The following are the known types of zipfile extra fields as of this writing. Extra fields are documented in PKWARE's appnote.txt and are intended to allow for backward- and forward-compatible extensions to the zipfile format. Multiple extra-field types may be chained together, provided that the total length of all extra-field data is less than 64KB. (In fact, PKWARE requires that the total length of the entire file header, including timestamp, file attributes, filename, comment, extra field, etc., be no more than 64KB.) Each extra-field type (or subblock) must contain a four-byte header con- sisting of a two-byte header ID and a two-byte length (little-endian) for the remaining data in the subblock. If there are additional subblocks within the extra field, the header for each one will appear immediately following the data for the previous subblock (i.e., with no padding for alignment). All integer fields in the descriptions below are in little-endian (Intel) format unless otherwise specified. Note that "Short" means two bytes, "Long" means four bytes, and "Long-Long" means eight bytes, regardless of their native sizes. Unless specifically noted, all integer fields should be interpreted as unsigned (non-negative) numbers. Christian Spieler, 20010517 Updated to include the Unicode extra fields. Added new Unix extra field. Ed Gordon, 20060819, 20070607, 20070909, 20080426, 20080509 ------------------------- 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 0x0009 OS/2 extended attributes (also Info-ZIP) 0x000a NTFS (Win9x/WinNT FileTimes) 0x000c OpenVMS (also Info-ZIP) 0x000d Unix 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 The Header ID mappings defined by Info-ZIP and third parties are: 0x0065 IBM S/390 attributes - uncompressed 0x0066 IBM S/390 attributes - compressed 0x07c8 Info-ZIP Macintosh (old, J. Lee) 0x2605 ZipIt Macintosh (first version) 0x2705 ZipIt Macintosh v 1.3.5 and newer (w/o full filename) 0x334d Info-ZIP Macintosh (new, D. Haase's 'Mac3' field ) 0x4154 Tandem NSK 0x4341 Acorn/SparkFS (David Pilling) 0x4453 Windows NT security descriptor (binary ACL) 0x4704 VM/CMS 0x470f MVS 0x4854 Theos, old inofficial port 0x4b46 FWKCS MD5 (see below) 0x4c41 OS/2 access control list (text ACL) 0x4d49 Info-ZIP OpenVMS (obsolete) 0x4d63 Macintosh SmartZIP, by Macro Bambini 0x4f4c Xceed original location extra field 0x5356 AOS/VS (binary ACL) 0x5455 extended timestamp 0x5855 Info-ZIP Unix (original; also OS/2, NT, etc.) 0x554e Xceed unicode extra field 0x6375 Info-ZIP Unicode Comment 0x6542 BeOS (BeBox, PowerMac, etc.) 0x6854 Theos 0x7075 Info-ZIP Unicode Path 0x756e ASi Unix 0x7855 Info-ZIP Unix (previous new) 0x7875 Info-ZIP Unix (new) 0xfb4a SMS/QDOS The following are detailed descriptions of the known extra-field block types: -OS/2 Extended Attributes Extra Field: ==================================== The following is the layout of the OS/2 extended attributes "extra" block. (Last Revision 19960922) Note: all fields stored in Intel low-byte/high-byte order. Local-header version: Value Size Description ----- ---- ----------- (OS/2) 0x0009 Short tag for this extra block type TSize Short total data size for this block BSize Long uncompressed EA data size CType Short compression type EACRC Long CRC value for uncompressed EA data (var.) variable compressed EA data Central-header version: Value Size Description ----- ---- ----------- (OS/2) 0x0009 Short tag for this extra block type TSize Short total data size for this block (4) BSize Long size of uncompressed local EA data The value of CType is interpreted according to the "compression method" section above; i.e., 0 for stored, 8 for deflated, etc. The OS/2 extended attribute structure (FEA2LIST) is compressed and then stored in its entirety within this structure. There will only ever be one block of data in the variable-length field. -OS/2 Access Control List Extra Field: ==================================== The following is the layout of the OS/2 ACL extra block. (Last Revision 19960922) Local-header version: Value Size Description ----- ---- ----------- (ACL) 0x4c41 Short tag for this extra block type ("AL") TSize Short total data size for this block BSize Long uncompressed ACL data size CType Short compression type EACRC Long CRC value for uncompressed ACL data (var.) variable compressed ACL data Central-header version: Value Size Description ----- ---- ----------- (ACL) 0x4c41 Short tag for this extra block type ("AL") TSize Short total data size for this block (4) BSize Long size of uncompressed local ACL data The value of CType is interpreted according to the "compression method" section above; i.e., 0 for stored, 8 for deflated, etc. The uncompressed ACL data consist of a text header of the form "ACL1:%hX,%hd\n", where the first field is the OS/2 ACCINFO acc_attr member and the second is acc_count, followed by acc_count strings of the form "%s,%hx\n", where the first field is acl_ugname (user group name) and the second acl_access. This block type will be extended for other operating systems as needed. -Windows NT Security Descriptor Extra Field: ========================================== The following is the layout of the NT Security Descriptor (another type of ACL) extra block. (Last Revision 19960922) Local-header