SimpleX

Detailed Description of SimpleX Chat: A Fully Private Messaging Platform

Introduction to SimpleX Chat

SimpleX Chat is an innovative, privacy-focused messaging platform designed with the core principle that user identifiers are unnecessary for secure communication. Unlike traditional messaging apps—such as Signal or WhatsApp—which rely on phone numbers or unique user IDs to identify individuals, SimpleX eliminates persistent identifiers entirely. This approach ensures that users’ identities remain anonymous even within their own conversations, making it one of the most privacy-preserving messaging solutions available today.

The platform operates under a client-server architecture with a unique network topology that leverages disposable message relay nodes for asynchronous message transmission. Unlike peer-to-peer (P2P) networks, where messages are directly exchanged between users, SimpleX employs a unidirectional message queue system, ensuring that no global identifiers exist to link conversations across different contacts. This design prevents metadata leakage and enhances anonymity.

Core Features and Security Principles

1. Complete Privacy of Identity, Profile, Contacts, and Metadata

One of the most revolutionary aspects of SimpleX Chat is its lack of persistent user identifiers. Unlike other messaging platforms—even those with strong end-to-end encryption (E2EE)—SimpleX does not assign any unique identifier to users. Instead, it uses pairwise pseudonymous identifiers for each message queue between two users. This means:

No phone numbers or email addresses are required.
No persistent user profiles exist on the servers.
Metadata (who you talk to and when) remains hidden from SimpleX’s infrastructure.

This design prevents third parties, including service providers, from tracking users across different conversations. Even if a user connects with multiple contacts via SimpleX, those connections remain isolated—no metadata is shared between them.

2. Protection Against Spam and Abuse

Since SimpleX does not rely on persistent identifiers, it is nearly impossible for spammers or abusers to target users. Unlike centralized platforms where spam bots can exploit user profiles, SimpleX requires users to share a one-time invitation link (or an optional temporary address) to initiate communication. This ensures that:

Users are only contacted via trusted channels.
No personal data is exposed in the initial connection process.

3. Complete Ownership and Security of User Data

SimpleX prioritizes user sovereignty over their data. Unlike many messaging apps that store messages on centralized servers, SimpleX follows a "store-then-delete" model:

Messages are temporarily stored on SimpleX’s relay servers but are not permanently retained.
Users retain full control over their data, which is encrypted locally on their devices.
If users upgrade to a newer version of the app (e.g., from v4.0 onward), they must manually enable local encryption for past messages.

This approach minimizes exposure to potential breaches and ensures that no third party can access user communications without explicit consent.

4. Users Own the SimpleX Network

SimpleX allows users to run their own servers, enabling them to:

Host private messaging networks.
Connect with others using pre-configured servers or custom SMP (Simple Messaging Protocol) relays.
Avoid reliance on centralized infrastructure by running their own nodes.

This decentralized model reduces dependency on a single point of failure and enhances resilience against censorship or surveillance.

Technical Security Implementation

1. End-to-End Encryption with Double Ratchet

SimpleX employs a double ratchet encryption algorithm, similar to Signal, but with additional layers for redundancy:

Each message is encrypted using NaCl cryptobox (a secure symmetric encryption library).
A post-quantum-resistant key exchange ensures that even if quantum computers break classical encryption, SimpleX remains secure.
The double ratchet mechanism provides forward secrecy, meaning past messages remain encrypted even after a user’s account is compromised.

2. Additional Encryption Layers

To further enhance security, SimpleX adds an extra layer of encryption for messages sent from servers to recipients:

This prevents any common ciphertext between sent and received traffic, reducing the risk of interception.
Only TLS 1.2/1.3 is allowed, with restricted cryptographic algorithms (e.g., CHACHA20POLY1305_SHA256, Ed25519/Ed448).

3. Metadata Protection

SimpleX ensures that even if TLS is compromised:

Message metadata (timestamps, sender/receiver identities) remains encrypted.
No metadata is stored on servers beyond the moment a message is received.

4. Private Message Routing and Tor Support

To protect against IP exposure, SimpleX Chat clients use private message routing by default (since v6.0):

Messages are routed through multiple relays to obscure the sender’s and recipient’s IPs.
Users can also connect via Tor, ensuring anonymity even when accessing messaging servers.

5. Local Database Encryption

All user data—including contacts, groups, and messages—is encrypted locally on the device:

Users must enable encryption manually (if not done in v4.0+).
This prevents unauthorized access to communications if a device is compromised.

User Experience and Accessibility

1. Installation and Platform Support

SimpleX Chat is available across multiple platforms, ensuring accessibility for users regardless of their device:

Mobile Apps:
Android: Available on Google Play (link).
iOS: Available via the App Store (link) and TestFlight (limited to 10,000 users for early access).
F-Droid: Open-source alternative (link).
Desktop CLI:
A terminal-based client for Linux, macOS, and Windows.
Supports groups, files, and end-to-end encryption via the command line.

