Multi-Layer E2EE Architecture
Arc Protocol: Signal Protocol (libsignal) as the foundation, with PQXDH (ML-KEM-1024) post-quantum cryptography, XEdDSA signatures, and client-side Sealed Sender.
PQXDH Key Exchange
Hybrid post-quantum key exchange combining X25519 (Curve25519) and ML-KEM-1024 (NIST FIPS 203). Resistant to both classical and quantum attacks.
Double Ratchet
Per-message forward secrecy using DH ratchet + symmetric ratchet. Compromise of one key cannot decrypt past or future messages.
AES-256-GCM Encryption
Authenticated encryption with 256-bit keys. Each message encrypted with a unique key derived from the Double Ratchet.
XEdDSA Signatures (libsignal)
XEdDSA signatures via libsignal. Identity Key (X25519) doubles as signing key. Device list integrity verification included.
Client-Side Sealed Sender
Ephemeral X25519 key per message + HKDF-SHA256 derived AES key. Even the server cannot see who sent a message.
Rosetta AI has an explicit privacy boundary
Rosetta automatic translation and every TranslateGemma first pass stay on-device. After per-message consent, Premium, free access, and trials use Gemini 3.5 Flash-Lite; Intelligence uses Gemini 3.6 Flash. Only the current outgoing draft and first-pass review are sent; received messages, chat history, and encryption keys are excluded. On-device only is always available.
Read the privacy details →Comparison with 20 Major Messengers
Independent review comparing Arc V2 against 19 competitors (Signal, iMessage, WhatsApp, Telegram, LINE, Threema, Wire, Element, Session, Viber, XChat, KakaoTalk, Slack, Discord, Chatwork, Google Messages) using a 9-axis 100-point rubric.
ML-KEM-1024 Parameters
NIST FIPS 203 standardized post-quantum Key Encapsulation Mechanism.
| Algorithm | ML-KEM-1024 (via libsignal-client) |
| NIST Security Level | Level 3 (AES-192 equivalent) |
| Classical Security | 2^128 bit (X25519) |
| Quantum Security | NIST Level 3 |
| Foundation | Module Lattice (FIPS 203) |
| Public Key Size | 1,184 bytes |
| Secret Key Size | 2,400 bytes |
| Ciphertext Size | 1,088 bytes |
Compliance & Standards
🇺🇸NIST CSF 2.0
NIST framework. 6 functions for systematic cyber risk management.
🇺🇸NIST SP 800-53
Federal security controls. FedRAMP foundation.
🇺🇸FIPS 140-3
Federal cryptographic module validation. Covers ML-KEM-1024.
🇺🇸NIST SP 800-175B
Cryptographic algorithm selection guide. Based on FIPS 203.
🌐ISO/IEC 27001
International ISMS certification. B2B/B2G trust foundation.
🇪🇺GDPR
EU General Data Protection Regulation. World's highest protection standard.
🇬🇧UK Cyber Essentials+
UK government-certified cybersecurity certification.
🇬🇧NCSC Cloud Security
UK NCSC 14 Principles. Cloud security assessment standard.
Developed in compliance with all prerequisites of US NIST, EU GDPR, UK NCSC, and international ISO.
System Architecture Documentation
Complete technical specification of Arc V2 — covering the 5-layer architecture, E2EE pipeline, PQXDH implementation, key lifecycle, group encryption, multi-device architecture, BLE Mesh networking, and on-device AI.
15+ Technical Sections
Layer architecture, PQC implementation, encryption pipeline, data storage, and more
Bilingual (EN/JP)
Full documentation available in English and Japanese with one-click toggle
Version 3.1 — March 2026
Includes Elixir PreKey Server, Sealed Sender, Sender Keys, and PQXDH ML-KEM-1024
This document is classified as confidential and available exclusively to NDA-bound partners, investors, and authorized technical reviewers. Access requires prior approval by Atlas Associates.