Atlas Associates

Arc / SECURITY

Arsitektur E2EE Multi-Lapisan

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ILLUSTRATED 1:1 FLOW · 10-SECOND PREVIEW

Encrypted here.Opened there.

A message between people. Private keys stay on the devices; servers carry ciphertext and delivery data.

  1. 01
    Encrypt on device

    The message is encrypted before it leaves.

  2. 02
    Transport ciphertext

    Firestore carries ciphertext and delivery data.

  3. 03
    Open on device

    The recipient’s device decrypts the message.

FunctionsExpiry & notifications
FCMPush notification

Concept animation of one delivery path, not a recording of the app. Other paths, server-visible metadata and exceptions are documented below.

ARCHITECTURE

Arc system architecture

Explore the system diagram

Private keys are stored in the device Keychain / Keystore and never sent to servers. Messages to other people are encrypted on the device before they are sent. Phoenix hands out public PreKeys, Firestore carries ciphertext, receipts and delivery data, and Cloud Functions handle expiry deletion and notifications. Mesh bypasses servers.

One role at a time.

Open full-size diagram

Devices (iOS / Android / macOS)

Arc Protocol

1:1 · libsignal v0.96.2 · Rust FFI

  • PQXDH
  • Kyber-1024
  • Double Ratchet
Private keys
Keychain / Keystore
Decrypted text
SQLite / Hive

Message text and private keys never go to servers (except AI chats, link previews)

Explore the message flows

The dots move in the numbered order. On each of these paths, message text is encrypted on the device before it is sent.

Follow one path at a time.

Open full-size diagram
1:1 message. Post-quantum. First time: fetch B's keys. Encrypt on the device. Send ciphertext only. Notify (no content). Decrypt on B's device. Read / decrypt receipts. Only A's and B's devices can read the text

Post-quantum

1:1 message

  1. First time: fetch B's keys
  2. Encrypt on the device
  3. Send ciphertext only
  4. Notify (no content)
  5. Decrypt on B's device
  6. Read / decrypt receipts

Only A's and B's devices can read the text

On smaller screens, scroll within the diagram. Open the original using the link above.

1:1 is post-quantum (PQXDH). Group messages are not (shared key + X25519 ECIES). On Mesh, nearby Arc phones may forward the ciphertext without being able to read it. Routed relay is in development.

Arc Protocol — 1:1 encryption pipeline

Phase 1

PQXDH

Key agreement with X25519 + Kyber-1024 (post-quantum)

Phase 2

Double Ratchet

A new key for every message

Phase 3

AES-256-GCM

Encrypts message bodies and media

Technology stack

Flutter 3.44
Dart
Riverpod 2.6
Rust
Arc Protocol

App

Flutter 3.44 / Riverpod 2.6 / Rust FFI (libsignal v0.96.2)

Elixir
Phoenix
Cloud Run

Key distribution API

Elixir / Phoenix on Google Cloud Run (europe-west1)

Authentication
Firestore
Storage
Functions
Messaging
App Check
Crashlytics

Delivery and auth

Firebase (Auth / Firestore / Storage / Functions / FCM / App Check / Crashlytics)

Android
Kotlin
Swift

Mesh

BLE implementation (Dart + Android Kotlin + iOS Swift, in-house, beta)

Technical specifications

The four encryption layers

Arc core specification

Arc's core specification is ML-KEM-1024/PQXDH, E2EE for 1:1 and group chats, IGF, and offline Mesh. This Security page documents the scope and technical details.

01

Pertukaran Kunci PQXDH

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02

Double Ratchet

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03

Enkripsi AES-256-GCM

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04

Tanda tangan XEdDSA (libsignal)

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Parameter ML-KEM-1024

POST-QUANTUM

Mekanisme Enkapsulasi Kunci post-quantum yang distandarisasi NIST FIPS 203.

AlgoritmaML-KEM-1024 (via libsignal-client)
Level Keamanan NISTSecurity category 5
Keamanan Klasik2^128 bit (X25519)
Keamanan KuantumNIST security category 5
FondasiModule Lattice (FIPS 203)
Ukuran Kunci Publik1,568 bytes
Ukuran Kunci Rahasia3,168 bytes
Ukuran Ciphertext1,568 bytes

Kepatuhan & Standar

NIST CSF 2.0

Framework NIST. 6 fungsi untuk manajemen risiko siber yang sistematis.

NIST SP 800-53

Kontrol keamanan federal. Dasar FedRAMP.

FIPS 140-3

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NIST SP 800-175B

Panduan pemilihan algoritma kriptografi. Berdasarkan FIPS 203.

ISO/IEC 27001

Sertifikasi ISMS internasional. Dasar kepercayaan B2B/B2G.

GDPR

Regulasi Perlindungan Data Umum UE. Standar perlindungan tertinggi di dunia.

UK Cyber Essentials+

Sertifikasi keamanan siber bersertifikat pemerintah Inggris.

NCSC Cloud Security

14 Prinsip NCSC Inggris. Standar penilaian keamanan cloud.

Dirancang dengan mengacu pada panduan yang diterbitkan NIST AS, GDPR UE, NCSC Inggris, dan ISO. Ini bukan sertifikasi atau audit pihak ketiga.