version: Value Size Description ----- ---- ----------- (SD) 0x4453 Short tag for this extra block type ("SD") TSize Short total data size for this block BSize Long uncompressed SD data size Version Byte version of uncompressed SD data format CType Short compression type EACRC Long CRC value for uncompressed SD data (var.) variable compressed SD data Central-header version: Value Size Description ----- ---- ----------- (SD) 0x4453 Short tag for this extra block type ("SD") TSize Short total data size for this block (4) BSize Long size of uncompressed local SD data The value of CType is interpreted according to the "compression method" section above; i.e., 0 for stored, 8 for deflated, etc. Version specifies how the compressed data are to be interpreted and allows for future expansion of this extra field type. Currently only version 0 is defined. For version 0, the compressed data are to be interpreted as a single valid Windows NT SECURITY_DESCRIPTOR data structure, in self-relative format. -PKWARE Win95/WinNT Extra Field: ============================== The following description covers PKWARE's "NTFS" attributes "extra" block, introduced with the release of PKZIP 2.50 for Windows. (Last Revision 20001118) (Note: At this time the Mtime, Atime and Ctime values may be used on any WIN32 system.) [Info-ZIP note: In the current implementations, this field has a fixed total data size of 32 bytes and is only stored as local extra field.] Value Size Description ----- ---- ----------- (NTFS) 0x000a Short Tag for this "extra" block type TSize Short Total Data Size for this block Reserved Long for future use Tag1 Short NTFS attribute tag value #1 Size1 Short Size of attribute #1, in bytes (var.) SubSize1 Attribute #1 data . . . TagN Short NTFS attribute tag value #N SizeN Short Size of attribute #N, in bytes (var.) SubSize1 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 (24) Mtime 8 bytes 64-bit NTFS file last modification time Atime 8 bytes 64-bit NTFS file last access time Ctime 8 bytes 64-bit NTFS file creation time The total length for this block is 28 bytes, resulting in a fixed size value of 32 for the TSize field of the NTFS block. The NTFS filetimes are 64-bit unsigned integers, stored in Intel (least significant byte first) byte order. They determine the number of 1.0E-07 seconds (1/10th microseconds!) past WinNT "epoch", which is "01-Jan-1601 00:00:00 UTC". -PKWARE OpenVMS Extra Field: ========================== The following is the layout of PKWARE's OpenVMS attributes "extra" block. (Last Revision 12/17/91) Note: all fields stored in Intel low-byte/high-byte order. Value Size Description ----- ---- ----------- (VMS) 0x000c Short Tag for this "extra" block type TSize Short Total Data Size for this block CRC Long 32-bit CRC for remainder of the block Tag1 Short OpenVMS attribute tag value #1 Size1 Short Size of attribute #1, in bytes (var.) Size1 Attribute #1 data . . . TagN Short OpenVMS attribute tage value #N SizeN Short 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. -Info-ZIP VMS Extra Field: ======================== The following is the layout of Info-ZIP's VMS attributes extra block for VAX or Alpha AXP. The local-header and central-header versions are identical. (Last Revision 19960922) Value Size Description ----- ---- ----------- (VMS2) 0x4d49 Short tag for this extra block type ("JM") TSize Short total data size for this block ID Long block ID Flags Short info bytes BSize Short uncompressed block size Reserved Long (reserved) (var.) variable compressed VMS file-attributes block The block ID is one of the following unterminated strings: "VFAB" struct FAB "VALL" struct XABALL "VFHC" struct XABFHC "VDAT" struct XABDAT "VRDT" struct XABRDT "VPRO" struct XABPRO "VKEY" struct XABKEY "VMSV" version (e.g., "V6.1"; truncated at hyphen) "VNAM" reserved The lower three bits of Flags indicate the compression method. The currently defined methods are: 0 stored (not compressed) 1 simple "RLE" 2 deflated The "RLE" method simply replaces zero-valued bytes with zero-valued bits and non-zero-valued bytes with a "1" bit followed by the byte value. The variable-length compressed data contains only the data corre- sponding to the indicated structure or string. Typically multiple VMS2 extra fields are present (each with a unique block type). -Info-ZIP Macintosh Extra Field: ============================== The following is the layout of the (old) Info-ZIP resource-fork extra block for Macintosh. The local-header and central-header versions are identical. (Last Revision 19960922) Value Size Description ----- ---- ----------- (Mac) 0x07c8 Short tag for this extra block type TSize Short total data size for this block "JLEE" beLong extra-field signature FInfo 16 bytes Macintosh FInfo structure CrDat beLong HParamBlockRec fileParam.ioFlCrDat MdDat beLong HParamBlockRec fileParam.ioFlMdDat Flags beLong info bits DirID beLong HParamBlockRec fileParam.ioDirID VolName 28 bytes volume name (optional) All fields but the first two are in native Macintosh format (big-endian Motorola order, not little-endian Intel). The least significant bit of Flags is 1 if the file is a data fork, 0 other- wise. In addition, if this extra field is present, the filename has an extra 'd' or 'r' appended to indicate data