specific resources to + word or page boundaries so they can be easily mapped into memory. + + Value Size Description + ----- ---- ----------- + 0xa11e Short tag for this extra block type + TSize Short total data size for this block (2+padding) + alignment Short required alignment and indicator + 0x00 Variable padding + + The alignment field (lower 15 bits) defines the minimal alignment + required by the data stream. Bit 15 of alignment field indicates + whether the compression method of this entry can be changed when + recompressing the zip file. The value 0 means the compression method + should not be changed. The value 1 indicates the compression method + may be changed. The padding field contains padding to ensure the correct + alignment. It can be changed at any time when the offset or required + alignment changes. (see https://issues.apache.org/jira/browse/COMPRESS-391) + + +4.7 Manifest Files +------------------ + + 4.7.1 Applications using ZIP files MAY have a need for additional + information that MUST be included with the files placed into + a ZIP file. Application specific information that cannot be + stored using the defined ZIP storage records SHOULD be stored + using the extensible Extra Field convention defined in this + document. However, some applications MAY use a manifest + file as a means for storing additional information. One + example is the META-INF/MANIFEST.MF file used in ZIP formatted + files having the .JAR extension (JAR files). + + 4.7.2 A manifest file is a file created for the application process + that requires this information. A manifest file MAY be of any + file type required by the defining application process. It is + placed within the same ZIP file as files to which this information + applies. By convention, this file is typically the first file placed + into the ZIP file and it MAY include a defined directory path. + + 4.7.3 Manifest files MAY be compressed or encrypted as needed for + application processing of the files inside the ZIP files. + + Manifest files are outside of the scope of this specification. + + +5.0 Explanation of compression methods +-------------------------------------- + + +5.1 UnShrinking - Method 1 +-------------------------- + + 5.1.1 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: + + 5.1.2 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. + + 5.1.3 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. + +5.2 Expanding - Methods 2-5 +--------------------------- + + 5.2.1 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. + + 5.2.2 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. + + 5.2.3 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. + + 5.2.4 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. + + 5.2.5 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. + +5.3 Imploding - Method 6 +------------------------ + + 5.3.1 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. + + 5.3.2 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. + + 5.3.3 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. + + 5.3.4 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. + + 5.3.5 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. + + 5.3.6 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. + + 5.3.7 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) + + 5.3.8 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. + + 5.3.9 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 + +5.4 Tokenizing - Method 7 +------------------------- + + 5.4.1 This method is not used by PKZIP. + +5.5 Deflating - Method 8 +------------------------ + + 5.5.1 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. + + 5.5.2 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. + + 5.5.3 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 + + 5.5.4 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 + +5.6 Enhanced Deflating - Method 9 +--------------------------------- + + 5.6.1 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. + +5.7 BZIP2 - Method 12 +--------------------- + + 5.7.1 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. + +5.8 LZMA - Method 14 +--------------------- + + 5.8.1 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: + + 5.8.2 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. + + 5.8.3 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. + + 5.8.4 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] + + 5.8.5 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] + + 5.8.6 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. + + 5.8.7 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. + + 5.8.8 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" + + 5.8.8.1 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. + + 5.8.8.2 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 arising in the future due + to changes in this compression algorithm. + + 5.8.8.3 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. + + 5.8.8.4 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 4.3 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. + + 5.8.9 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 MUSY be set. If + general purpose bit 1 is not set, the EOS marker is not present. + +5.9 WavPack - Method 97 +----------------------- + + 5.9.1 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. + + 5.9.2 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. + + 5.9.3 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. + +5.10 PPMd - Method 98 +--------------------- + + 5.10.1 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. + + 5.10.2 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: + + 5.10.3 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 + + 5.10.4 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) + + +5.11 AE-x Encryption marker - Method 99 +------------------------------------------- + +5.12 JPEG variant - Method 96 +------------------------------------------- + +5.13 PKWARE Data Compression Library Imploding - Method 10 +----------------------------------------------------------- + +5.14 Reserved - Method 11 +------------------------------------------- + +5.15 Reserved - Method 13 +------------------------------------------- + +5.16 Reserved - Method 15 +------------------------------------------- + +5.17 IBM z/OS CMPSC Compression - Method 16 +------------------------------------------- + +Method 16 utilizes the IBM hardware compression facility available +on most IBM mainframes. Hardware compression can significantly +increase the speed of data compression. This method uses a variant +of the LZ78 algorithm. CMPSC hardware compression is performed +using the COMPRESSION CALL instruction. + +ZIP archives can be created using this method only on mainframes +supporting the CP instruction. Extraction MAY occur on any +platform supporting this compression algorithm. Use of this +algorithm requires creation of a compression dictionary and +an expansion dictionary. The