SimpleX Chat — Private Messenger with No User Identifiers

Introduction

SimpleX Chat is a messaging platform designed around a fundamental privacy principle: no user identifiers. Unlike Signal (phone numbers) or Matrix (user IDs), SimpleX uses pairwise anonymous addressing so that no server or third party can correlate a user's contacts or build a social graph.

What SimpleX Chat Does

• Sends end-to-end encrypted messages without requiring user accounts or identifiers
• Uses pairwise per-connection addresses so no single ID links conversations
• Supports text, images, files, voice messages, video calls, and groups
• Routes messages through relay servers that cannot correlate senders and recipients
• Allows self-hosting relay servers (SMP and XFTP) for full infrastructure control

Architecture Overview

SimpleX uses the SimpleX Messaging Protocol (SMP) where each conversation creates a unique unidirectional queue on a relay server. The sender and recipient connect through separate queues with independent addresses, preventing the relay from linking them. Messages are encrypted with the double-ratchet algorithm (same as Signal). File transfers use the XFTP protocol with chunked, deduplicated storage across multiple relays.

Self-Hosting & Configuration

• Deploy SMP relay server via Docker or the standalone binary
• Deploy XFTP server for file transfer relay
• Configure server addresses in the client settings to use your own relays
• TLS certificates are generated automatically on first run
• Servers store only encrypted message queues; no user data persists

Key Features

• No phone numbers, usernames, or any user identifiers required
• Double-ratchet end-to-end encryption with perfect forward secrecy
• Decentralized relay architecture with no central server dependency
• Disappearing messages and message editing support
• Incognito mode for joining groups without revealing your profile

Comparison with Similar Tools

• Signal — requires phone number; centralized server infrastructure
• Matrix / Element — uses persistent user IDs; metadata visible to homeserver
• Session — no phone number but uses a blockchain-based routing layer
• Wire — end-to-end encrypted but requires email or phone for registration
• Briar — peer-to-peer with no servers but requires both parties online simultaneously

FAQ

Q: How do I connect with someone if there are no usernames? A: You share a one-time invitation link or QR code. Each link creates a unique private channel.

Q: Can SimpleX relay servers read my messages? A: No. Messages are end-to-end encrypted. Relay servers only see encrypted blobs and cannot link sender to recipient.

Q: What happens if a relay server goes down? A: You can migrate connections to different relay servers. The protocol supports server changes without losing contacts.

Q: Is there a web version? A: No. SimpleX is available as native desktop (Electron-based) and mobile apps. There is also a terminal CLI client.

Sources

• https://github.com/simplex-chat/simplex-chat
• https://simplex.chat