End-to-End Encrypted Chat: Implementing Signal Protocol in React Native

Privacy-first messaging requires more than TLS. Here is how Whisper implements the Signal Protocol for true end-to-end encryption.

1. The Double Ratchet Algorithm

Every message uses a unique encryption key derived from a continuously evolving chain. Even if one key is compromised, past and future messages remain secure:

typescript
class DoubleRatchet {
  async ratchetEncrypt(plaintext: string): Promise<EncryptedMessage> {
    const messageKey = await this.deriveMessageKey(this.sendingChainKey);
    this.sendingChainKey = await this.advanceChain(this.sendingChainKey);
    return { ciphertext: await aesEncrypt(plaintext, messageKey), header: this.getHeader() };
  }
}

2. WebRTC Video Calling

Peer-to-peer video calls bypass the server entirely. The Node.js backend only handles ICE candidate signaling via Socket.IO.

3. SQLCipher Local Storage

All local message history is encrypted at rest using SQLCipher, preventing extraction even if the device is physically compromised.

Summary

Layering protocol-level encryption with encrypted local storage and peer-to-peer calling creates a messaging app where privacy is guaranteed by design.