Appendix A: Property IDs

This appendix provides a complete reference of all property IDs used in 7z archive headers.

Property ID Table

ID	Hex	Name	Context	Description
0	0x00	End	All	End of section marker
1	0x01	Header	Top-level	Main header marker
2	0x02	ArchiveProperties	Header	Archive-wide properties
3	0x03	AdditionalStreamsInfo	Header	Additional data streams
4	0x04	MainStreamsInfo	Header	Primary stream information
5	0x05	FilesInfo	Header	File metadata section
6	0x06	PackInfo	StreamsInfo	Pack stream information
7	0x07	UnpackInfo	StreamsInfo	Unpack/folder information
8	0x08	SubStreamsInfo	StreamsInfo	Per-file stream information
9	0x09	Size	Various	Size array marker
10	0x0A	CRC	Various	CRC/digest marker
11	0x0B	Folder	UnpackInfo	Folder definition marker
12	0x0C	CodersUnpackSize	UnpackInfo	Coder output sizes
13	0x0D	NumUnpackStream	SubStreamsInfo	Streams per folder
14	0x0E	EmptyStream	FilesInfo	Empty stream bitmap
15	0x0F	EmptyFile	FilesInfo	Empty file bitmap
16	0x10	Anti	FilesInfo	Anti-item bitmap
17	0x11	Name	FilesInfo	File names
18	0x12	CTime	FilesInfo	Creation time
19	0x13	ATime	FilesInfo	Access time
20	0x14	MTime	FilesInfo	Modification time
21	0x15	Attributes	FilesInfo	Windows attributes
22	0x16	Comment	FilesInfo	Archive comment
23	0x17	EncodedHeader	Top-level	Encoded header marker
24	0x18	StartPos	Rare	Start position
25	0x19	Dummy	FilesInfo	Padding/alignment

Property Contexts

Top-Level Context

Properties that can appear at the start of header data:

ID	Property
0x01	Header (plain header)
0x17	EncodedHeader (compressed header)

Header Context

Properties within a Header (0x01) section:

ID	Property	Required
0x02	ArchiveProperties	Optional
0x04	MainStreamsInfo	Optional
0x05	FilesInfo	Optional
0x00	End	Required

StreamsInfo Context

Properties within MainStreamsInfo (0x04):

ID	Property	Required
0x06	PackInfo	Optional
0x07	UnpackInfo	Optional
0x08	SubStreamsInfo	Optional
0x00	End	Required

PackInfo Context

Properties within PackInfo (0x06):

ID	Property	Required
0x09	Size	If NumPackStreams > 0
0x0A	CRC	Optional
0x00	End	Required

UnpackInfo Context

Properties within UnpackInfo (0x07):

ID	Property	Required
0x0B	Folder	Required
0x0C	CodersUnpackSize	Required
0x0A	CRC	Optional
0x00	End	Required

SubStreamsInfo Context

Properties within SubStreamsInfo (0x08):

ID	Property	Required
0x0D	NumUnpackStream	Optional
0x09	Size	If multiple substreams
0x0A	CRC	Optional
0x00	End	Required

FilesInfo Context

Properties within FilesInfo (0x05):

ID	Property	Required	Order
0x0E	EmptyStream	Optional	1
0x0F	EmptyFile	Optional	2
0x10	Anti	Optional	3
0x11	Name	Recommended	4
0x12	CTime	Optional	5
0x13	ATime	Optional	6
0x14	MTime	Optional	7
0x15	Attributes	Optional	8
0x16	Comment	Optional	9
0x19	Dummy	Optional	10
0x00	End	Required	Last

Property Structures

End (0x00)

No data. Marks end of containing section.

Header (0x01)

Header ::= 0x01 [ArchiveProperties] [MainStreamsInfo] [FilesInfo] 0x00

ArchiveProperties (0x02)

ArchiveProperties ::= 0x02 Property* 0x00
Property ::= PropertyID Size Data

Rarely used. Contains archive-level settings.

AdditionalStreamsInfo (0x03)

Status: Deprecated. This property is rarely used in practice and implementations SHOULD NOT generate archives using it. Implementations MUST support reading archives that contain this property for backward compatibility.

