quic-go initiates a 1-RTT key update partway through every transferloss
or transfercorruption test (KEY_PHASE bit flips 0→1 around server pn=100
by default). Pre-fix our parser used the OLD application keys for every
post-update packet, AEAD-failed all of them, never sent another ACK,
the server fell into PTO mode, and throughput collapsed (~24kbps over
60s vs the 10Mbps the path supports).
The fix is end-to-end:
- ShortHeaderPacket.peekKeyPhase: HP-unmasks just the first byte to
surface the key-phase bit BEFORE running AEAD. The parser uses this
to pick the right keys instead of paying for a doomed AEAD.
- QuicConnection: tracks the live application secrets (server- and
client-side) and current send/receive key phase, plus a
previousReceiveProtection slot for RFC §6.1 reorder-window decryption.
deriveNextPhaseReceiveKeys derives the next phase via
HKDF-Expand-Label("quic ku", "", Hash.length) without committing;
commitKeyUpdate installs them only after AEAD has succeeded, then
rolls the send side forward in lockstep so our next outbound
carries the matching KEY_PHASE bit (peer needs that to confirm the
rotation completed). HP key is NOT rotated, per spec.
- QuicConnectionParser.feedShortHeaderPacket: three-way dispatch on
the peeked bit — matches current → live keys; matches retained
previous → previous keys (reordered packet); else → derive
next-phase, attempt AEAD, commit on success.
- QuicConnectionWriter: ShortHeaderPlaintextPacket(... keyPhase =
conn.currentSendKeyPhase) at both 1-RTT build sites (steady-state
and CONNECTION_CLOSE).
We don't drive key updates ourselves — only echo the peer's. Avoids
the bookkeeping for RFC 9001 §6.6 packet-count limits and the safety
benefits of voluntary rotation aren't load-bearing at our connection
scale.
Tests: peekKeyPhase round-trip + long-header rejection;
2-byte-pn round-trip when largestReceived is far behind (the original
suspected-but-not-actual cause before the key-phase reveal).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Vitor Pamplona
b622d0c936