feat(core+host): negotiate ChaCha20-Poly1305 as the session cipher for soft-AES clients

Lifts the ~100 Mbps decrypt ceiling on clients without hardware AES — the armv7 soft-AES targets (webOS TVs), where AES-128-GCM resolves to fixsliced software AES + software GHASH (~50-100 cpb) while ChaCha20-Poly1305's ARX construction runs ~10-17 cpb portable, a 4-7x lift that PyroWave-on-TV needs (design/chacha20-session-cipher.md). Phase 1 (core crypto, no wire change): SessionKey merges cipher choice and key material (invalid combinations unrepresentable, zeroize + redacted-Debug discipline kept); SessionCrypto dispatches both aead-0.5 ciphers per call — the salt||seq nonce scheme, per-direction salts, seq-as-AAD and replay window carry over verbatim (same 96-bit nonce / 16-byte tag, const-asserted). Config.key becomes SessionKey; validate's zero-key rejection follows the active variant. The C ABI keeps its fixed 16-byte key mapped to AES — no ABI_VERSION bump. Phase 2 (negotiation): VIDEO_CAP_CHACHA20 (0x40) — support-plus-request in one bit, the VIDEO_CAP_444 precedent. Welcome grows cipher@68 + key_chacha@69..101, emitted only when non-zero so an AES session's Welcome stays byte-identical to the pre-cipher form; decode is fail-closed (short key or unknown id -> Err, never a silent AES fallback). No WIRE_VERSION bump; downgrade resistance inherited from the pinned-TLS control channel. Phase 3 (host): grant only when the client advertised the bit and the PUNKTFUNK_CHACHA20 kill-switch (default on, documented) allows; fresh 32-byte per-session key from the same RNG discipline, legacy key field stays independently random; resolved cipher logged at session start. Verification: seal/open suites parameterized over both ciphers + a cross-cipher tamper case; Welcome roundtrip/truncation/fail-closed tests; ChaCha lossy-loopback soak (loss/replay is cipher-independent); bench gains _chacha20 series (AES ids unchanged for CI history) — host-side sealing line-rate-trivial on both x86 (~640 MiB/s) and Apple Silicon (~535 MiB/s). punktfunk-probe drives the interop matrix via PUNKTFUNK_CLIENT_CHACHA20=1 and logs the negotiated cipher. Phase 4 (pf-webos pin bump + unconditional cap bit) follows the next core release. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
2026-07-21 21:58:26 +02:00
parent abc54a7d13
commit d36bec6e9d
17 changed files with 663 additions and 160 deletions
@@ -33,6 +33,11 @@ reed-solomon-simd = "3.1"      # GF(2^16) Leopard-RS, SIMD, O(n log n) — the w
 # NOT interoperable.) See vendor/fec-rs/LICENSE (BSD-2-Clause).
 fec-rs = { path = "vendor/fec-rs" }
 aes-gcm = "0.10"               # AES-128-GCM session crypto, matches GameStream
+# ChaCha20-Poly1305 session crypto, negotiated by clients without hardware AES (the soft-AES
+# armv7 targets — webOS TVs — where GCM caps decrypt at ~100 Mbps; ARX runs 4-7x faster there).
+# Same RustCrypto `aead 0.5` generation as aes-gcm: identical trait/nonce/tag shapes, pure Rust,
+# cross-compiles like aes-gcm (no cmake). See design/chacha20-session-cipher.md.
+chacha20poly1305 = "0.10"
 zerocopy = { version = "0.8", features = ["derive"] }
 bytes = "1"
 socket2 = { version = "0.6", features = [