expansion dictionary MUST be +placed into the ZIP archive for use on the system where +extraction will occur. + +Additional information on this compression algorithm and dictionaries +can be found in the IBM provided document titled IBM ESA/390 Data +Compression (SA22-7208-01). Storage requirements for using CMPSC +compression are as follows. + +The format for the compressed data stream placed into the ZIP +archive following the Local Header is: + + [dictionary header] + [expansion dictionary] + [CMPSC compressed data] + +If encryption is used to encrypt a file compressed with CMPSC, these +sections MUST be encrypted as a single entity. + +The format of the dictionary header is: + + Value Size Description + ----- ---- ----------- + Version 1 byte 1 + Flags/Symsize 1 byte Processing flags and + symbol size + DictionaryLen 4 bytes Length of the + expansion dictionary + +Explanation of processing flags and symbol size: + +The high 4 bits are used to store the processing flags. The low +4 bits represent the size of a symbol, in bits (values range +from 9-13). Flag values are defined below. + + 0x80 - expansion dictionary + 0x40 - expansion dictionary is compressed using Deflate + 0x20 - Reserved + 0x10 - Reserved + + +5.18 Reserved - Method 17 +------------------------------------------- + +5.19 IBM TERSE - Method 18 +------------------------------------------- + +5.20 IBM LZ77 z Architecture - Method 19 +----------------------------------------- + +6.0 Traditional PKWARE Encryption +---------------------------------- + + 6.0.1 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. + +6.1 Traditional PKWARE Decryption +--------------------------------- + + 6.1.1 PKWARE is grateful to Mr. Roger Schlafly for his expert + contribution towards the development of PKWARE's traditional + encryption. + + 6.1.2 PKZIP encrypts the compressed data stream. Encrypted files + MUST be decrypted before they can be extracted to their original + form. + + 6.1.3 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. + + 6.1.4 The following are 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. + + 6.1.5 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. + + 6.1.6 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. + + 6.1.7 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 + + +7.0 Strong Encryption Specification +----------------------------------- + + 7.0.1 Portions of the Strong Encryption technology defined in this + specification are covered under patents and pending patent applications. + Refer to the section in this document entitled "Incorporating + PKWARE Proprietary Technology into Your Product" for more information. + +7.1 Strong Encryption Overview +------------------------------ + + 7.1.1 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. + + 7.1.2 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. + + 7.1.3 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. + + 7.1.4 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 + + + 7.1.5 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. + + 7.1.6 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 file's name, its original + size, timestamp and CRC32 value. + + 7.1.7 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. + + 7.1.8 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. + + 7.1.9 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. + + 7.1.10 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. + + 7.1.11 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. + + 7.1.12 Encryption provides data confidentiality and privacy. It is + recommended that you combine X.509 digital signing with encryption + to add authentication and non-repudiation. + + +7.2 Single Password Symmetric Encryption Method +----------------------------------------------- + + 7.2.1 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: + + 7.2.2 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. + + + 7.2.3 Extra Field 0x0017 in central header only. + + Fields to consider in this record are: + + 7.2.3.1 Format - the data format identifier for this record. The only + value allowed at this time is the integer value 2. + + 7.2.3.2 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 + + 7.2.3.3 Bitlen - Explicit bit length of key + + 32 - 448 bits + + 7.2.3.4 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 + + + 7.2.4 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 + + 7.2.4.1 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). + + 7.2.4.2 Format - the data format identifier for this record. The only + value allowed at this time is the integer value 3. + + 7.2.4.3 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 + + 7.2.4.4 Bitlen - Explicit bit length of key + + 32 - 448 bits + + 7.2.4.5 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 + + 7.2.4.6 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. + + + 7.2.4.7 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. + + 7.2.4.8 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. + + 7.2.4.9 VSize - This size value will always include the 4 bytes of the + VCRC32 data and will be greater than 4 bytes. + + 7.2.4.10 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. + + + 7.2.5 Useful Tips + + 7.2.5.1 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 IDs 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. + + 7.2.5.2 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 + + 7.2.5.3 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. + + + 7.3 Single Password - Central Directory Encryption + -------------------------------------------------- + + 7.3.1 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. + + 7.3.2 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 NOT 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. + + 7.3.3 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. + + 7.3.4 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 + + 7.3.5 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. + + 7.3.6 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. + + 7.3.7 Decrypting and decompressing the Central Directory is accomplished + in the same manner as decrypting and decompressing a file. + + 7.4 Certificate Processing Method + --------------------------------- + + The Certificate Processing Method for ZIP file encryption + defines the following additional data fields: + + 7.4.1 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 + + + 7.4.2 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. + + + 7.4.3 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. + + + 7.4.4 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. + +7.5 Certificate Processing - Central Directory Encryption +--------------------------------------------------------- + + 7.5.1 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. + + 7.5.2 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. + + 7.5.3 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. + +7.6 