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uc2/docs/license-audit.md
Eremey Valetov 844c1ab092 Add HN/Lobsters writeup; fix Bezemer/Sagunov attribution 
The 2015 LGPL re-release was initiated by Vladislav Sagunov's request
to Nico de Vries; de Vries personally re-released the source.  Earlier
CREDITS.md (and the inherited license-audit.md) misattributed this to
Danny Bezemer.  Bezemer was a co-developer of UC2 during the original
1992-1996 work, per de Vries's release notes.

Add docs/blog/uc2-revival-writeup.md (1200 words) drafted from the
codex-reviewed revision: tightened scoping language ('byte-bitstream-
compatible' rather than ambiguous 'byte-compatible'), removed
overclaims about borg/restic/Kopia equivalence, dropped speculative
PQ/Filecoin/ZK details, and trimmed the demo to one compatibility
example + one OTS example.

Closes git-bug 98904d0.
2026-05-03 12:46:51 -04:00

8.5 KiB
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UC2 License Audit

Status: 2026-05-03. Maintained by Eremey Valetov.

UC2 v3 builds on three layers of prior work, each released under its own free-software licence. This document records per-file provenance, the LGPL-3.0 -> GPL-3.0 transition rationale, and the SPDX identifiers applied across the source tree.

Layer 1: Nico de Vries (1992-1996), released 2015

Nico de Vries authored UltraCompressor II as proprietary DOS software between 1992 and 1996, with co-development from Danny Bezemer, Jan-Pieter Cornet, and others credited in the original U_MANUAL.TXT. In December 2015, Vladislav Sagunov asked de Vries whether the source could be re-released under a free licence; de Vries agreed and personally published the full source under the GNU Lesser General Public License v3 (LGPL-3.0), with a small Borland C/C++ runtime carve-out for DOS-specific code.

The 2015 release is preserved in this repository under original/UC2_source/ byte-for-byte unchanged, including its license header (GNU LESSER GENERAL PUBLIC LICENSE V3.txt) and the original binaries (uc2pro.exe, uc237b.exe, ue.exe). No file in lib/ or cli/ is a verbatim copy of any file in that release. The 2015 source serves as the format specification: it is read for documentation purposes (the on-disk archive layout, the SuperMaster dictionary contents, the Huffman tree encoding) but its C code is not linked in.

Relicensing impact: none. Layer 1 is preserved under its original LGPL-3.0 licence; nothing is moved upward to GPL-3.0.

Layer 2: Jan Bobrowski (2020-2021), libunuc2 / unuc2

Jan Bobrowski wrote a clean-room portable decompressor for UC2 v3 archives between 2020 and 2021. He released two products:

  • libunuc2 (decompression library) under LGPL-3.0
  • unuc2 (CLI tool) under GPL-3.0-or-later

The upstream source is preserved in original/unuc2-0.6/. The following files in this repository derive from Bobrowski's work and retain his original licence:

Current file Upstream origin Licence
lib/src/decompress.c original/unuc2-0.6/libunuc2.c LGPL-3.0-only
lib/src/list.h original/unuc2-0.6/list.h (identical) LGPL-3.0-only
lib/src/super.bin original/unuc2-0.6/super.bin (identical) data (de Vries)
lib/include/uc2/libuc2.h original/unuc2-0.6/libunuc2.h LGPL-3.0-only
cli/src/main.c original/unuc2-0.6/unuc2.c GPL-3.0-or-later
cli/src/compat/compat_win32.c original/unuc2-0.6/compat/compat.c (Win32 portions) LGPL-3.0-only
cli/src/compat/compat_dos.c derived from compat/compat.c (DOS adaptation by Valetov) LGPL-3.0-only

Modifications by Valetov in 2026 are released under the same licence as the file's upstream origin (LGPL-3.0 stays LGPL-3.0; GPL-3.0 stays GPL-3.0). No unilateral upgrade from LGPL to GPL has been applied to Bobrowski's work.

lib/src/super.bin is the SuperMaster dictionary block from the 1992 distribution. It is data, not code: a fixed binary table used as a compression-context priming dictionary. It is bit-identical to the file in Bobrowski's release and to the data extracted from de Vries's 1992 binaries.

