ARCHITECTURE

技術アーキテクチャ

Flutterクロスプラットフォームクライアント、Elixir PreKeyサーバー、Firebaseバックエンド、Arc Protocol（Signal Protocol E2EE + PQXDH ML-KEM-1024）。

02 / 06

Mesh Network · BLE Offline

圏外でも、つながる。

BLE オフライン P2P 通信で、インターネットや携帯回線が断絶しても近隣ユーザー同士で E2EE 通信を継続。災害・検閲・通信逼迫下の代替手段に。

NO INTERNET. NO PROBLEM.

📡 NO INTERNET

🔋 BLE ACTIVE

🔒 E2EE

あなた

技術スタック

Layer	Technology
Client	Flutter 3.44 + Dart
State Management	Riverpod 3.0 (AsyncNotifier / Generator)
Backend	Firebase (Firestore / Auth / Storage / FCM) + GCP
PreKey Server	Elixir/Phoenix (Cloud Run, europe-west1) — Firestore transaction-based atomic PreKey consumption
Mesh Network	Bridgefy BLE SDK
Cryptography	Arc Protocol (libsignal-client Rust FFI): PQXDH (X25519 + ML-KEM-1024), XEdDSA signatures, Sender Key (Group)
Local Database	Hive (NoSQL, type-safe)
Key Storage	FlutterSecureStorage (Keychain / Keystore / Web Crypto API)
Image Cache	CachedNetworkImage

PreKey Server — Elixir/Phoenix

Dedicated server for atomic PreKey consumption during Signal Protocol session establishment. Built with Elixir/Phoenix on Cloud Run (europe-west1), optimized for EMEA users.

Elixir 1.19

Erlang/OTP 28 · BEAM VM

Phoenix 1.8

API only · Bandit HTTP

Cloud Run

europe-west1 · EMEA

Firestore

REST API · eur3 multi-region

Rust (libsignal)

PQXDH · XEdDSA · Sender Key

Flutter 3.44

iOS · Android · macOS · Web

E2EE暗号化パイプライン

Phase 1: PQXDH (Post-Quantum Extended Diffie-Hellman)
  IKa(X25519) × SPKb(X25519) → DH1
  EKa(X25519) × IKb(X25519) → DH2
  EKa(X25519) × SPKb(X25519) → DH3
  EKa(X25519) × OPKb(X25519) → DH4
  EKa(ML-KEM-1024) → PQ encapsulate → ss_pq
  HKDF(DH1 ‖ DH2 ‖ DH3 ‖ DH4 ‖ ss_pq) → Root Key

Phase 2: Double Ratchet
  Root Key → Chain Key → Message Key (per message)
  DH Ratchet: New X25519 key pair per exchange
  Symmetric Ratchet: KDF chain for sequential messages

Phase 3: AES-256-GCM
  Message Key → AES-256-GCM encrypt(plaintext)
  12-byte random IV per message
  Authentication tag for integrity

Phase 4: AEGIS (XEdDSA Signature via libsignal)
  Sign(senderId ‖ timestamp ‖ content) → signature
  XEdDSA: Identity Key (X25519) doubles as signing key

Phase 5: Sealed Sender
  Generate ephemeral X25519 key pair
  ECDH with recipient → HKDF-SHA256 → AES key
  Encrypt(senderId ‖ ciphertext) → sealed message

グループ暗号化（ECIES + AES-256-GCM）

Key Distribution (per member):
  GroupKey(AES-256) → ECIES encrypt(member.publicKey) → Firestore

Message Encryption:
  AES-256-GCM(groupKey, plaintext, AAD = senderId ‖ groupId ‖ timestamp)

Key Retrieval (fast path):
  Memory Cache → SecureStorage → Firestore ECIES decrypt

O(N) key distribution, O(1) message encryption. Each member receives the group key encrypted with their public key via ECIES. Messages are encrypted once with AES-256-GCM using Additional Authenticated Data (AAD) for integrity.

全アプリ状態でのE2EE保護

メッセージは受信時に即座に復号され、永続ストレージにキャッシュされます。フォアグラウンド・バックグラウンド・終了状態を問わず、E2EE保護を保証します。

App State	1:1 Chat	Group Chat	Mechanism
Chat screen active	✅	✅	StreamBuilder decrypt → LRU + SentMessageCache
Foreground (other screen)	✅	✅	FCM pre-decrypt → SentMessageCache
Pre-session reset	✅	N/A	Pre-decrypt before ratchet reset
Background / Terminated	✅	✅	SharedPreferences queue → bulk decrypt on resume

マルチデバイスアーキテクチャ

Device 1 (e.g., iPhone)

[X25519] Identity Key
[Ed25519] Signing Key
[X25519] Signed PreKey
[X25519] OTPKs x 100
[ML-KEM-1024] PQ PreKey
Independent Double Ratchet sessions

Device 2 (e.g., macOS)

[X25519] Identity Key
[Ed25519] Signing Key
[X25519] Signed PreKey
[X25519] OTPKs x 100
[ML-KEM-1024] PQ PreKey
Independent Double Ratchet sessions

Device List Signing: Ed25519 signature on deviceListV1:{sorted_ids}:{timestamp} for tamper detection. No session sharing between devices.

Mesh Network（BLEオフラインE2EE）

[Device A] ──BLE── [Device B] ──BLE── [Device C] ──Multi-hop── [Device D]
   100m radius         100m radius         100m radius

Parameter	Value
Direct P2P	BLE 100m radius
Multi-hop	N relay x 100m
Protocol	Bridgefy SDK
Encryption	X3DH + Double Ratchet + AES-256-GCM
Offline	Store & Forward queue
Use Case	Disaster, winery fields, remote areas

architecture.ondeviceTitle

architecture.ondeviceDesc

Rosetta

Offline近日公開

architecture.rosettaDesc

Model: Gemma 4 (TranslateGemma)
Languages: 55
Processing: 100% on-device
Data leakage: zero

Pet Companion

Offline近日公開

architecture.petDesc

Model: Gemma 4 (4B parameters)
Storage: Hive (TypeID 96-97)
Processing: 100% on-device
Server communication: none

SUM

Offline近日公開

PDF・スライド・文書をアップロードすると、要約・深層洞察・視座をオンデバイスで生成。URLのAI要約（Gemini）も対応。Intelligenceプランの機能。

Model: Gemma 4 (planned)
Input: PDF / DOCX / PPTX
Processing: 100% on-device
Plan: Intelligence

4-Pillar Vision:
  🛡️ DefenseTech     ─── Online: E2EE (PQXDH + ML-KEM-1024) + AEGIS + Sealed Sender
  📡 DisasterTech    ─── Offline: BLE Mesh + additional encryption layers
  🌍 Language Bridge ─── Offline: Gemma 4 (TranslateGemma) on-device translation
  🐾 AI Pet         ─── Offline: Gemma 4 companion, zero server communication

Model Pipeline:
  Firestore config → Download check → Ad gate → Model download → Hive cache
  User input → On-device inference (Gemma 4) → Result → No data leaves device

鍵ライフサイクル & ローテーション

Key Type	Rotation	Purpose
Identity Key (X25519)	Account lifetime	Core identity
Signing Key (Ed25519)	90 days + grace period	AEGIS message signatures
Signed PreKey (X25519)	7-30 days	X3DH handshake
One-Time PreKeys (X25519)	Single use	Forward secrecy per session
PQ PreKey (ML-KEM-1024)	Account lifetime	Post-quantum key encapsulation
Double Ratchet Keys	Per message exchange	Per-message forward secrecy