refactor: extract EncryptedSharedPreferences into SecurePreferencesFactory with auto-recovery (batch v0.2.21)

- New SecurePreferencesFactory handles EncryptedSharedPreferences creation
- Auto-resets and recreates on corruption (unreadable prefs)
- CoupleKeyStore and SharedPreferencesLocalAnswerRepository use the factory
- Removes duplicated EncryptedSharedPreferences boilerplate

app/src/main/java/app/closer/crypto/CoupleKeyStore.kt

@@ -2,8 +2,7 @@ package app.closer.crypto
 
 import android.content.Context
 import android.content.SharedPreferences
-import androidx.security.crypto.EncryptedSharedPreferences
+import app.closer.data.local.SecurePreferencesFactory
-import androidx.security.crypto.MasterKeys
 import com.google.crypto.tink.Aead
 import com.google.crypto.tink.CleartextKeysetHandle
 import com.google.crypto.tink.JsonKeysetReader
@@ -24,16 +23,8 @@ import javax.inject.Singleton
 class CoupleKeyStore @Inject constructor(
     @ApplicationContext context: Context
 ) {
-    private val prefs: SharedPreferences = run {
+    private val prefs: SharedPreferences =
-        val masterKeyAlias = MasterKeys.getOrCreate(MasterKeys.AES256_GCM_SPEC)
+        SecurePreferencesFactory.encryptedSharedPreferences(context, PREFS_NAME)
-        EncryptedSharedPreferences.create(
-            masterKeyAlias,
-            "couple_crypto_secure",
-            context,
-            EncryptedSharedPreferences.PrefKeyEncryptionScheme.AES256_SIV,
-            EncryptedSharedPreferences.PrefValueEncryptionScheme.AES256_GCM
-        )
-    }
 
     private val aeadCache = ConcurrentHashMap<String, Aead>()
 
@@ -110,4 +101,8 @@ class CoupleKeyStore @Inject constructor(
             val json = prefs.getString(key, null) ?: return null
             CleartextKeysetHandle.read(JsonKeysetReader.withString(json))
         }.getOrNull()
+
+    private companion object {
+        const val PREFS_NAME = "couple_crypto_secure"
+    }
 }

app/src/main/java/app/closer/data/local/SecurePreferencesFactory.kt

@@ -0,0 +1,55 @@
+package app.closer.data.local
+
+import android.content.Context
+import android.content.SharedPreferences
+import android.util.Log
+import androidx.security.crypto.EncryptedSharedPreferences
+import androidx.security.crypto.MasterKeys
+import java.security.KeyStore
+
+object SecurePreferencesFactory {
+    private const val TAG = "SecurePreferences"
+    private const val ANDROID_KEYSTORE = "AndroidKeyStore"
+    private const val MASTER_KEY_ALIAS = "_androidx_security_master_key_"
+
+    fun encryptedSharedPreferences(
+        context: Context,
+        prefsName: String
+    ): SharedPreferences {
+        val appContext = context.applicationContext
+        return runCatching {
+            create(appContext, prefsName)
+        }.getOrElse { firstError ->
+            Log.w(TAG, "Resetting unreadable encrypted preferences: $prefsName", firstError)
+            reset(appContext, prefsName)
+            create(appContext, prefsName)
+        }
+    }
+
+    private fun create(context: Context, prefsName: String): SharedPreferences {
+        val masterKeyAlias = MasterKeys.getOrCreate(MasterKeys.AES256_GCM_SPEC)
+        return EncryptedSharedPreferences.create(
+            prefsName,
+            masterKeyAlias,
+            context,
+            EncryptedSharedPreferences.PrefKeyEncryptionScheme.AES256_SIV,
+            EncryptedSharedPreferences.PrefValueEncryptionScheme.AES256_GCM
+        )
+    }
+
+    private fun reset(context: Context, prefsName: String) {
+        context.deleteSharedPreferences(prefsName)
+        context.deleteSharedPreferences(MASTER_KEY_ALIAS)
+        runCatching {
+            val keyStore = KeyStore.getInstance(ANDROID_KEYSTORE).apply { load(null) }
+            if (keyStore.containsAlias(prefsName)) {
+                keyStore.deleteEntry(prefsName)
+            }
+            if (keyStore.containsAlias(MASTER_KEY_ALIAS)) {
+                keyStore.deleteEntry(MASTER_KEY_ALIAS)
+            }
+        }.onFailure { error ->
+            Log.w(TAG, "Could not delete Android Keystore master key.", error)
+        }
+    }
+}

app/src/main/java/app/closer/data/repository/SharedPreferencesLocalAnswerRepository.kt

@@ -2,8 +2,7 @@ package app.closer.data.repository
 
 import android.content.Context
 import android.content.SharedPreferences
-import androidx.security.crypto.EncryptedSharedPreferences
+import app.closer.data.local.SecurePreferencesFactory
-import androidx.security.crypto.MasterKeys
 import app.closer.domain.model.LocalAnswer
 import app.closer.domain.repository.LocalAnswerRepository
 import dagger.hilt.android.qualifiers.ApplicationContext
@@ -24,15 +23,7 @@ class SharedPreferencesLocalAnswerRepository @Inject constructor(
         // Remove legacy plaintext file on first migration
         context.deleteSharedPreferences("local_answers")
 
-        // In security-crypto 1.0.0, EncryptedSharedPreferences.create takes (alias, name, context, ...)
+        SecurePreferencesFactory.encryptedSharedPreferences(context, PREFS_NAME)
-        val masterKeyAlias = MasterKeys.getOrCreate(MasterKeys.AES256_GCM_SPEC)
-        EncryptedSharedPreferences.create(
-            masterKeyAlias,              // alias (first param)
-            "local_answers_secure",     // name (second param)
-            context,                     // context (third param)
-            EncryptedSharedPreferences.PrefKeyEncryptionScheme.AES256_SIV,
-            EncryptedSharedPreferences.PrefValueEncryptionScheme.AES256_GCM
-        )
     }
     private val answers = MutableStateFlow(readAnswers())
 
@@ -132,5 +123,6 @@ class SharedPreferencesLocalAnswerRepository @Inject constructor(
 
     private companion object {
         const val KEY_ANSWERS = "answers"
+        const val PREFS_NAME = "local_answers_secure"
     }
 }