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
consisting 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, Ed Gordon, 20080717
-------------------------
Header ID's of 0 through 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
0x0007 AV Info
0x0008 Reserved for extended language encoding data (PFS)
0x0009 OS/2 extended attributes (also Info-ZIP)
0x000a NTFS (Win9x/WinNT FileTimes)
0x000c OpenVMS (also Info-ZIP)
0x000d UNIX
0x000e Reserved for file stream and fork descriptors
0x000f Patch Descriptor
0x0014 PKCS#7 Store for X.509 Certificates
0x0015 X.509 Certificate ID and Signature for
individual file
0x0016 X.509 Certificate ID for Central Directory
0x0017 Strong Encryption Header
0x0018 Record Management Controls
0x0019 PKCS#7 Encryption Recipient Certificate List
0x0065 IBM S/390 (Z390), AS/400 (I400) attributes
- uncompressed
0x0066 Reserved for IBM S/390 (Z390), AS/400 (I400)
attributes - compressed
0x4690 POSZIP 4690 (reserved)
The Header ID mappings defined by Info-ZIP and third parties are:
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)
0x2805 ZipIt Macintosh 1.3.5+
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 unofficial port
0x4b46 FWKCS MD5 (see below)
0x4c41 OS/2 access control list (text ACL)
0x4d49 Info-ZIP OpenVMS ("IM", obsolete)
0x4d63 Macintosh SmartZIP, by Macro Bambini
0x4f4c Xceed original location extra field
0x5356 AOS/VS (binary ACL)
0x5455 extended timestamp
0x554e Xceed unicode extra field
0x5855 Info-ZIP UNIX (original; also OS/2, NT, etc.)
0x6375 Info-ZIP UTF-8 comment field
0x6542 BeOS (BeBox, PowerMac, etc.)
0x6854 Theos
0x7075 Info-ZIP UTF-8 name field
0x7441 AtheOS (AtheOS/Syllable attributes)
0x756e ASi UNIX
0x7855 Info-ZIP UNIX (16-bit UID/GID info)
0x7875 Info-ZIP UNIX 3rd generation (generic UID/GID, ...)
0xa220 Microsoft Open Packaging Growth Hint
0xfb4a SMS/QDOS
The following are detailed descriptions of the known extra-field block types:
-Zip64 Extended Information (0x0001):
===================================
The following is the layout of the Zip64 extended information
extra block. If one of the size or offset fields in the Local
or Central directory record is too small to hold the required
data, a Zip64 extended information record is created. The
order of the fields in the Zip64 extended information record
is fixed, but the fields will only appear if the corresponding
Local or Central directory record field is set to 0xFFFF or
0xFFFFFFFF.
Note: All fields stored in Intel low-byte/high-byte order.
Value Size Description
----- ---- -----------
(ZIP64) 0x0001 2 bytes Tag for this extra block type
Size 2 bytes Size of this extra block
Original
Size 8 bytes Original uncompressed file size
Compressed
Size 8 bytes Size of compressed data
Relative Header
Offset 8 bytes Offset of local header record
Disk Start
Number 4 bytes Number of the disk on which
this file starts
This entry in the Local header must include BOTH original
and compressed file size fields. If encrypting the
central directory and bit 13 of the general purpose bit
flag is set indicating masking, the value stored in the
Local Header for the original file size will be zero.
-OS/2 Extended Attributes (0x0009):
=================================
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:
========================
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 (0x4453):
=======================================
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 block 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 (0x000a):
===========================
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 stored only as a
local extra block.]
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.) SubSizeN 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 (0x000c):
=======================
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 tag 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 atrdef.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 "IM":
=================
The following is the layout of Info-ZIP's "IM" VMS attributes
extra block. The local-header and central-header versions are
identical. (Last Revision 19960922)
Value Size Description
----- ---- -----------
(VMS2) 0x4d49 Short tag for this extra block type ("IM")
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
corresponding to the indicated structure or string.
Typically, multiple VMS2 extra blocks are present (each with a
unique block ID).
