What encryption does Arc use?

Arc uses the Signal Protocol combined with PQXDH (Post-Quantum Extended Diffie-Hellman) using ML-KEM-1024, providing both classical X25519 and quantum-resistant key exchange. Every message is end-to-end encrypted — the server has zero access to message content.

Is Arc quantum-resistant?

Yes. Arc uses PQXDH with ML-KEM-1024 (FIPS 203, NIST Level 3), the same post-quantum algorithm standardized by NIST in 2024. This protects against 'harvest now, decrypt later' quantum attacks.

Can Arc's server read my messages?

No. Arc uses end-to-end encryption with the Signal Protocol and Sealed Sender, meaning the server cannot read message content or determine who is sending a message. Messages are encrypted on your device before transmission.

How is Arc different from Signal?

Both use Signal Protocol, but Arc adds post-quantum cryptography (PQXDH ML-KEM-1024), IGF automatic message expiry, offline BLE Mesh communication, Sealed Sender, and username-based identity with no phone number required.

Arc Security — PQXDH ML-KEM-1024 Post-Quantum Encryption

SECURITY

Seni Bina E2EE Berbilang Lapisan

Arc Protocol: Signal Protocol (libsignal) sebagai asas, dengan kriptografi post-quantum PQXDH (ML-KEM-1024), tandatangan XEdDSA, dan Sealed Sender sisi klien.

Pertukaran Kunci PQXDH

Pertukaran kunci post-quantum hibrid menggabungkan X25519 (Curve25519) dan ML-KEM-1024 (NIST FIPS 203). Tahan terhadap serangan klasik dan kuantum.

Double Ratchet

Forward secrecy setiap mesej menggunakan DH ratchet + symmetric ratchet. Kompromi satu kunci tidak boleh menyahsulit mesej lalu atau akan datang.

Penyulitan AES-256-GCM

Penyulitan tersahkan dengan kunci 256-bit. Setiap mesej disulitkan dengan kunci unik yang diterbitkan dari Double Ratchet.

Tandatangan XEdDSA (libsignal)

Tandatangan XEdDSA melalui libsignal. Identity Key (X25519) turut berfungsi sebagai kunci tandatangan. Termasuk pengesahan integriti senarai peranti.

Sealed Sender Sisi Klien

Kunci ephemeral X25519 setiap mesej + kunci AES terbitan HKDF-SHA256. Pelayan pun tidak dapat melihat siapa yang menghantar mesej.

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 17 Major Messengers

Independent review comparing Arc V2 against 16 competitors (Signal, iMessage, WhatsApp, Telegram, LINE, Threema, Wire, Element, Session, Viber, XChat, KakaoTalk, Slack, Discord, Chatwork, Google Messages) using an 8-axis 100-point rubric.

Open Competitive Comparison →

POST-QUANTUM

Parameter ML-KEM-1024

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

Algoritma	ML-KEM-1024 (via libsignal-client)
Tahap Keselamatan NIST	Level 3 (AES-192 equivalent)
Keselamatan Klasik	2^128 bit (X25519)
Keselamatan Kuantum	NIST Level 3
Asas	Module Lattice (FIPS 203)
Saiz Kunci Awam	1,184 bytes
Saiz Kunci Rahsia	2,400 bytes
Saiz Ciphertext	1,088 bytes

Pematuhan & Standard

🇺🇸NIST CSF 2.0

Rangka kerja NIST. 6 fungsi untuk pengurusan risiko siber yang sistematik.

🇺🇸NIST SP 800-53

Kawalan keselamatan persekutuan. Asas FedRAMP.

🇺🇸FIPS 140-3

Pengesahan modul kriptografi persekutuan. Meliputi ML-KEM-1024.

🇺🇸NIST SP 800-175B

Panduan pemilihan algoritma kriptografi. Berdasarkan FIPS 203.

🌐ISO/IEC 27001

Pensijilan ISMS antarabangsa. Asas kepercayaan B2B/B2G.

🇪🇺GDPR

Peraturan Perlindungan Data Am EU. Standard perlindungan tertinggi di dunia.

🇬🇧UK Cyber Essentials+

Pensijilan keselamatan siber bertauliah kerajaan Britain.

🇬🇧NCSC Cloud Security

14 Prinsip NCSC Britain. Standard penilaian keselamatan awan.

Dibangunkan mematuhi semua prasyarat NIST AS, GDPR EU, NCSC UK dan ISO antarabangsa.

CONFIDENTIAL

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.

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