End-to-End Encryption

// Notice: NO encryption/decryption logic on server!
// Server just stores and forwards encrypted blobs.

app.post('/api/messages', authMiddleware, async (req, res) => {
  // req.body looks like: { to: 'user_42', ciphertext: 'AbCdEf...' }
  // Server has NO idea what's inside ciphertext

  await Message.create({
    fromUserId: req.user.userId,
    toUserId:   req.body.to,
    ciphertext: req.body.ciphertext  // store as-is
  });

  res.json({ success: true });
});

app.get('/api/messages', authMiddleware, async (req, res) => {
  const msgs = await Message.find({ toUserId: req.user.userId });
  // Send back encrypted blobs. Server NEVER decrypted them.
  res.json(msgs);
});

// e2ee.service.ts — encryption happens ENTIRELY in the browser
@Injectable({ providedIn: 'root' })
export class E2EEService {
  // User's private key derived from their PASSWORD (server never sees it)
  private myPrivateKey: CryptoKey | null = null;

  async unlockKey(userPassword: string) {
    // Derive key from password using PBKDF2 — slow on purpose
    const salt = new TextEncoder().encode('your-app-salt');
    const passwordBytes = new TextEncoder().encode(userPassword);

    const baseKey = await crypto.subtle.importKey(
      'raw', passwordBytes, { name: 'PBKDF2' }, false, ['deriveKey']
    );

    this.myPrivateKey = await crypto.subtle.deriveKey(
      { name: 'PBKDF2', salt, iterations: 600000, hash: 'SHA-256' },
      baseKey,
      { name: 'AES-GCM', length: 256 },
      false,
      ['encrypt', 'decrypt']
    );
    // ⚠️ Server NEVER sees this key, never sees the password
  }

  async sendMessage(toUserId: string, plaintext: string) {
    // Encrypt with recipient's public key (fetched separately)
    const recipientPubKey = await this.fetchPublicKey(toUserId);
    const iv = crypto.getRandomValues(new Uint8Array(12));

    const enc = await crypto.subtle.encrypt(
      { name: 'RSA-OAEP' },
      recipientPubKey,
      new TextEncoder().encode(plaintext)
    );

    // Send only the ciphertext blob
    return this.http.post('/api/messages', {
      to: toUserId,
      ciphertext: this.toBase64(new Uint8Array(enc))
    });
  }

  async readMessage(encryptedBlob: string) {
    // Decrypt with MY private key — only my browser can do this
    const buf = this.fromBase64(encryptedBlob);
    const plain = await crypto.subtle.decrypt(
      { name: 'RSA-OAEP' },
      this.myPrivateKey!,
      buf
    );
    return new TextDecoder().decode(plain);
  }
}