SUP

Privacy-preserving push notification system using Signal as transport

Setup • Real-World Examples • Architecture

⚠️ Early Alpha: SUP is under rapid development. The Android app is being actively developed and the current version is not thoroughly tested. There are no stable releases yet. Use at your own risk.

SUP is a UnifiedPush server and distributor that routes push notifications through Signal, allowing you to receive app notifications without exposing unique network fingerprints to any network observers. All notification traffic appears as regular Signal messages.

Why?

Traditional push notification systems require persistent connections to specific servers, creating unique network fingerprints. Relying on traditional push notification services like Android's built-in FCM (Firebase Cloud Messaging) may also expose your notification metadata. SUP blends your notification traffic with regular Signal usage for better privacy.

SUP also includes an optional Proton Mail integration, allowing you to receive email notifications as Signal messages without exposing IMAP connections.

Note that you'll need to run SUP on your own server at home since it uses your personal Signal and Proton Mail credentials. A Raspberry Pi works perfectly for this, using minimal power (3-5W) while running SUP 24/7.

� Background: For a detailed explanation of the privacy paradox of self-hosting that motivated this project, see MOTIVATION.md.

�💡 Privacy Tip: Use Molly.im (hardened Signal fork) with WebSocket notifications instead of the official Signal app. This ensures all Signal traffic, including SUP notifications, goes through WebSockets, making it indistinguishable from regular Signal messages.

How?

SUP functions as a UnifiedPush server to proxy http-based requests to Signal groups via signal-cli.

For the optional Proton Mail integration, SUP requires a server that runs Proton's official proton-bridge. SUP's docker compose process will run an image from protonmail-bridge-docker. Once authenticated, the communication between SUP and proton-bridge will be over IMAP.

Setup

1. Install Android App (Optional)

⚠️ Early Alpha: The Android app is currently unavailable, but is planned for the full release of SUP.

An Android app is optionally available to connect UnifiedPush Android apps to the SUP server. It can also provide a better experience for displaying SUP-based notifications if the ENABLE_ANDROID_INTEGRATION environment variable is enabled on the server.

Download the latest APK from GitHub Releases.

Certificate Fingerprint:

0D:3C:99:15:0E:12:1A:DE:0D:AE:05:CB:16:46:5E:65:31:56:DC:D6:98:87:59:4E:79:B1:0D:AE:1E:56:F2:E8

2. Proton Mail Integration (Optional)

⚠️ Early Alpha: Currently only docker-compose.dev.yml dev deployments are available.

A Proton Mail Bridge is optionally available if you want to receive push notifications for incoming emails.

Note: The default Proton Mail Bridge image uses shenxn/protonmail-bridge:build which compiles from source and supports multiple architectures. For x86_64 systems, you can use shenxn/protonmail-bridge:latest (pre-built binary, smaller and faster). For ARM devices (Raspberry Pi), stick with :build.

To receive Proton Mail notifications via Signal:

1. Initialize Proton Mail Bridge (one-time setup):

# Download docker-compose.yml
curl -L -O https://raw.githubusercontent.com/lone-cloud/sup/master/docker-compose.yml

docker compose run --rm protonmail-bridge init

2.Login to Proton Mail Bridge:

• At the >>> prompt, run: login
• Enter your email
• Enter your password
• Enter your 2FA code

3.Get IMAP credentials:

• Run: info
• Copy the Username and Password shown
• Run: exit to quit

4.Add credentials to .env:

# Add these to your .env file
PROTON_IMAP_USERNAME=bridge-username-from-info-command
PROTON_IMAP_PASSWORD=bridge-generated-password-from-info-command

5.Start all services with Proton Mail:

docker compose --profile protonmail up -d

Your phone will now receive Signal notifications when Proton Mail receives new emails.

Note that the bridge will first need to sync all of your old emails before you can start getting new email notifications which may take a while, but this is a one-time setup.

3. Install SUP Server

⚠️ Early Alpha: Currently only docker-compose.dev.yml dev deployments are available.

# Download docker-compose.yml
curl -L -O https://raw.githubusercontent.com/lone-cloud/sup/master/docker-compose.yml

# Download .env.example (optional)
curl -L -O https://raw.githubusercontent.com/lone-cloud/sup/master/server/.env.example

# Configure SUP server through environment variables (optional)
cp .env.example .env
nano .env

# Start SUP server
docker compose up -d

4. Link Your Signal Account

Visit http://localhost:8080 and link your Signal account (one-time setup):

1. Authenticate with your API_KEY

2. Scan the QR code from your Signal app

Go to Settings → Linked Devices → Link New Device in Signal.

3. Verify the setup

Once linked, you'll see the status dashboard:

With optional Proton Mail integration:

Development

For local development, install Bun and signal-cli:

# Install Bun (use your package manager and this is a backup)
curl -fsSL https://bun.sh/install | bash

git clone https://github.com/lone-cloud/sup.git
cd sup

bun install
cd server
bun start

Then build and run with docker-compose.dev.yml:

docker compose --profile protonmail -f docker-compose.dev.yml up -d

or just the proton-bridge:

docker compose -f docker-compose.dev.yml up protonmail-bridge

Real-World Examples

Proton Mail Notifications

Receive instant Signal notifications when new emails arrive in your Proton Mail inbox.

SUP monitors your Proton Mail account via the local Proton Mail Bridge and forwards email alerts through Signal. This relies on the same technology that a third-party email client like Thunderbird would be using to integrate with Proton Mail.

Home Assistant Alerts

Add a rest notification configuration (eg. add to configuration.yaml) to Home Assistant like:

notify:
  - platform: rest
    name: SUP
    resource: "http://<Your SUP server network IP>/Home Assistant"
    method: POST
    data:
      package: "io.homeassistant.companion.android"
    headers:
      Authorization: !secret sup_basic_auth

Note how Home Assistant is also a self-hosted server. As such, it is advisable to turn on ALLOW_INSECURE_HTTP environment variable for SUP and to refer to it by its LAN IP address.

Add the Base64 version of your API_KEY environment variable secret to your secrets.yaml. This secret must be prepended by a colon and the simplest way to get this value is to run btoa(':<API_KEY>') in your browser's console.

sup_basic_auth: "Basic <Base64 Hash value>"

Reboot your Home Assistant system and you'll then be able to send Signal notifications to yourself by using this notify sup action.

Monitoring

The health of the system can be viewed in the same admin UI used for linking Signal. SUP uses basic access authentication - provide your API_KEY as the password (username can be anything).

For API-based monitoring, call /api/health which returns JSON:

{"uptime":"3s","signal":{"daemon":"running","linked":true},"protonMail":"connected"}

Architecture

SUP consists of two services that MUST run together on the same machine:

• sup-server (Bun): Receives webhooks, sends Signal messages via signal-cli. Optional: monitors Proton Mail IMAP
• protonmail-bridge (Official Proton, optional): Decrypts Proton Mail emails, runs local IMAP server

All services communicate over a private Docker network with no external exposure except Signal protocol. Separating these services across multiple machines would expose plaintext IMAP traffic and compromise security.

Android App (Kotlin): Monitors Signal notifications, extracts UnifiedPush payloads, delivers to apps