-Info-ZIP Macintosh:
==================
The following is the layout of the (old) Info-ZIP
resource-fork extra block for Macintosh (pre-Mac-OS-X). 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 otherwise. 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 (long):
======================
The following is the layout of the ZipIt extra block for
Macintosh (pre-Mac-OS-X). 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 (short, for files):
==================================
The following is the layout of a shortened variant of the
ZipIt extra block for Macintosh (pre-Mac-OS-X) (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. (Last Revision 20030602)
Value Size Description
----- ---- -----------
(Mac2b) 0x2705 Short tag for this extra block type
TSize Short total data size for this block (min. 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 (short, for directories):
========================================
The following is the layout of a shortened variant of the
ZipIt extra block for Macintosh (pre-Mac-OS-X) 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;
-Info-ZIP Macintosh (new):
========================
The following is the layout of the (new) Info-ZIP extra block
for Macintosh (pre-Mac-OS-X), designed by Dirk Haase. All
values are in little-endian order. (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:
==================
The following is the layout of the SmartZIP extra block for
Macintosh (pre-Mac-OS-X), 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:
=============
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:
======
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:
===
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 (0x000d):
====================
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 block has a minimum data size of 12 bytes and is only
stored as a 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 (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 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 auto detection
1 Treat as a self-patch
2-3 RESERVED
4-5 Action (see below)
6-7 RESERVED
8-9 Reaction (see below) to absent file
10-11 Reaction (see below) to newer file
12-13 Reaction (see below) to unknown file
14-15 RESERVED
16-31 RESERVED
Actions
Action Value
------ -----
none 0
add 1
delete 2
patch 3
Reactions
Reaction Value
-------- -----
ask 0
skip 1
ignore 2
fail 3
Patch support is provided by PKPatchMaker(tm) technology and
is covered under U.S. Patents and Patents Pending. The use or
implementation in a product of certain technological aspects
set forth in the current APPNOTE, including those with regard
to strong encryption, patching, or extended tape operations
requires a license from PKWARE. Please contact PKWARE with
regard to acquiring a license.
-PKCS#7 Store for X.509 Certificates (0x0014):
============================================
This field contains information about each of the certificates
files may be signed with. When the Central Directory
Encryption feature is enabled for a ZIP file, this record will
appear in the Archive Extra Data Record, otherwise it will
appear in the first central directory record and will be
ignored in any other record.
Note: All fields stored in Intel low-byte/high-byte order.
Value Size Description
----- ---- -----------
(Store) 0x0014 2 bytes Tag for this extra block type
TSize 2 bytes Size of the store data
SData TSize 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 (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
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 (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, 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
TSize 2 bytes Size of data that follows
TData TSize Data
-Strong Encryption Header (0x0017):
=================================
Value Size Description
----- ---- -----------
0x0017 2 bytes Tag for this extra block type
TSize 2 bytes Size of data that follows
Format 2 bytes Format definition for this record
AlgID 2 bytes Encryption algorithm identifier
Bitlen 2 bytes Bit length of encryption key
Flags 2 bytes Processing flags
CertData TSize-8 Certificate decryption extra field data
(Refer to the explanation for CertData in
the section describing the Certificate
Processing Method under the Strong
Encryption Specification.)
-Record Management Controls (0x0018):
===================================
Value Size Description
----- ---- -----------
(Rec-CTL) 0x0018 2 bytes Tag for this extra block type
CSize 2 bytes Size of total extra block data
Tag1 2 bytes Record control attribute 1
Size1 2 bytes Size of attribute 1, in bytes
Data1 Size1 Attribute 1 data
.
.
.
TagN 2 bytes Record control attribute N
SizeN 2 bytes Size of attribute N, in bytes
DataN SizeN Attribute N data
-PKCS#7 Encryption Recipient Certificate List (0x0019):
=====================================================
This field contains information about each of the certificates
used in encryption processing and it can be used to identify
who is allowed to decrypt encrypted files. This field should
only appear in the archive extra data record. This field is
not required and serves only to aid archive modifications by
preserving public encryption key data. Individual security
requirements may dictate that these 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 (PKWARE, 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 (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
-Info-ZIP Unicode Path:
=====================
The following is the layout of the Info-ZIP Unicode Path extra
block. It stores the UTF-8 version of the entry path as
stored (in some other form) 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 Byte version of this extra field, currently 1
NameCRC32 Long CRC-32 checksum of standard name field
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.
