security-and-hardening

Security and Hardening

Overview

Security is a development constraint, not an afterthought. This skill provides a three-tier framework — Always Do, Ask First, Never Do — covering the OWASP Mobile Top 10, Android-specific attack vectors, and hardening patterns for production apps.

When to Use

• Handling user credentials, tokens, or personal data
• Implementing network communication
• Before shipping any release to the Play Store
• Reviewing code that touches authentication or authorization
• Setting up ProGuard/R8 rules
• Implementing WebView features

Skip when: Changes are purely cosmetic with no data or network impact.

Core Process: Three-Tier Framework

Always Do

1. Secure data storage. Jetpack Security Crypto (EncryptedSharedPreferences/MasterKey) is deprecated and unmaintained — do not add it to new code. Encrypt with a key held in the Android Keystore and persist the ciphertext (DataStore or a file):

// Key lives in the Android Keystore — never leaves secure hardware
val keyGenerator = KeyGenerator.getInstance(KeyProperties.KEY_ALGORITHM_AES, "AndroidKeyStore")
keyGenerator.init(
    KeyGenParameterSpec.Builder("auth_token_key", KeyProperties.PURPOSE_ENCRYPT or KeyProperties.PURPOSE_DECRYPT)
        .setBlockModes(KeyProperties.BLOCK_MODE_GCM)
        .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_NONE)
        .build()
)
val secretKey = keyGenerator.generateKey()

// Encrypt, then persist iv + ciphertext (e.g. in Proto DataStore)
val cipher = Cipher.getInstance("AES/GCM/NoPadding").apply { init(Cipher.ENCRYPT_MODE, secretKey) }
val encrypted = cipher.iv + cipher.doFinal(token.toByteArray())

Existing apps already on EncryptedSharedPreferences can keep it (the format is stable), but plan a migration and never store new categories of secrets with it.

1. Network Security Config:

<!-- res/xml/network_security_config.xml -->
<network-security-config>
    <!-- Enforce HTTPS for all connections -->
    <base-config cleartextTrafficPermitted="false">
        <trust-anchors>
            <certificates src="system" />
        </trust-anchors>
    </base-config>

    <!-- Certificate pinning for your API -->
    <domain-config>
        <domain includeSubdomains="true">api.example.com</domain>
        <pin-set expiration="2025-12-31">
            <pin digest="SHA-256">base64EncodedPin=</pin>
            <!-- Backup pin -->
            <pin digest="SHA-256">base64EncodedBackupPin=</pin>
        </pin-set>
    </domain-config>
</network-security-config>