The FSP XK rekey handshake has a race condition where the initiator
can cut over (K-bit flip) and send data encrypted with the new session
before msg3 reaches the responder. The responder has no pending session
yet, so K-bit detection fails and packets are dropped.
Defer FSP initiator cutover by 2 seconds after handshake completion
(FSP_CUTOVER_DELAY_MS) to give msg3 time to traverse the mesh. FMP
(IK, 2 messages) is unaffected since the responder completes during
msg1 processing.
Also fix MMP metric corruption after rekey cutover: the new session
starts with counter 0 but MMP state carries highest_counter and
GapTracker.expected_next from the old session, producing false
reorder counts, jitter spikes, and invalid OWD trends. Add
reset_for_rekey() methods that clear counter-dependent state while
preserving RTT estimates.
Additional fixes:
- Remove stale peers_by_index entry on abandon_rekey error path
- Replace redundant peers_by_index inserts with debug assertions
verifying the pre-registration invariant
- Tighten rekey integration test to zero tolerance (was 4 failures)
Phase 3 (post-first-rekey connectivity) can see brief disruptions while
links are mid-cutover. Add a 5s settle time after the rekey wait and
allow up to 4 transient pair failures in Phase 3. Phase 5 remains
strict, ensuring full recovery after the second rekey cycle.
Implement periodic full rekey at both protocol layers using fresh DH
key exchanges. Uses the existing K-bit flag (FLAG_KEY_EPOCH /
FSP_FLAG_K) to coordinate cutover between peers.
FMP layer (IK pattern):
- ActivePeer gains rekey state: pending/previous sessions, K-bit epoch
tracking, drain window, dampening timer
- Handshake state stored on ActivePeer with msg1 sent on existing link
- Encrypted frame handler detects K-bit flips, promotes pending
sessions, falls back to previous session during drain
- Handshake handlers distinguish rekey from new connections using
addr_to_link lookup with identity-based fallback
- Free all session indices (current, rekey, pending, previous) on
peer removal
FSP layer (XK pattern):
- SessionEntry gains parallel rekey fields with XK-specific state
for the 3-message handshake
- Route availability check before FSP rekey initiation
- Encrypted session handler adds K-bit flip detection and dual-session
decrypt fallback
- SessionSetup/Ack/Msg3 handlers extended for rekey paths
Defense-in-depth:
- Consecutive decryption failure detector (threshold=20) triggers
forced peer removal instead of waiting for link-dead timeout
- Identity-based rekey detection as fallback when addr_to_link
doesn't match (e.g., TCP ephemeral ports)
Configuration: RekeyConfig with enabled flag, after_secs (default 120),
and after_messages (default 65536) thresholds.
Logging: info for successful K-bit cutover completions, warn for
failures, debug for intermediate handshake steps, trace for routine
operations (resends, drain cleanup).
Rekey lifecycle:
1. Timer/counter fires -> initiator starts new handshake
2. Old session continues handling traffic during handshake
3. Handshake completes -> initiator cuts over, flips K-bit
4. Responder sees flipped K-bit -> promotes new session
5. Both keep old session for 10s drain window
6. After drain, old session discarded
Integration test: Docker-based multi-phase test exercising both FMP
and FSP rekey with aggressive timers (35s). Verifies connectivity
across all 20 directed pairs survives two consecutive rekey cycles.
Includes rekey topology, docker-compose profile, and CI matrix entry.
Increase ping test convergence wait from 3s to 5s for CI reliability.
Implement TCP transport for FIPS enabling firewall traversal and serving
as the foundation for future Tor transport. This is the first
connection-oriented transport in the system.
Key design decisions:
- FMP header-based framing: reuses existing 4-byte FMP common prefix for
packet boundary recovery with zero framing overhead
- Session survives TCP reconnection: Noise/MMP/FSP state bound to npub,
not TCP connection; MMP liveness is sole authority for peer death
- Connect-on-send: fresh connection on first send, transparent reconnect
- close_connection() trait method for cross-connection deduplication cleanup
New transport files:
- src/transport/tcp/mod.rs: TcpTransport, connection pool, accept loop
- src/transport/tcp/stream.rs: FMP-aware stream reader (shared with Tor)
Modified: transport trait (close_connection), TcpConfig, TransportHandle
match arms, create_transports(), initiate_connection() for connection-
oriented links, cross-connection tie-breaker cleanup, design docs.
Tree announce loop and TCP stability fixes:
- Preserve tree announce rate-limit state across reconnection: carry
forward last_tree_announce_sent_ms when a peer reconnects so the
rate-limit window isn't reset to zero
- Drop oversize TCP packets at sender: pre-send MTU check returns
MtuExceeded instead of writing to the stream, preventing receiver-side
connection teardown and reset-reconnect cycles
Chaos harness:
- TCP transport support: tcp_edges/has_tcp/tcp_peers in SimTopology,
transport-aware config_gen with per-edge transport type, TCP port 443,
pure-TCP node support
- Include all non-Ethernet edges in directed_outbound()
- Fix netem/links log messages to say "IP-based" instead of "UDP"
- Add tcp-chain, tcp-only, and tcp-mesh scenario files
Static harness:
- Transport-aware config generation (get_default_transport, transport_port)
- TCP transport injection via Python post-processing
- Add tcp-chain topology and docker-compose profile
Update the default UDP bind port from 4000 to 2121 (decimal) and the
default Ethernet EtherType from 0x88B5 to 0x2121 across all source
code, documentation, configuration templates, test fixtures, and
scripts. Remove references to "IEEE 802 experimental range" since
0x2121 is not in that range.
Johnathan Corgan