2. Connecting with Others

To start messaging:

Share a QR code or invitation link with friends in person or during video calls.
Scan the QR code or open the link to establish a connection.
Verify the security of your connection using a connection verification code.

3. User Groups and Communities

SimpleX supports:

User-created groups via the SimpleX Directory.
A bot-based directory (SimpleX bot) for discovering and joining communities.
Dedicated groups for users (#SimpleX users group) and developers (#simplex-devs).

4. Translations

SimpleX Chat is available in multiple languages, thanks to contributions from the community: | Language | Contributor | |----------------|----------------------| | English | - | | Arabic | jermanuts | | Bulgarian | - | | Czech | zen0bit | | German | mlanp | | Spanish | Mateyhv | | Finnish | - | | French | ishi_sama | | Hebrew | - | | Hungarian | - | | Italian | unbranched | | Japanese | - | | Dutch | mika-nl | | Polish | BxOxSxS | | Portuguese | - | | Russian | - | | Thai | titapa-punpun | | Turkish | - | | Ukrainian | - | | Chinese (Simplified) | sith-on-mars, Float-hu |

5. Community Engagement

SimpleX encourages user participation through:

Open-source contributions (e.g., developing chat bots).
Translations via Weblate.
Supporting the project via donations (GitHub Sponsors, OpenCollective).

Recent Updates and Roadmap

SimpleX Chat has been evolving rapidly with new features and security improvements: | Date | Release Details | |--------------------|-------------------------------------------------------------------------------| | July 29, 2025 | SimpleX Chat v6.4.1: Welcome contacts, review group members, improved app security. | | July 3, 2025 | New connection experience in beta (v6.4-beta.4). | | March 8, 2025 | Improved user experience and safety in public groups (v6.3). | | January 14, 2025 | Large group support and privacy-preserving content moderation. | | December 10, 2024 | Preset servers by Flux, business chats, and improved mobile apps (v6.2). | | October 14, 2024 | Security review by Trail of Bits; better calls and user experience (v6.1). | | August 14, 2024 | Investment from Jack Dorsey & Asymmetric; private message routing (v6.0). | | June 4, 2024 | Private message routing, IP protection, and chat themes (v5.8). | | March 14, 2024 | Quantum-resistant Signal double ratchet algorithm (v5.6 beta). |

Upcoming Features

SimpleX’s roadmap includes:

Automatic queue rotation for temporary identifiers.
Message "mixing" to delay delivery and prevent traffic correlation.
Recipients’ XFTP relays to reduce relay IP exposure.
Desktop client support.
Disappearing messages with recipient opt-in.
Voice and video calls with end-to-end encryption.
Privacy-preserving identity server for optional DNS-based contact addresses.

Why SimpleX Stands Out

Comparison to Other Privacy-Focused Messaging Apps

| Feature | Signal/WhatsApp | Matrix/Session | Ricochet/Cwtch | SimpleX Chat | |------------------------|-----------------------|---------------------|----------------------|-----------------------| | User Identifiers | Phone number | Anonymous ID | Pseudonymous ID | No identifiers | | Metadata Exposure | High (who you talk to) | Moderate | Low | None | | Ownership Control | Centralized | Federated | Decentralized | User-owned network| | Encryption | E2EE only | E2EE + TLS | E2EE | Double ratchet + post-quantum |

Key Advantages

True Anonymity: No persistent identifiers mean no metadata leaks.
Decentralized Infrastructure: Users can run their own servers.
Strong Security: End-to-end encryption, double ratchet, and post-quantum resistance.
No Spam Risk: Since users are not identified, spam is nearly impossible.
Open-Source & Transparent: All protocols are in the public domain.

Potential Limitations

While SimpleX Chat offers unparalleled privacy, it is still a relatively new platform with some limitations:

Bugs and Missing Features: Early-stage development means some features may not be fully polished.
Limited Server Infrastructure: Default servers operate on a best-effort basis; users can run their own nodes for reliability.
No Built-in Group Management: Some advanced group features (e.g., moderation) are still evolving.

Conclusion

SimpleX Chat represents a paradigm shift in messaging privacy, offering a platform where users retain full control over their communications without sacrificing security or anonymity. By eliminating persistent identifiers and adopting a decentralized, redundant message relay system, SimpleX ensures that conversations remain private even when shared with multiple contacts. Whether used for personal communication, secure group discussions, or running private servers, SimpleX Chat provides a robust alternative to traditional messaging apps.

For users prioritizing privacy above all else, SimpleX Chat is an excellent choice—one that continues to evolve with new features and security enhancements.

Further Reading: