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Zip File Format

2024年03月17日

来源 # 从APPNOTE.TXT - .ZIP File Format Specification找来备份，以防需要时找不到。内容 # 内容有些长😄。很奇怪，排板总是有些问题。 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 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2604 2605 2606 2607 2608 2609 2610 2611 2612 2613 2614 2615 2616 2617 2618 2619 2620 2621 2622 2623 2624 2625 2626 2627 2628 File: APPNOTE.TXT - .ZIP File Format Specification Version: 6.2.0 - NOTIFICATION OF CHANGE Revised: 04/26/2004 Copyright (c) 1989 - 2004 PKWARE Inc., All Rights Reserved. I. Purpose ---------- This specification is intended to define a cross-platform, interoperable file format. Since its first publication in 1989, PKWARE has remained committed to ensuring the interoperability of the .ZIP file format through this specification. We trust that all .ZIP compatible vendors and application developers that have adopted this format will share and support this commitment. II. Disclaimer -------------- Although PKWARE will attempt to supply current and accurate information relating to its file formats, algorithms, and the subject programs, the possibility of error or omission can not be eliminated. PKWARE therefore expressly disclaims any warranty that the information contained in the associated materials relating to the subject programs and/or the format of the files created or accessed by the subject programs and/or the algorithms used by the subject programs, or any other matter, is current, correct or accurate as delivered. Any risk of damage due to any possible inaccurate information is assumed by the user of the information. Furthermore, the information relating to the subject programs and/or the file formats created or accessed by the subject programs and/or the algorithms used by the subject programs is subject to change without notice. If the version of this file is marked as a NOTIFICATION OF CHANGE, the content defines an Early Feature Specification (EFS) change to the .ZIP file format that may be subject to modification prior to publication of the Final Feature Specification (FFS). This document may also contain information on Planned Feature Specifications (PFS) defining recognized future extensions. III. Change Log --------------- Version Change Description Date ------- ------------------ ---------- 5.2 -Single Password Symmetric Encryption 07/16/2003 storage 6.1.0 -Smart Card 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 VI. General Format of a .ZIP file --------------------------------- Files stored in arbitrary order. Large .ZIP files can span multiple diskette media or be split into user-defined segment sizes. Overall .ZIP file format: [local file header 1] [file data 1] [data descriptor 1] . . . [local file header n] [file data n] [data descriptor n] [archive decryption header] (EFS) [archive extra data record] (EFS) [central directory] [zip64 end of central directory record] [zip64 end of central directory locator] [end of central directory record] A. Local file header: local file header signature 4 bytes (0x04034b50) version needed to extract 2 bytes general purpose bit flag 2 bytes compression method 2 bytes last mod file time 2 bytes last mod file date 2 bytes crc-32 4 bytes compressed size 4 bytes uncompressed size 4 bytes file name length 2 bytes extra field length 2 bytes file name (variable size) extra field (variable size) B. File data Immediately following the local header for a file is the compressed or stored data for the file. The series of [local file header][file data][data descriptor] repeats for each file in the .ZIP archive. C. Data descriptor: crc-32 4 bytes compressed size 4 bytes uncompressed size 4 bytes This descriptor exists only if bit 3 of the general purpose bit flag is set (see below). It is byte aligned and immediately follows the last byte of compressed data. This descriptor is used only when it was not possible to seek in the output .ZIP file, e.g., when the output .ZIP file was standard output or a non seekable device. For Zip64 format archives, the compressed and uncompressed sizes are 8 bytes each. D. Archive decryption header: (EFS) The Archive Decryption Header is introduced in version 6.2 of the ZIP format specification. This record exists in support of the Central Directory Encryption Feature implemented as part of the Strong Encryption Specification as described in this document. When the Central Directory Structure is encrypted, this decryption header will precede the encrypted data segment. The encrypted data segment will consist of the Archive extra data record (if present) and the encrypted Central Directory Structure data. The format of this data record is identical to the Decryption header record preceding compressed file data. If the central directory structure is encrypted, the location of the start of this data record is determined using the Start of Central Directory field in the Zip64 End of Central Directory record. Refer to the section on the Strong Encryption Specification for information on the fields used in the Archive Decryption Header record. E. Archive extra data record: (EFS) archive extra data signature 4 bytes (0x08064b50) extra field length 4 bytes extra field data (variable size) The Archive Extra Data Record is introduced in version 6.2 of the ZIP format specification. This record exists in support of the Central Directory Encryption Feature implemented as part of the Strong Encryption Specification as described in this document. When present, this record immediately precedes the central directory data structure. The size of this data record will be included in the Size of the Central Directory field in the End of Central Directory record. If the central directory structure is compressed, but not encrypted, the location of the start of this data record is determined using the Start of Central Directory field in the Zip64 End of Central Directory record. F. Central directory structure: [file header 1] . . . [file header n] [digital signature] File header: central file header signature 4 bytes (0x02014b50) version made by 2 bytes version needed to extract 2 bytes general purpose bit flag 2 bytes compression method 2 bytes last mod file time 2 bytes last mod file date 2 bytes crc-32 4 bytes compressed size 4 bytes uncompressed size 4 bytes file name length 2 bytes extra field length 2 bytes file comment length 2 bytes disk number start 2 bytes internal file attributes 2 bytes external file attributes 4 bytes relative offset of local header 4 bytes file name (variable size) extra field (variable size) file comment (variable size) Digital signature: header signature 4 bytes (0x05054b50) size of data 2 bytes signature data (variable size) With the introduction of the Central Directory Encryption feature in version 6.2 of this specification, the Central Directory Structure may be stored both compressed and encrypted. Although not required, it is assumed when encrypting the Central Directory Structure, that it will be compressed for greater storage efficiency. Information on the Central Directory Encryption feature can be found in the section describing the Strong Encryption Specification. The Digital Signature record will be neither compressed nor encrypted. G. Zip64 end of central directory record zip64 end of central dir signature 4 bytes (0x06064b50) size of zip64 end of central directory record 8 bytes version made by 2 bytes version needed to extract 2 bytes number of this disk 4 bytes number of the disk with the start of the central directory 4 bytes total number of entries in the central directory on this disk 8 bytes total number of entries in the central directory 8 bytes size of the central directory 8 bytes offset of start of central directory with respect to the starting disk number 8 bytes zip64 extensible data sector (variable size) The 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(tm) 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. H. Zip64 end of central directory locator zip64 end of central dir locator signature 4 bytes (0x07064b50) number of the disk with the start of the zip64 end of central directory 4 bytes relative offset of the zip64 end of central directory record 8 bytes total number of disks 4 bytes I. End of central directory record: end of central dir signature 4 bytes (0x06054b50) number of this disk 2 bytes number of the disk with the start of the central directory 2 bytes total number of entries in the central directory on this disk 2 bytes total number of entries in the central directory 2 bytes size of the central directory 4 bytes offset of start of central directory with respect to the starting disk number 4 bytes .ZIP file comment length 2 bytes .ZIP file comment (variable size) J. Explanation of fields: version made by (2 bytes) The upper byte indicates the compatibility of the file attribute information. If the external file attributes are compatible with MS-DOS and can be read by PKZIP for DOS version 2.04g then this value will be zero. If these attributes are not compatible, then this value will identify the host system on which the attributes are compatible. Software can use this information to determine the line record format for text files etc. The current mappings are: 0 - MS-DOS and OS/2 (FAT / VFAT / FAT32 file systems) 1 - Amiga 2 - OpenVMS 3 - Unix 4 - VM/CMS 5 - Atari ST 6 - OS/2 H.P.F.S. 7 - Macintosh 8 - Z-System 9 - CP/M 10 - Windows NTFS 11 - MVS (OS/390 - Z/OS) 12 - VSE 13 - Acorn Risc 14 - VFAT 15 - alternate MVS 16 - BeOS 17 - Tandem 18 - OS/400 19 - OS/X (Darwin) 20 thru 255 - unused The lower byte indicates the ZIP specification version (the version of this document) supported by the software used to encode the file. The value/10 indicates the major version number, and the value mod 10 is the minor version number. version needed to extract (2 bytes) The minimum supported ZIP specification version needed to extract the file, mapped as above. This value is based on the specific format features a ZIP program must support to be able to extract the file. If multiple features are applied to a file, the minimum version should be set to the feature having the highest value. New features or feature changes affecting the published format specification will be implemented using higher version numbers than the last published value to avoid conflict. Current minimum feature versions are as defined below: 1.0 - Default value 1.1 - File is a volume label 2.0 - File is a folder (directory) 2.0 - File is compressed using Deflate compression 2.0 - File is encrypted using traditional PKWARE encryption 2.1 - File is compressed using Deflate64(tm) 2.5 - File is compressed using PKWARE DCL Implode 2.7 - File is a patch data set 4.5 - File uses ZIP64 format extensions 4.6 - File is compressed using BZIP2 compression* 5.0 - File is encrypted using DES 5.0 - File is encrypted using 3DES 5.0 - File is encrypted using original RC2 encryption 5.0 - File is encrypted using RC4 encryption 5.1 - File is encrypted using AES encryption 5.1 - File is encrypted using corrected RC2 encryption** 5.2 - File is encrypted using corrected RC2-64 encryption** 6.1 - File is encrypted using non-OAEP key wrapping*** 6.2 - Central directory encryption * Early 7.x (pre-7.2) versions of PKZIP incorrectly set the version needed to extract for BZIP2 compression to be 50 when it should have been 46. ** Refer to the section on Strong Encryption Specification for additional information regarding RC2 corrections. *** Certificate encryption using non-OAEP key wrapping is the intended mode of operation for all versions beginning with 6.1. Support for OAEP key wrapping should only be used for backward compatibility when sending ZIP files to be opened by versions of PKZIP older than 6.1 (5.0 or 6.0). When using ZIP64 extensions, the corresponding value in the Zip64 end of central directory record should also be set. This field currently supports only the value 45 to indicate ZIP64 extensions are present. 