5c01fec996
uc2_sha256: pure-C FIPS 180-4 implementation, one-shot and incremental API, validated against published vectors (empty, abc, 56-byte, 1M 'a', byte-by-byte, every-split-point boundary). uc2_ots: parser, serializer, and walker for the standard .ots binary format. Strict canonical varint with 64-bit overflow check, depth- bounded recursion, varbytes cap, max-digest cap. Walker supports the calendar-path subset (APPEND, PREPEND, SHA256); proofs that include other crypto ops (SHA1, RIPEMD160, KECCAK256) are accepted as structurally valid but flagged for follow-up via the standard 'ots verify'. UC2-OTS trailer: magic-bracketed sidecar appended after the recorded archive bytes. Reverse-scan-safe; original UC2 Pro reader ignores trailing bytes past its recorded length so backward compatibility is preserved. Layout (all integers little-endian uint32): front-magic + version + archive_len + proof_len + proof + proof_len + back-magic. CLI: --ots-attach validates that the proof's leaf digest equals SHA-256(archive[0..archive_len)) before appending and refuses to overwrite an existing trailer unless -f is given. --ots-extract writes the proof verbatim, byte-compatible with the standard 'ots verify'. --ots-info parses and prints the leaf, archive-match status, and attestation list. uc2 -t recomputes the archive SHA-256 and walks the proof. Tests: 17 OTS unit tests (varint round-trip, canonical/overflow rejection, file-envelope round-trip, walker on append/sha256/ sibling/unsupported-op/truncated/trailing-garbage, attest_name, trailer round-trip + corruption rejection in 4 scenarios). Plus an optional ctest target ots_cross_check that round-trips the .ots through python-opentimestamps when the package is installed; skipped (return code 77) otherwise.
UC2 v3.0.0 -- UltraCompressor II
A cross-platform revival of UltraCompressor II, the DOS-era archiver by Nico de Vries (1992--1996). UC2 was notable for its advanced deduplication ("master blocks"), file versioning, and competitive compression ratios on the hardware of its day.
UC2 v3 brings it back as a modern, portable C99 tool with full backward compatibility -- archives created by UC2 v3 can be extracted by the original 1992 UC2 Pro, and vice versa.
Features
- Full compression and decompression -- LZ77+Huffman (levels 2--5), rANS entropy coding (levels 6--9), LZ4 ultra-fast mode
- Backward compatible with the original UC2 Pro (verified via automated DOSBox-X cross-tool round-trip testing)
- Content-defined chunking (CDC) with Gear rolling hash for position-independent deduplication
- Merkle DAG content addressing with 64-bit hashes
- Cross-archive dedup via shared block store
- Near-duplicate detection via SimHash
- Delta compression for binary patching
- Content-aware preprocessing -- BCJ (x86), BWT (text), delta filter
- BLAKE3 cryptographic hashing for archive integrity
- Benchmark mode -- test all methods on input data
- Personality -- warm, confident status messages (
-qfor scripting) - Directory archival with nested hierarchies
- Cross-platform: Linux, macOS, Windows (MSVC), DOS (DJGPP)
Building
Requires CMake >= 3.16 and a C99 compiler (GCC, Clang, or MSVC).
cmake -B build
cmake --build build
ctest --test-dir build # 16 unit tests
Usage
uc2 -w archive.uc2 files... # Create archive
uc2 archive.uc2 # Extract all files
uc2 -l archive.uc2 # List contents
uc2 -t archive.uc2 # Test integrity
uc2 -d /tmp/out archive.uc2 # Extract to directory
uc2 -w -L 8 archive.uc2 files... # Create with rANS Tight
uc2 -B files... # Benchmark all methods
Compression Levels
| Level | Method | Description |
|---|---|---|
| 2 | Huffman | Fast |
| 3 | Huffman | Normal |
| 4 | Huffman | Tight (default) |
| 5 | Huffman | Ultra |
| 6 | rANS | Fast |
| 7 | rANS | Normal |
| 8 | rANS | Tight |
| 9 | rANS | Ultra |
Levels 2--5 produce archives readable by the original 1992 UC2 Pro. Levels 6--9 use rANS entropy coding (UC2 v3 only, better compression).
Options
| Flag | Description |
|---|---|
-w |
Create archive |
-l |
List archive contents |
-t |
Test archive integrity |
-L n |
Compression level (2--9) |
-B |
Benchmark all methods on input files |
-d path |
Extract to specified directory |
-f |
Overwrite existing files |
-p |
Extract to stdout |
-q |
Quiet (suppress status messages) |
-a |
Include all file versions |
-D |
Skip directory metadata; -DD also skips file metadata |
-T |
Tab-separated output |
Project Structure
UC2/
lib/ libuc2 compression/decompression library
include/uc2/ public headers (libuc2, uc2_cdc, uc2_merkle, uc2_rans, ...)
src/ library implementation
cli/ uc2 command-line tool
tests/ unit tests and test corpus
original/ preserved original UC2 Pro sources (reference only)
docs/ Sphinx documentation
Credits
- Nico de Vries -- Original UltraCompressor II (1992--1996)
- Danny Bezemer -- Facilitated source code release (2015)
- Jan Bobrowski -- Clean-room portable decompressor (unuc2/libunuc2, 2020--2021)
- Eremey Valetov -- UC2 v3 revival, compression engine, deduplication, and ongoing development
See CREDITS.md for full attribution.
History
- v1.0--v2.3 (1992--1996) Original DOS releases by Nico de Vries
- 2015 Source code released under LGPL-3.0 by Danny Bezemer
- 2020--2021 Jan Bobrowski writes unuc2/libunuc2 (portable decompressor)
- 2026 UC2 v3.0.0: cross-platform revival with full compression engine, backward compatibility, and modern deduplication
License
GPL-3.0. See LICENSE and CREDITS.md.