quicproquo/docs/plans/mesh-protocol-gaps.md

Mesh Protocol Gaps — Honest Assessment & Action Plan

Goal: Identify real weaknesses in QuicProChat's mesh protocol compared to Reticulum, Meshtastic, and LXMF. Plan concrete improvements.

Created: 2026-03-30

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Executive Summary

QuicProChat has strong cryptography (MLS, PQ-KEM) but real gaps in the mesh layer:

Gap	Severity	Status
MLS overhead too large for LoRa	Critical	MEASURED — see actual sizes below
No lightweight messaging mode	High	DONE — MLS-Lite implemented
KeyPackage distribution over mesh	High	Not solved
Announce/routing not battle-tested	Medium	S3-S4 done, needs real-world test
No DTN bundle protocol integration	Medium	Priority field added
Battery/duty-cycle optimization	Medium	Basic tracker exists

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Gap 1: MLS Overhead is Prohibitive for Constrained Links

The Problem

MLS was designed for Internet messaging, not LoRa.

Actual Measured Sizes (2026-03-30)

Component	Size (bytes)	LoRa SF12 fragments	At 1% duty
MLS KeyPackage	306	6	~4 sec
MLS Welcome	840	17	~10 sec
MLS Commit (add)	736	15	~9 sec
MLS AppMessage (5B)	143	3	~2 sec
MLS Commit (update)	544	11	~7 sec
MLS KeyPackage (PQ)	2,676	53	~32 sec
MLS Welcome (PQ)	5,504	108	~65 sec
MeshEnvelope V1 (CBOR)	410	9	~5 sec
MeshEnvelope V2 (truncated)	336	7	~4 sec
MLS-Lite (no sig)	129	3	~2 sec
MLS-Lite (with sig)	262	6	~4 sec
Reticulum LXMF	~100-150	2-3	~1-2 sec
Meshtastic max	237	5	~3 sec

Key insights:

• Classical MLS is viable for LoRa — 6 fragments for KeyPackage
• Post-quantum hybrid MLS is prohibitive — 53+ fragments for KeyPackage
• MLS-Lite matches Meshtastic efficiency while adding proper auth
• Total group setup (KeyPackage + Welcome): ~23 fragments, ~14 sec

The math NOW works for classical MLS on LoRa:

• LoRa SF12/BW125: ~51 byte MTU, ~300 bps effective
• EU868 duty cycle: 1% = 36 seconds TX per hour
• One MLS KeyPackage = 6 fragments = 4 sec = acceptable
• Group setup = 14 sec = half duty budget, but feasible

Post-quantum is still problematic for constrained links.

Current State (Updated 2026-03-30)

• ✅ MeshEnvelope V1 uses CBOR, ~410 bytes for empty payload
• ✅ MeshEnvelope V2 uses truncated 16-byte addresses, ~336 bytes (~18% savings)
• ✅ MLS-Lite implemented: ~129 bytes without signature, ~262 with
• ✅ Classical MLS KeyPackage measured at 306 bytes (much better than expected)
• ⚠️ PQ-hybrid MLS still large (2.6KB KeyPackage)

Proposed Solutions

Option A: Hybrid Crypto Modes (Recommended)

┌─────────────────────────────────────────────────────────────────┐
│  Mode Selection Based on Transport Capability                   │
├─────────────────────────────────────────────────────────────────┤
│                                                                 │
│  QUIC/TCP/WiFi (>10 kbps):                                     │
│    → Full MLS groups with PQ-KEM                               │
│    → KeyPackage distribution via server                        │
│    → Standard protocol                                          │
│                                                                 │
│  LoRa/Serial (<1 kbps):                                        │
│    → "MLS-Lite" mode:                                          │
│      • Pre-shared group epoch key (exchanged out-of-band)      │
│      • ChaCha20-Poly1305 symmetric encryption                  │
│      • Ed25519 signatures (64 bytes)                           │
│      • No per-message KeyPackage exchange                      │
│      • Manual key rotation via QR code or faster link          │
│                                                                 │
│  Upgrade path:                                                  │
│    When faster transport available → full MLS epoch sync       │
│                                                                 │
└─────────────────────────────────────────────────────────────────┘

Trade-off: Lose automatic PCS on constrained links. Gain usability.