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. Note: Bits 1 and 2 are undefined if the compression method is any other. Bit 3: If this bit is set, the fields crc-32, compressed size and uncompressed size are set to zero in the local header. The correct values are put in the data descriptor immediately following the compressed data. (Note: PKZIP version 2.04g for DOS only recognizes this bit for method 8 compression, newer versions of PKZIP recognize this bit for any compression method.) Bit 4: Reserved for use with method 8, for enhanced deflating. Bit 5: If this bit is set, this indicates that the file is compressed patched data. (Note: Requires PKZIP version 2.70 or greater) Bit 6: Strong encryption. If this bit is set, you should set the version needed to extract value to at least 50 and you must also set bit 0. If AES encryption is used, the version needed to extract value must be at least 51. Bit 7: Currently unused. Bit 8: Currently unused. Bit 9: Currently unused. Bit 10: Currently unused. Bit 11: Currently unused. Bit 12: Reserved by PKWARE for enhanced compression. Bit 13: Used when encrypting the Central Directory to indicate selected data values in the Local Header are masked to hide their actual values. See the section describing the Strong Encryption Specification for details. Bit 14: Reserved by PKWARE. Bit 15: Reserved by PKWARE. compression method: (2 bytes) (see accompanying documentation for algorithm descriptions) 0 - The file is stored (no compression) 1 - The file is Shrunk 2 - The file is Reduced with compression factor 1 3 - The file is Reduced with compression factor 2 4 - The file is Reduced with compression factor 3 5 - The file is Reduced with compression factor 4 6 - The file is Imploded 7 - Reserved for Tokenizing compression algorithm 8 - The file is Deflated 9 - Enhanced Deflating using Deflate64(tm) 10 - PKWARE Data Compression Library Imploding 11 - Reserved by PKWARE 12 - File is compressed using BZIP2 algorithm date and time fields: (2 bytes each) The date and time are encoded in standard MS-DOS format. If input came from standard input, the date and time are those at which compression was started for this data. If encrypting the central directory and general purpose bit flag 13 is set indicating masking, the value stored in the Local Header will be zero. CRC-32: (4 bytes) The CRC-32 algorithm was generously contributed by David Schwaderer and can be found in his excellent book "C Programmers Guide to NetBIOS" published by Howard W. Sams & Co. Inc. The 'magic number' for the CRC is 0xdebb20e3. The proper CRC pre and post conditioning is used, meaning that the CRC register is pre-conditioned with all ones (a starting value of 0xffffffff) and the value is post-conditioned by taking the one's complement of the CRC residual. If bit 3 of the general purpose flag is set, this field is set to zero in the local header and the correct value is put in the data descriptor and in the central directory. 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. compressed size: (4 bytes) uncompressed size: (4 bytes) The size of the file compressed and uncompressed, respectively. 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. If encrypting the central directory and general purpose bit flag 13 is set indicating masking, the value stored for the uncompressed size in the Local Header will be zero. file name length: (2 bytes) extra field length: (2 bytes) file comment length: (2 bytes) The length of the file name, extra field, and comment fields respectively. The combined length of any directory record and these three fields should not generally exceed 65,535 bytes. If input came from standard input, the file name length is set to zero. disk number start: (2 bytes) The number of the disk on which this file begins. If an archive is in zip64 format and the value in this field is 0xFFFF, the size will be in the corresponding 4 byte zip64 extended information extra field. internal file attributes: (2 bytes) Bits 1 and 2 are reserved for use by PKWARE. The lowest bit of this field indicates, if set, that the file is apparently an ASCII or text file. If not set, that the file apparently contains binary data. The remaining bits are unused in version 1.0. The 0x0002 bit of this field indicates, if set, that a 4 byte variable record length control field precedes each logical record indicating the length of the record. This flag is independent of text control characters, and if used in conjunction with text data, includes any control characters in the total length of the record. This value is provided for mainframe data transfer support. external file attributes: (4 bytes) The mapping of the external attributes is host-system dependent (see 'version made by'). For MS-DOS, the low order byte is the MS-DOS directory attribute byte. If input came from standard input, this field is set to zero. relative offset of local header: (4 bytes) This is the offset from the start of the first disk on which this file appears, to where the local header should be found. If an archive is in zip64 format and the value in this field is 0xFFFFFFFF, the size will be in the corresponding 8 byte zip64 extended information extra field. file name: (Variable) The name of the file, with optional relative path. The path stored should not contain a drive or device letter, or a leading slash. All slashes should be forward slashes '/' as opposed to backwards slashes '\' for compatibility with Amiga and Unix file systems etc. If input came from standard input, there is no file name field. If encrypting the central directory and general purpose bit flag 13 is set indicating masking, the file name stored in the Local Header will not be the actual file name. A masking value consisting of a unique hexadecimal value will be stored. This value will be sequentially incremented for each file in the archive. See the section on the Strong Encryption Specification for details on retrieving the encrypted file name. extra field: (Variable) This is for expansion. If additional information needs to be stored for special needs or for specific platforms, it should be stored here. Earlier versions of the software can then safely skip this file, and find the next file or header. This field will be 0 length in version 1.0. In order to allow different programs and different types of information to be stored in the 'extra' field in .ZIP files, the following structure should be used for all programs storing data in this field: header1+data1 + header2+data2 . . . Each header should consist of: Header ID - 2 bytes Data Size - 2 bytes Note: all fields stored in Intel low-byte/high-byte order. The Header ID field indicates the type of data that is in the following data block. Header ID's of 0 thru 31 are reserved for use by PKWARE. The remaining ID's can be used by third party vendors for proprietary usage. The current Header ID mappings defined by PKWARE are: 0x0001 ZIP64 extended information extra field 0x0007 AV Info 0x0008 Reserved for future Unicode file name data (PFS) 0x0009 OS/2 0x000a NTFS 0x000c OpenVMS 0x000d Unix 0x000e Reserved for file stream and fork descriptors 0x000f Patch Descriptor 0x0014 PKCS#7 Store for X.509 Certificates 0x0015 X.509 Certificate ID and Signature for individual file 0x0016 X.509 Certificate ID for Central Directory 0x0017 Strong Encryption Header 0x0018 Record Management Controls 0x0019 PKCS#7 Encryption Recipient Certificate List 0x0065 IBM S/390 (Z390), AS/400 (I400) attributes - uncompressed 0x0066 Reserved for IBM S/390 (Z390), AS/400 (I400) attributes - compressed Third party mappings commonly used are: 0x07c8 Macintosh 0x2605 ZipIt Macintosh 0x2705 ZipIt Macintosh 1.3.5+ 0x2805 ZipIt Macintosh 1.3.5+ 0x334d Info-ZIP Macintosh 0x4341 Acorn/SparkFS 0x4453 Windows NT security descriptor (binary ACL) 0x4704 VM/CMS 0x470f MVS 0x4b46 FWKCS MD5 (see below) 0x4c41 OS/2 access control list (text ACL) 0x4d49 Info-ZIP OpenVMS 0x4f4c Xceed original location extra field 0x5356 AOS/VS (ACL) 0x5455 extended timestamp 0x554e Xceed unicode extra field 0x5855 Info-ZIP Unix (original, also OS/2, NT, etc) 0x6542 BeOS/BeBox 0x756e ASi Unix 0x7855 Info-ZIP Unix (new) 0xfd4a SMS/QDOS Detailed descriptions of Extra Fields defined by third party mappings will be documented as information on these data structures is made available to PKWARE. PKWARE does not guarantee the accuracy of any published third party data. The Data Size field indicates the size of the following data block. Programs can use this value to skip to the next header block, passing over any data blocks that are not of interest. Note: As stated above, the size of the entire .ZIP file header, including the file name, comment, and extra field should not exceed 64K in size. In case two different programs should appropriate the same Header ID value, it is strongly recommended that each program place a unique signature of at least two bytes in size (and preferably 4 bytes or bigger) at the start of each data area. Every program should verify that its unique signature is present, in addition to the Header ID value being correct, before assuming that it is a block of known type. -ZIP64 Extended Information Extra Field (0x0001): The following is the layout of the ZIP64 extended information "extra" block. If one of the size or offset fields in the Local or Central directory record is too small to hold the required data, a ZIP64 extended information record is created. The order of the fields in the ZIP64 extended information record is fixed, but the fields will only appear if the corresponding Local or Central directory record field is set to 0xFFFF or 0xFFFFFFFF. Note: all fields stored in Intel low-byte/high-byte order. Value Size Description ----- ---- ----------- (ZIP64) 0x0001 2 bytes Tag for this "extra" block type Size 2 bytes Size of this "extra" block Original Size 8 bytes Original uncompressed file size Compressed Size 8 bytes Size of compressed data Relative Header Offset 8 bytes Offset of local header record Disk Start Number 4 bytes Number of the disk on which this file starts This entry in the Local header must include BOTH original and compressed file sizes. -OS/2 Extra Field (0x0009): The following is the layout of the OS/2 attributes "extra" block. (Last Revision 09/05/95) Note: all fields stored in Intel low-byte/high-byte order. Value Size Description ----- ---- ----------- (OS/2) 0x0009 2 bytes Tag for this "extra" block type TSize 2 bytes Size for the following data block BSize 4 bytes Uncompressed Block Size CType 2 bytes Compression type EACRC 4 bytes CRC value for uncompress block (var) variable Compressed block The OS/2 extended attribute structure (FEA2LIST) is compressed and then stored in it's entirety within this structure. There will only ever be one "block" of data in VarFields[]. -NTFS Extra Field (0x000a): The following is the layout of the NTFS attributes "extra" block. (Note: At this time the Mtime, Atime and Ctime values may be used on any WIN32 system.) Note: all fields stored in Intel low-byte/high-byte order. Value Size Description ----- ---- ----------- (NTFS) 0x000a 2 bytes Tag for this "extra" block type TSize 2 bytes Size of the total "extra" block Reserved 4 bytes Reserved for future use Tag1 2 bytes NTFS attribute tag value #1 Size1 2 bytes Size of attribute #1, in bytes (var.) Size1 Attribute #1 data . . . TagN 2 bytes NTFS attribute tag value #N SizeN 2 bytes Size of attribute #N, in bytes (var.) SizeN Attribute #N data For NTFS, values for Tag1 through TagN are as follows: (currently only one set of attributes is defined for NTFS) Tag Size Description ----- ---- ----------- 0x0001 2 bytes Tag for attribute #1 Size1 2 bytes Size of attribute #1, in bytes Mtime 8 bytes File last modification time Atime 8 bytes File last access time Ctime 8 bytes File creation time -OpenVMS Extra Field (0x000c): The following is the layout of the OpenVMS attributes "extra" block. Note: all fields stored in Intel low-byte/high-byte order. Value Size Description ----- ---- ----------- (VMS) 0x000c 2 bytes Tag for this "extra" block type TSize 2 bytes Size of the total "extra" block CRC 4 bytes 32-bit CRC for remainder of the block Tag1 2 bytes OpenVMS attribute tag value #1 Size1 2 bytes Size of attribute #1, in bytes (var.) Size1 Attribute #1 data . . . TagN 2 bytes OpenVMS attribute tage value #N SizeN 2 bytes Size of attribute #N, in bytes (var.) SizeN Attribute #N data Rules: 1. There will be one or more of attributes present, which will each be preceded by the above TagX & SizeX values. These values are identical to the ATR$C_XXXX and ATR$S_XXXX constants which are defined in ATR.H under OpenVMS C. Neither of these values will ever be zero. 2. No word alignment or padding is performed. 