Appendix B: Method IDs

This appendix provides a complete reference of compression, filter, and encryption method IDs used in 7z archives.

Method ID Format

Method IDs are variable-length byte sequences (1-15 bytes). The length is encoded in the coder flags byte.

Method ID bytes are stored and compared in the order shown in this document. For example, the LZMA method ID 03 01 01 is stored with 03 first, followed by 01, then 01. This is the natural byte order (not reversed).

Method Categories

Category	ID Prefix	Description
Simple	0x00-0x20	Basic methods
7z Native	0x03XXXX	LZMA, PPMd, BCJ filters
ZIP Compat	0x04XXXX	Deflate, BZip2
Extended	0x04F7XXXX	Modern codecs (Zstd, etc.)
Crypto	0x06XXXX	Encryption methods

Compression Methods

Mandatory Methods

Implementations MUST support these methods:

Method ID	Name	Properties	Description
00	Copy	None	No compression
03 01 01	LZMA	5 bytes	LZMA compression
21	LZMA2	1 byte	Modern LZMA variant

Recommended Methods

Implementations SHOULD support these methods:

Method ID	Name	Properties	Description
04 01 08	Deflate	None	ZIP-compatible
04 02 02	BZip2	None	BWT compression
03 04 01	PPMd	5 bytes	Prediction-based

Optional Methods

Implementations MAY support these methods:

Method ID	Name	Properties	Description
04 01 09	Deflate64	None	Extended Deflate
04 F7 11 01	Zstandard	Variable	Facebook codec
04 F7 11 02	Brotli	Variable	Google codec
04 F7 11 04	LZ4	Variable	Fast compression
04 F7 11 05	LZ5/LZS	Variable	LZ5 variant
04 F7 11 06	Lizard	Variable	LZ5 variant

Filter Methods

Mandatory Filters

Method ID	Name	Properties	Description
03	Delta	1 byte	Delta encoding

BCJ Filters (Recommended)

Method ID	Short ID	Name	Architecture
03 03 01 03	04	BCJ	x86/x64
03 03 02 05	05	BCJ_PPC	PowerPC
03 03 04 01	06	BCJ_IA64	Itanium
03 03 05 01	07	BCJ_ARM	ARM 32-bit
03 03 07 01	08	BCJ_ARMT	ARM Thumb
03 03 08 05	09	BCJ_SPARC	SPARC

Modern Filters (Optional)

Method ID	Name	Description
0A	ARM64	ARM 64-bit filter
0B	RISC-V	RISC-V filter

Complex Filters

Method ID	Name	Streams	Description
03 03 01 1B	BCJ2	4 in / 1 out	Advanced x86 filter

Encryption Methods

Method ID	Name	Description
06 F1 07 01	AES-256-SHA256	7z standard encryption

Crypto Method ID Structure

06        - Crypto category
F1        - 7z crypto
07        - Key size: 07 = 256-bit
01        - Hash: 01 = SHA-256

Key Size Variants

Byte	Key Size
01	128 bits
03	192 bits
07	256 bits

Note: Only AES-256-SHA256 (0x06F10701) is commonly used.

Legacy Methods

These methods exist but are rarely used:

Method ID	Name	Notes
02 03 02	SWAP2	Byte swap (2 bytes)
02 03 04	SWAP4	Byte swap (4 bytes)
04 01	MISC_ZIP	ZIP method marker
04 05	MISC_Z	LZW compression
04 06	MISC_LZH	LZH compression
04 09 01	NSIS_DEFLATE	NSIS Deflate
04 09 02	NSIS_BZIP2	NSIS BZip2

Method Properties

Copy (0x00)

No properties. Data passes through unchanged.

LZMA (0x030101)

5 bytes:

Byte	Description
0	lc + lp * 9 + pb * 45
1-4	Dictionary size (UINT32)

Constraints:

• lc: 0-8 (literal context bits)
• lp: 0-4 (literal position bits)
• pb: 0-4 (position bits)
• lc + lp ≤ 4

Default: 5D 00 00 10 00 (lc=3, lp=0, pb=2, dict=16 MiB)

LZMA2 (0x21)

1 byte encoding dictionary size. See [10-COMPRESSION-METHODS](/7z/10-compression-methods#lzma2) for the complete dictionary size formula and encoding table.

Quick reference (common values):

• 0x14: 1 MiB
• 0x18: 4 MiB
• 0x1C: 16 MiB
• 0x1E: 32 MiB
• 0x20: 64 MiB
• 0x28: 4 GiB - 1 (maximum)
• 0x29+: Reserved; implementations SHOULD reject

PPMd (0x030401)

5 bytes:

Byte	Description
0	Order (model order, 2-16)
1-4	Memory size (UINT32)

Delta (0x03)

1 byte (optional, default 1):

Byte	Description
0	Distance - 1 (0 = distance 1)

BCJ Filters

Optional 4-byte property:

Bytes	Description
0-3	Start offset (UINT32, default 0)

AES-256-SHA256 (0x06F10701)

2-18 bytes:

Byte	Description
0	(salt_size) | (iv_size << 4)
1	num_cycles_power (iterations = 2^n, MUST be <= 30)
2-n	Salt bytes (0-16)
n+1-m	IV bytes (0-16)

See [12-ENCRYPTION](/7z/12-encryption) for complete encryption details and security limits.

Method Support Matrix

Method	zesven	7-Zip	p7zip	py7zr
Copy	R/W	R/W	R/W	R/W
LZMA	R/W	R/W	R/W	R/W
LZMA2	R/W	R/W	R/W	R/W
Deflate	R/W	R/W	R/W	R/W
BZip2	R/W	R/W	R/W	R/W
PPMd	R/W	R/W	R/W	R/W
BCJ	R/W	R/W	R/W	R/W
BCJ2	R/W	R/W	R/W	-
Delta	R/W	R/W	R/W	R/W
AES	R/W	R/W	R/W	R/W
Zstd	R/W	R/W*	R/W*	R/W
LZ4	R/W	R/W*	-	-
Brotli	R/W	R/W*	-	-

R = Read, W = Write, * = Requires 7-Zip-zstd fork

Unknown Methods

When encountering an unknown method:

1. Report method ID in error
2. Skip the entry (cannot decompress)
3. Continue processing other entries

function handle_unknown_method(method_id):
    error(ERROR_UNSUPPORTED,
        "Unknown compression method: 0x{}".format(hex(method_id)))

See Also

• Unpack Info - Coder definitions in folders
• Compression Methods - Compression algorithm details
• Filters - Filter specifications
• Encryption - Encryption details