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Session 65: RX loop integration test and session layer doc correction

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Add test_run_rx_loop_handshake exercising the full packet dispatch
path (UDP → channel → run_rx_loop → process_packet → handler) using
tokio::select! with timeout to release &mut self for assertions.

Correct session layer documentation: sessions are always established
between communicating nodes regardless of adjacency, not only for
non-adjacent traffic. Add adjacent-peer encryption flow example,
fix table description, rename Link Layer subsection to "Hop-by-Hop".

267 tests pass (266 existing + 1 new).
This commit is contained in:
Johnathan Corgan
2026-02-10 18:45:41 +00:00
parent cd7064595d
commit 323bfa1ef7
2 changed files with 215 additions and 9 deletions
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34
docs/design/fips-intro.md
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@@ -196,17 +196,17 @@ traffic.
FIPS uses independent encryption at two layers:
| Layer | Scope | Pattern | Purpose |
|-------------|-------------|----------|--------------------------------------|
| **Link** | Hop-by-hop | Noise IK | Encrypt all traffic on each link |
| **Session** | End-to-end | Noise IK | Encrypt payload across multiple hops |
| Layer | Scope | Pattern | Purpose |
|-------------|-------------|----------|------------------------------------------------|
| **Link** | Hop-by-hop | Noise IK | Encrypt all traffic on each link |
| **Session** | End-to-end | Noise IK | Encrypt application payload between endpoints |
### Link Layer (Peer-to-Peer)
### Link Layer (Hop-by-Hop)
When two nodes establish a direct connection, they perform a Noise IK handshake.
This authenticates both parties and establishes symmetric keys for encrypting
all traffic on that link. Every packet between direct peers is encrypted—gossip
messages, routing queries, and forwarded traffic alike.
messages, routing queries, and forwarded session datagrams alike.
The IK pattern is used because outbound connections know the peer's npub from
configuration, while inbound connections learn the initiator's identity from
@@ -214,15 +214,31 @@ the first handshake message.
### Session Layer (End-to-End)
For traffic between non-adjacent nodes, FIPS establishes end-to-end encrypted
sessions using Noise IK. The initiator knows the destination's npub; the
FIPS establishes end-to-end encrypted sessions between any two communicating
nodes using Noise IK, regardless of whether they are direct peers or separated
by intermediate routers. The initiator knows the destination's npub; the
responder learns the initiator's identity from the handshake—the same asymmetry
as link-layer connections.
Both layers always apply. For adjacent peers, application traffic is encrypted
twice: once by the session layer (end-to-end) and once by the link layer
(hop-by-hop). This uniform model means:
- No special case for "local peer" vs "remote destination"
- Topology changes (a direct peer becomes reachable only through intermediaries)
don't affect sessions
- The link layer remains purely a transport concern
A packet from A to adjacent peer B:
1. A encrypts payload with A↔B session key
2. A wraps in SessionDatagram, encrypts with A↔B link key, sends to B
3. B decrypts link layer, then decrypts session layer to get payload
A packet from A to D through intermediate node B:
1. A encrypts payload with A↔D session key
2. A encrypts that with A↔B link key, sends to B
2. A wraps in SessionDatagram, encrypts with A↔B link key, sends to B
3. B decrypts link layer, sees destination, re-encrypts with B↔D link key
4. D decrypts link layer, then decrypts session layer to get payload