<div><li><p>Add a secure <strong>end-to-end encryption (E2EE)</strong> system for all messages sent via the mobile chat app. </p> </li><li><p>Each message should be <strong>encrypted on the sender’s device</strong> and <strong>only decrypted on the recipient’s device</strong>. </p> </li><li><p>The server should <strong>only relay encrypted messages</strong>—it must not store or access the decrypted content. </p> </li><li><p>Use modern encryption protocols suitable for mobile (lightweight + secure): </p><ul><li><p><strong>Asymmetric encryption</strong> for key exchange (e.g., ECDH) </p> </li><li><p><strong>Symmetric encryption</strong> (e.g., AES-256) for actual message content </p> </li> </ul> </li><li><p>Ensure encryption works for: </p><ul><li><p>Text messages </p> </li><li><p>Media (images, audio, video) </p> </li><li><p>Files/documents </p> </li> </ul> </li><li><p>Store encryption keys securely on the device (e.g., using secure storage like Keychain on iOS, Keystore on Android). </p> </li><li><p>Handle edge cases like: </p><ul><li><p>Switching devices (re-keying or secure key sync) </p> </li><li><p>Group chats (manage shared keys or encrypt per member) </p> </li><li><p>Offline message encryption/decryption </p> </li> </ul> </li><li><p>Maintain performance: encryption/decryption should not slow down the app noticeably. </p> </li><li><p>Add a visual indicator that a chat is encrypted (e.g., lock icon, tooltip). </p> </li><br> </div>