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SessionDatagram redesign: add src_addr, reclassify error signals
Add src_addr to SessionDatagram envelope (34-byte header: msg_type + src_addr + dest_addr + hop_limit) so transit routers can route error signals back to the packet's originator. Reclassify CoordsRequired/PathBroken as link-layer error signals (plaintext inside SessionDatagram) rather than e2e encrypted session messages. Transit routers generate these when forwarding fails and route them to src_addr; if source is also unreachable, drop silently. Remove redundant src_addr/dest_addr/hop_limit from SessionSetup, SessionAck, and DataPacket (now in envelope). DataPacket header reduced from 36 to 4 bytes. Remove PathBroken.original_src. Fix routing loop vulnerability: gate bloom filter path on having cached dest_coords to prevent blind forwarding between peers. Simplify select_best_candidate() to require coordinates. Fix gossip protocol type codes (0x11->0x20, 0x12->0x30, 0x13->0x31) for consistency across all design docs. All 5 design docs updated and cross-checked for consistency. 335 tests pass, zero warnings.
This commit is contained in:
Johnathan Corgan
@@ -423,26 +423,39 @@ handshakes succeed regardless of the responder's actual key parity. See
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### 6.4 Handshake Integration with SessionSetup
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The Noise handshake messages embed in SessionSetup/SessionAck:
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The Noise handshake messages embed in SessionSetup/SessionAck, which are
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carried inside a SessionDatagram envelope that provides addressing:
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```text
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SessionSetup {
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// Routing portion (processed by routers)
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src_coords: Vec<NodeAddr>,
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dest_coords: Vec<NodeAddr>,
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src_addr: Ipv6Addr,
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dest_addr: Ipv6Addr,
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SessionDatagram {
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// Addressing (used by routers for forwarding and error routing)
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src_addr: NodeAddr,
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dest_addr: NodeAddr,
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hop_limit: u8,
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// Crypto portion (opaque to routers, processed by destination)
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handshake_payload: Vec<u8>, // Noise IK message 1
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// Payload: SessionSetup
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payload: SessionSetup {
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// Routing portion (processed by routers for cache warming)
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src_coords: Vec<NodeAddr>,
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dest_coords: Vec<NodeAddr>,
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// Crypto portion (opaque to routers, processed by destination)
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handshake_payload: Vec<u8>, // Noise IK message 1
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}
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}
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SessionAck {
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// Routing portion
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src_coords: Vec<NodeAddr>, // Responder's coordinates
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SessionDatagram {
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src_addr: NodeAddr, // Responder
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dest_addr: NodeAddr, // Original sender
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hop_limit: u8,
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// Crypto portion
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handshake_payload: Vec<u8>, // Noise IK message 2
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payload: SessionAck {
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// Routing portion
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src_coords: Vec<NodeAddr>, // Responder's coordinates
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// Crypto portion
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handshake_payload: Vec<u8>, // Noise IK message 2
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}
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}
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```
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@@ -529,44 +542,97 @@ for TreeAnnounce and FilterAnnounce wire formats.
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## 8. Session Layer Wire Format
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Session layer messages are carried inside `SessionDatagram` (type 0x40) at the
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link layer. The session datagram is encrypted hop-by-hop with link keys, but
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the inner payload is encrypted end-to-end with session keys.
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link layer. The session datagram provides source and destination addressing for
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multi-hop forwarding: it is encrypted hop-by-hop with link keys, and the inner
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payload is either encrypted end-to-end with session keys (for data traffic) or
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plaintext (for link-layer error signals from transit routers).
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### 8.1 Message Type Codes
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### 8.0 SessionDatagram Envelope
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The SessionDatagram is a link-layer message (type 0x40) that carries all
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routable traffic through the mesh. It provides the source and destination
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addresses that transit routers use for forwarding decisions.
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```text
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┌─────────────────────────────────────────────────────────────────────────────┐
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│ SESSION DATAGRAM (0x40) │
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├────────┬──────────────────┬───────────┬─────────────────────────────────────┤
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│ Offset │ Field │ Size │ Description │
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├────────┼──────────────────┼───────────┼─────────────────────────────────────┤
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│ 0 │ msg_type │ 1 byte │ 0x40 (link-layer SessionDatagram) │
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│ 1 │ src_addr │ 16 bytes │ Source node_addr │
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│ 17 │ dest_addr │ 16 bytes │ Destination node_addr │
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│ 33 │ hop_limit │ 1 byte │ Decremented each hop │
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│ 34 │ payload │ variable │ Session-layer message (see §8.1) │
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└────────┴──────────────────┴───────────┴─────────────────────────────────────┘
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Fixed header: 34 bytes
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```
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**src_addr**: The originator of the datagram. For data traffic, this is the
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source endpoint. For error signals (CoordsRequired, PathBroken), this is the
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transit router that generated the error. Transit routers use `src_addr` to
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route error signals back to the packet's originator.