3. A well-behaved PKZIP/OpenVMS program should never produce more than one sub-block with the same TagX value. Also, there will never be more than one "extra" block of type 0x000c in a particular directory record. -UNIX Extra Field (0x000d): The following is the layout of the Unix "extra" block. Note: all fields are stored in Intel low-byte/high-byte order. Value Size Description ----- ---- ----------- (UNIX) 0x000d 2 bytes Tag for this "extra" block type TSize 2 bytes Size for the following data block Atime 4 bytes File last access time Mtime 4 bytes File last modification time Uid 2 bytes File user ID Gid 2 bytes File group ID (var) variable Variable length data field The variable length data field will contain file type specific data. Currently the only values allowed are the original "linked to" file names for hard or symbolic links, and the major and minor device node numbers for character and block device nodes. Since device nodes cannot be either symbolic or hard links, only one set of variable length data is stored. Link files will have the name of the original file stored. This name is NOT NULL terminated. Its size can be determined by checking TSize - 1. Device entries will have eight bytes stored as two 4 byte entries (in little endian format). The first entry will be the major device number, and the second the minor device number. -PATCH Descriptor Extra Field (0x000f): The following is the layout of the Patch Descriptor "extra" block. Note: all fields stored in Intel low-byte/high-byte order. Value Size Description ----- ---- ----------- (Patch) 0x000f 2 bytes Tag for this "extra" block type TSize 2 bytes Size of the total "extra" block Version 2 bytes Version of the descriptor Flags 4 bytes Actions and reactions (see below) OldSize 4 bytes Size of the file about to be patched OldCRC 4 bytes 32-bit CRC of the file to be patched NewSize 4 bytes Size of the resulting file NewCRC 4 bytes 32-bit CRC of the resulting file Actions and reactions Bits Description ---- ---------------- 0 Use for auto detection 1 Treat as a self-patch 2-3 RESERVED 4-5 Action (see below) 6-7 RESERVED 8-9 Reaction (see below) to absent file 10-11 Reaction (see below) to newer file 12-13 Reaction (see below) to unknown file 14-15 RESERVED 16-31 RESERVED Actions Action Value ------ ----- none 0 add 1 delete 2 patch 3 Reactions Reaction Value -------- ----- ask 0 skip 1 ignore 2 fail 3 Patch support is provided by PKPatchMaker(tm) technology and is covered under U.S. Patents and Patents Pending. -PKCS#7 Store for X.509 Certificates (0x0014): This field contains information about each of the certificates files may be signed with. When the Central Directory Encryption feature is enabled for a ZIP file, this record will appear in the Archive Extra Data Record, otherwise it will appear in the first central directory record and will be ignored in any other record. Note: all fields stored in Intel low-byte/high-byte order. Value Size Description ----- ---- ----------- (Store) 0x0014 2 bytes Tag for this "extra" block type TSize 2 bytes Size of the store data TData TSize Data about the store -X.509 Certificate ID and Signature for individual file (0x0015): This field contains the information about which certificate in the PKCS#7 store was used to sign a particular file. It also contains the signature data. This field can appear multiple times, but can only appear once per certificate. Note: all fields stored in Intel low-byte/high-byte order. Value Size Description ----- ---- ----------- (CID) 0x0015 2 bytes Tag for this "extra" block type TSize 2 bytes Size of data that follows TData TSize Signature Data -X.509 Certificate ID and Signature for central directory (0x0016): This field contains the information about which certificate in the PKCS#7 store was used to sign the central directory structure. When the Central Directory Encryption feature is enabled for a ZIP file, this record will appear in the Archive Extra Data Record, otherwise it will appear in the first central directory record. Note: all fields stored in Intel low-byte/high-byte order. Value Size Description ----- ---- ----------- (CDID) 0x0016 2 bytes Tag for this "extra" block type TSize 2 bytes Size of data that follows TData TSize Data -Strong Encryption Header (0x0017) (EFS): Value Size Description ----- ---- ----------- 0x0017 2 bytes Tag for this "extra" block type TSize 2 bytes Size of data that follows Format 2 bytes Format definition for this record AlgID 2 bytes Encryption algorithm identifier Bitlen 2 bytes Bit length of encryption key Flags 2 bytes Processing flags CertData TSize-8 Certificate decryption extra field data (refer to the explanation for CertData in the section describing the Certificate Processing Method under the Strong Encryption Specification) -Record Management Controls (0x0018): Value Size Description ----- ---- ----------- (Rec-CTL) 0x0018 2 bytes Tag for this "extra" block type CSize 2 bytes Size of total extra block data Tag1 2 bytes Record control attribute 1 Size1 2 bytes Size of attribute 1, in bytes Data1 Size1 Attribute 1 data . . . TagN 2 bytes Record control attribute N SizeN 2 bytes Size of attribute N, in bytes DataN SizeN Attribute N data -PKCS#7 Encryption Recipient Certificate List (0x0019): (EFS) This field contains the information about each of the certificates that files may be encrypted with. This field should only appear in the archive extra data record. This field is not required and serves only to aide archive modifications by preserving public encryption data. Individual security requirements may dictate that this data be omitted to deter information exposure. Note: all fields stored in Intel low-byte/high-byte order. Value Size Description ----- ---- ----------- (CStore) 0x0019 2 bytes Tag for this "extra" block type TSize 2 bytes Size of the store data TData TSize Data about the store TData: Value Size Description ----- ---- ----------- Version 2 bytes Format version number - must 0x0001 at this time CStore (var) PKCS#7 data blob -MVS Extra Field (0x0065): The following is the layout of the MVS "extra" block. Note: Some fields are stored in Big Endian format. All text is in EBCDIC format unless otherwise specified. Value Size Description ----- ---- ----------- (MVS) 0x0065 2 bytes Tag for this "extra" block type TSize 2 bytes Size for the following data block ID 4 bytes EBCDIC "Z390" 0xE9F3F9F0 or "T4MV" for TargetFour (var) TSize-4 Attribute data -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 Third-party Mappings: -ZipIt Macintosh Extra Field (long) (0x2605): The following is the layout of the ZipIt extra block for Macintosh. The local-header and central-header versions are identical. This block must be present if the file is stored MacBinary-encoded and it should not be used if the file is not stored MacBinary-encoded. Value Size Description ----- ---- ----------- (Mac2) 0x2605 Short tag for this extra block type TSize Short total data size for this block "ZPIT" beLong extra-field signature FnLen Byte length of FileName FileName variable full Macintosh filename FileType Byte[4] four-byte Mac file type string Creator Byte[4] four-byte Mac creator string -ZipIt Macintosh Extra Field (short, for files) (0x2705): The following is the layout of a shortened variant of the ZipIt extra block for Macintosh (without "full name" entry). This variant is used by ZipIt 1.3.5 and newer for entries of files (not directories) that do not have a MacBinary encoded file. The local-header and central-header versions are identical. Value Size Description ----- ---- ----------- (Mac2b) 0x2705 Short tag for this extra block type TSize Short total data size for this block (12) "ZPIT" beLong extra-field signature FileType Byte[4] four-byte Mac file type string Creator Byte[4] four-byte Mac creator string fdFlags beShort attributes from FInfo.frFlags, may be omitted 0x0000 beShort reserved, may be omitted -ZipIt Macintosh Extra Field (short, for directories) (0x2805): The following is the layout of a shortened variant of the ZipIt extra block for Macintosh used only for directory entries. This variant is used by ZipIt 1.3.5 and newer to save some optional Mac-specific information about directories. The local-header and central-header versions are identical. Value Size Description ----- ---- ----------- (Mac2c) 0x2805 Short tag for this extra block type TSize Short total data size for this block (12) "ZPIT" beLong extra-field signature frFlags beShort attributes from DInfo.frFlags, may be omitted View beShort ZipIt view flag, may be omitted The View field specifies ZipIt-internal settings as follows: Bits of the Flags: bit 0 if set, the folder is shown expanded (open) when the archive contents are viewed in ZipIt. bits 1-15 reserved, zero; -FWKCS MD5 Extra Field (0x4b46): The FWKCS Contents_Signature System, used in automatically identifying files independent of file name, optionally adds and uses an extra field to support the rapid creation of an enhanced contents_signature: Header ID = 0x4b46 Data Size = 0x0013 Preface = 'M','D','5' followed by 16 bytes containing the uncompressed file's 128_bit MD5 hash(1), low byte first. When FWKCS revises a .ZIP file central directory to add this extra field for a file, it also replaces the central directory entry for that file's uncompressed file length with a measured value. FWKCS provides an option to strip this extra field, if present, from a .ZIP file central directory. In adding this extra field, FWKCS preserves .ZIP file Authenticity Verification; if stripping this extra field, FWKCS preserves all versions of AV through PKZIP version 2.04g. FWKCS, and FWKCS Contents_Signature System, are trademarks of Frederick W. Kantor. (1) R. Rivest, RFC1321.TXT, MIT Laboratory for Computer Science and RSA Data Security, Inc., April 1992. ll.76-77: "The MD5 algorithm is being placed in the public domain for review and possible adoption as a standard." file comment: (Variable) The comment for this file. number of this disk: (2 bytes) The number of this disk, which contains central directory end record. If an archive is in zip64 format and the value in this field is 0xFFFF, the size will be in the corresponding 4 byte zip64 end of central directory field. number of the disk with the start of the central directory: (2 bytes) The number of the disk on which the central directory starts. If an archive is in zip64 format and the value in this field is 0xFFFF, the size will be in the corresponding 4 byte zip64 end of central directory field. total number of entries in the central dir on this disk: (2 bytes) The number of central directory entries on this disk. If an archive is in zip64 format and the value in this field is 0xFFFF, the size will be in the corresponding 8 byte zip64 end of central directory field. total number of entries in the central dir: (2 bytes) The total number of files in the .ZIP file. If an archive is in zip64 format and the value in this field is 0xFFFF, the size will be in the corresponding 8 byte zip64 end of central directory field. size of the central directory: (4 bytes) The size (in bytes) of the entire central directory. If an archive is in zip64 format and the value in this field is 0xFFFFFFFF, the size will be in the corresponding 8 byte zip64 end of central directory field. offset of start of central directory with respect to the starting disk number: (4 bytes) Offset of the start of the central directory on the disk on which the central directory starts. If an archive is in zip64 format and the value in this field is 0xFFFFFFFF, the size will be in the corresponding 8 byte zip64 end of central directory field. .ZIP file comment length: (2 bytes) The length of the comment for this .ZIP file. .ZIP file comment: (Variable) The comment for this .ZIP file. ZIP file comment data is stored unsecured. No encryption or data authentication is applied to this area at this time. Confidential information should not be stored in this section. zip64 extensible data sector (variable size) (currently reserved for use by PKWARE) K. General notes: 1) All fields unless otherwise noted are unsigned and stored in Intel low-byte:high-byte, low-word:high-word order. 2) String fields are not null terminated, since the length is given explicitly. 3) Local headers should not span disk boundaries. Also, even though the central directory can span disk boundaries, no single record in the central directory should be split across disks. 4) The entries in the central directory may not necessarily be in the same order that files appear in the .ZIP file. 5) Spanned/Split archives created using PKZIP for Windows (V2.50 or greater), PKZIP Command Line (V2.50 or greater), or PKZIP Explorer will include a special spanning signature as the first 4 bytes of the first segment of the archive. This signature (0x08074b50) will be followed immediately by the local header signature for the first file in the archive. A special spanning marker may also appear in spanned/split archives if the spanning or splitting process starts but only requires one segment. In this case the 0x08074b50 signature will be replaced with the temporary spanning marker signature of 0x30304b50. Spanned/split archives created with this special signature are compatible with all versions of PKZIP from PKWARE. Split archives can only be uncompressed by other versions of PKZIP that know how to create a split archive. 6) 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. 7) 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. V. UnShrinking - Method 1 ------------------------- Shrinking is a Dynamic Ziv-Lempel-Welch compression algorithm with partial clearing. The initial code size is 9 bits, and the maximum code size is 13 bits. Shrinking differs from conventional Dynamic Ziv-Lempel-Welch implementations in several respects: 1) The code size is controlled by the compressor, and is not automatically increased when codes larger than the current code size are created (but not necessarily used). When the decompressor encounters the code sequence 256 (decimal) followed by 1, it should increase the code size read from the input stream to the next bit size. No blocking of the codes is performed, so the next code at the increased size should be read from the input stream immediately after where the previous code at the smaller bit size was read. Again, the decompressor should not increase the code size used until the sequence 256,1 is encountered. 