In today’s digital landscape, securing user data in Android applications is more critical than ever. With increasing privacy regulations and growing user awareness about data protection, developers must implement robust security measures. This comprehensive guide covers best practices and techniques to protect sensitive user information in your Android apps.

Photo by Anna Might on Unsplash

In 2023, over 60% of mobile breaches stemmed from insecure app storage and communication practices.

Why Android Data Security Matters

Before diving into implementation, let’s understand why securing user data is essential:

1. Privacy Regulations: Compliance with GDPR, CCPA, and other data protection laws
2. User Trust: Protecting your app’s reputation and maintaining user confidence
3. Security Threats: Preventing data breaches, leaks, and unauthorized access
4. Play Store Requirements: Meeting Google’s increasingly strict data safety requirements

1. Data Storage Security

Shared Preferences

 

// Secure SharedPreferences example
val masterKey = MasterKey.Builder(context)
    .setKeyScheme(MasterKey.KeyScheme.AES256_GCM)
    .build()

val sharedPreferences = EncryptedSharedPreferences.create(
    context,
    "secret_shared_prefs",
    masterKey,
    EncryptedSharedPreferences.PrefKeyEncryptionScheme.AES256_SIV,
    EncryptedSharedPreferences.PrefValueEncryptionScheme.AES256_GCM
)
// Store data
sharedPreferences.edit().putString("API_KEY", "sensitive_value").apply()

 

Tip: Avoid storing PII unless necessary. Use Jetpack Security Library to simplify encrypted data handling.

Room Database Encryption

 

// Add SQLCipher dependency to your build.gradle
// implementation 'net.zetetic:android-database-sqlcipher:4.5.0'

fun getEncryptedDatabase(context: Context): AppDatabase {
    val passphrase = "your_secure_passphrase".toCharArray()
    val factory = SupportFactory(passphrase)
    return Room.databaseBuilder(
        context,
        AppDatabase::class.java,
        "encrypted-db"
    ).openHelperFactory(factory)
    .build()
}

 

File Storage Best Practices

• Use Context.getFilesDir() for internal storage
• Avoid MODE_WORLD_READABLE or MODE_WORLD_WRITEABLE
• Encrypt sensitive files before storage:

 

fun encryptFile(context: Context, originalFile: File) {
    val cipher = Cipher.getInstance("AES/GCM/NoPadding")
    val key = generateSecretKey()
    cipher.init(Cipher.ENCRYPT_MODE, key)

    FileOutputStream(File(context.filesDir, "encrypted_file")).use { output ->
            CipherOutputStream(output, cipher).use { cipherOutput ->
                FileInputStream(originalFile).use { input ->
                    input.copyTo(cipherOutput)
                }
            }
        }
  }

 

2. Network Security

Implement HTTPS with Certificate Pinning

 

<!-- network_security_config.xml -->
<network-security-config>
    <domain-config>
        <domain includeSubdomains="true">yourdomain.com</domain>
        <pin-set expiration="2023-12-31">
            <pin digest="SHA-256">7HIpactkIAq2Y49orFOOQKurWxmmSFZhBCoQYcRhJ3Y=</pin>
            <pin digest="SHA-256">fwza0LRMXouZHRC8Ei+4PyuldPDcf3UKgO/04cDM1oE=</pin>
        </pin-set>
    </domain-config>
</network-security-config>

 

Pro Tip: Use TrustKit or Conscrypt for enhanced SSL pinning and secure connections.

Secure API Communication

• Always use HTTPS (not HTTP)
• Implement OAuth2, API keys, or tokens for authentication
• Use Retrofit with OkHttp for secure networking:

 

val client = OkHttpClient.Builder()
    .sslSocketFactory(sslContext.socketFactory, trustManager)
    .addInterceptor(HttpLoggingInterceptor().apply {
        level = HttpLoggingInterceptor.Level.BODY
    })
    .build()

val retrofit = Retrofit.Builder()
    .baseUrl("https://api.yourservice.com/")
    .client(client)
    .build()

 

