Hawkynt

LZMS

Microsoft’s LZ77 compression format, introduced with Windows 8 for the WIM (Windows Imaging Format) archiver and msdelta, succeeding LZX/Xpress-Huffman in that lineage. Interleaves a forward Huffman stream for literals, lengths and offset slots with a backward range-coded stream for the binary decisions. Clean-room implementation: no official Microsoft specification exists.

Properties

Property	Value
Category	Compression Algorithms
Sub-category	Dictionary
Security status	Not classified
Complexity	Expert
Inventor	Microsoft Corporation
Year	2012
Origin	🇺🇸 United States
Source	algorithms/compression/lzms.js

Security

Status: not classified — treat as unverified.

No vulnerabilities are recorded for this implementation.

Documentation

• wimlib - free implementation of the WIM/SWM/ESD formats (documents the reverse-engineered LZMS design)
• wimlib source repository

References

• Windows Imaging Format (WIM) overview
• LZMA SDK - adaptive binary range coder reference design

Test vectors

6 vectors ship with this algorithm and run in the test suite. Byte values are hexadecimal.

Vector 1 — LZMS - empty input (header only)

Field	Value
input	(empty)
expected	00000000

Vector 2 — LZMS - single byte

Field	Value
input	21
expected	010000002100000000

Vector 3 — LZMS - long repetitive run (300x 0x42)

Field	Value
input	42424242424242424242424242424242 42424242424242424242424242424242 42424242424242424242424242424242 42424242424242424242424242424242 … (300 bytes; the full value is in the source)
expected	2c01000042fe2cde1f5e5c

Vector 4 — LZMS - alternating byte pattern (0xAA/0x55)

Field	Value
input	aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55 aa55aa55aa55aa55aa55aa55aa55aa55
expected	00010000aa5500fe70df987126

Vector 5 — LZMS - pseudo-random binary sample

Field	Value
input	00004080004000000000400000003800 00400000004080800000408000000000 0040004000400000004080c000400000 00000000400000003800000000000000 … (512 bytes; the full value is in the source)
expected	000200000000408000400010208e00a4 4080802045203e201203c5800a74054b 000c0605409aa05cb0e015ee02c0c197 3041580c413d60bf205eb01897015ae8 24b00f9831460e8d60e6c418f5828540 12070040bb6c17ad038760340e82a940 ad4051083262080b069d012501fcac19 558383701927013d60ad7c109d0668c1 6e608e40a3820c20833820e2841c6301 dcb021390160e03ef205eb60e0140b05 a03c82b160dca8193102c8c2de6c2f9c 73bcba10c3489bff26d3a3aaff392907 7e83506403

Vector 6 — LZMS - WIM-flavoured text

Field	Value
input	546869732057494d202857696e646f77 7320496d6167696e6720466f726d6174 2920696d6167652075736573204c5a4d 5320636f6d7072657373696f6e20666f 72206d6178696d756d20726174696f2e
expected	50000000546869732057494d20285769 6e646f777320496d6167696e6720466f 726d617429206903e2ca40eae6cae640 98b49aa640c6dedae0e4cae6e6d2dedc 40ccdee440dac2f0d2daeada40e4c2e8 d2de5c00004f12572e0000

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