2) When the table becomes full, total clearing is not performed. Rather, when the compressor emits the code sequence 256,2 (decimal), the decompressor should clear all leaf nodes from the Ziv-Lempel tree, and continue to use the current code size. The nodes that are cleared from the Ziv-Lempel tree are then re-used, with the lowest code value re-used first, and the highest code value re-used last. The compressor can emit the sequence 256,2 at any time. VI. Expanding - Methods 2-5 --------------------------- The Reducing algorithm is actually a combination of two distinct algorithms. The first algorithm compresses repeated byte sequences, and the second algorithm takes the compressed stream from the first algorithm and applies a probabilistic compression method. The probabilistic compression stores an array of 'follower sets' S(j), for j=0 to 255, corresponding to each possible ASCII character. Each set contains between 0 and 32 characters, to be denoted as S(j)[0],...,S(j)[m], where m<32. The sets are stored at the beginning of the data area for a Reduced file, in reverse order, with S(255) first, and S(0) last. The sets are encoded as { N(j), S(j)[0],...,S(j)[N(j)-1] }, where N(j) is the size of set S(j). N(j) can be 0, in which case the follower set for S(j) is empty. Each N(j) value is encoded in 6 bits, followed by N(j) eight bit character values corresponding to S(j)[0] to S(j)[N(j)-1] respectively. If N(j) is 0, then no values for S(j) are stored, and the value for N(j-1) immediately follows. Immediately after the follower sets, is the compressed data stream. The compressed data stream can be interpreted for the probabilistic decompression as follows: let Last-Character <- 0. loop until done if the follower set S(Last-Character) is empty then read 8 bits from the input stream, and copy this value to the output stream. otherwise if the follower set S(Last-Character) is non-empty then read 1 bit from the input stream. if this bit is not zero then read 8 bits from the input stream, and copy this value to the output stream. otherwise if this bit is zero then read B(N(Last-Character)) bits from the input stream, and assign this value to I. Copy the value of S(Last-Character)[I] to the output stream. assign the last value placed on the output stream to Last-Character. end loop B(N(j)) is defined as the minimal number of bits required to encode the value N(j)-1. The decompressed stream from above can then be expanded to re-create the original file as follows: let State <- 0. loop until done read 8 bits from the input stream into C. case State of 0: if C is not equal to DLE (144 decimal) then copy C to the output stream. otherwise if C is equal to DLE then let State <- 1. 1: if C is non-zero then let V <- C. let Len <- L(V) let State <- F(Len). otherwise if C is zero then copy the value 144 (decimal) to the output stream. let State <- 0 2: let Len <- Len + C let State <- 3. 3: move backwards D(V,C) bytes in the output stream (if this position is before the start of the output stream, then assume that all the data before the start of the output stream is filled with zeros). copy Len+3 bytes from this position to the output stream. let State <- 0. end case end loop The functions F,L, and D are dependent on the 'compression factor', 1 through 4, and are defined as follows: For compression factor 1: L(X) equals the lower 7 bits of X. F(X) equals 2 if X equals 127 otherwise F(X) equals 3. D(X,Y) equals the (upper 1 bit of X) * 256 + Y + 1. For compression factor 2: L(X) equals the lower 6 bits of X. F(X) equals 2 if X equals 63 otherwise F(X) equals 3. D(X,Y) equals the (upper 2 bits of X) * 256 + Y + 1. For compression factor 3: L(X) equals the lower 5 bits of X. F(X) equals 2 if X equals 31 otherwise F(X) equals 3. D(X,Y) equals the (upper 3 bits of X) * 256 + Y + 1. For compression factor 4: L(X) equals the lower 4 bits of X. F(X) equals 2 if X equals 15 otherwise F(X) equals 3. D(X,Y) equals the (upper 4 bits of X) * 256 + Y + 1. VII. Imploding - Method 6 ------------------------- The Imploding algorithm is actually a combination of two distinct algorithms. The first algorithm compresses repeated byte sequences using a sliding dictionary. The second algorithm is used to compress the encoding of the sliding dictionary output, using multiple Shannon-Fano trees. The Imploding algorithm can use a 4K or 8K sliding dictionary size. The dictionary size used can be determined by bit 1 in the general purpose flag word; a 0 bit indicates a 4K dictionary while a 1 bit indicates an 8K dictionary. The Shannon-Fano trees are stored at the start of the compressed file. The number of trees stored is defined by bit 2 in the general purpose flag word; a 0 bit indicates two trees stored, a 1 bit indicates three trees are stored. If 3 trees are stored, the first Shannon-Fano tree represents the encoding of the Literal characters, the second tree represents the encoding of the Length information, the third represents the encoding of the Distance information. When 2 Shannon-Fano trees are stored, the Length tree is stored first, followed by the Distance tree. The Literal Shannon-Fano tree, if present is used to represent the entire ASCII character set, and contains 256 values. This tree is used to compress any data not compressed by the sliding dictionary algorithm. When this tree is present, the Minimum Match Length for the sliding dictionary is 3. If this tree is not present, the Minimum Match Length is 2. The Length Shannon-Fano tree is used to compress the Length part of the (length,distance) pairs from the sliding dictionary output. The Length tree contains 64 values, ranging from the Minimum Match Length, to 63 plus the Minimum Match Length. The Distance Shannon-Fano tree is used to compress the Distance part of the (length,distance) pairs from the sliding dictionary output. The Distance tree contains 64 values, ranging from 0 to 63, representing the upper 6 bits of the distance value. The distance values themselves will be between 0 and the sliding dictionary size, either 4K or 8K. The Shannon-Fano trees themselves are stored in a compressed format. The first byte of the tree data represents the number of bytes of data representing the (compressed) Shannon-Fano tree minus 1. The remaining bytes represent the Shannon-Fano tree data encoded as: High 4 bits: Number of values at this bit length + 1. (1 - 16) Low 4 bits: Bit Length needed to represent value + 1. (1 - 16) The Shannon-Fano codes can be constructed from the bit lengths using the following algorithm: 1) Sort the Bit Lengths in ascending order, while retaining the order of the original lengths stored in the file. 2) Generate the Shannon-Fano trees: Code <- 0 CodeIncrement <- 0 LastBitLength <- 0 i <- number of Shannon-Fano codes - 1 (either 255 or 63) loop while i >= 0 Code = Code + CodeIncrement if BitLength(i) <> LastBitLength then LastBitLength=BitLength(i) CodeIncrement = 1 shifted left (16 - LastBitLength) ShannonCode(i) = Code i <- i - 1 end loop 3) Reverse the order of all the bits in the above ShannonCode() vector, so that the most significant bit becomes the least significant bit. For example, the value 0x1234 (hex) would become 0x2C48 (hex). 4) Restore the order of Shannon-Fano codes as originally stored within the file. Example: This example will show the encoding of a Shannon-Fano tree of size 8. Notice that the actual Shannon-Fano trees used for Imploding are either 64 or 256 entries in size. Example: 0x02, 0x42, 0x01, 0x13 The first byte indicates 3 values in this table. Decoding the bytes: 0x42 = 5 codes of 3 bits long 0x01 = 1 code of 2 bits long 0x13 = 2 codes of 4 bits long This would generate the original bit length array of: (3, 3, 3, 3, 3, 2, 4, 4) There are 8 codes in this table for the values 0 thru 7. Using the algorithm to obtain the Shannon-Fano codes produces: Reversed Order Original Val Sorted Constructed Code Value Restored Length --- ------ ----------------- -------- -------- ------ 0: 2 1100000000000000 11 101 3 1: 3 1010000000000000 101 001 3 2: 3 1000000000000000 001 110 3 3: 3 0110000000000000 110 010 3 4: 3 0100000000000000 010 100 3 5: 3 0010000000000000 100 11 2 6: 4 0001000000000000 1000 1000 4 7: 4 0000000000000000 0000 0000 4 The values in the Val, Order Restored and Original Length columns now represent the Shannon-Fano encoding tree that can be used for decoding the Shannon-Fano encoded data. How to parse the variable length Shannon-Fano values from the data stream is beyond the scope of this document. (See the references listed at the end of this document for more information.) However, traditional decoding schemes used for Huffman variable length decoding, such as the Greenlaw algorithm, can be successfully applied. The compressed data stream begins immediately after the compressed Shannon-Fano data. The compressed data stream can be interpreted as follows: loop until done read 1 bit from input stream. if this bit is non-zero then (encoded data is literal data) if Literal Shannon-Fano tree is present read and decode character using Literal Shannon-Fano tree. otherwise read 8 bits from input stream. copy character to the output stream. otherwise (encoded data is sliding dictionary match) if 8K dictionary size read 7 bits for offset Distance (lower 7 bits of offset). otherwise read 6 bits for offset Distance (lower 6 bits of offset). using the Distance Shannon-Fano tree, read and decode the upper 6 bits of the Distance value. using the Length Shannon-Fano tree, read and decode the Length value. Length <- Length + Minimum Match Length if Length = 63 + Minimum Match Length read 8 bits from the input stream, add this value to Length. move backwards Distance+1 bytes in the output stream, and copy Length characters from this position to the output stream. (if this position is before the start of the output stream, then assume that all the data before the start of the output stream is filled with zeros). end loop VIII. Tokenizing - Method 7 --------------------------- This method is not used by PKZIP. IX. Deflating - Method 8 ------------------------ The Deflate algorithm is similar to the Implode algorithm using a sliding dictionary of up to 32K with secondary compression from Huffman/Shannon-Fano codes. The compressed data is stored in blocks with a header describing the block and the Huffman codes used in the data block. The header format is as follows: Bit 0: Last Block bit This bit is set to 1 if this is the last compressed block in the data. Bits 1-2: Block type 00 (0) - Block is stored - All stored data is byte aligned. Skip bits until next byte, then next word = block length, followed by the ones compliment of the block length word. Remaining data in block is the stored data. 01 (1) - Use fixed Huffman codes for literal and distance codes. Lit Code Bits Dist Code Bits --------- ---- --------- ---- 0 - 143 8 0 - 31 5 144 - 255 9 256 - 279 7 280 - 287 8 Literal codes 286-287 and distance codes 30-31 are never used but participate in the huffman construction. 