fork or resource fork. The 28-byte VolName field may be omitted. -ZipIt Macintosh Extra Field (long): ================================== The following is the layout of the ZipIt extra block for Macintosh. The local-header and central-header versions are identical. (Last Revision 19970130) 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): =================================== 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 that do not need a "full Mac filename" record. The local-header and central-header versions are identical. (Last Revision 19980903) 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 -Info-ZIP Macintosh Extra Field (new): ==================================== The following is the layout of the (new) Info-ZIP extra block for Macintosh, designed by Dirk Haase. All values are in little-endian. (Last Revision 19981005) Local-header version: Value Size Description ----- ---- ----------- (Mac3) 0x334d Short tag for this extra block type ("M3") TSize Short total data size for this block BSize Long uncompressed finder attribute data size Flags Short info bits fdType Byte[4] Type of the File (4-byte string) fdCreator Byte[4] Creator of the File (4-byte string) (CType) Short compression type (CRC) Long CRC value for uncompressed MacOS data Attribs variable finder attribute data (see below) Central-header version: Value Size Description ----- ---- ----------- (Mac3) 0x334d Short tag for this extra block type ("M3") TSize Short total data size for this block BSize Long uncompressed finder attribute data size Flags Short info bits fdType Byte[4] Type of the File (4-byte string) fdCreator Byte[4] Creator of the File (4-byte string) The third bit of Flags in both headers indicates whether the LOCAL extra field is uncompressed (and therefore whether CType and CRC are omitted): Bits of the Flags: bit 0 if set, file is a data fork; otherwise unset bit 1 if set, filename will be not changed bit 2 if set, Attribs is uncompressed (no CType, CRC) bit 3 if set, date and times are in 64 bit if zero date and times are in 32 bit. bit 4 if set, timezone offsets fields for the native Mac times are omitted (UTC support deactivated) bits 5-15 reserved; Attributes: Attribs is a Mac-specific block of data in little-endian format with the following structure (if compressed, uncompress it first): Value Size Description ----- ---- ----------- fdFlags Short Finder Flags fdLocation.v Short Finder Icon Location fdLocation.h Short Finder Icon Location fdFldr Short Folder containing file FXInfo 16 bytes Macintosh FXInfo structure FXInfo-Structure: fdIconID Short fdUnused[3] Short unused but reserved 6 bytes fdScript Byte Script flag and number fdXFlags Byte More flag bits fdComment Short Comment ID fdPutAway Long Home Dir ID FVersNum Byte file version number may be not used by MacOS ACUser Byte directory access rights FlCrDat ULong date and time of creation FlMdDat ULong date and time of last modification FlBkDat ULong date and time of last backup These time numbers are original Mac FileTime values (local time!). Currently, date-time width is 32-bit, but future version may support be 64-bit times (see flags) CrGMTOffs Long(signed!) difference "local Creat. time - UTC" MdGMTOffs Long(signed!) difference "local Modif. time - UTC" BkGMTOffs Long(signed!) difference "local Backup time - UTC" These "local time - UTC" differences (stored in seconds) may be used to support timestamp adjustment after inter-timezone transfer. These fields are optional; bit 4 of the flags word controls their presence. Charset Short TextEncodingBase (Charset) valid for the following two fields FullPath variable Path of the current file. Zero terminated string (C-String) Currently coded in the native Charset. Comment variable Finder Comment of the current file. Zero terminated string (C-String) Currently coded in the native Charset. -SmartZIP Macintosh Extra Field: ==================================== The following is the layout of the SmartZIP extra block for Macintosh, designed by Marco Bambini. Local-header version: Value Size Description ----- ---- ----------- 0x4d63 Short tag for this extra block type ("cM") TSize Short total data size for this block (64) "dZip" beLong extra-field signature fdType Byte[4] Type of the File (4-byte string) fdCreator Byte[4] Creator of the File (4-byte string) fdFlags beShort Finder Flags fdLocation.v beShort Finder Icon Location fdLocation.h beShort Finder Icon Location fdFldr beShort Folder containing file CrDat beLong HParamBlockRec fileParam.ioFlCrDat MdDat beLong HParamBlockRec fileParam.ioFlMdDat frScroll.v Byte vertical pos. of folder's scroll bar fdScript Byte Script flag and number frScroll.h Byte horizontal pos. of folder's scroll bar fdXFlags Byte More flag bits FileName Byte[32] full Macintosh filename (pascal string) All fields but the first two are in native Macintosh format (big-endian Motorola order, not little-endian Intel). The extra field size is fixed to 64 bytes. The local-header and central-header versions are identical. -Acorn SparkFS Extra Field: ========================= The following is the layout of David Pilling's SparkFS extra block for Acorn RISC OS. The local-header and central-header versions are identical. (Last Revision 19960922) Value Size Description ----- ---- ----------- (Acorn) 0x4341 Short tag for this extra block type ("AC") TSize Short total data size for this block (20) "ARC0" Long extra-field signature LoadAddr Long load address or file type ExecAddr Long exec address Attr Long file permissions Zero Long reserved; always zero The following bits of Attr are associated with the given file permissions: bit 0 user-writable ('W') bit 1 user-readable ('R') bit 2 reserved bit 3 locked ('L') bit 4 publicly writable ('w') bit 5 publicly readable ('r') bit 6 reserved bit 7 reserved -VM/CMS Extra Field: ================== The following is the layout of the file-attributes extra block for VM/CMS. The local-header and central-header versions are identical. (Last Revision 19960922) Value Size Description ----- ---- ----------- (VM/CMS) 0x4704 Short tag for this extra block type TSize Short total data size for this block flData variable file attributes data flData is an uncompressed fldata_t struct. -MVS Extra Field: =============== The following is the layout of the file-attributes extra block for MVS. The local-header and central-header versions are identical. (Last Revision 19960922) Value Size Description ----- ---- ----------- (MVS) 0x470f Short tag for this extra block type TSize Short total data size for this block flData variable file attributes data flData is an uncompressed fldata_t struct. -PKWARE Unix Extra Field: ======================== The following is the layout of PKWARE's Unix "extra" block. It was introduced with the release of PKZIP for Unix 2.50. Note: all fields are stored in Intel low-byte/high-byte order. (Last Revision 19980901) This field has a minimum data size of 12 bytes and is only stored as local extra field. Value Size Description ----- ---- ----------- (Unix0) 0x000d Short Tag for this "extra" block type TSize Short Total Data Size for this block AcTime Long time of last access (UTC/GMT) ModTime Long time of last modification (UTC/GMT) UID Short Unix user ID GID Short Unix group ID (var) variable Variable length data field The variable length data field will contain file type specific data. Currently the only values allowed are the original "linked to" file names for hard or symbolic links, and the major and minor device node numbers for character and block device nodes. Since device nodes cannot be either symbolic or hard links, only one set of variable length data is stored. Link files will have the name of the original file stored. This name is NOT NULL terminated. Its size can be determined by checking TSize - 12. Device entries will have eight bytes stored as two 4 byte entries (in little-endian format). The first entry will be the major device number, and the second the minor device number. [Info-ZIP note: The fixed part of this field has the same layout as Info-ZIP's abandoned "Unix1 timestamps & owner ID info" extra field; only the two tag bytes are different.] -PATCH Descriptor Extra Field: ============================ 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 Short Tag for this "extra" block type TSize Short Size of the total "extra" block Version Short Version of the descriptor Flags Long Actions and reactions (see below) OldSize Long Size of the file about to be patched OldCRC Long 32-bit CRC of the file about to be patched NewSize Long Size of the resulting file NewCRC Long 32-bit CRC of the resulting file Actions and reactions Bits Description ---- ---------------- 0 Use for autodetection 1 Treat as selfpatch 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 -PKCS#7 Store for X.509 Certificates: =================================== This field is contains the information about each certificate a file is signed with. This field should only 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 SSize 2 bytes Size of the store data SData (variable) Data about the store SData Value Size Description ----- ---- ----------- Version 2 bytes Version number, 0x0001 for now StoreD (variable) Actual store data The StoreD member is suitable for passing as the pbData member of a CRYPT_DATA_BLOB to the CertOpenStore() function in Microsoft's CryptoAPI. The SSize member above will be cbData + 6, where cbData is the cbData member of the same CRYPT_DATA_BLOB. The encoding type to pass to CertOpenStore() should be PKCS_7_ANS_ENCODING | X509_ASN_ENCODING. -X.509 Certificate ID and Signature for individual file: ====================================================== This field contains the information about which certificate in the PKCS#7 Store was used to sign the 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 CSize 2 bytes Size of Method Method (variable) Method Value Size Description ----- ---- ----------- Version 2 bytes Version number, for now 0x0001 AlgID 2 bytes Algorithm ID used for signing IDSize 2 bytes Size of Certificate ID data CertID (variable) Certificate ID data SigSize 2 bytes Size of Signature data Sig (variable) Signature data CertID Value Size Description ----- ---- ----------- Size1 4 bytes Size of CertID, should be (IDSize - 4) Size1 4 bytes A bug in version one causes this value to appear twice. IssSize 4 bytes Issuer data size Issuer (variable) Issuer data SerSize 4 bytes Serial Number size Serial (variable) Serial Number data The Issuer and IssSize members are suitable