Handling Application Security

import android.security.keystore.KeyGenParameterSpec
import android.security.keystore.KeyProperties
import java.security.KeyStore

val keyStore = KeyStore.getInstance("AndroidKeyStore")
keyStore.load(null)

val keyGenerator = KeyGenerator.getInstance(KeyProperties.KEY_ALGORITHM_AES, "AndroidKeyStore")
val keyGenParameterSpec = KeyGenParameterSpec.Builder(
    "my_key",
    KeyProperties.PURPOSE_ENCRYPT or KeyProperties.PURPOSE_DECRYPT
).setBlockModes(KeyProperties.BLOCK_MODE_CBC)
    .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_PKCS7)
    .build()

keyGenerator.init(keyGenParameterSpec)
keyGenerator.generateKey()

import javax.crypto.Cipher
import android.security.keystore.KeyProperties

val cipher = Cipher.getInstance(KeyProperties.KEY_ALGORITHM_AES + "/" +
    KeyProperties.BLOCK_MODE_CBC + "/" +
    KeyProperties.ENCRYPTION_PADDING_PKCS7)

val keyStore = KeyStore.getInstance("AndroidKeyStore")
keyStore.load(null)
val secretKey = keyStore.getKey("my_key", null) as SecretKey

cipher.init(Cipher.ENCRYPT_MODE, secretKey)
val encryptedData = cipher.doFinal("Sensitive data".toByteArray())

import javax.crypto.Cipher
import android.security.keystore.KeyProperties

val cipher = Cipher.getInstance(KeyProperties.KEY_ALGORITHM_AES + "/" +
    KeyProperties.BLOCK_MODE_CBC + "/" +
    KeyProperties.ENCRYPTION_PADDING_PKCS7)

val keyStore = KeyStore.getInstance("AndroidKeyStore")
keyStore.load(null)
val secretKey = keyStore.getKey("my_key", null) as SecretKey

cipher.init(Cipher.DECRYPT_MODE, secretKey)
val decryptedData = cipher.doFinal(encryptedData)

import android.security.biometrics.BiometricPrompt
import android.security.biometrics.BiometricManager
import androidx.fragment.app.FragmentActivity

class BiometricAuthFragment : FragmentActivity() {
    private lateinit var biometricPrompt: BiometricPrompt
    private lateinit var promptInfo: BiometricPrompt.PromptInfo

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        biometricPrompt = BiometricPrompt(this, object : BiometricPrompt.AuthenticationCallback() {
            override fun onAuthenticationSucceeded(result: BiometricPrompt.AuthenticationResult) {
                // Handle successful authentication
            }

            override fun onAuthenticationFailed() {
                // Handle failed authentication
            }
        })

        promptInfo = BiometricPrompt.PromptInfo.Builder()
            .setTitle("Authenticate")
            .setSubtitle("Use fingerprint to proceed")
            .setDescription("Touch sensor to authenticate")
            .setConfirmationRequired(true)
            .setDeviceCredentialAllowed(true)
            .build()
    }

    fun authenticate() {
        biometricPrompt.authenticate(promptInfo)
    }
}

import okhttp3.*
import java.security.cert.Certificate
import java.security.cert.CertificateFactory
import java.io.InputStream

class PinningInterceptor : Interceptor {
    override fun intercept(chain: Interceptor.Chain): Response {
        val request = chain.request()
        val response = chain.proceed(request)

        // Validate certificate against pinned values
        if (!isCertificateValid(response)) {
            throw IOException("Certificate pinning failed")
        }

        return response
    }

    private fun isCertificateValid(response: Response): Boolean {
        val certificates = response.handshake?.peerCertificates ?: return false
        // Compare with pinned certificates (simplified)
        return true
    }
}

// Usage in OkHttpClient
val client = OkHttpClient.Builder()
    .addInterceptor(PinningInterceptor())
    .build()

fun validateEmail(email: String): Boolean {
    val emailRegex = Regex("^[A-Za-z0-9+_.-]+@([A-Za-z0-9.-]+\\.[A-Za-z]{2,})$")
    return emailRegex.matches(email)
}

fun validatePhone(phone: String): Boolean {
    val phoneRegex = Regex("^\\+?[1-9]\\d{1,14}$")
    return phoneRegex.matches(phone)
}

fun sanitizeInput(input: String): String {
    return input
        .replace("<", "&lt;")
        .replace(">", "&gt;")
        .replace("&", "&amp;")
        .replace("\"", "&quot;")
}

val prefs = getSharedPreferences("secure_prefs", Context.MODE_PRIVATE)
val editor = prefs.edit()
editor.putString("user_token", "abc123xyz")
editor.apply()

<?xml version="1.0" encoding="utf-8"?>
<network-security-config>
    <base-config cleartextTrafficPermitted="false">
        <trust-anchors>
            <certificates src="@raw/trusted_certs"/>
        </trust-anchors>
    </base-config>
</network-security-config>

<application
    android:name=".MyApplication"
    android:networkSecurityConfig="@xml/network_security_config"
    ... >
</application>

keytool -genkey -v -keystore my-release-key.keystore -alias my-key-alias -keyalg RSA -keysize 2048 -validity 10000

android {
    signingConfigs {
        release {
            storeFile file('my-release-key.keystore')
            storePassword 'password'
            keyAlias 'my-key-alias'
            keyPassword 'password'
        }
    }
    buildTypes {
        release {
            signingConfig signingConfigs.release
        }
    }
}

@Dao
interface UserDao {
    @Query("SELECT * FROM users WHERE email = :email")
    fun findUserByEmail(email: String): User?
}

# Keep the main application class
-keep public class com.example.MyApplication {
    public static void main(java.lang.String[]);
}

# Keep all public classes and methods in a specific package
-keep public class com.example.api.** {
    public <methods>;
}

# Do not obfuscate specific classes
-keepnames class com.example.MyClass

# Keep annotations
-keepattributes *Annotation*

class ApiClient {
    companion object {
        const val API_KEY = BuildConfig.API_KEY
    }
}