Certificate Processing Differences +-------------------------------------- + + 7.6.1 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. + + 7.6.2 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. + +7.7 OAEP Processing with Certificate-based Encryption +----------------------------------------------------- + + 7.7.1 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. + + 7.7.2 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. + + 7.7.3 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. + +7.8 Additional Encryption/Decryption Data Records +----------------------------------------------------- + + 7.8.1 Additional information MAY be stored within a ZIP file in support + of the strong password and certificate encryption methods defined above. + These include, but are not limited to the following record types. + + 0x0021 Policy Decryption Key Record + 0x0022 Smartcrypt Key Provider Record + 0x0023 Smartcrypt Policy Key Data Record + +8.0 Splitting and Spanning ZIP files +------------------------------------- + + 8.1 Spanned ZIP files + + 8.1.1 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. + + 8.2 Split ZIP files + + 8.2.1 File splitting is a newer derivation 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. + + 8.3 File Naming Differences + + 8.3.1 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. + + 8.3.2 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. + + 8.3.3 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 + + 8.3.4 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. + + 8.4 Spanned Self-extracting ZIP Files + + 8.4.1 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. + + 8.5 Capacities and Markers + + 8.5.1 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 + + 8.5.2 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 NOT 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. + + 8.5.3 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. + + 8.5.4 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. + + 8.5.5 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. + +9.0 Change Process +------------------ + + 9.1 In order for the .ZIP file format to remain a viable technology, 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. + + 9.2 If your application requires new definitions to the + extensible sections in this format, or if you would like to + submit new data structures or new capabilities, 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. + + 9.3 Periodic revisions to this specification will be published as + DRAFT or as FINAL status to ensure interoperability. We encourage + comments and feedback that MAY help improve clarity or content. + + +10.0 Incorporating PKWARE Proprietary Technology into Your Product +------------------------------------------------------------------ + + 10.1 The Use or Implementation in a product of APPNOTE technological + components pertaining to either strong encryption or patching requires + a separate, executed license agreement from PKWARE. Please contact + PKWARE at zipformat@pkware.com or +1-414-289-9788 with regard to + acquiring such a license. + + 10.2 Additional information regarding PKWARE proprietary technology is + available at http://www.pkware.com/appnote. + +11.0 Acknowledgements +--------------------- + + In addition to the above mentioned contributors to PKZIP and PKUNZIP, + PKWARE would like to extend special thanks to Robert Mahoney for + suggesting the extension .ZIP for this software. + +12.0 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 +-------------------------------------------------------------- + +A.1 Field Definition Structure: + + a. field length including length 2 bytes Big Endian + b. field code 2 bytes + c. data x bytes + +A.2 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 Time of last file status change 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 +------------------------------------------------------------ + +B.1 Field Definition Structure: + + a. field length including length 2 bytes Big Endian + b. field code 2 bytes + c. data x bytes + +B.2 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 + 0075 Native I/O Flags 2 bytes + 0081 Unix File Type 1 byte enumerated + 0082 Unix File Format 1 byte enumerated + 0083 Unix File Character Set Tag Info 4 bytes + 0090 ZIP Environmental Processing Info 4 bytes + 0091 EAV EATTR Flags 1 byte + 0092 DSNTYPE Flags 1 byte + 0093 Total Space Allocation (Cyls) 4 bytes Big Endian + 009D NONVSAM DSORG 2 bytes + 009E Program Virtual Object Info 3 bytes + 009F Encapsulated file Info 9 bytes + 00A2 Cluster Log 4 bytes Binary + 00A3 Cluster LSID Length 4 bytes Binary + 00A4 Cluster LSID 26 bytes EBCDIC + 400C Unix File Creation Time 4 bytes + 400D Unix File Access Time 4 bytes + 400E Unix File Modification time 4 bytes + 4101 IBMCMPSC Compression Info variable + 4102 IBMCMPSC Compression Size 8 bytes Big Endian + +APPENDIX C - Zip64 Extensible Data Sector Mappings +--------------------------------------------------- + + -Z390 Extra Field: + + The following is the general layout of the attributes for the + ZIP 64 "extra" block for extended tape operations. + + 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) +------------------------------------ + +D.1 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. + +D.2 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). + +D.3 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. + +D.4 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. + +D.5 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. + +D.6 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. + +D.7 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). + +D.8 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. + +APPENDIX E - AE-x encryption marker +----------------------------------- + +E.1 AE-x defines an alternate password-based encryption method used +in ZIP files that is based on a file encryption utility developed by +Dr. Brian Gladman. Information on Dr. Gladman's method is available at + + http://www.gladman.me.uk/cryptography_technology/fileencrypt/ + +E.2 AE-x uses AES with CTR (counter mode) and HMAC-SHA1. It defines +encryption using key sizes of 128 bits or 256 bits. It does not +restrict support for decrypting 192 bits. + +E.3 This method uses the standard ZIP encryption bit (bit 0) +of the general purpose bit flag (section 4.4.4) to indicate a +file is encrypted. + +E.4 The compression method field (section 4.4.5) is set to 99 +to indicate a file has been encrypted using this method. + +E.5 The actual compression method is stored in an extra field +structure identified by a Header ID of 0x9901. Information on this +record structure can be found at http://www.winzip.com/aes_info.htm. + +E.6 Two versions are defined for the 0x9901 structure. + + E.6.1 Version 1 stores the file CRC value in the CRC-32 field + (section 4.4.7). + + E.6.2 Version 2 stores a value of 0 in the CRC-32 field. + |