SimpleX Chat

SimpleX Chat is a revolutionary messaging application that takes a fundamentally different approach to user privacy. While most messengers - even privacy-focused ones - use some form of user identifier (phone number, username, or randomly generated ID), SimpleX has no user identifiers at all. This unique architecture makes it impossible to build a social graph of SimpleX users, even for the server operators.

UK Development with Global Privacy Focus

SimpleX Chat is developed by SimpleX Chat Ltd, a UK-based company founded by Evgeny Poberezkin. Despite the UK's sometimes controversial surveillance laws, SimpleX's architecture makes it technically impossible to comply with many data retention requirements - there's simply no user data to retain. The company has been transparent about its privacy-first mission and has received backing from privacy-focused investors.

The open-source nature and self-hosting options mean that users aren't dependent on any single jurisdiction. Anyone can run their own SimpleX relay servers, allowing organizations to keep all traffic within their preferred jurisdiction while still communicating with the broader SimpleX network.

No User Identifiers - A Revolutionary Approach

SimpleX's defining feature is the complete absence of user identifiers. Unlike Signal (phone number), Session (Session ID), or even Threema (Threema ID), SimpleX users have no global identifier at all. Instead, each conversation uses unique, random identifiers that are different for each contact. This means:

There's no way to search for someone on SimpleX - connections must be initiated by sharing a one-time invitation link. The servers never see who is talking to whom - they only relay encrypted messages without knowing which conversations belong to the same user. Even if all SimpleX servers were compromised, it would be impossible to reconstruct the social graph of users.

How Connection Works Without User IDs

To connect with someone on SimpleX, you share a one-time invitation link or QR code. This link contains the information needed to establish an encrypted connection. Once scanned, both parties have a direct encrypted channel - there's no account registration, no verification code, nothing linking your real identity to your SimpleX conversations.

Each conversation gets its own unique queue on relay servers. Your contacts don't share any common identifier - they each see a different "you." This architectural decision makes traffic analysis and correlation attacks extremely difficult, even for sophisticated adversaries.

Double Ratchet Encryption

SimpleX uses the Double Ratchet algorithm (the same used by Signal Protocol) for end-to-end encryption. This provides perfect forward secrecy and post-compromise security. Each message is encrypted with a unique key, so compromising one message doesn't help decrypt others. The protocol has been extensively studied and is considered the gold standard for messaging encryption.

Unlike some messengers that only encrypt messages in transit, SimpleX encrypts everything including metadata. The relay servers see only encrypted blobs with no information about senders, recipients, or conversation relationships. Additional encryption layers protect against traffic analysis.

Self-Hostable Infrastructure

SimpleX is designed to work with federated, self-hosted relay servers. Organizations can run their own servers, ensuring that their messages never leave their infrastructure. Individual users can also run personal servers for maximum control. The default configuration uses SimpleX-operated servers, but switching to self-hosted or third-party servers is straightforward.

This federated model means there's no single point of failure or control. Even if SimpleX Chat Ltd ceased operations, the network would continue functioning. Users can choose servers based on jurisdiction, trust, or organizational requirements.

Features and Functionality

Despite its radical privacy architecture, SimpleX offers a full-featured messaging experience. One-to-one messaging supports text, images, voice notes, files, and disappearing messages. Group chats allow private communication among multiple contacts. Voice and video calls are available with the same privacy protections as messaging.

The app includes useful features like message reactions, editing, and deletion. A built-in browser allows viewing links without leaving the app. Incognito mode creates separate profiles for different contexts, allowing complete separation between personal and professional communications on the same device.

Cross-Platform Support

SimpleX is available on all major platforms. Mobile apps for iOS and Android provide the primary experience, with full support for notifications, calls, and background message delivery. Desktop apps for Windows, macOS, and Linux enable messaging from computers. A terminal-based client is available for advanced users and automation.

Unlike some privacy messengers, SimpleX provides a polished, modern user experience that doesn't require technical expertise. The UI is intuitive and comparable to mainstream messengers, making it accessible to non-technical users while providing maximum privacy.

Security Audits and Transparency

SimpleX has undergone multiple independent security audits by Trail of Bits, a respected security firm. The audit reports are published publicly, demonstrating a commitment to transparency. The audits found the cryptographic implementation to be sound, with identified issues promptly addressed.

All SimpleX code is open source under the AGPLv3 license, allowing anyone to audit the implementation. The protocol specification is also publicly documented, enabling independent analysis of the security model. Bug bounties encourage responsible disclosure of vulnerabilities.

Limitations to Consider

The lack of user identifiers means there's no way to "find" someone on SimpleX - connections require exchanging invitation links through another channel. This adds friction compared to phone number-based messengers but is fundamental to the privacy model. Backup and recovery requires manually exporting your database, as there's no account to restore.

SimpleX is newer than established alternatives with a smaller user base. Some features like groups have limitations compared to more mature platforms. The UK jurisdiction may concern some users, though the technical architecture provides protection regardless of legal environment.

Who Should Use SimpleX

SimpleX Chat is ideal for privacy maximalists who want the strongest possible protection against metadata analysis and social graph construction. Journalists protecting sources, activists concerned about surveillance, and anyone who believes messaging services shouldn't know anything about their users will appreciate SimpleX's unique approach. Users tired of giving their phone number to messaging apps will find SimpleX liberating. If you believe that the best way to protect data is to never collect it, SimpleX Chat embodies that philosophy.