Option B: Compressed MLS (Research)

• Strip unused extensions from KeyPackages
• Use shorter credential identifiers (16 bytes instead of 32)
• Batch multiple KeyPackages into single transfer over fast link
• Cache and reuse KeyPackages more aggressively

Trade-off: Still large. May not be enough for SF12 LoRa.

Option C: LXMF-Compatible Mode

Implement Reticulum's LXMF format as an alternative wire format:

pub struct LxmfMessage {
    destination: [u8; 16],   // Truncated hash
    source: [u8; 16],
    signature: [u8; 64],     // Ed25519
    payload: Vec<u8>,        // msgpack: {timestamp, content, title, fields}
}
// Total: ~100-150 bytes for short message

Trade-off: Lose MLS group properties. Gain Reticulum interop and efficiency.

Action Items

• Measure actual MLS sizes — done, see table above
• Design MLS-Lite spec — docs/plans/mls-lite-design.md
• Implement MLS-Lite — crates/quicprochat-p2p/src/mls_lite.rs
• Implement MeshEnvelope V2 — truncated addresses, priority field
• Implement transport capability negotiation in TransportManager
• Test MLS-Lite vs full MLS on real LoRa

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Gap 2: KeyPackage Distribution Over Mesh

The Problem

MLS requires pre-positioned KeyPackages for adding members to groups. On Internet: server stores KeyPackages, clients fetch on demand. On mesh: no server.

Current flow (broken for pure mesh):

Alice wants to add Bob to group:
1. Alice fetches Bob's KeyPackage from server    ← requires Internet
2. Alice creates Welcome + Commit
3. Alice sends to Bob via mesh

Proposed Solution: Announce-Based KeyPackage Distribution

Bob announces on mesh:
1. MeshAnnounce includes: identity_key, capabilities, AND current_keypackage_hash
2. Nearby nodes cache Bob's latest KeyPackage (if they have it)
3. Alice receives Bob's announce, requests KeyPackage via mesh RPC

KeyPackage propagation:
1. Bob periodically broadcasts KeyPackage update (larger message, less frequent)
2. Nodes with capacity (CAP_STORE) cache KeyPackages for relaying
3. TTL-based expiry (KeyPackages are single-use, but we can cache N of them)

Action Items

• Extend MeshAnnounce with optional keypackage_hash field
• Add KeyPackage request/response to mesh protocol
• Implement KeyPackage cache in MeshStore (separate from message queue)
• Design KeyPackage refresh protocol for mesh-only scenarios

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Gap 3: No DTN/Bundle Protocol Integration

The Problem

NASA/IETF Bundle Protocol (RFC 9171) is the standard for delay-tolerant networking. Reticulum effectively reinvented it. QuicProChat should learn from both.

Key DTN concepts we're missing:

Concept	DTN/BPv7	Reticulum	QuicProChat
Custody transfer	Yes	No	No
Fragmentation at bundle layer	Yes	No	Yes (LoRa transport)
Convergence layer adapters	Formal spec	Interfaces	MeshTransport trait
Routing protocols	CGR, EPIDEMIC	Announce-based	Announce-based
Priority scheduling	Yes	No	No

Proposed Improvements

1. Priority levels in MeshEnvelope (emergency > data > announce)
2. Custody transfer option — intermediate node takes responsibility
3. Better congestion control — backpressure signals in announce

Action Items

• Add priority field to MeshEnvelope
• Research custody transfer — is it worth the complexity?
• Implement priority queue in MeshStore and DutyCycleTracker

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Gap 4: Battery/Duty-Cycle Optimization

The Problem

Briar drains 4x battery due to constant BT scanning. We claim to be better but haven't proven it.