10 (2) - Dynamic Huffman codes. (See expanding Huffman codes) 11 (3) - Reserved - Flag a "Error in compressed data" if seen. Expanding Huffman Codes ----------------------- If the data block is stored with dynamic Huffman codes, the Huffman codes are sent in the following compressed format: 5 Bits: # of Literal codes sent - 256 (256 - 286) All other codes are never sent. 5 Bits: # of Dist codes - 1 (1 - 32) 4 Bits: # of Bit Length codes - 3 (3 - 19) The Huffman codes are sent as bit lengths and the codes are built as described in the implode algorithm. The bit lengths themselves are compressed with Huffman codes. There are 19 bit length codes: 0 - 15: Represent bit lengths of 0 - 15 16: Copy the previous bit length 3 - 6 times. The next 2 bits indicate repeat length (0 = 3, ... ,3 = 6) Example: Codes 8, 16 (+2 bits 11), 16 (+2 bits 10) will expand to 12 bit lengths of 8 (1 + 6 + 5) 17: Repeat a bit length of 0 for 3 - 10 times. (3 bits of length) 18: Repeat a bit length of 0 for 11 - 138 times (7 bits of length) The lengths of the bit length codes are sent packed 3 bits per value (0 - 7) in the following order: 16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15 The Huffman codes should be built as described in the Implode algorithm except codes are assigned starting at the shortest bit length, i.e. the shortest code should be all 0's rather than all 1's. Also, codes with a bit length of zero do not participate in the tree construction. The codes are then used to decode the bit lengths for the literal and distance tables. The bit lengths for the literal tables are sent first with the number of entries sent described by the 5 bits sent earlier. There are up to 286 literal characters; the first 256 represent the respective 8 bit character, code 256 represents the End-Of-Block code, the remaining 29 codes represent copy lengths of 3 thru 258. There are up to 30 distance codes representing distances from 1 thru 32k as described below. Length Codes ------------ Extra Extra Extra Extra Code Bits Length Code Bits Lengths Code Bits Lengths Code Bits Length(s) ---- ---- ------ ---- ---- ------- ---- ---- ------- ---- ---- --------- 257 0 3 265 1 11,12 273 3 35-42 281 5 131-162 258 0 4 266 1 13,14 274 3 43-50 282 5 163-194 259 0 5 267 1 15,16 275 3 51-58 283 5 195-226 260 0 6 268 1 17,18 276 3 59-66 284 5 227-257 261 0 7 269 2 19-22 277 4 67-82 285 0 258 262 0 8 270 2 23-26 278 4 83-98 263 0 9 271 2 27-30 279 4 99-114 264 0 10 272 2 31-34 280 4 115-130 Distance Codes -------------- Extra Extra Extra Extra Code Bits Dist Code Bits Dist Code Bits Distance Code Bits Distance ---- ---- ---- ---- ---- ------ ---- ---- -------- ---- ---- -------- 0 0 1 8 3 17-24 16 7 257-384 24 11 4097-6144 1 0 2 9 3 25-32 17 7 385-512 25 11 6145-8192 2 0 3 10 4 33-48 18 8 513-768 26 12 8193-12288 3 0 4 11 4 49-64 19 8 769-1024 27 12 12289-16384 4 1 5,6 12 5 65-96 20 9 1025-1536 28 13 16385-24576 5 1 7,8 13 5 97-128 21 9 1537-2048 29 13 24577-32768 6 2 9-12 14 6 129-192 22 10 2049-3072 7 2 13-16 15 6 193-256 23 10 3073-4096 The compressed data stream begins immediately after the compressed header data. The compressed data stream can be interpreted as follows: do read header from input stream. if stored block skip bits until byte aligned read count and 1's compliment of count copy count bytes data block otherwise loop until end of block code sent decode literal character from input stream if literal < 256 copy character to the output stream otherwise if literal = end of block break from loop otherwise decode distance from input stream move backwards distance bytes in the output stream, and copy length characters from this position to the output stream. end loop while not last block if data descriptor exists skip bits until byte aligned read crc and sizes endif X. Enhanced Deflating - Method 9 -------------------------------- The Enhanced Deflating algorithm is similar to Deflate but uses a sliding dictionary of up to 64K. Deflate64(tm) is supported by the Deflate extractor. XI. BZIP2 - Method 12 --------------------- BZIP2 is an open-source data compression algorithm developed by Julian Seward. Information and source code for this algorithm can be found on the internet. XII. Traditional PKWARE Encryption ---------------------------------- The following information discusses the decryption steps required to support traditional PKWARE encryption. This form of encryption is considered weak by today's standards and its use is recommended only for situations with low security needs or for compatibility with older .ZIP applications. XIII. Decryption ---------------- The encryption used in PKZIP was generously supplied by Roger Schlafly. PKWARE is grateful to Mr. Schlafly for his expert help and advice in the field of data encryption. PKZIP encrypts the compressed data stream. Encrypted files must be decrypted before they can be extracted. Each encrypted file has an extra 12 bytes stored at the start of the data area defining the encryption header for that file. The encryption header is originally set to random values, and then itself encrypted, using three, 32-bit keys. The key values are initialized using the supplied encryption password. After each byte is encrypted, the keys are then updated using pseudo-random number generation techniques in combination with the same CRC-32 algorithm used in PKZIP and described elsewhere in this document. The following is the basic steps required to decrypt a file: 1) Initialize the three 32-bit keys with the password. 2) Read and decrypt the 12-byte encryption header, further initializing the encryption keys. 3) Read and decrypt the compressed data stream using the encryption keys. Step 1 - Initializing the encryption keys ----------------------------------------- Key(0) <- 305419896 Key(1) <- 591751049 Key(2) <- 878082192 loop for i <- 0 to length(password)-1 update_keys(password(i)) end loop Where update_keys() is defined as: update_keys(char): Key(0) <- crc32(key(0),char) Key(1) <- Key(1) + (Key(0) & 000000ffH) Key(1) <- Key(1) * 134775813 + 1 Key(2) <- crc32(key(2),key(1) >> 24) end update_keys Where crc32(old_crc,char) is a routine that given a CRC value and a character, returns an updated CRC value after applying the CRC-32 algorithm described elsewhere in this document. Step 2 - Decrypting the encryption header ----------------------------------------- The purpose of this step is to further initialize the encryption keys, based on random data, to render a plaintext attack on the data ineffective. Read the 12-byte encryption header into Buffer, in locations Buffer(0) thru Buffer(11). loop for i <- 0 to 11 C <- buffer(i) ^ decrypt_byte() update_keys(C) buffer(i) <- C end loop Where decrypt_byte() is defined as: unsigned char decrypt_byte() local unsigned short temp temp <- Key(2) | 2 decrypt_byte <- (temp * (temp ^ 1)) >> 8 end decrypt_byte After the header is decrypted, the last 1 or 2 bytes in Buffer should be the high-order word/byte of the CRC for the file being decrypted, stored in Intel low-byte/high-byte order. Versions of PKZIP prior to 2.0 used a 2 byte CRC check; a 1 byte CRC check is used on versions after 2.0. This can be used to test if the password supplied is correct or not. Step 3 - Decrypting the compressed data stream ---------------------------------------------- The compressed data stream can be decrypted as follows: loop until done read a character into C Temp <- C ^ decrypt_byte() update_keys(temp) output Temp end loop XIV. Strong Encryption Specification (EFS) ------------------------------------------ Version 5.x of this specification introduced support for strong encryption algorithms. These algorithms can be used with either a password or an X.509v3 digital certificate to encrypt each file. This format specification supports either password or certificate based encryption to meet the security needs of today, to enable interoperability between users within both PKI and non-PKI environments, and to ensure interoperability between different computing platforms that are running a ZIP program. Password based encryption is the most common form of encryption people are familiar with. However, inherent weaknesses with passwords (e.g. susceptibility to dictionary/brute force attack) as well as password management and support issues make certificate based encryption a more secure and scalable option. Industry efforts and support are defining and moving towards more advanced security solutions built around X.509v3 digital certificates and Public Key Infrastructures(PKI) because of the greater scalability, administrative options, and more robust security over traditional password based encryption. Most standard encryption algorithms are supported with this specification. Reference implementations for many of these algorithms are available from either commercial or open source distributors. Readily available cryptographic toolkits make implementation of the encryption features straight-forward. This document is not intended to provide a treatise on data encryption principles or theory. Its purpose is to document the data structures required for implementing interoperable data encryption within the .ZIP format. It is strongly recommended that you have a good understanding of data encryption before reading further. The algorithms introduced in Version 5.0 of this specification include: RC2 40 bit, 64 bit, and 128 bit RC4 40 bit, 64 bit, and 128 bit DES 3DES 112 bit and 168 bit Version 5.1 adds support for the following: AES 128 bit, 192 bit, and 256 bit Version 6.1 introduces encryption data changes to support interoperability with SmartCard and USB Token certificate storage methods which do not support the OAEP strengthening standard. Version 6.2 introduces support for encrypting metadata by compressing and encrypting the central directory data structure to reduce information leakage. Information leakage can occur in legacy ZIP applications through exposure of information about a file even though that file is stored encrypted. The information exposed consists of file characteristics stored within the records and fields defined by this specification. This includes data such as a files name, its original size, timestamp and CRC32 value. Central Directory Encryption provides greater protection against information leakage by encrypting the Central Directory structure and by masking key values that are replicated in the unencrypted Local Header. ZIP compatible programs that cannot interpret an encrypted Central Directory structure cannot rely on the data in the corresponding Local Header for decompression information. Extra Field records that may contain information about a file that should not be exposed should not be stored in the Local Header and should only be written to the Central Directory where they can be encrypted. This design currently does not support streaming. Information in the End of Central Directory record, the ZIP64 End of Central Directory Locator, and the ZIP64 End of Central Directory record are not encrypted. Access to view data on files within a ZIP file with an encrypted Central Directory requires the appropriate password or private key for decryption prior to viewing any files, or any information about the files, in the archive. Older ZIP compatible programs not familiar with the Central Directory Encryption feature will no longer be able to recognize the Central Directory and may assume the ZIP file is corrupt. Programs that attempt streaming access using Local Headers will see invalid information for each file. Central Directory Encryption need not be used for every ZIP file. Its use is recommended for greater security. ZIP files not using Central Directory Encryption should operate as in the past. The details of the strong encryption specification for certificates remain under development as design and testing issues are worked out for the range of algorithms, encryption methods, certificate processing and cross-platform support necessary to meet the advanced security needs of .ZIP file users today and in the future. This feature specification is intended to support basic encryption needs of today, such as password support. However this specification is also designed to lay the foundation for future advanced security needs. Encryption provides data confidentiality and privacy. It is recommended that you combine X.509 digital signing with encryption to add authentication and non-repudiation. Single Password Symmetric Encryption Method: ------------------------------------------- The Single Password Symmetric Encryption Method using strong encryption algorithms operates similarly to the traditional PKWARE encryption defined in this format. Additional data structures are added to support the processing needs of the strong algorithms. The Strong Encryption data structures are: 1. General Purpose Bits - Bits 0 and 6 of the General Purpose bit flag in both local and central header records. Both bits set indicates strong encryption. Bit 13, when set indicates the Central Directory is encrypted and that selected fields in the Local Header are masked to hide their actual value. 