Enforce Android lifecycle and presentation security (#100)

android/platform/src/main/kotlin/de/rfc1437/ironstorage/platform/AndroidKeystoreAdapter.kt

@@ -39,6 +39,7 @@ class AndroidKeystoreAdapter(context: Context) : AndroidKeystore {
     private val handler = Handler(Looper.getMainLooper())
     private var activity = WeakReference<FragmentActivity>(null)
     private val pending = AtomicReference<Pending?>()
+    val authenticationPending: Boolean get() = pending.get() != null
 
     fun attach(host: FragmentActivity) {
         activity = WeakReference(host)

android/platform/src/main/kotlin/de/rfc1437/ironstorage/platform/AndroidSecretClipboard.kt

@@ -1,29 +1,61 @@
 package de.rfc1437.ironstorage.platform
 
 import android.content.ClipData
+import android.content.ClipDescription
 import android.content.ClipboardManager
 import android.content.Context
 import android.os.Build
 import android.os.PersistableBundle
 import de.rfc1437.ironstorage.core.SecretClipboard
+import java.io.IOException
+import java.util.UUID
 
-class AndroidSecretClipboard(context: Context) : SecretClipboard {
+class AndroidSecretClipboard(private val context: Context) : SecretClipboard {
     private val manager = context.getSystemService(ClipboardManager::class.java)
-    override fun read(): ByteArray? = manager.primaryClip?.let { clip ->
-        if (clip.itemCount == 1) clip.getItemAt(0).text?.toString()?.toByteArray() else null
+    private val identity = UUID.randomUUID().toString()
+    private var timestamp: Long? = null
+    override fun beginCopy(): SecretClipboard = AndroidSecretClipboard(context)
+    private fun owns(clip: ClipData) = clip.description.extras?.getString(OWNER) == identity &&
+        timestamp != null && clip.description.timestamp == timestamp
+    override fun read(): ByteArray? = access {
+        manager.primaryClip?.takeIf(::owns)?.let { clip ->
+            if (clip.itemCount == 1) clip.getItemAt(0).text?.toString()?.toByteArray() else null
+        }
     }
-    override fun write(value: ByteArray) {
+    override fun write(value: ByteArray) = access {
         val clip = ClipData.newPlainText("IronStorage", value.toString(Charsets.UTF_8))
         clip.description.extras = PersistableBundle().apply {
-            putBoolean("android.content.extra.IS_SENSITIVE", true)
+            putBoolean(
+                if (Build.VERSION.SDK_INT >=
+                    33
+                ) {
+                    ClipDescription.EXTRA_IS_SENSITIVE
+                } else {
+                    "android.content.extra.IS_SENSITIVE"
+                },
+                true
+            )
+            putString(OWNER, identity)
         }
         manager.setPrimaryClip(clip)
+        timestamp = manager.primaryClipDescription?.takeIf {
+            it.extras?.getString(OWNER) == identity
+        }?.timestamp
     }
-    override fun clear() {
+    override fun clear() = access {
+        if (manager.primaryClip?.let(::owns) != true) return@access
         if (Build.VERSION.SDK_INT >= 28) {
             manager.clearPrimaryClip()
         } else {
             manager.setPrimaryClip(ClipData.newPlainText("", ""))
         }
     }
+    private fun <T> access(block: () -> T): T = try {
+        block()
+    } catch (_: RuntimeException) {
+        throw IOException("Android clipboard access is unavailable.")
+    }
+    private companion object {
+        const val OWNER = "de.rfc1437.ironstorage.clipboard-owner"
+    }
 }