Closes the v3.1 unlinkability gap and resists volume/timing correlation:
1) Per-hop client cert (identity-unlinkable hops). [[client.circuit.hops]]
now accepts {addr, cert_path, key_path, [server_name]} per hop — each
hop sees a different CN, so a relay and an exit cannot correlate the
same client by certificate. Old flat `hops = ["ip:port"]` form still
parses (serde untagged enum) and falls back to [pki] cert/key.
`aura provision-client --circuit-hops N` mints N fresh UUIDv4 certs.
2) Cell padding. CellPaddingConn wrapper pads every outgoing packet to a
fixed size (default 1280 bytes; `cell_size = N` configurable) before
it hits the inner AEAD. Format: u16_be(real_len) || pkt || zero_pad.
On-wire sizes become constant -> defeats volume/timing fingerprints.
Opt-in via [client.circuit] cell_padding = true and the mirror
[server] cell_padding_for_circuit_clients = true.
3) 3-hop support. dial_circuit now accepts N >= 2 hops; iterative
ExtendBridge nests N-1 forwarders and N handshakes. Client owns the
full chain via CircuitConnection (forwarders abort on drop).
New integration test multihop_v3_2_three_hops_end_to_end runs three
in-process actors (A relay -> B relay -> C exit) on loopback and
verifies peer_id == C's CN.
4) CIDR whitelist. [server.relay] allow_extend_to entries accept
"10.0.0.0/24" (subnet, any port), "10.0.0.0/24:443" (subnet + port),
"[2001:db8::/32]:443" (IPv6 with port), as well as exact IP:port.
Empty list keeps the v3.1 open-relay (warn).
19 new tests; workspace 276 passed (+19), clippy -D warnings clean, fmt clean.
257 baseline tests untouched; all v2 / v3.1 / LE configs work as before.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Completes v3.1 multi-hop / onion routing (2 hops: client → entry-relay →
exit-server). Combined with the scaffold commit (6c14c0d), the property
holds: entry-relay knows the client IP + client_id but cannot decrypt the
data; exit knows the destination but sees the relay's IP as source.
- aura-cli::circuit: dial_circuit(&[entry, exit], proto_cfg, udp_opts) →
CircuitConnection. Connects to entry as a normal UdpClient, sends an
ExtendBridge control envelope, awaits CircuitReady, then runs a SECOND
Aura handshake to the exit through a local loopback UDP proxy — the
forwarder ferries datagrams between that proxy socket and the outer
relay PacketConnection. The inner handshake therefore authenticates the
EXIT cert (verified by the integration test asserting
circuit.peer_id() == "localhost-exit"); the relay never sees the inner
session keys.
- aura-cli::relay: rendezvous(conn, whitelist) -> Bridged{bridge} |
Fallback{first_pkt} | Refused. 2-second window after handshake to receive
ExtendBridge. Whitelist enforced; CircuitFailed on miss. Empty whitelist
logs a warning and runs open. Timeout / non-control → Fallback so the
same server can be both relay (for circuit clients) and exit (for direct
clients) simultaneously.
- aura-cli::client: when [client.circuit] enabled → dial_circuit; falls
back to normal aura_transport::dial when disabled.
- aura-cli::server: relay rendezvous wired before pool/CRL/router path.
run_bridge spawns two forwarder tasks (conn↔bridge UDP socket).
- 3 integration tests: end-to-end (with peer_id assertion), whitelist
rejection, back-compat (relay disabled → Err). 3 unit tests in relay.rs.
Workspace: 253 tests passed (247 baseline + 6 new), clippy -D warnings clean,
fmt clean. No new workspace deps. All 28 tracked tasks (v1 + v2 + v3.1) now
complete.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
xah30