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**dest_addr**: The intended recipient. Transit routers use this for next-hop
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selection via `find_next_hop()`.
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**hop_limit**: Decremented at each forwarding hop. When it reaches zero, the
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datagram is dropped silently. This prevents infinite forwarding loops. Initial
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value is configurable (default 64).
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### 8.1 Payload Message Types
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The SessionDatagram payload begins with a message type byte, followed by the
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message-specific content.
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**Session-layer messages** (end-to-end encrypted with session keys):
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| Type Code | Message | Direction | Purpose |
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|-----------|----------------|-----------|-----------------------------------|
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| 0x00 | SessionSetup | S → D | Establish session + warm caches |
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| 0x01 | SessionAck | D → S | Confirm session establishment |
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| 0x10 | DataPacket | Both | Application data |
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**Link-layer error signals** (plaintext, generated by transit routers):
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| Type Code | Message | Direction | Purpose |
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|-----------|----------------|-----------|-----------------------------------|
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| 0x20 | CoordsRequired | R → S | Router cache miss |
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| 0x21 | PathBroken | R → S | Greedy routing failed |
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> **Address terminology**: The `src_addr` and `dest_addr` fields in session packet
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> headers are node_addrs (16-byte truncated SHA-256 hashes of pubkeys). These are visible to
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> intermediate routers for routing decisions. The actual FIPS addresses (pubkeys/npubs)
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> are exchanged only during the Noise IK handshake and never appear in packet
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> headers—routers cannot determine endpoint identities from the node_addrs they see.
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Error signals are generated by transit router R and sent back to the source S
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inside a *new* SessionDatagram with `src_addr=R, dest_addr=S`. They are
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plaintext (not end-to-end encrypted) because the transit router has no session
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with the source. Link-layer encryption protects them hop-by-hop.
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> **Address terminology**: The `src_addr` and `dest_addr` fields in the
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> SessionDatagram header are node_addrs (16-byte truncated SHA-256 hashes of
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> pubkeys). These are visible to intermediate routers for routing decisions. The
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> actual FIPS addresses (pubkeys/npubs) are exchanged only during the Noise IK
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> handshake and never appear in packet headers—routers cannot determine endpoint
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> identities from the node_addrs they see.
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### 8.2 SessionSetup (0x00)
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Establishes a crypto session and warms router coordinate caches along the path.
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The `src_addr` and `dest_addr` are carried in the enclosing SessionDatagram
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envelope (§8.0); the SessionSetup payload carries only coordinates and the
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Noise handshake.
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```text
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┌─────────────────────────────────────────────────────────────────────────────┐
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│ SESSION SETUP PACKET │
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│ SESSION SETUP PAYLOAD (inside SessionDatagram) │
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├────────┬──────────────────┬───────────┬─────────────────────────────────────┤
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│ Offset │ Field │ Size │ Description │
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├────────┼──────────────────┼───────────┼─────────────────────────────────────┤
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│ 0 │ msg_type │ 1 byte │ 0x00 │
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│ 1 │ flags │ 1 byte │ Bit 0: REQUEST_ACK │
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│ │ │ │ Bit 1: BIDIRECTIONAL │
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│ 2 │ src_addr │ 16 bytes │ Source node_addr │
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│ 18 │ dest_addr │ 16 bytes │ Destination node_addr │
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│ 34 │ src_coords_count │ 2 bytes │ u16 LE, number of src coord entries │
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│ 36 │ src_coords │ 16 × n │ NodeAddr array (self → root) │
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│ 2 │ src_coords_count │ 2 bytes │ u16 LE, number of src coord entries │
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│ 4 │ src_coords │ 16 × n │ NodeAddr array (self → root) │
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│ ... │ dest_coords_count│ 2 bytes │ u16 LE, number of dest coord entries│
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│ ... │ dest_coords │ 16 × m │ NodeAddr array (dest → root) │
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│ ... │ dest_coords │ 16 × m │ NodeAddr array (dest → root) │
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│ ... │ handshake_len │ 2 bytes │ u16 LE, Noise payload length │
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│ ... │ handshake_payload│ variable │ Noise IK msg1 (82 bytes typical) │
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└────────┴──────────────────┴───────────┴─────────────────────────────────────┘
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@@ -575,33 +641,32 @@ Establishes a crypto session and warms router coordinate caches along the path.