for creating a CRYPT_DATA_BLOB to be the Issuer member of a CERT_INFO struct. The Serial and SerSize members would be the SerialNumber member of the same CERT_INFO struct. This struct would be used to find the certificate in the store the file was signed with. Those structures are from the MS CryptoAPI. Sig and SigSize are the actual signature data and size generated by signing the file with the MS CryptoAPI using a hash created with the given AlgID. -X.509 Certificate ID and Signature for central directory: ======================================================== This field contains the information about which certificate in the PKCS#7 Store was used to sign the central directory. It should only appear with the first central directory record, along with the store. The data structure is the same as the CID, except that SigSize will be 0, and there will be no Sig member. This field is also kept after the last central directory record, as the signature data (ID 0x05054b50, it looks like a central directory record of a different type). This second copy of the data is the Signature Data member of the record, and will have a SigSize that is non-zero, and will have Sig data. Note: all fields stored in Intel low-byte/high-byte order. Value Size Description ----- ---- ----------- (CDID) 0x0016 2 bytes Tag for this "extra" block type CSize 2 bytes Size of Method Method (variable) -ZIP64 Extended Information Extra Field: ====================================== 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 uncompresseed 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. -Extended Timestamp Extra Field: ============================== The following is the layout of the extended-timestamp extra block. (Last Revision 19970118) Local-header version: Value Size Description ----- ---- ----------- (time) 0x5455 Short tag for this extra block type ("UT") TSize Short total data size for this block Flags Byte info bits (ModTime) Long time of last modification (UTC/GMT) (AcTime) Long time of last access (UTC/GMT) (CrTime) Long time of original creation (UTC/GMT) Central-header version: Value Size Description ----- ---- ----------- (time) 0x5455 Short tag for this extra block type ("UT") TSize Short total data size for this block Flags Byte info bits (refers to local header!) (ModTime) Long time of last modification (UTC/GMT) The central-header extra field contains the modification time only, or no timestamp at all. TSize is used to flag its presence or absence. But note: If "Flags" indicates that Modtime is present in the local header field, it MUST be present in the central header field, too! This correspondence is required because the modification time value may be used to support trans-timezone freshening and updating operations with zip archives. The time values are in standard Unix signed-long format, indicating the number of seconds since 1 January 1970 00:00:00. The times are relative to Coordinated Universal Time (UTC), also sometimes referred to as Greenwich Mean Time (GMT). To convert to local time, the software must know the local timezone offset from UTC/GMT. The lower three bits of Flags in both headers indicate which time- stamps are present in the LOCAL extra field: bit 0 if set, modification time is present bit 1 if set, access time is present bit 2 if set, creation time is present bits 3-7 reserved for additional timestamps; not set Those times that are present will appear in the order indicated, but any combination of times may be omitted. (Creation time may be present without access time, for example.) TSize should equal (1 + 4*(number of set bits in Flags)), as the block is currently defined. Other timestamps may be added in the future. -Info-ZIP Unix Extra Field (type 1): ================================== The following is the layout of the old Info-ZIP extra block for Unix. It has been replaced by the extended-timestamp extra block (0x5455) and the Unix type 2 extra block (0x7855). (Last Revision 19970118) Local-header version: Value Size Description ----- ---- ----------- (Unix1) 0x5855 Short tag for this extra block type ("UX") TSize Short total data size for this block AcTime Long time of last access (UTC/GMT) ModTime Long time of last modification (UTC/GMT) UID Short Unix user ID (optional) GID Short Unix group ID (optional) Central-header version: Value Size Description ----- ---- ----------- (Unix1) 0x5855 Short tag for this extra block type ("UX") TSize Short total data size for this block AcTime Long time of last access (GMT/UTC) ModTime Long time of last modification (GMT/UTC) The file access and modification times are in standard Unix signed- long format, indicating the number of seconds since 1 January 1970 00:00:00. The times are relative to Coordinated Universal Time (UTC), also sometimes referred to as Greenwich Mean Time (GMT). To convert to local time, the software must know the local timezone offset from UTC/GMT. The modification time may be used by non-Unix systems to support inter-timezone freshening and updating of zip archives. The local-header extra block may optionally contain UID and GID info for the file. The local-header TSize value is the only indication of this. Note that Unix UIDs and GIDs are usually specific to a particular machine, and they generally