2. Extra Field 0x0017 in central header only. Fields to consider in this record are: Format - the data format identifier for this record. The only value allowed at this time is the integer value 2. AlgId - integer identifier of the encryption algorithm from the following range 0x6601 - DES 0x6602 - RC2 (version needed to extract < 5.2) 0x6603 - 3DES 168 0x6609 - 3DES 112 0x660E - AES 128 0x660F - AES 192 0x6610 - AES 256 0x6702 - RC2 (version needed to extract >= 5.2) 0x6801 - RC4 0xFFFF - Unknown algorithm Bitlen - Explicit bit length of key 40 56 64 112 128 168 192 256 Flags - Processing flags needed for decryption 0x0001 - Password is required to decrypt 0x0002 - Certificates only 0x0003 - Password or certificate required to decrypt Values > 0x0003 reserved for certificate processing 3. Decryption header record preceding compressed file data. -Decryption Header: Value Size Description ----- ---- ----------- IVSize 2 bytes Size of initialization vector (IV) IVData IVSize Initialization vector for this file Size 4 bytes Size of remaining decryption header data Format 2 bytes Format definition for this record AlgID 2 bytes Encryption algorithm identifier Bitlen 2 bytes Bit length of encryption key Flags 2 bytes Processing flags ErdSize 2 bytes Size of Encrypted Random Data ErdData ErdSize Encrypted Random Data Reserved1 4 bytes Reserved certificate processing data Reserved2 (var) Reserved for certificate processing data VSize 2 bytes Size of password validation data VData VSize-4 Password validation data VCRC32 4 bytes Standard ZIP CRC32 of password validation data IVData - The size of the IV should match the algorithm block size. The IVData can be completely random data. If the size of the randomly generated data does not match the block size it should be complemented with zero's or truncated as necessary. If IVSize is 0,then IV = CRC32 + Uncompressed File Size (as a 64 bit little-endian, unsigned integer value). Format - the data format identifier for this record. The only value allowed at this time is the integer value 3. AlgId - integer identifier of the encryption algorithm from the following range 0x6601 - DES 0x6602 - RC2 (version needed to extract < 5.2) 0x6603 - 3DES 168 0x6609 - 3DES 112 0x660E - AES 128 0x660F - AES 192 0x6610 - AES 256 0x6702 - RC2 (version needed to extract >= 5.2) 0x6801 - RC4 0xFFFF - Unknown algorithm Bitlen - Explicit bit length of key 40 56 64 112 128 168 192 256 Flags - Processing flags needed for decryption 0x0001 - Password is required to decrypt 0x0002 - Certificates only 0x0003 - Password or certificate required to decrypt Values > 0x0003 reserved for certificate processing ErdData - Encrypted random data is used to 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. Reserved1 - Reserved for certificate processing, if value is zero, then Reserved2 data is absent. See the explanation under the Certificate Processing Method for details on this data structure. Reserved2 - If present, the size of the Reserved2 data structure is located by skipping the first 4 bytes of this field and using the next 2 bytes as the remaining size. See the explanation under the Certificate Processing Method for details on this data structure. VSize - This size value will always include the 4 bytes of the VCRC32 data and will be greater than 4 bytes. VData - Random data for password validation. This data is VSize in length and VSize must be a multiple of the encryption block size. VCRC32 is a checksum value of VData. VData and VCRC32 are stored encrypted and start the stream of encrypted data for a file. 4. Single Password Central Directory Encryption Central Directory Encryption is achieved within the .ZIP format by encrypting the Central Directory structure. This encapsulates the metadata most often used for processing .ZIP files. Additional metadata is stored for redundancy in the Local Header for each file. The process of concealing metadata by encrypting the Central Directory does not protect the data within the Local Header. To avoid information leakage from the exposed metadata in the Local Header, the fields containing information about a file are masked. Local Header: Masking replaces the true content of the fields for a file in the Local Header with false information. When masked, the Local Header is not suitable for streaming access and the options for data recovery of damaged archives is reduced. Extra Data fields that may contain confidential data should not be stored within the Local Header. The value set into the Version needed to extract field should be the correct value needed to extract the file without regard to Central Directory Encryption. The fields within the Local Header targeted for masking when the Central Directory is encrypted are: Field Name Mask Value ------------------ --------------------------- compression method 0 last mod file time 0 last mod file date 0 crc-32 0 compressed size 0 uncompressed size 0 file name (variable size) Base 16 value from the range 1 - FFFFFFFFFFFFFFFF represented as a string whose size will be set into the file name length field The Base 16 value assigned as a masked file name is simply a sequentially incremented value for each file starting with 1 for the first file. Modifications to a ZIP file may cause different values to be stored for each file. For compatibility, the file name field in the Local Header should never be left blank. As of Version 6.2 of this specification, the Compression Method and Compressed Size fields are not yet masked. 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 first 48 bytes will remain identical to that of Version 1. The record signature for both Version 1 and Version 2 will be 0x06064b50. Immediately following the 48th byte, which identifies the end of the field known as the Offset of Start of Central Directory With Respect to the Starting Disk Number will begin the new fields defining Version 2 of this record. New fields for Version 2: Note: all fields stored in Intel low-byte/high-byte order. Value Size Description ----- ---- ----------- Compression Method 2 bytes Method used to compress the Central Directory Compressed Size 8 bytes Size of the compressed data Original Size 8 bytes Original uncompressed size AlgId 2 bytes Encryption algorithm ID BitLen 2 bytes Encryption key length Flags 2 bytes Encryption flags HashID 2 bytes Hash algorithm identifier Hash Length 2 bytes Length of hash data Hash Data (variable) Hash data The Compression Method accepts the same range of values as the corresponding field in the Central Header. The Compressed Size and Original Size values will not include the data of the Central Directory Signature which is compressed or encrypted. The AlgId, BitLen, and Flags fields accept the same range of values the corresponding fields within the 0x0017 record. Hash ID identifies the algorithm used to hash the Central Directory data. This data does not have to be hashed, in which case the values for both the HashID and Hash Length will be 0. Possible values for HashID are: Value Algorithm ------ --------- 0x0000 none 0x0001 CRC32 0x8003 MD5 0x8004 SHA1 When the Central Directory data is signed, the same hash algorithm used to hash the Central Directory for signing should be used. This is recommended for processing efficiency, however, it is permissible for any of the above algorithms to be used independent of the signing process. The Hash Data will contain the hash data for the Central Directory. The length of this data will vary depending on the algorithm used. The Version Needed to Extract should be set to 62. The value for the Total Number of Entries on the Current Disk will be 0. These records will no longer support random access when encrypting the Central Directory. When the Central Directory is compressed and/or encrypted, the End of Central Directory record will store the value 0xFFFFFFFF as the value for the Total Number of Entries in the Central Directory. The value stored in the Total Number of Entries in the Central Directory on this Disk field will be 0. The actual values will be stored in the equivalent fields of the ZIP64 End of Central Directory record. Decrypting and decompressing the Central Directory is accomplished in the same manner as decrypting and decompressing a file. 5. Useful Tips Strong Encryption is always applied to a file after compression. The block oriented algorithms all operate in Cypher Block Chaining (CBC) mode. The block size used for AES encryption is 16. All other block algorithms use a block size of 8. Two ID's are defined for RC2 to account for a discrepancy found in the implementation of the RC2 algorithm in the cryptographic library on Windows XP SP1 and all earlier versions of Windows. A pseudo-code representation of the encryption process is as follows: Password = GetUserPassword() RD = Random() ERD = Encrypt(RD,DeriveKey(SHA1(Password))) For Each File IV = Random() VData = Random() FileSessionKey = DeriveKey(SHA1(IV + RD)) Encrypt(VData + VCRC32 + FileData,FileSessionKey) Done The function names and parameter requirements will depend on the choice of the cryptographic toolkit selected. Almost any toolkit supporting the reference implementations for each algorithm can be used. The RSA BSAFE(r), OpenSSL, and Microsoft CryptoAPI libraries are all known to work well. Certificate Processing Method: ----------------------------- The Certificate Processing Method for ZIP file encryption remains under development. The information provided here serves as a guide to those interested in certificate-based data decryption. This information may be subject to change in future versions of this specification and is subject to change without notice. OAEP Processing with Certificate-based Encryption: Versions of PKZIP available during this development phase of the certificate processing method may 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. OAEP stands for Optimal Asymmetric Encryption Padding. It is a strengthening technique used for small encoded items such as decryption keys. This is commonly applied in cryptographic key-wrapping techniques and is supported by PKCS #1. Versions 5.0 and 6.0 of this specification were designed to support OAEP key-wrapping for certificate-based decryption keys for additional security. Support for private keys stored on Smart Cards 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. Certificate Processing Data Fields: The Certificate Processing Method of this specification defines the following additional data fields: 1. Certificate Flag Values Additional processing flags that can be present in the Flags field of both the 0x0017 field of the central directory Extra Field and the Decryption header record preceding compressed file data are: 0x0007 - reserved for future use 0x000F - reserved for future use 0x0100 - Indicates non-OAEP key wrapping was used. If this this field is set, the version needed to extract must be at least 61. This means OAEP key wrapping is not used when generating a Master Session Key using ErdData. 0x4000 - ErdData must be decrypted using 3DES-168, otherwise use the same algorithm used for encrypting the file contents. 0x8000 - reserved for future use 2. CertData - Extra Field 0x0017 record certificate data structure The data structure used to store certificate data within the section of the Extra Field defined by the CertData field of the 0x0017 record are as shown: Value Size Description ----- ---- ----------- RCount 4 bytes Number of recipients. HashAlg 2 bytes Hash algorithm identifier HSize 2 bytes Hash size SRList (var) Simple list of recipients hashed public keys RCount This defines the number intended recipients whose public keys were used for encryption. This identifies the number of elements in the SRList. HashAlg This defines the hash algorithm used to calculate the public key hash of each public key used for encryption. This field currently supports only the following value for SHA-1 0x8004 - SHA1 HSize This defines the size of a hashed public key. SRList This is a variable length list of the hashed public keys for each intended recipient. Each element in this list is HSize. The total size of SRList is determined using RCount * HSize. 3. Reserved1 - Certificate Decryption Header Reserved1 Data: Value Size Description ----- ---- ----------- RCount 4 bytes Number of recipients. RCount This defines the number intended recipients whose public keys were used for encryption. This defines the number of elements in the REList field defined below. 4. Reserved2 - Certificate Decryption Header Reserved2 Data Structures: Value Size Description ----- ---- ----------- HashAlg 2 bytes Hash algorithm identifier HSize 2 bytes Hash size REList (var) List of recipient data elements HashAlg This defines the hash algorithm used to calculate the public key hash of each public key used for encryption. This field currently supports only the following value for SHA-1 0x8004 - SHA1 HSize This defines the size of a hashed public key defined in REHData. REList This is a variable length of list of recipient data. Each element in this list consists of a Recipient Element data structure as follows: Recipient Element (REList) Data Structure: Value Size Description ----- ---- ----------- RESize 2 bytes Size of REHData + REKData REHData HSize Hash of recipients public key REKData (var) Simple key blob RESize This defines the size of an individual REList element. This value is the combined size of the REHData field + REKData field. REHData is defined by HSize. REKData is variable and can be calculated for each REList element using RESize and HSize. REHData Hashed public key for this recipient. REKData Simple Key Blob. The format of this data structure is identical to that defined in the Microsoft CryptoAPI and generated using the CryptExportKey() function. The version of the Simple Key Blob supported at this time is 0x02 as defined by Microsoft. 