Layer 3: Eremey Valetov (2026), UC2 v3 revival

The following files are new work by Valetov, originally authored for the UC2 v3 revival project, released under GPL-3.0-or-later:

File Function
lib/src/compress.c LZ77+Huffman compressor (inverse of decompress.c)
lib/src/uc2_tables.c Huffman delta-coding lookup tables
lib/src/uc2_internal.h Shared compressor/decompressor types and constants
lib/src/uc2_cdc.c + .h Content-defined chunking (Gear hash)
lib/src/uc2_merkle.c + .h Merkle DAG of deduplicated blocks
lib/src/uc2_blockstore.c + .h Cross-archive content-addressable block store
lib/src/uc2_simhash.c + .h SimHash near-duplicate detection
lib/src/uc2_delta.c + .h Binary delta compression
lib/src/uc2_rans.c + .h rANS entropy coder (method 10)
lib/src/uc2_dict.c + .h Dictionary metadata for cross-archive sharing
lib/src/uc2_preprocess.c + .h BCJ / BWT / delta-filter preprocessing
lib/src/uc2_lz4.c + .h LZ4 ultra-fast compression
lib/src/uc2_blake3.c + .h BLAKE3 cryptographic hashing
lib/src/uc2_sha256.c + .h SHA-256 (FIPS 180-4)
lib/src/uc2_ots.c + .h OpenTimestamps proof parser, walker, trailer
cli/src/compat/getopt.c Minimal POSIX getopt for MSVC
cli/src/main.c (post-9525a81 additions) OTS attach/extract/info, archive creation, scanning, benchmark

The Phase 3-7 modules are independent implementations. They reference the UC2 v3 archive format (which is a bitstream layout, not a copyrighted work) and use BLAKE3, SHA-256, LZ4, rANS, etc. from public-domain or self-authored reference implementations. None of these modules link to or derive from Bobrowski's code beyond using shared header types declared in uc2_internal.h.

Relicensing rationale

The composite project links Bobrowski's LGPL-3.0 library (lib/) into a GPL-3.0-or-later executable (cli/). This combination is permitted by LGPL-3.0 sec. 4 (Combined Works): the LGPL library may be used in GPL-licensed work without requiring the library itself to be relicensed.

No code has been moved from LGPL-3.0 to GPL-3.0 in this project. LGPL §3 permits a one-way upgrade from LGPL to GPL but exercising it is unnecessary here: the LGPL files remain LGPL, the GPL files remain GPL, and the combined work is distributable under GPL-3.0-or-later (as recorded in the project root LICENSE file).

If a downstream user wishes to redistribute lib/ standalone under LGPL-3.0, the LGPL-3.0 files are individually identifiable via their SPDX-License-Identifier headers.

SPDX policy

All source files in lib/ and cli/ carry one of two SPDX identifiers near the top:

  • SPDX-License-Identifier: LGPL-3.0-only for files derived from Bobrowski's libunuc2 / compat code.
  • SPDX-License-Identifier: GPL-3.0-or-later for cli/src/main.c (matches Bobrowski's original GPL-3.0-or-later choice for the CLI tool) and for all Valetov-authored Phase 2 through Phase 7 work.

Original copyright lines authored by Bobrowski are preserved verbatim where present. Where Valetov has added substantial new content to a Bobrowski-originated file (notably cli/src/main.c and compat_dos.c), an additional Valetov copyright line has been added without removing the original.

The 2015 LGPL-3.0 release in original/UC2_source/ and the 2020-2021 release in original/unuc2-0.6/ are preserved unchanged and are not subject to this policy: they retain whatever licence headers their authors shipped them with.

Audit checklist

  • LGPL-3.0 release by Bezemer/de Vries preserved unchanged in original/UC2_source/
  • LGPL-3.0 / GPL-3.0 release by Bobrowski preserved unchanged in original/unuc2-0.6/
  • Per-file provenance table above
  • SPDX-License-Identifier on every source file in lib/ and cli/
  • CREDITS.md attributes Bobrowski specifically for libunuc2-derived files, not as generic "inspiration"
  • LICENSE-HISTORY summary published as this file (docs/license-audit.md)
  • No silent LGPL-to-GPL upgrade: every Bobrowski-origin file retains LGPL-3.0-only

References

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