feat: kick off a very basic passphrase cache

app/src/main/java/app/passwordstore/data/crypto/GPGPassphraseCache.kt

@@ -0,0 +1,67 @@
+package app.passwordstore.data.crypto
+
+import android.content.Context
+import androidx.core.content.edit
+import androidx.security.crypto.EncryptedSharedPreferences
+import androidx.security.crypto.MasterKey
+import app.passwordstore.crypto.GpgIdentifier
+import app.passwordstore.util.coroutines.DispatcherProvider
+import app.passwordstore.util.extensions.getString
+import javax.inject.Inject
+import kotlinx.coroutines.withContext
+
+/** Implements a rudimentary [EncryptedSharedPreferences]-backed cache for GPG passphrases. */
+@Suppress("Unused") // Soon
+class GPGPassphraseCache
+@Inject
+constructor(
+  private val dispatcherProvider: DispatcherProvider,
+) {
+
+  private suspend fun cachePassphrase(
+    context: Context,
+    identifier: GpgIdentifier,
+    passphrase: String,
+  ) {
+    withContext(dispatcherProvider.io()) {
+      getPreferences(context).edit { putString(identifier.toString(), passphrase) }
+    }
+  }
+
+  private suspend fun retrieveCachedPassphrase(
+    context: Context,
+    identifier: GpgIdentifier,
+  ): String? {
+    return withContext(dispatcherProvider.io()) {
+      getPreferences(context).getString(identifier.toString())
+    }
+  }
+
+  private suspend fun getPreferences(context: Context) =
+    withContext(dispatcherProvider.io()) {
+      EncryptedSharedPreferences.create(
+        context,
+        ANDROIDX_SECURITY_KEYSET_PREF_NAME,
+        getOrCreateWrappingMasterKey(context),
+        EncryptedSharedPreferences.PrefKeyEncryptionScheme.AES256_SIV,
+        EncryptedSharedPreferences.PrefValueEncryptionScheme.AES256_GCM,
+      )
+    }
+
+  private suspend fun getOrCreateWrappingMasterKey(context: Context) =
+    withContext(dispatcherProvider.io()) {
+      MasterKey.Builder(context, "passphrase")
+        .setKeyScheme(MasterKey.KeyScheme.AES256_GCM)
+        .setRequestStrongBoxBacked(true)
+        .setUserAuthenticationRequired(
+          /* authenticationRequired = */ true,
+          /* userAuthenticationValidityDurationSeconds = */ 60,
+        )
+        .build()
+    }
+
+  private companion object {
+
+    private const val ANDROIDX_SECURITY_KEYSET_PREF_NAME = "androidx_passphrase_keyset_prefs"
+  }
+}