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**Example** (depth 3 source, depth 4 destination, with Noise handshake):
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```text
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┌──────┬───────┬──────────────────┬──────────────────┬───────┬─────────────┐
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│ 0x00 │ 0x01 │ src_addr │ dest_addr │ 0x03 │ src_coords │
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│ type │ flags │ 16 bytes │ 16 bytes │ count │ 3 × 16 bytes│
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├──────┴───────┴──────────────────┴──────────────────┴───────┴─────────────┤
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│ 0x04 │ dest_coords │ 0x52 │ handshake_payload │
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│ count │ 4 × 16 bytes │ len=82│ 82 bytes (Noise IK msg1) │
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└───────┴───────────────┴───────┴──────────────────────────────────────────┘
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SessionDatagram { src: S, dest: D, hop_limit: 64 } +
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┌──────┬───────┬───────┬─────────────┬───────┬───────────────┬───────┬───────┐
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│ 0x00 │ 0x01 │ 0x03 │ src_coords │ 0x04 │ dest_coords │ 0x52 │ noise │
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│ type │ flags │ count │ 3 × 16 bytes│ count │ 4 × 16 bytes │ len=82│ msg1 │
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└──────┴───────┴───────┴─────────────┴───────┴───────────────┴───────┴───────┘
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Total: 1 + 1 + 16 + 16 + 2 + 48 + 2 + 64 + 2 + 82 = 234 bytes
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SessionDatagram header: 34 bytes
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SessionSetup payload: 1 + 1 + 2 + 48 + 2 + 64 + 2 + 82 = 202 bytes
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Total: 236 bytes
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```
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### 8.3 SessionAck (0x01)
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Confirms session establishment and completes the Noise handshake.
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Confirms session establishment and completes the Noise handshake. Addressing
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is in the enclosing SessionDatagram envelope.
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```text
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┌─────────────────────────────────────────────────────────────────────────────┐
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│ SESSION ACK PACKET │
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│ SESSION ACK PAYLOAD (inside SessionDatagram) │
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├────────┬──────────────────┬───────────┬─────────────────────────────────────┤
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│ Offset │ Field │ Size │ Description │
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├────────┼──────────────────┼───────────┼─────────────────────────────────────┤
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│ 0 │ msg_type │ 1 byte │ 0x01 │
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│ 1 │ flags │ 1 byte │ Reserved │
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│ 2 │ src_addr │ 16 bytes │ Acknowledger's node_addr │
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│ 18 │ dest_addr │ 16 bytes │ Original sender's node_addr │
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│ 34 │ src_coords_count │ 2 bytes │ u16 LE │
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│ 36 │ src_coords │ 16 × n │ Acknowledger's coords (for caching) │
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│ 2 │ src_coords_count │ 2 bytes │ u16 LE │
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│ 4 │ src_coords │ 16 × n │ Acknowledger's coords (for caching) │
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│ ... │ handshake_len │ 2 bytes │ u16 LE, Noise payload length │
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│ ... │ handshake_payload│ variable │ Noise IK msg2 (33 bytes typical) │
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└────────┴──────────────────┴───────────┴─────────────────────────────────────┘
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@@ -609,79 +674,90 @@ Confirms session establishment and completes the Noise handshake.
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### 8.4 DataPacket (0x10)
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Carries encrypted application data (typically IPv6 payloads).
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Carries encrypted application data (typically IPv6 payloads). Addressing and
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hop limit are in the enclosing SessionDatagram envelope.