require root access to restore. This extra field type is obsolete, but it has been in use since mid-1994. Therefore future archiving software should continue to support it. Some guidelines: An archive member should either contain the old "Unix1" extra field block or the new extra field types "time" and/or "Unix2". If both the old "Unix1" block type and one or both of the new block types "time" and "Unix2" are found, the "Unix1" block should be considered invalid and ignored. Unarchiving software should recognize both old and new extra field block types, but the info from new types overrides the old "Unix1" field. Archiving software should recognize "Unix1" extra fields for timestamp comparison but never create it for updated, freshened or new archive members. When copying existing members to a new archive, any "Unix1" extra field blocks should be converted to the new "time" and/or "Unix2" types. -Info-ZIP Unix Extra Field (type 2): ================================== The following is the layout of the new Info-ZIP extra block for Unix. (Last Revision 19960922) Local-header version: Value Size Description ----- ---- ----------- (Unix2) 0x7855 Short tag for this extra block type ("Ux") TSize Short total data size for this block (4) UID Short Unix user ID GID Short Unix group ID Central-header version: Value Size Description ----- ---- ----------- (Unix2) 0x7855 Short tag for this extra block type ("Ux") TSize Short total data size for this block (0) The data size of the central-header version is zero; it is used solely as a flag that UID/GID info is present in the local-header extra field. If additional fields are ever added to the local version, the central version may be extended to indicate this. Note that Unix UIDs and GIDs are usually specific to a particular machine, and they generally require root access to restore. -ASi Unix Extra Field: ==================== The following is the layout of the ASi extra block for Unix. The local-header and central-header versions are identical. (Last Revision 19960916) Value Size Description ----- ---- ----------- (Unix3) 0x756e Short tag for this extra block type ("nu") TSize Short total data size for this block CRC Long CRC-32 of the remaining data Mode Short file permissions SizDev Long symlink'd size OR major/minor dev num UID Short user ID GID Short group ID (var.) variable symbolic link filename Mode is the standard Unix st_mode field from struct stat, containing user/group/other permissions, setuid/setgid and symlink info, etc. If Mode indicates that this file is a symbolic link, SizDev is the size of the file to which the link points. Otherwise, if the file is a device, SizDev contains the standard Unix st_rdev field from struct stat (includes the major and minor numbers of the device). SizDev is undefined in other cases. If Mode indicates that the file is a symbolic link, the final field will be the name of the file to which the link points. The file- name length can be inferred from TSize. [Note that TSize may incorrectly refer to the data size not counting the CRC; i.e., it may be four bytes too small.] -BeOS Extra Field: ================ The following is the layout of the file-attributes extra block for BeOS. (Last Revision 19970531) Local-header version: Value Size Description ----- ---- ----------- (BeOS) 0x6542 Short tag for this extra block type ("Be") TSize Short total data size for this block BSize Long uncompressed file attribute data size Flags Byte info bits (CType) Short compression type (CRC) Long CRC value for uncompressed file attribs Attribs variable file attribute data Central-header version: Value Size Description ----- ---- ----------- (BeOS) 0x6542 Short tag for this extra block type ("Be") TSize Short total data size for this block (5) BSize Long size of uncompr. local EF block data Flags Byte info bits The least significant bit of Flags in both headers indicates whether the LOCAL extra field is uncompressed (and therefore whether CType and CRC are omitted): bit 0 if set, Attribs is uncompressed (no CType, CRC) bits 1-7 reserved; if set, assume error or unknown data Currently the only supported compression types are deflated (type 8) and stored (type 0); the latter is not used by Info-ZIP's Zip but is supported by UnZip. Attribs is a BeOS-specific block of data in big-endian format with the following structure (if compressed, uncompress it first): Value Size Description ----- ---- ----------- Name variable attribute name (null-terminated string) Type Long attribute type (32-bit unsigned integer) Size Long Long data size for this sub-block (64 bits) Data variable attribute data The attribute structure is repeated for every attribute. The Data field may contain anything--text, flags, bitmaps, etc. -SMS/QDOS Extra Field: ==================== The following is the layout of the file-attributes extra block for SMS/QDOS. The local-header and central-header versions are identical. (Last Revision 19960929) Value Size Description ----- ---- ----------- (QDOS) 0xfb4a Short tag for this extra block type TSize Short total data size for this block LongID Long extra-field signature (ExtraID) Long additional signature/flag bytes QDirect 64 bytes qdirect structure LongID may be "QZHD" or "QDOS". In the latter case, ExtraID will be