CellFi is a groundbreaking mobile application that enables users to perform cryptocurrency transactions on the blockchain using only SMS (text messages). Designed to democratize access to decentralized finance, CellFi makes crypto accessible to everyone, even in low-connectivity regions or areas with no internet access.
CellFi eliminates the need for an active internet connection to interact with the Ethereum network. By combining robust blockchain technology with traditional SMS infrastructure, we've created a seamless bridge for users in off-grid or limited-connectivity environments.
The process is designed to be secure, fast, and entirely offline for the user:
- Offline Signature: The CellFi mobile app generates a standard Ethereum transaction and creates a cryptographic signature using the user's securely stored private key—all offline on the device.
- SMS Transmission: The signed transaction data is sent via a standard SMS to a designated virtual phone number.
- Backend Verification: A dedicated Node.js backend receives the SMS using a custom macro-based scanning system. It verifies the cryptographic signature to ensure the transaction is authentic and hasn't been tampered with.
- Blockchain Execution: Once validated, the backend broadcasts the transaction to the Ethereum network via Infura or Alchemy RPC endpoints.
- Real-Time Confirmation: An instant status update and transaction confirmation are sent back to the user via SMS using Vonage’s SMS API.
CellFi is currently operational on a public testnet:
- Network: Ethereum Sepolia Testnet
- Transaction Types: Transferring and swapping tokens.
- Mobile App: Built with React Native and Ethers.js.
- Backend: Node.js with a custom macro-based SMS scanning system.
- Messaging Service: Integrated with Vonage for reliable two-way SMS communication.
See how simple it is to initiate an offline transaction directly from the CellFi app.
Proof of the transaction successfully executed on the Sepolia Testnet after being sent via SMS.
| Component | Technology | Role |
|---|---|---|
| Mobile App | React Native & Ethers.js | Offline transaction generation and signing |
| Messaging | SMS & Vonage SMS API | Data transfer and real-time confirmations |
| Backend | Node.js | Receives, verifies, and executes transactions |
| Blockchain | Ethereum Sepolia Testnet | Target network for transactions |
| RPC | Infura / Alchemy | Connects the backend to the Ethereum network |
Developing a system that relies on SMS for blockchain interaction presented unique technical and logistical hurdles:
- Backend Communication Stability: Maintaining a stable and reliable connection between the virtual phone number and the Node.js backend to ensure all messages were parsed correctly and rapidly.
- Virtual Phone Number Acquisition: Based in India, we faced significant difficulties and regional restrictions in obtaining and managing a dedicated virtual phone number for long-term use and integration with the carrier network.
- Technical Hurdles: Overcoming numerous bugs related to message parsing, cryptographic signature verification, and backend-to-blockchain synchronization.
We are continually refining CellFi to expand its reach and capabilities:
- Support for additional blockchain networks (e.g., Polygon, BNB Chain).
- Introduction of more complex transaction types (e.g., interacting with DeFi protocols).
- Advanced, conversational SMS-based interactions for querying account balances and history.