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```text
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┌─────────────────────────────────────────────────────────────────────────────┐
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│ DATA PACKET (Minimal Header) │
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│ DATA PACKET (Minimal Header, inside SessionDatagram) │
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├────────┬──────────────────┬───────────┬─────────────────────────────────────┤
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│ Offset │ Field │ Size │ Description │
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├────────┼──────────────────┼───────────┼─────────────────────────────────────┤
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│ 0 │ msg_type │ 1 byte │ 0x10 │
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│ 1 │ flags │ 1 byte │ Bit 0: COORDS_PRESENT │
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│ 2 │ hop_limit │ 1 byte │ Decremented each hop │
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│ 3 │ reserved │ 1 byte │ Alignment padding │
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│ 4 │ payload_length │ 2 bytes │ u16 LE │
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│ 6 │ src_addr │ 16 bytes │ Source node_addr │
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│ 22 │ dest_addr │ 16 bytes │ Destination node_addr │
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│ 38 │ payload │ variable │ Encrypted application data │
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│ 2 │ payload_length │ 2 bytes │ u16 LE │
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│ 4 │ payload │ variable │ Encrypted application data │
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└────────┴──────────────────┴───────────┴─────────────────────────────────────┘
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Minimal header: 38 bytes
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Minimal header: 4 bytes (+ 34 SessionDatagram header = 38 bytes total)
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```
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When `COORDS_PRESENT` flag is set (route warming after CoordsRequired):
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```text
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┌─────────────────────────────────────────────────────────────────────────────┐
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│ DATA PACKET (With Coordinates) │
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│ DATA PACKET (With Coordinates, inside SessionDatagram) │
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├────────┬──────────────────┬───────────┬─────────────────────────────────────┤
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│ Offset │ Field │ Size │ Description │
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├────────┼──────────────────┼───────────┼─────────────────────────────────────┤
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│ 0 │ msg_type │ 1 byte │ 0x10 │
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│ 1 │ flags │ 1 byte │ 0x01 (COORDS_PRESENT) │
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│ 2 │ hop_limit │ 1 byte │ Decremented each hop │
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│ 3 │ reserved │ 1 byte │ Alignment padding │
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│ 4 │ payload_length │ 2 bytes │ u16 LE │
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│ 6 │ src_addr │ 16 bytes │ Source node_addr │
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│ 22 │ dest_addr │ 16 bytes │ Destination node_addr │
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│ 38 │ src_coords_count │ 2 bytes │ u16 LE │
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│ 40 │ src_coords │ 16 × n │ Source coordinates │
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│ 2 │ payload_length │ 2 bytes │ u16 LE │
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│ 4 │ src_coords_count │ 2 bytes │ u16 LE │
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│ 6 │ src_coords │ 16 × n │ Source coordinates │
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│ ... │ dest_coords_count│ 2 bytes │ u16 LE │
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│ ... │ dest_coords │ 16 × m │ Destination coordinates │
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│ ... │ payload │ variable │ Encrypted application data │
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└────────┴──────────────────┴───────────┴─────────────────────────────────────┘
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With depth-4 coords both directions: 38 + 2 + 64 + 2 + 64 = 170 bytes header
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With depth-4 coords both directions:
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DataPacket: 4 + 2 + 64 + 2 + 64 = 136 bytes header
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+ SessionDatagram: 34 bytes
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Total: 170 bytes header
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```
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### 8.5 CoordsRequired (0x20)
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Sent by an intermediate router when it cannot forward a DataPacket due to
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coordinate cache miss.
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Sent by an intermediate router when it cannot forward a SessionDatagram due to
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coordinate cache miss for the destination. This is a **link-layer error signal**:
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the transit router generates a new SessionDatagram addressed back to the
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original source, with the CoordsRequired payload in plaintext (not end-to-end
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encrypted, since the transit router has no session with the source).
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**Error routing**: Router R receives a SessionDatagram `{src: S, dest: D}` but
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cannot route to D. R creates a new SessionDatagram `{src: R, dest: S}` carrying
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a CoordsRequired payload, and calls `find_next_hop(S)` to route it back to S.
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If R also cannot route to S, the error is dropped silently (no cascading errors).
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**CoordsRequired payload** (inside SessionDatagram):
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```text
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┌─────────────────────────────────────────────────────────────────────────────┐
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│ COORDS REQUIRED PACKET │
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│ COORDS REQUIRED PAYLOAD │
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├────────┬──────────────────┬───────────┬─────────────────────────────────────┤
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│ Offset │ Field │ Size │ Description │
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├────────┼──────────────────┼───────────┼─────────────────────────────────────┤
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│ 0 │ msg_type │ 1 byte │ 0x20 │
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│ 1 │ flags │ 1 byte │ Reserved │
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│ 2 │ dest_addr │ 16 bytes │ The node_addr we couldn't route │
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│ 2 │ dest_addr │ 16 bytes │ The node_addr we couldn't route to │
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│ 18 │ reporter │ 16 bytes │ NodeAddr of reporting router │
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└────────┴──────────────────┴───────────┴─────────────────────────────────────┘
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Total: 34 bytes
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Payload: 34 bytes
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Wrapped in SessionDatagram: 34 + 34 = 68 bytes total
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```
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### 8.6 PathBroken (0x21)
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Sent when greedy routing fails (no peer is closer to destination).
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Sent when greedy routing fails (no peer is closer to destination). Like
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CoordsRequired, this is a **link-layer error signal** carried inside a new
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SessionDatagram addressed back to the original source.
