Android App: Securing Encrypted Data

TL;DR

Protecting encrypted content in your Android app requires a multi-layered approach. This guide covers key storage, secure communication, and runtime protection to minimise risks.

Securing Encrypted Content on Android

1. Key Storage – Use the Android Keystore System
   • The Android Keystore system provides a secure container for cryptographic keys.
   • Avoid storing keys directly in your app’s code or shared preferences.
   • Use hardware-backed keystores whenever possible (e.g., StrongBox).
   • Consider using Jetpack Security library to simplify key management.

   // Example: Generating a KeyPair in Keystore
   KeyGenParameterSpec spec = new KeyGenParameterSpec.Builder("my_alias", KeyProperties.PURPOSE_ENCRYPT_DECRYPT)
           .setBlockModes(KeyProperties.BLOCK_MODE_CBC)
           .setUserAuthenticationRequired(true) // Require user authentication (fingerprint/PIN)
           .build();
   KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore");
   keyStore.load(null);
   KeyPairGenerator generator = KeyPairGenerator.getInstance("AES", "AndroidKeyStore");
   generator.initialize(spec);
   KeyPair keyPair = generator.generateKeyPair();

2. Encryption Algorithm Choice
   • Use strong, modern encryption algorithms like AES (Advanced Encryption Standard) with a 256-bit key.
   • Avoid weaker or deprecated algorithms such as DES or RC4.
   • Use authenticated encryption modes (e.g., GCM) to protect against tampering.
3. Secure Communication – HTTPS and Certificate Pinning
   • Always use HTTPS for all network communication. This encrypts data in transit.
   • Implement certificate pinning to verify the server’s identity and prevent man-in-the-middle attacks.
   • Use a trusted root certificate authority (CA).
4. Runtime Protection – Obfuscation and Tamper Detection
   • Obfuscate your code using tools like ProGuard or R8 to make it harder for attackers to reverse engineer.
   • Implement tamper detection mechanisms to identify if the app has been modified. This could involve checksums of critical files or code integrity checks.
   • Consider root detection, but be aware that it can be bypassed and may impact user experience.
5. Data Storage – Encrypt Sensitive Data at Rest
   • Encrypt sensitive data before storing it on the device (e.g., using Room with encryption support, or directly encrypting files).
   • Use a unique initialization vector (IV) for each encryption operation. Store the IV securely alongside the encrypted data.
   • Consider using Android’s EncryptedSharedPreferences to protect small amounts of sensitive data.
6. Input Validation – Prevent Injection Attacks
   • Validate all user input to prevent injection attacks (e.g., SQL injection, cross-site scripting).
   • Sanitize input before using it in any cryptographic operations.
7. Regular Security Audits and Updates
   • Conduct regular security audits of your app’s code and dependencies.
   • Keep your app’s libraries and SDKs up to date to patch known vulnerabilities.
   • Monitor for new security threats and update your app accordingly.

Important Note: cyber security is an ongoing process, not a one-time fix. Regularly review and improve your security practices to stay ahead of potential threats.