present. Its first three bytes are "02\0"; the last byte is currently undefined. QDirect contains the file's uncompressed directory info (qdirect struct). Its elements are in native (big-endian) format: d_length beLong file length d_access byte file access type d_type byte file type d_datalen beLong data length d_reserved beLong unused d_szname beShort size of filename d_name 36 bytes filename d_update beLong time of last update d_refdate beLong file version number d_backup beLong time of last backup (archive date) -AOS/VS Extra Field: ================== The following is the layout of the extra block for Data General AOS/VS. The local-header and central-header versions are identical. (Last Revision 19961125) Value Size Description ----- ---- ----------- (AOSVS) 0x5356 Short tag for this extra block type ("VS") TSize Short total data size for this block "FCI\0" Long extra-field signature Version Byte version of AOS/VS extra block (10 = 1.0) Fstat variable fstat packet AclBuf variable raw ACL data ($MXACL bytes) Fstat contains the file's uncompressed fstat packet, which is one of the following: normal fstat packet (P_FSTAT struct) DIR/CPD fstat packet (P_FSTAT_DIR struct) unit (device) fstat packet (P_FSTAT_UNIT struct) IPC file fstat packet (P_FSTAT_IPC struct) AclBuf contains the raw ACL data; its length is $MXACL. -Tandem NSK Extra Field: ====================== The following is the layout of the file-attributes extra block for Tandem NSK. The local-header and central-header versions are identical. (Last Revision 19981221) Value Size Description ----- ---- ----------- (TA) 0x4154 Short tag for this extra block type ("TA") TSize Short total data size for this block (20) NSKattrs 20 Bytes NSK attributes -THEOS Extra Field: ================= The following is the layout of the file-attributes extra block for Theos. The local-header and central-header versions are identical. (Last Revision 19990206) Value Size Description ----- ---- ----------- (Theos) 0x6854 Short 'Th' signature size Short size of extra block flags Byte reserved for future use filesize Long file size fileorg Byte type of file (see below) keylen Short key length for indexed and keyed files, data segment size for 16 bits programs reclen Short record length for indexed,keyed and direct, text segment size for 16 bits programs filegrow Byte growing factor for indexed,keyed and direct protect Byte protections (see below) reserved Short reserved for future use File types ========== 0x80 library (keyed access list of files) 0x40 directory 0x10 stream file 0x08 direct file 0x04 keyed file 0x02 indexed file 0x0e reserved 0x01 16 bits real mode program (obsolete) 0x21 16 bits protected mode program 0x41 32 bits protected mode program Protection codes ================ User protection --------------- 0x01 non readable 0x02 non writable 0x04 non executable 0x08 non erasable Other protection ---------------- 0x10 non readable 0x20 non writable 0x40 non executable Theos before 4.0 0x40 modified Theos 4.x 0x80 not hidden -THEOS old inofficial Extra Field: ================================ The following is the layout of an inoffical former version of a Theos file-attributes extra blocks. This layout was never published and is no longer created. However, UnZip can optionally support it when compiling with the option flag OLD_THEOS_EXTRA defined. Both the local-header and central-header versions are identical. (Last Revision 19990206) Value Size Description ----- ---- ----------- (THS0) 0x4854 Short 'TH' signature size Short size of extra block flags Short reserved for future use filesize Long file size reclen Short record length for indexed,keyed and direct, text segment size for 16 bits programs keylen Short key length for indexed and keyed files, data segment size for 16 bits programs filegrow Byte growing factor for indexed,keyed and direct reserved 3 Bytes reserved for future use -FWKCS MD5 Extra Field: ===================== The FWKCS Contents_Signature System, used in automatically identifying files independent of filename, optionally adds and uses an extra field to support the rapid creation of an enhanced contents_signature. There is no local-header version; the following applies only to the central header. (Last Revision 19961207) Central-header version: Value Size Description ----- ---- ----------- (MD5) 0x4b46 Short tag for this extra block type ("FK") TSize Short total data size for this block (19) "MD5" 3 bytes extra-field signature MD5hash 16 bytes 128-bit MD5 hash of uncompressed data (low byte first) When FWKCS revises a .ZIP file central directory to add this extra field for a file, it also replaces the central directory entry for that file's uncompressed file length with a measured value. FWKCS provides an option to strip this extra field, if present, from a .ZIP file central directory. In adding this extra field, FWKCS preserves .ZIP file Authenticity Verification; if stripping this extra field, FWKCS preserves all versions of AV through PKZIP version 2.04g. FWKCS, and FWKCS Contents_Signature System, are trademarks of Frederick W. Kantor. (1) R. Rivest, RFC1321.TXT, MIT Laboratory for Computer Science and RSA Data Security, Inc., April 1992. ll.76-77: "The MD5 algorithm is being placed in the public domain for review and