Clear sensitive clipboard content after a delay

After copying the nsec, ncryptsec or seed words, schedule the clipboard to
be cleared after 60 seconds. The clipboard is only cleared if it still
holds the copied secret, so later copies are left untouched.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015enAP3dJTvB521BuULqU8P

app/src/main/java/com/greenart7c3/nostrsigner/models/Account.kt

@@ -3,13 +3,12 @@ package com.greenart7c3.nostrsigner.models
 import android.widget.Toast
 import androidx.compose.runtime.Immutable
 import androidx.compose.runtime.Stable
-import androidx.compose.ui.platform.ClipEntry
 import androidx.compose.ui.platform.Clipboard
 import com.greenart7c3.nostrsigner.Amber
 import com.greenart7c3.nostrsigner.DataStoreAccess
 import com.greenart7c3.nostrsigner.R
 import com.greenart7c3.nostrsigner.service.nip44v3.Nip44v3
-import com.greenart7c3.nostrsigner.ui.newSensitivePlainText
+import com.greenart7c3.nostrsigner.ui.setSensitiveClip
 import com.vitorpamplona.quartz.nip01Core.core.Event
 import com.vitorpamplona.quartz.nip01Core.core.HexKey
 import com.vitorpamplona.quartz.nip01Core.core.hexToByteArray
@@ -120,11 +119,7 @@ class Account(
             didBackup = true
             val nsec = getNsec()
             Amber.instance.applicationIOScope.launch(Dispatchers.Main) {
-                clipboardManager.setClipEntry(
-                    ClipEntry(
-                        newSensitivePlainText("", nsec),
-                    ),
-                )
+                clipboardManager.setSensitiveClip("", nsec)
 
                 Toast.makeText(
                     Amber.instance,

app/src/main/java/com/greenart7c3/nostrsigner/ui/SensitiveClipboard.kt

@@ -4,6 +4,15 @@ import android.content.ClipData
 import android.content.ClipDescription
 import android.os.Build
 import android.os.PersistableBundle
+import androidx.compose.ui.platform.ClipEntry
+import androidx.compose.ui.platform.Clipboard
+import com.greenart7c3.nostrsigner.Amber
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.launch
+
+/** How long a copied secret stays on the clipboard before it is cleared. */
+const val SENSITIVE_CLIPBOARD_CLEAR_DELAY_MS = 60_000L
 
 /**
  * Creates a [ClipData] flagged as sensitive so the system (Android 13+) avoids
@@ -22,3 +31,43 @@ fun newSensitivePlainText(label: CharSequence, text: CharSequence): ClipData {
     clipData.description.extras = extras
     return clipData
 }
+
+/**
+ * Copies a secret to the clipboard flagged as sensitive content and schedules it
+ * to be cleared after [clearAfterMillis]. The clipboard is only cleared if it
+ * still contains the copied secret, so anything the user copies afterwards is
+ * left untouched.
+ */
+suspend fun Clipboard.setSensitiveClip(
+    label: CharSequence,
+    text: CharSequence,
+    scope: CoroutineScope = Amber.instance.applicationIOScope,
+    clearAfterMillis: Long = SENSITIVE_CLIPBOARD_CLEAR_DELAY_MS,
+) {
+    setClipEntry(ClipEntry(newSensitivePlainText(label, text)))
+    scheduleSensitiveClear(text, scope, clearAfterMillis)
+}
+
+private fun Clipboard.scheduleSensitiveClear(
+    copiedValue: CharSequence,
+    scope: CoroutineScope,
+    delayMillis: Long,
+) {
+    scope.launch {
+        delay(delayMillis)
+        val currentText = getClipEntry()?.clipData?.let { clip ->
+            if (clip.itemCount > 0) clip.getItemAt(0).text?.toString() else null
+        }
+        if (currentText == copiedValue.toString()) {
+            clearClipboard()
+        }
+    }
+}
+
+private suspend fun Clipboard.clearClipboard() {
+    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.P) {
+        nativeClipboard.clearPrimaryClip()
+    } else {
+        setClipEntry(ClipEntry(ClipData.newPlainText("", "")))
+    }
+}

app/src/main/java/com/greenart7c3/nostrsigner/ui/actions/AccountBackupScreen.kt

@@ -69,7 +69,6 @@ import androidx.compose.ui.Modifier
 import androidx.compose.ui.autofill.ContentType
 import androidx.compose.ui.draw.clip
 import androidx.compose.ui.graphics.Color
-import androidx.compose.ui.platform.ClipEntry
 import androidx.compose.ui.platform.Clipboard
 import androidx.compose.ui.platform.LocalClipboard
 import androidx.compose.ui.platform.LocalContext
@@ -106,7 +105,7 @@ import com.greenart7c3.nostrsigner.ui.components.IconRow
 import com.greenart7c3.nostrsigner.ui.components.MarkdownText
 import com.greenart7c3.nostrsigner.ui.components.SeedWordsPage
 import com.greenart7c3.nostrsigner.ui.navigation.Route
-import com.greenart7c3.nostrsigner.ui.newSensitivePlainText
+import com.greenart7c3.nostrsigner.ui.setSensitiveClip
 import com.greenart7c3.nostrsigner.ui.theme.Size35dp
 import com.greenart7c3.nostrsigner.ui.theme.fromHex
 import com.vitorpamplona.quartz.nip06KeyDerivation.Nip06
@@ -797,7 +796,7 @@ private fun encryptCopyNSec(
                 account.didBackup = true
                 onBackupDone()
                 Amber.instance.applicationIOScope.launch(Dispatchers.Main) {
-                    clipboardManager.setClipEntry(ClipEntry(newSensitivePlainText("", key)))
+                    clipboardManager.setSensitiveClip("", key)
                     Toast.makeText(context, context.getString(R.string.secret_key_copied_to_clipboard), Toast.LENGTH_SHORT).show()
                 }
                 onLoading(false)

app/src/main/java/com/greenart7c3/nostrsigner/ui/components/SeedWordsPage.kt

@@ -19,7 +19,6 @@ import androidx.compose.runtime.DisposableEffect
 import androidx.compose.runtime.rememberCoroutineScope
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
-import androidx.compose.ui.platform.ClipEntry
 import androidx.compose.ui.platform.LocalClipboard
 import androidx.compose.ui.res.stringResource
 import androidx.compose.ui.text.font.FontWeight
@@ -31,7 +30,7 @@ import androidx.lifecycle.LifecycleEventObserver
 import androidx.lifecycle.compose.LocalLifecycleOwner
 import com.greenart7c3.nostrsigner.Amber
 import com.greenart7c3.nostrsigner.R
-import com.greenart7c3.nostrsigner.ui.newSensitivePlainText
+import com.greenart7c3.nostrsigner.ui.setSensitiveClip
 import com.greenart7c3.nostrsigner.ui.verticalScrollbar
 import kotlinx.coroutines.launch
 
@@ -74,11 +73,7 @@ fun SeedWordsPage(
             AmberButton(
                 onClick = {
                     scope.launch {
-                        clipboardManager.setClipEntry(
-                            ClipEntry(
-                                newSensitivePlainText("", seedWords.joinToString(" ")),
-                            ),
-                        )
+                        clipboardManager.setSensitiveClip("", seedWords.joinToString(" "))
                     }
                 },
                 text = stringResource(R.string.copy_to_clipboard),