AdditionalStreamsInfo ::= 0x03 StreamsInfo

Contains auxiliary streams for external data storage. This was originally intended for storing encrypted file names or other metadata separately from the main data streams. In modern archives, external data references (via External == 0x01 in various properties) typically point to streams defined within AdditionalStreamsInfo.

MainStreamsInfo (0x04)

MainStreamsInfo ::= 0x04 [PackInfo] [UnpackInfo] [SubStreamsInfo] 0x00

FilesInfo (0x05)

FilesInfo ::= 0x05 NumFiles Property* 0x00

PackInfo (0x06)

PackInfo ::= 0x06 PackPos NumPackStreams [Sizes] [Digests] 0x00

UnpackInfo (0x07)

UnpackInfo ::= 0x07 Folders [CodersUnpackSize] [Digests] 0x00

SubStreamsInfo (0x08)

SubStreamsInfo ::= 0x08 [NumUnpackStream] [Sizes] [Digests] 0x00

Size (0x09)

Sizes ::= 0x09 NUMBER* 0x00

Array of size values (context-dependent count).

CRC (0x0A)

Digests ::= 0x0A AllAreDefined [BitField] CRC*

Array of CRC-32 checksums.

Folder (0x0B)

Folders ::= 0x0B NumFolders External FolderData

CodersUnpackSize (0x0C)

CodersUnpackSize ::= 0x0C NUMBER*

Unpack sizes for all coder outputs across all folders.

NumUnpackStream (0x0D)

NumUnpackStream ::= 0x0D NUMBER[NumFolders]

Number of files per folder. Note: This section has no End marker; the count of NUMBER values equals NumFolders from UnpackInfo. See 08-SUBSTREAMS-INFO for details.

EmptyStream (0x0E)

EmptyStream ::= 0x0E Size BitField

Bitmap: 1 = entry has no data stream.

EmptyFile (0x0F)

EmptyFile ::= 0x0F Size BitField

Bitmap for empty streams: 1 = file, 0 = directory.

Anti (0x10)

Anti ::= 0x10 Size BitField

Bitmap for empty streams: 1 = anti-item (deletion marker).

Name (0x11)

Name ::= 0x11 Size External [DataIndex | UTF16Names]

File names in UTF-16-LE, null-terminated.

CTime (0x12)

CTime ::= 0x12 Size AllAreDefined [BitField] External [DataIndex | Times]

Creation timestamps (FILETIME).

ATime (0x13)

ATime ::= 0x13 Size AllAreDefined [BitField] External [DataIndex | Times]

Access timestamps (FILETIME).

MTime (0x14)

MTime ::= 0x14 Size AllAreDefined [BitField] External [DataIndex | Times]

Modification timestamps (FILETIME).

Attributes (0x15)

Attributes ::= 0x15 Size AllAreDefined [BitField] External [DataIndex | Attrs]

Windows/Unix file attributes (UINT32).

Comment (0x16)

Comment ::= 0x16 Size External [DataIndex | UTF16Text]

Archive comment in UTF-16-LE.

EncodedHeader (0x17)

EncodedHeader ::= 0x17 PackInfo UnpackInfo 0x00

Indicates header is compressed/encrypted.

StartPos (0x18)

Status: Deprecated. This property is rarely used in practice and implementations SHOULD NOT generate archives using it. Implementations SHOULD ignore this property when reading.

StartPos ::= 0x18 Size Data

Originally intended for storing file start positions within streams. This property is not used by modern versions of 7-Zip and has no defined semantics. Archives containing this property are extremely rare.

Dummy (0x19)

Dummy ::= 0x19 Size Zeros

Padding bytes (all zeros). Used for alignment.

Unknown Properties

Properties with unknown IDs SHOULD be skipped:

function skip_unknown_property(stream, property_id):
    size = stream.read_number()
    stream.skip(size)
    log_warning("Unknown property ID: 0x{:02X}", property_id)

This enables forward compatibility with future format extensions.

See Also

• Header Structure - Header organization
• Files Info - File property details
• Data Encoding - NUMBER and BitField encoding