possible adoption as a standard." -Info-ZIP Unicode Path Extra Field: ================================= Stores the UTF-8 version of the entry path as stored in the local header and central directory header. (Last Revision 20070912) Value Size Description ----- ---- ----------- (UPath) 0x7075 Short tag for this extra block type ("up") TSize Short total data size for this block Version 1 byte version of this extra field, currently 1 NameCRC32 4 bytes File Name Field CRC32 Checksum UnicodeName Variable UTF-8 version of the entry File Name Currently Version is set to the number 1. If there is a need to change this field, the version will be incremented. Changes may not be backward compatible so this extra field should not be used if the version is not recognized. The NameCRC32 is the standard zip CRC32 checksum of the File Name field in the header. This is used to verify that the header File Name field has not changed since the Unicode Path extra field was created. This can happen if a utility renames the entry but does not update the UTF-8 path extra field. If the CRC check fails, this UTF-8 Path Extra Field should be ignored and the File Name field in the header used instead. The UnicodeName is the UTF-8 version of the contents of the File Name field in the header. As UnicodeName is defined to be UTF-8, no UTF-8 byte order mark (BOM) is used. The length of this field is determined by subtracting the size of the previous fields from TSize. If both the File Name and Comment fields are UTF-8, the new General Purpose Bit Flag, bit 11 (Language encoding flag (EFS)), can be used to indicate that both the header File Name and Comment fields are UTF-8 and, in this case, the Unicode Path and Unicode Comment extra fields are not needed and should not be created. Note that, for backward compatibility, bit 11 should only be used if the native character set of the paths and comments being zipped up are already in UTF-8. The same method, either bit 11 or extra fields, should be used in both the local and central directory headers. -Info-ZIP Unicode Comment Extra Field: ==================================== Stores the UTF-8 version of the entry comment as stored in the central directory header. (Last Revision 20070912) Value Size Description ----- ---- ----------- (UCom) 0x6375 Short tag for this extra block type ("uc") TSize Short total data size for this block Version 1 byte version of this extra field, currently 1 ComCRC32 4 bytes Comment Field CRC32 Checksum UnicodeCom Variable UTF-8 version of the entry comment Currently Version is set to the number 1. If there is a need to change this field, the version will be incremented. Changes may not be backward compatible so this extra field should not be used if the version is not recognized. The ComCRC32 is the standard zip CRC32 checksum of the Comment field in the central directory header. This is used to verify that the comment field has not changed since the Unicode Comment extra field was created. This can happen if a utility changes the Comment field but does not update the UTF-8 Comment extra field. If the CRC check fails, this Unicode Comment extra field should be ignored and the Comment field in the header used. The UnicodeCom field is the UTF-8 version of the entry comment field in the header. As UnicodeCom is defined to be UTF-8, no UTF-8 byte order mark (BOM) is used. The length of this field is determined by subtracting the size of the previous fields from TSize. If both the File Name and Comment fields are UTF-8, the new General Purpose Bit Flag, bit 11 (Language encoding flag (EFS)), can be used to indicate both the header File Name and Comment fields are UTF-8 and, in this case, the Unicode Path and Unicode Comment extra fields are not needed and should not be created. Note that, for backward compatibility, bit 11 should only be used if the native character set of the paths and comments being zipped up are already in UTF-8. The same method, either bit 11 or extra fields, should be used in both the local and central directory headers. -Info-ZIP New Unix Extra Field: ==================================== Currently stores Unix UIDs/GIDs up to 32 bits. (Last Revision 20080509) Value Size Description ----- ---- ----------- (UnixN) 0x7875 Short tag for this extra block type ("ux") TSize Short total data size for this block Version 1 byte version of this extra field, currently 1 UIDSize 1 byte Size of UID field UID Variable UID for this entry GIDSize 1 byte Size of GID field GID Variable GID for this entry Currently Version is set to the number 1. If there is a need to change this field, the version will be incremented. Changes may not be backward compatible so this extra field should not be used if the version is not recognized. UIDSize is the size of the UID field in bytes. This size should match the size of the UID field on the target OS. UID is the UID for this entry in standard little endian format. GIDSize is the size of the GID field in bytes. This size should match the size of the GID field on the target OS. GID is the GID for this entry in standard little endian format. If both the old 16-bit Unix extra field (tag 0x7855, Info-ZIP Unix) and this extra field are present, the values in this extra field supercede the values in that extra field.