3. Authentication and Authorization

Biometric Authentication

 

private fun showBiometricPrompt() {
    val promptInfo = BiometricPrompt.PromptInfo.Builder()
        .setTitle("Biometric login")
        .setSubtitle("Log in using your biometric credential")
        .setNegativeButtonText("Use account password")
        .build()

    val biometricPrompt = BiometricPrompt(this, executor,
            object : BiometricPrompt.AuthenticationCallback() {
                override fun onAuthenticationSucceeded(
                    result: BiometricPrompt.AuthenticationResult
                ) {
                    super.onAuthenticationSucceeded(result)
                    // Authentication succeeded - proceed
                }
            })
    biometricPrompt.authenticate(promptInfo)
}

 

Fallback Tip: Always include fallback options like PIN/password login for accessibility.

Secure Token Storage

• Store tokens using:
  → Android Keystore for encryption keys
  → EncryptedSharedPreferences or EncryptedFile
• Implement token refresh & expiration
• Consider Firebase or other secure identity platforms

4. Code Security

ProGuard/R8 Obfuscation

 

android {
    buildTypes {
        release {
            minifyEnabled true
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
}

 

Extra Tips:

• Use the Secrets Gradle Plugin for managing secrets
• Use NDK to store secrets if needed

Secure Sensitive Strings

 

val apiKey = BuildConfig.API_KEY
external fun getApiKey(): String

 

5. Permission Management

Runtime Permissions

 

when {
    ContextCompat.checkSelfPermission(
            this,
            Manifest.permission.ACCESS_FINE_LOCATION
        ) == PackageManager.PERMISSION_GRANTED -> {
        // Permission granted
    }
    shouldShowRequestPermissionRationale(Manifest.permission.ACCESS_FINE_LOCATION) -> {
        // Explain why you need the permission
    }
    else -> {
        requestPermissions(
            arrayOf(Manifest.permission.ACCESS_FINE_LOCATION),
            LOCATION_PERMISSION_REQUEST_CODE
        )
    }
}

 

Best Practices

• Request only necessary permissions
• Use Permission Dashboard (API 30+) to audit access
• Group related permissions
• Provide explanations before asking

6. Data Minimization and Privacy

Key Principles

1. Collect only what you need
2. Anonymize when possible
3. Set data retention policies
4. Be transparent (Privacy Policy, usage disclosure)

Example Data Retention

 

fun cleanOldData() {
    val cutoff = System.currentTimeMillis() - TimeUnit.DAYS.toMillis(30)
    database.userDao().deleteInactiveUsers(cutoff)

    val cacheDir = context.cacheDir
        cacheDir.listFiles()?.forEach { file ->
            if (file.lastModified() < cutoff) {
                file.delete()
            }
        }
}

 

📝 Note: Align your app’s Play Console Data Safety section with these practices.

7. Security Libraries to Consider

Native Libraries

• Jetpack Security: Encryption for files & SharedPreferences
• Biometric API
• Android Identity Credential

Third-party Libraries

• SQLCipher
• Tink (Google)
• AppAuth
• OAuth2 SDKs (e.g., Okta, Auth0)

8. Regular Security Updates

1. Use Dependabot or similar tools
2. Monitor Android Security Bulletins
3. Subscribe to Android Security Blog
4. Perform regular code audits & reviews
5. Use CI/CD pipelines to detect outdated or vulnerable libraries

9. Testing Your Security

Tools

• MobSF: Mobile vulnerability scanner

• Burp Suite: Network analysis
• Android Lint: Static code analysis
• Checkmarx / SonarQube: Enterprise-grade SAST tools
• adb backup: Test exposed backup data

 

adb backup -noapk your.app.package

 

✅ Developer Checklist

 

✅ Use EncryptedSharedPreferences  
✅ Encrypt local files with AES/GCM  
✅ Use HTTPS with certificate pinning  
✅ Implement OAuth2 or strong token auth  
✅ Obfuscate code with ProGuard/R8  
✅ Handle runtime permissions properly  
✅ Minimize data collection and anonymize where possible  
✅ Stay updated with security patches and libraries  
✅ Perform static and dynamic security testing  
✅ Have a security incident response plan

 

This article was previously published on proandroiddev.com.