5. Certificate Processing - Central Directory Encryption: Central Directory Encryption using Digital Certificates will operate in a manner similar to that of Single Password Central Directory Encryption. This record will only be present when there is data to place into it. Currently, data is placed into this record when digital certificates are used for either encrypting or signing the files within a ZIP file. When only password encryption is used with no certificate encryption or digital signing, this record is not currently needed. When present, this record will appear before the start of the actual Central Directory data structure and will be located immediately after the Archive Decryption Header if the Central Directory is encrypted. The Archive Extra Data record will be used to store the following information. Additional data may be added in future versions. Extra Data Fields: 0x0014 - PKCS#7 Store for X.509 Certificates 0x0016 - X.509 Certificate ID and Signature for central directory 0x0019 - PKCS#7 Encryption Recipient Certificate List The 0x0014 and 0x0016 Extra Data records that otherwise would be located in the first record of the Central Directory for digital certificate processing. When encrypting or compressing the Central Directory, the 0x0014 and 0x0016 records must be located in the Archive Extra Data record and they should not remain in the first Central Directory record. The Archive Extra Data record will also be used to store the 0x0019 data. When present, the size of the Archive Extra Data record will be included in the size of the Central Directory. The data of the Archive Extra Data record will also be compressed and encrypted along with the Central Directory data structure. 6. Certificate Processing Differences: The Certificate Processing Method of encryption differs from the Single Password Symmetric Encryption Method as follows. Instead of using a user-defined password to generate a master session key, cryptographically random data is used. The key material is then wrapped using standard key-wrapping techniques. This key material is wrapped using the public key of each recipient that will need to decrypt the file using their corresponding private key. This specification currently assumes digital certificates will follow the X.509 V3 format for 1024 bit and higher RSA format digital certificates. Implementation of this Certificate Processing Method requires supporting logic for key access and management. This logic is outside the scope of this specification. License Agreement: ----------------- The features set forth in this Section XIV (the "Strong Encryption Specification") are covered by a pending patent application. Portions of this Strong Encryption technology are available for use at no charge under the following terms and conditions. 1. License Grant. a. NOTICE TO USER. PLEASE READ THIS ENTIRE SECTION XIV OF THE APPNOTE (THE "AGREEMENT") CAREFULLY. BY USING ALL OR ANY PORTION OF THE LICENSED TECHNOLOGY, YOU ACCEPT ALL THE TERMS AND CONDITIONS OF THIS AGREEMENT AND YOU AGREE THAT THIS AGREEMENT IS ENFORCEABLE LIKE ANY WRITTEN NEGOTIATED AGREEMENT SIGNED BY YOU. IF YOU DO NOT AGREE, DO NOT USE THE LICENSED TECHNOLOGY. b. Definitions. i. "Licensed Technology" shall mean that proprietary technology now or hereafter owned or controlled by PKWare, Inc. ("PKWARE") or any subsidiary or affiliate that covers or is necessary to be used to give software the ability to a) extract and decrypt data from zip files encrypted using any methods of data encryption and key processing which are published in this APPNOTE or any prior APPNOTE, as supplemented by any Additional Compatibility Information; and b) encrypt file contents as part of .ZIP file processing using only the Single Password Symmetric Encryption Method as published in this APPNOTE or any prior APPNOTE, as supplemented by any Additional Compatibility Information. For purposes of this AGREEMENT, "Additional Compatibility Information" means, with regard to any method of data encryption and key processing published in this or any prior APPNOTE, any corrections, additions, or clarifications to the information in such APPNOTE that are required in order to give software the ability to successfully extract and decrypt zip files (or, but solely in the case of the Single Password Symmetric Encryption Method, to successfully encrypt zip files) in a manner interoperable with the actual implementation of such method in any PKWARE product that is documented or publicly described by PKWARE as being able to create, or to extract and decrypt, zip files using that method. ii. "Licensed Products" shall mean any products you produce that incorporate the Licensed Technology. c. License to Licensed Technology. PKWARE hereby grants to you a non-exclusive license to use the Licensed Technology for the purpose of manufacturing, offering, selling and using Licensed Products, which license shall extend to permit the practice of all claims in any patent or patent application (collectively, "Patents") now or hereafter owned or controlled by PKWARE in any jurisdiction in the world that are infringed by implementation of the Licensed Technology. You have the right to sublicense rights you receive under the terms of this AGREEMENT for the purpose of allowing sublicensee to manufacture, offer, sell and use products that incorporate all or a portion of any of your Licensed Products, but if you do, you agree to i) impose the same restrictions on any such sublicensee as these terms impose on you and ii) notify the sublicensee, by means chosen by you in your unfettered discretion, including a notice on your web site, of the terms of this AGREEMENT and make available to each sublicensee the full text of this APPNOTE. Further, PKWARE hereby grants to you a non-exclusive right to reproduce and distribute, in any form, copies of this APPNOTE, without modification. Notwithstanding anything to the contrary in this AGREEMENT, you have the right to sublicense the rights, without any of the restrictions described above or elsewhere in this AGREEMENT, to use, offer to sell and sell Licensed Technology as incorporated in executable object code or byte code forms of your Licensed Products. Any sublicense to use the Licensed Technology incorporated in a Licensed Product granted by you shall survive the termination of this AGREEMENT for any reason. PKWARE warrants that this license shall continue to encumber the Licensed Technology regardless of changes in ownership of the Licensed Technology. d. Proprietary Notices. i. With respect to any Licensed Product that is distributed by you either in source code form or in the form of an object code library of externally callable functions that has been designed by you for incorporation into third party products, you agree to include, in the source code, or in the case of an object code library, in accompanying documentation, a notice using the words "patent pending" until a patent is issued to PKWARE covering any portion of the Licensed Technology or PKWARE provides notice, by means chosen by PKWARE in its unfettered discretion, that it no longer has any patent pending covering any portion of the Licensed Technology. With respect to any Licensed Product, upon your becoming aware that at least one patent has been granted covering the Licensed Technology, you agree to include in any revisions made by you to the documentation (or any source code distributed by you) the words "Pat. No.", or "Patent Number" and the patent number or numbers of the applicable patent or patents. PKWARE shall, from time to time, inform you of the patent number or numbers of the patents covering the Licensed Technology, by means chosen by PKWARE in its unfettered discretion, including a notice on its web site. It shall be a violation of the terms of this AGREEMENT for you to sell Licensed Products without complying with the foregoing marking provisions. ii. You acknowledge that the terms of this AGREEMENT do not grant you any license or other right to use any PKWARE trademark in connection with the sale, offering for sale, distribution and delivery of the Licensed Products, or in connection with the advertising, promotion and offering of the Licensed Products. You acknowledge PKWARE's ownership of the PKZIP trademark and all other marks owned by PKWARE. e. Covenant of Compliance and Remedies. To the extent that you have elected to implement portions of the Licensed Technology, you agree to use reasonable diligence to comply with those portions of this Section XIV, as modified or supplemented by Additional Compatibility Information available to you, describing the portions of the Licensed Technology that you have elected to implement. Upon reasonable request by PKWARE, you will provide written notice to PKWARE identifying which version of this APPNOTE you have relied upon for your implementation of any specified Licensed Product. If any substantial non-compliance with the terms of this AGREEMENT is determined to exist, you will make such changes as necessary to bring your Licensed Products into substantial compliance with the terms of this AGREEMENT. If, within sixty days of receipt of notice that a Licensed Product fails to comply with the terms of this AGREEMENT, you fail to make such changes as necessary to bring your Licensed Products into compliance with the terms of this AGREEMENT, PKWARE may terminate your rights under this AGREEMENT. PKWARE does not waive and expressly reserves the right to pursue any and all additional remedies that are or may become available to PKWARE. f. Warranty and Indemnification Regarding Exportation. You realize and acknowledge that, as between yourself and PKWARE, you are fully responsible for compliance with the import and export laws and regulations of any country in or to which you import or export any Licensed Products, and you agree to hold PKWARE harmless from any claim of violation of any such import or export laws. g. Patent Infringement. You agree that you will not bring or threaten to bring any action against PKWARE for infringement of the claims of any patent owned or controlled by you solely as a result of PKWARE's own implementation of the Licensed Technology. As its exclusive remedy for your breach of the foregoing agreement, PKWARE reserves the right to suspend or terminate all rights granted under the terms of this AGREEMENT if you bring or threaten to bring any such action against PKWARE, effective immediately upon delivery of written notice of suspension or termination to you. h. Governing Law. The license granted in this AGREEMENT shall be governed by and construed under the laws of the State of Wisconsin and the United States. i. Revisions and Notice. The license granted in this APPNOTE is irrevocable, except as expressly set forth above. You agree and understand that any changes which PKWARE determines to make to this APPNOTE shall be posted at the same location as the current APPNOTE or at a location which will be identified by means chosen by PKWARE, including a notice on its web site, and shall be available for adoption by you immediately upon such posting, or at such other time as PKWARE shall determine. Any changes to the terms of the license published in a subsequent version of this AGREEMENT shall be binding upon you only with respect to your products that (i) incorporate any Licensed Technology (as defined in the subsequent AGREEMENT) that is not otherwise included in the definition of Licensed Technology under this AGREEMENT, or (ii) that you expressly identify are to be licensed under the subsequent AGREEMENT, which identification shall be by written notice with reference to the APPNOTE (version and release date or other unique identifier) in which the subsequent AGREEMENT is published. PKWARE agrees to identify each change to this APPNOTE by using a unique version and release date identifier or other unique identifier. j. Warranty by PKWARE PKWare, Inc. warrants that it has the right to grant the license hereunder. XV. Change Process ------------------ In order for the .ZIP file format to remain a viable definition, this specification should be considered as open for periodic review and revision. Although this format was originally designed with a certain level of extensibility, not all changes in technology (present or future) were or will be necessarily considered in its design. If your application requires new definitions to the extensible sections in this format, or if you would like to submit new data structures, please forward your request to [email protected]. All submissions will be reviewed by the ZIP File Specification Committee for possible inclusion into future versions of this specification. Periodic revisions to this specification will be published to ensure interoperability. We encourage comments and feedback that may help improve clarity or content. XVI. Acknowledgements --------------------- In addition to the above mentioned contributors to PKZIP and PKUNZIP, I would like to extend special thanks to Robert Mahoney for suggesting the extension .ZIP for this software. XVII. 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.

