Bitcoin Message Signer is a secure, open-source mobile app that signs arbitrary messages using a Bitcoin private key and instantly sends the resulting cryptographic signature to any URL (webhook). Built with simplicity, transparency, and privacy in mind — no servers, no tracking — just pure cryptographic proof.
You can download the latest release APK here:
📱 Scan QR codes to sign messages with a selected Bitcoin private key
🔑 Securely store multiple WIF-format Bitcoin private keys
➕ Import keys via QR, manual input, or generate random ones
✅ Select which key/address to use per message
📤 Automatically send the signature to a webhook of your choice
💡 Open-source and transparent under the MIT License
🚫 No servers. No tracking. No nonsense.
To sign a message, the app expects a QR code (or JSON string) with the following fields:
- msg: The actual message that should be signed
- url: The webhook where the signature should be POSTed
- addr: (optional) If present, the app will sign the message using the private key tied to this address
If addr is omitted, the currently selected default key/address is used.
Example:
{
"msg": "The message to sign",
"url": "https://example.com/webhook",
"addr": "1BitcoinAddress..."
}After signing, the app will send a POST request to the specified url with the following JSON payload:
{
"address": "1BitcoinAddress...",
"message": "The message that was signed",
"signature": "Base64-encoded signature string"
}Here’s how the app looks in light mode:
This app was built using FlutterFlow and can be exported and modified using the Flutter SDK. All code is available in the 'flutterflow' branch of this repository.
Here are some applications that are using this app:
- Hivemind Protocol: A decentralized Condorcet ranked choice voting system that uses Bitcoin signatures to verify votes and stores the data on IPFS.
MIT License. See the full MIT License for more details.