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feat(net): AcDream.Core.Net scaffold + ISAAC keystream (Phase 4.1)

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First step of Phase 4 (networking). Adds a new AcDream.Core.Net project
for the AC UDP protocol implementation and a matching AcDream.Core.Net.Tests
project. Keeps networking isolated from rendering and the dat layer,
which also keeps the AGPL-reference-material hygiene cleaner.

AcDream.Core.Net/NOTICE.md documents the attribution policy: we read
ACE's AGPL network code (and holtburger's Rust ac-protocol crate) to
understand AC's wire format, but we reimplement everything in acdream's
own style. Wire-format facts aren't copyrightable; specific code is.

This commit adds one component: IsaacRandom — AC's variant of Bob
Jenkins' ISAAC PRNG, used to XOR a keystream into the CRC field of
every outbound packet for authentication. Clean-room reimplementation
based on reading:
  - references/ACE/Source/ACE.Common/Cryptography/ISAAC.cs (AGPL oracle)
  - Bob Jenkins' public ISAAC algorithm description

Implementation notes:
  - 256 uint32 mm[] state, 256 uint32 rsl[] output buffer, a/b/c regs
  - Initialize() runs 4 golden-ratio Mix() warmup rounds then two fold-in
    passes over rsl[] and mm[] (fresh instance → both start as zeroes)
  - AC variant: seed is exactly 4 bytes, interpreted as little-endian
    uint32 assigned to a = b = c before the first Scramble()
  - Scramble() produces 256 output words in one pass; Next() consumes
    them backwards from offset 255 → 0, re-scrambling at offset -1
  - Test seed 0x12345678 matches ACE's reference output byte-for-byte
    across the first 16 values (golden vectors transcribed from a
    throwaway oracle harness that compiled ACE's ISAAC.cs and printed
    its output; the harness was deleted after extracting the values)

Tests (5, all passing):
  - Next_Seed12345678_MatchesAceGoldenVectors: 16 golden uint32 values
  - Next_TwoInstancesSameSeed_ProduceIdenticalSequence: 1000 outputs
  - Next_DifferentSeeds_ProduceDifferentFirstOutput
  - Next_512Calls_SpansTwoScrambleBatches: >400 distinct values in 512
    outputs (catches all-zero / stuck-at-one bugs at scramble boundary)
  - Ctor_ShortSeed_Throws

Both test projects still green: 77 core + 5 net = 82/82.

Phase 4.2 (packet framing + checksum) next.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
This commit is contained in:
Erik 2026-04-11 14:14:28 +02:00
parent e0dfecdf23
commit 293584d6e8
6 changed files with 313 additions and 0 deletions
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AcDream.slnx
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@ -3,11 +3,13 @@
<Project Path="src/AcDream.App/AcDream.App.csproj" />
<Project Path="src/AcDream.Cli/AcDream.Cli.csproj" />
<Project Path="src/AcDream.Core/AcDream.Core.csproj" />
<Project Path="src/AcDream.Core.Net/AcDream.Core.Net.csproj" />
<Project Path="src/AcDream.Plugin.Abstractions/AcDream.Plugin.Abstractions.csproj" />
<Project Path="src/AcDream.Plugins.Smoke/AcDream.Plugins.Smoke.csproj" />
</Folder>
<Folder Name="/tests/">
<Project Path="tests/AcDream.Core.Tests.Fixtures.HelloPlugin/AcDream.Core.Tests.Fixtures.HelloPlugin.csproj" />
<Project Path="tests/AcDream.Core.Tests/AcDream.Core.Tests.csproj" />
<Project Path="tests/AcDream.Core.Net.Tests/AcDream.Core.Net.Tests.csproj" />
</Folder>
</Solution>