Current state:

• DutyCycleTracker enforces EU868 1% limit
• Announce interval is configurable (default 10 min)
• No adaptive power management

Proposed Improvements

1. Adaptive announce interval — more frequent when activity, less when idle
2. Listen-before-talk — don't TX if channel is busy (LoRa CAD)
3. Scheduled wake windows — coordinate with peers for efficient sync
4. Power profiles — "always-on", "hourly-sync", "manual-only"

Action Items

• Implement CAD (Channel Activity Detection) in LoRaTransport
• Add power profile config to P2pNode
• Measure actual power consumption with real hardware

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Gap 5: Real-World Testing

The Problem

All our mesh code runs against mocks. We claim LoRa support but haven't tested with real radios.

Testing Plan

Test	Hardware	Status
LoRa point-to-point	2x SX1262 dev boards	Not started
LoRa multi-hop	3x SX1262, different rooms	Not started
Mixed transport	LoRa + WiFi relay	Not started
Outdoor range test	LoRa, line-of-sight 1km	Not started
Duty cycle compliance	SDR spectrum analyzer	Not started

Action Items

• Procure hardware — 3x Heltec LoRa32 or similar
• Implement UART LoRaTransport for real modems
• Create test harness for automated multi-node testing
• Document actual performance numbers

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Gap 6: Comparison Claims Need Verification

The Problem

Our positioning doc claims superiority over Meshtastic/Reticulum/Briar, but:

• We haven't measured our actual overhead vs. theirs
• We haven't tested interop scenarios
• We haven't run security analysis against their threat models

Verification Plan

Claim	How to Verify
"MLS is better than shared-key AES"	Threat model comparison doc
"Multi-hop works"	Integration test with 5+ nodes
"LoRa-ready"	Actual LoRa hardware test
"Post-quantum protects groups"	Verify hybrid KEM in MLS path
"Relay nodes can't read content"	Formal verification of E2E path

Action Items

• Create benchmark suite comparing message sizes
• Write threat model comparison doc (Meshtastic CVEs, Reticulum link-level)
• Fuzz test mesh envelope parsing
• Get external review of mesh crypto design

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Implementation Priority

Phase 1: Make It Work (Next 2 Sprints)

1. S4: Multi-hop routing — complete the core mesh functionality
2. S5: Truncated addresses — reduce envelope overhead
3. Measure actual sizes — know the real numbers

Phase 2: Make It Efficient (Following 2 Sprints)

4. Design MLS-Lite — spec for constrained links
5. Priority queue — emergency messages first
6. Hardware testing — real LoRa validation

Phase 3: Make It Production-Ready

7. KeyPackage distribution — mesh-native key exchange
8. Power profiles — battery optimization
9. External review — security audit of mesh layer

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Success Metrics

Metric	Previous	Current	Target
MeshEnvelope overhead (empty)	~410 bytes	~336 (V2)	✅ Done
MLS-Lite message (no sig)	N/A	~129 bytes	✅ Done
Time to send "hello" over SF12 LoRa	~27 sec	~4 sec (MLS-Lite)	✅ Done
KeyPackage exchange over mesh	Not possible	Pending	Works
Multi-hop message delivery	Mock only	Code complete	Real hardware
Battery life (mesh mode)	Unknown	Unknown	Measured

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Honest Assessment

What we do well:

• MLS group crypto is genuinely better than Meshtastic/Reticulum
• Transport abstraction is clean
• Announce protocol is solid
• NEW: Classical MLS KeyPackage (306B) is actually LoRa-viable
• NEW: MLS-Lite provides Meshtastic-level efficiency with real auth

What we still need to fix:

• No solution for KeyPackage distribution without server
• No real-world testing with actual LoRa hardware
• Post-quantum hybrid mode too large for constrained links

What we can now claim:

• "MLS on LoRa" — YES, classical MLS works with ~14 sec group setup
• "MLS-Lite for constrained" — YES, ~2-4 sec messages with auth
• "Post-quantum on LoRa" — NO, hybrid mode is impractical (2.6KB KeyPackage)
• "Production-ready" — NO, still research-stage, pending hardware tests

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Last updated: 2026-03-30