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**PathBroken payload** (inside SessionDatagram):
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```text
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┌─────────────────────────────────────────────────────────────────────────────┐
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│ PATH BROKEN PACKET │
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│ PATH BROKEN PAYLOAD │
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├────────┬──────────────────┬───────────┬─────────────────────────────────────┤
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│ Offset │ Field │ Size │ Description │
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├────────┼──────────────────┼───────────┼─────────────────────────────────────┤
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@@ -714,34 +790,45 @@ A DataPacket from source S to destination D, transiting router R:
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│ │ Decrypt with S↔R link keys │
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│ ▼ │
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│ ┌───────────────────────────────────────────────────────────────────────┐ │
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│ │ LINK MESSAGE (plaintext for R) │ │
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│ ├───────────┬───────────────────────────────────────────────────────────┤ │
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│ │ 0x40 │ SessionDatagram payload │ │
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│ │ msg_type │ (routable by R, encrypted end-to-end) │ │
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│ └───────────┴───────────────────────────────────────────────────────────┘ │
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│ │ SESSION DATAGRAM (0x40) — plaintext for R │ │
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│ ├───────────┬──────────────┬──────────────┬──────────┬──────────────────┤ │
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│ │ 0x40 │ src_addr │ dest_addr │ hop_limit│ payload │ │
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│ │ msg_type │ S (16 bytes) │ D (16 bytes) │ 64 │ (session msg) │ │
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│ └───────────┴──────────────┴──────────────┴──────────┴──────────────────┘ │
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│ │ │
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│ │ R reads src_addr + dest_addr for routing │
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│ ▼ │
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│ ┌───────────────────────────────────────────────────────────────────────┐ │
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│ │ SESSION LAYER (S↔D encrypted) │ │
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│ │ SESSION LAYER PAYLOAD (S↔D encrypted) │ │
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│ ├───────────┬───────┬──────────┬──────────┬─────────────────────────────┤ │
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│ │ 0x10 │ flags │ hop_limit│ pay_len │ src_addr │ dest_addr │ │
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│ │ DataPacket│ 0x00 │ 64 │ 1400 │ 16 bytes │ 16 bytes │ │
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│ ├───────────┴───────┴──────────┴──────────┴──────────────┴──────────────┤ │
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│ │ │ │
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│ │ ENCRYPTED PAYLOAD (S↔D session keys) │ │
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│ │ ┌─────────────────────────────────────────────┐ │ │
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│ │ │ IPv6 packet or application data │ │ │
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│ │ │ (+ 16-byte AEAD tag) │ │ │
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│ │ └─────────────────────────────────────────────┘ │ │
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│ │ │ │
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│ └───────────────────────────────────────────────────────────────────────┘ │
|
||||
│ │ 0x10 │ flags │ reserved │ pay_len │ encrypted application data │ │
|
||||
│ │ DataPacket│ 0x00 │ 0x00 │ 1400 │ (S↔D session keys + tag) │ │
|
||||
│ └───────────┴───────┴──────────┴──────────┴─────────────────────────────┘ │
|
||||
│ │
|
||||
└─────────────────────────────────────────────────────────────────────────────┘
|
||||
|
||||
Router R can see: dest_addr (for routing decision)
|
||||
Router R cannot see: payload contents (encrypted with S↔D keys)
|
||||
Router R can see: src_addr, dest_addr, hop_limit (for routing/error signaling)
|
||||
Router R cannot see: payload contents (encrypted with S↔D session keys)
|
||||
```
|
||||
|
||||
### 8.7.1 Error Routing Example
|
||||
|
||||
When router R cannot forward a SessionDatagram from S to D:
|
||||
|
||||
```text
|
||||
1. R receives SessionDatagram { src: S, dest: D, payload: DataPacket{...} }
|
||||
2. R has no cached coordinates for D and no bloom filter hit
|
||||
3. R creates NEW SessionDatagram:
|
||||
{ src: R, dest: S, hop_limit: 64,
|
||||
payload: CoordsRequired { dest: D, reporter: R } }
|
||||
4. R calls find_next_hop(S) to route the error back
|
||||
5. If R can also not route to S: drop silently (no cascading errors)
|
||||
```
|
||||
|
||||
This avoids the need for transit routers to have end-to-end sessions with
|
||||
the source. The `src_addr` field in the original SessionDatagram tells the
|
||||
transit router where to send the error.
|
||||
|
||||
### 8.8 Encoding Rules
|
||||
|
||||
- All multi-byte integers are **little-endian**
|
||||
|
||||
Reference in New Issue
Block a user