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 should be used instead.
UnicodeName is the UTF-8 version of the contents of the File
Name field in the header, without any trailing NUL. The
standard name field in the Zip entry header remains filled
with the entry name coded in the local machine's extended
ASCII system charset. UnicodeName is defined to be UTF-8, so
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)), should 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 general purpose bit
11 or extra fields, should be used in both the Local and
Central Directory Header for a file.
Utilization rules:
1. This field shall never be created for names consisting
solely of 7-bit ASCII characters.
2. On a system that already uses UTF-8 as system charset, this
field shall not repeat the string pattern already stored in
the Zip entry's standard name field. Instead, a field of
exactly 9 bytes (70 75 05 00 01 and 4 bytes CRC) should be
created. In this form, with 5 data bytes, the field serves
to indicate the UTF-8 encoding of the standard Zip header's
name field.
3. This field shall not be used whenever the calculated CRC-32
of the entry's standard name field does not match the
provided CRC checksum value. A mismatch of the CRC check
indicates that the standard name field was changed by some
non-"up"-aware utility without synchronizing this UTF-8
name extra block.
-Info-ZIP Unicode Comment:
========================
The following is the layout of the Info-ZIP Unicode Comment
extra block. It stores the UTF-8 version of the entry comment
as stored (in some other form) 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.
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. UnicodeCom is defined to be UTF-8, so 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 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.
-Extended Timestamp:
==================
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 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 (type 1, "UX"):
============================
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, "UT") and the Unix type 2 extra block
(0x7855, "Ux"). (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 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 privilege 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 contain either the old "Unix1"
(0x5855, "UX") extra block or the new extra block types
"time" (0x5455, "UT") and/or "Unix2" (0x7855, "Ux").
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 block types, but the info from new types
overrides the old "Unix1" field.
Archiving software should recognize a "Unix1" extra field
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 blocks should
be converted to the new "time" and/or "Unix2" types.
-Info-ZIP UNIX (type 2, "Ux"):
============================
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 may be specific to a particular
machine, and they may require root privilege to restore.
-Info-ZIP New Unix ("ux"):
========================
The following is the layout of the Info-ZIP New Unix extra
block. It stores Unix UIDs/GIDs longer than 16 bits.
(Currently, 32 bits are used, but the format is not so
limited.) (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 block
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 block (Info-ZIP "Unix2",
0x7855. "Ux"), and this extra block are present, the values in
this extra block supercede the values in that extra block.
-ASi UNIX:
========
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 filename 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:
====
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.
-AtheOS:
======
The following is the layout of the file-attributes extra block
for AtheOS. This block is a very close spin-off from the BeOS
extra block. The only differences are:
- a new extra field signature
- numeric field in the attributes data are stored in
little-endian format ("i386" was initial hardware for AtheOS)
(Last Revision 20040908)
Local-header version:
Value Size Description
----- ---- -----------
(AtheOS) 0x7441 Short tag for this extra block type ("At")
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
----- ---- -----------
(AtheOS) 0x7441 Short tag for this extra block type ("At")
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 AtheOS-specific block of data in little-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:
========
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:
======
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:
==========
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:
=====
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 unofficial:
====================
The following is the layout of an unoffical 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. 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 (0x4b46, "FK"):
========================
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 block 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 block, if
present, from a .ZIP file central directory. In adding this
extra block, FWKCS preserves .ZIP file Authenticity
Verification; if stripping this extra block, 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."
-Microsoft Open Packaging Growth Hint (0xa220):
=============================================
Value Size Description
----- ---- -----------
0xa220 Short tag for this extra block type
TSize Short size of Sig + PadVal + Padding
Sig Short verification signature (A028)
PadVal Short Initial padding value
Padding variable filled with NULL characters