浅谈Service

2024年01月14日

一开始学习Android都会被告诉Android的四大组件有Activity、Service、Content Provider、Broadcast Receiver。除Service外的三者很早就接触了，并且认为有一点浅薄的理解。但是Service不是。工作以来没有接触过与Service相关的业务，尝试过理解Service，但一直不是很理解。最近刚好用到，浅浅的记录一下最近的理解。

2023年终总结

2023年12月29日

稀里糊涂又是一年，趁今天是2023的最后一个工作日，简简单单总结一下这一年发生的事和变化。工作 # 从年初开始打算离职，听说行情不好一直没能实践，知道六月份开始写鸿蒙应用，加上情感上的因素，综合在一起终于决定离职，还是推脱了很久才提出。

关于OTP、HOTP和TOTP

2023年11月12日

OTP # OTP(one-time passwords)，是MFA(multi-factor authentication)中常用的一种。添加除了账号密码之外额外的验证方式，例如某些APP会要求用户输入密码之后再次输入短信验证码，同时通过了才被允许登录，增加骇客访问被保护内容的难度。

略解Okhttp

2023年10月27日

使用 # 1 2 3 4 5 val okHttpClient = OkHttpClient() val request = Request.Builder().url("www.baidu.com").build() val response = okHttpClient.newCall(request).execute() response.body?.string() ... 流程 # 创建OkHttpClient对象创建Request对象同步/异步请求创建OkHttpClient对象 # 创建Request对象 # Request对象的创建由建造者完成，默认的方法是GET，headers为空。

一种诡异的方式判断Activity或Fragment状态

2023年10月27日

理论上可以Activity或者Fragment的状态: 1 lifecycle.currentState.isAtLeast(Lifecycle.State.STARTED)

Android抓包

2023年10月27日

原理 # 正常情况下，客户端和服务端通讯先要建立https连接，客户端公国CA证书里的公钥和一个随机数生成对称秘钥，后续通讯通过对称秘钥加密解密。流程图：抓包常用的有两种方式： Mitm（中间人攻击）安装CA证书中间人攻击的原理并不是代理软件使用原始证书解密一方的请求。而是同时担当客户端和服务端的角色，客户端和服务端建立连接时，就已经在中间起作用，客户端与服务端的三次握手变成了客户端和代理软件、代理软件和服务端分别完成三次握手共两次。

Shortcut in Android

2023年10月27日

Android 快捷方式 # 在Android系统中，快捷方式是一种非常方便的工具，可以帮助用户更快速地访问他们经常使用的应用程序或功能。用户可以在主屏幕或应用程序抽屉中创建快捷方式，并可自定义快捷方式的名称和图标。

Android中常见的尺寸单位

2023年10月27日

px dpi dp # px # 像素是组成光栅图片Raster graphics）的最小单位。 pixel，像素点，影像显示的基本单位。(单位！荧幕可以解析的最小的点，ps中放大到最大后的一个小块) 像素分为数码像素和屏幕像素数码像素是一种虚拟化的数字，大小可以任意，或者说没有实际的物理尺寸大小。通常我们理解的一个像素是1：1的正方形块，这只是它最常见的一种形式，有的摄像机捕获的像素并不是1：1的正方向，比如：1：1.21，1：1.09，1：1.46等等。

透明状态栏和透明导航栏

2023年10月27日

设置Window Flag要在setContentView前。不在前目前发现改变状态栏不会生效实现透明状态栏 # 透明状态栏以来官方提供的API，重要改动主要有三个： Android 4.4 Android 5.0 Android 6.0 Android 4.4 # 从4.4开始支持透明状态栏，这个版本是半透明，有一层遮罩：