# SimpleX Chat - Private Messaging Without Identifiers

**The most private messaging app - no phone number, email, or username required**

## 🎯 Threat Model

### What Problem Does This Solve?

Most "encrypted" messaging apps still leak critical metadata:

- **Phone/Email Linking**: Signal, WhatsApp, Telegram require phone numbers
- **Username Tracking**: Session, Threema use permanent usernames
- **Contact Graph**: Servers know who talks to whom
- **Central Compromise**: Single point of failure if servers are seized

### How SimpleX is Different

**No User Identifiers**
- No phone number
- No email address  
- No username
- No blockchain address
- **Nothing** that identifies you across connections

**Each Contact is Isolated**
- Every contact uses different message routing
- Server can't build a social graph
- Compromise of one contact doesn't expose others

**Decentralized Infrastructure**
- Run your own server or use defaults
- Messages routed through different servers
- Ephemeral message queues (deleted after delivery)

## 🔐 Privacy Features

- ✅ End-to-end encryption (Signal Double Ratchet + post-quantum)
- ✅ Perfect forward secrecy
- ✅ No metadata leakage to servers
- ✅ Disappearing messages
- ✅ Incognito mode (temporary identities)
- ✅ Voice/video calls (also E2E encrypted)
- ✅ Group chats (fully decentralized)
- ✅ File sharing (encrypted)

## 🚀 Installation

### Debian Trixie (glibc 2.40+)
```bash
cd ~/github/privacy-toolkit
./tools/simplex/install.sh
```

The script automatically selects:
- **Ubuntu 24.04 package** for Debian Trixie
- **Ubuntu 22.04 package** for older systems

### Manual Installation

Check your glibc version:
```bash
ldd --version | head -1
```

- If glibc ≥ 2.39: Download ubuntu-24-04 package
- If glibc < 2.39: Download ubuntu-22-04 package

Download from: https://github.com/simplex-chat/simplex-chat/releases/latest

## 📖 Usage

### First Launch
1. Open SimpleX from application menu
2. Choose "Create new profile"
3. Set display name (not sent to servers!)
4. Optionally set profile image

### Adding Contacts
1. Click "+" → "Add contact"
2. Share your connection link OR
3. Scan contact's QR code

**Important**: Each contact gets a unique connection link. You can't be tracked across contacts.

### Restoring from Backup

If you have a backup (from `/tmp/restore-simplex.sh`):
1. Launch SimpleX
2. It will automatically detect restored data
3. Verify your contacts appear
4. Database files are at `~/.local/share/simplex/`

## 🔒 Security Best Practices

### Message Retention
- Enable disappearing messages for sensitive conversations
- Default: Messages stored locally forever
- Recommendation: 1 week retention for most chats

### Connection Security
- **Delete old connection links** after contact accepts
- Use **incognito mode** for temporary conversations
- **Verify contact fingerprints** for high-security conversations

### Server Trust
- Default servers are run by SimpleX team (good reputation)
- For maximum privacy: Run your own SimpleX server
- Or use community servers you trust

### Backup Your Data
SimpleX stores everything locally:
```bash
~/.local/share/simplex/         # Databases
~/.config/simplex/              # Settings
```

**Backup regularly!** If you lose this data, you lose all messages.

## 🆚 Comparison with Other Apps

| Feature | SimpleX | Signal | Session | Matrix |
|---------|---------|--------|---------|--------|
| No phone/email | ✅ | ❌ | ✅ | ✅ |
| No username | ✅ | ❌ | ❌ | ❌ |
| No user ID at all | ✅ | ❌ | ❌ | ❌ |
| Decentralized routing | ✅ | ❌ | ✅ | ✅ |
| Contact graph hidden | ✅ | ❌ | ❌ | Partial |
| Post-quantum crypto | ✅ | Partial | ❌ | ❌ |
| Metadata resistance | Excellent | Good | Good | Moderate |

## 🛠️ Advanced: Run Your Own Server

For maximum privacy, run your own SimpleX SMP server:

```bash
# Docker method
docker run -d \
  --name simplex-smp \
  -p 5223:5223 \
  simplexchat/smp-server

# Configure SimpleX app to use your server
```

Instructions: https://github.com/simplex-chat/simplexmq#smp-server

## 🔗 Resources

- Official Website: https://simplex.chat/
- Documentation: https://simplex.chat/docs/
- GitHub: https://github.com/simplex-chat/simplex-chat
- Security Audit: https://simplex.chat/blog/simplex-chat-v5.8-private-message-routing-chat-themes/
- Whitepaper: https://github.com/simplex-chat/simplexmq/blob/stable/protocol/overview-tjr.md

## ⚠️ Limitations

- **No cloud sync**: Messages are device-local only
- **Manual backups**: You must backup yourself
- **Contact management**: Need to share new links for each contact
- **Group limitations**: Decentralized groups have size limits

**Trade-off**: Maximum privacy requires some inconvenience. SimpleX chooses privacy over convenience.

---

**Maintained by**: SimpleX Chat team
**License**: AGPL-3.0
**Last Updated**: 2025-11-12