[#551] Prevent screenshots when seed phrase is displayed on the screen (#590)

* [#551] Prevent screenshots when seed phrase is displayed on the screen

* Minor review changes

Make ScreenSecurity object simpler by eliminating additional ways of mutating its state.

* Add debug and test checks

* secured screens with seed phrase

* codereview fixes

* added test for Seed screen

* added Screen security test for backup views

* test for ScreenSecurity class

* added manual testing for Screen security

* ktlint format

* Clean up ScreenSecurityTest

* Remove debug check

I decided this would be annoying, especially for manual testing

* ktlint

* removed test logging

* removed test logging

Co-authored-by: Carter Jernigan <git@carterjernigan.com>

docs/testing/manual_testing/ScreenSecurity.md

@@ -0,0 +1,10 @@
+# Testing screens with secure flag
+1. install the app
+1. go to screens with seed phrase:
+   1. onboarding -> "Your Secret Recovery Phrase"
+   1. onboarding -> "Verify Your Backup"
+   1. onboarding -> "Import an Existing Wallet"   
+   1. settings -> "Backup wallet" 
+1. make screenshot
+1. verify that the screenshot is "blacked out"
+

ui-lib/src/androidTest/java/co/electriccoin/zcash/ui/common/ScreenSecurityTest.kt

@@ -0,0 +1,66 @@
+package co.electriccoin.zcash.ui.common
+
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.CompositionLocalProvider
+import androidx.compose.runtime.collectAsState
+import androidx.compose.runtime.getValue
+import androidx.compose.ui.test.junit4.ComposeContentTestRule
+import androidx.compose.ui.test.junit4.createComposeRule
+import androidx.test.filters.MediumTest
+import co.electriccoin.zcash.test.UiTestPrerequisites
+import co.electriccoin.zcash.ui.design.theme.ZcashTheme
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.update
+import kotlinx.coroutines.test.runTest
+import org.junit.Rule
+import org.junit.Test
+import kotlin.test.assertEquals
+
+@OptIn(ExperimentalCoroutinesApi::class)
+class ScreenSecurityTest : UiTestPrerequisites() {
+    @get:Rule
+    val composeTestRule = createComposeRule()
+
+    @Test
+    @MediumTest
+    fun acquireAndReleaseScreenSecurity() = runTest {
+        val testSetup = TestSetup(composeTestRule)
+
+        assertEquals(1, testSetup.getSecureScreenCount())
+
+        testSetup.mutableSecureScreenFlag.update { false }
+        composeTestRule.awaitIdle()
+        assertEquals(0, testSetup.getSecureScreenCount())
+    }
+
+    private class TestSetup(composeTestRule: ComposeContentTestRule) {
+
+        val mutableSecureScreenFlag = MutableStateFlow(true)
+
+        private val screenSecurity = ScreenSecurity()
+
+        fun getSecureScreenCount() = screenSecurity.referenceCount.value
+
+        init {
+            runTest {
+                composeTestRule.setContent {
+                    CompositionLocalProvider(LocalScreenSecurity provides screenSecurity) {
+                        ZcashTheme {
+                            val secureScreen by mutableSecureScreenFlag.collectAsState()
+
+                            TestView(secureScreen)
+                        }
+                    }
+                }
+            }
+        }
+
+        @Composable
+        private fun TestView(secureScreen: Boolean) {
+            if (secureScreen) {
+                SecureScreen()
+            }
+        }
+    }
+}

ui-lib/src/androidTest/java/co/electriccoin/zcash/ui/screen/backup/view/BackupViewsSecuredScreenTest.kt

@@ -0,0 +1,70 @@
+package co.electriccoin.zcash.ui.screen.backup.view
+
+import androidx.compose.runtime.CompositionLocalProvider
+import androidx.compose.ui.test.junit4.ComposeContentTestRule
+import androidx.compose.ui.test.junit4.createComposeRule
+import androidx.test.filters.MediumTest
+import cash.z.ecc.sdk.fixture.PersistableWalletFixture
+import co.electriccoin.zcash.test.UiTestPrerequisites
+import co.electriccoin.zcash.ui.common.LocalScreenSecurity
+import co.electriccoin.zcash.ui.common.ScreenSecurity
+import co.electriccoin.zcash.ui.design.theme.ZcashTheme
+import co.electriccoin.zcash.ui.fixture.TestChoicesFixture
+import co.electriccoin.zcash.ui.screen.backup.model.BackupStage
+import co.electriccoin.zcash.ui.screen.backup.state.BackupState
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.test.runTest
+import org.junit.Rule
+import org.junit.Test
+import kotlin.test.assertEquals
+
+@OptIn(ExperimentalCoroutinesApi::class)
+class BackupViewsSecuredScreenTest : UiTestPrerequisites() {
+    @get:Rule
+    val composeTestRule = createComposeRule()
+
+    private fun newTestSetup(initialStage: BackupStage) =
+        TestSetup(composeTestRule, initialStage).apply {
+            setContentView()
+        }
+
+    @Test
+    @MediumTest
+    fun acquireScreenSecuritySeedStage() = runTest {
+        val testSetup = newTestSetup(BackupStage.Seed)
+
+        assertEquals(1, testSetup.getSecureScreenCount())
+    }
+
+    @Test
+    @MediumTest
+    fun acquireScreenSecurityTestStage() = runTest {
+        val testSetup = newTestSetup(BackupStage.Test)
+
+        assertEquals(1, testSetup.getSecureScreenCount())
+    }
+
+    private class TestSetup(private val composeTestRule: ComposeContentTestRule, initialStage: BackupStage) {
+        private val screenSecurity = ScreenSecurity()
+        private val state = BackupState(initialStage)
+
+        fun getSecureScreenCount() = screenSecurity.referenceCount.value
+
+        fun setContentView() {
+            composeTestRule.setContent {
+                CompositionLocalProvider(LocalScreenSecurity provides screenSecurity) {
+                    ZcashTheme {
+                        BackupWallet(
+                            PersistableWalletFixture.new(),
+                            state,
+                            TestChoicesFixture.new(mutableMapOf()),
+                            onCopyToClipboard = { },
+                            onComplete = { },
+                            onChoicesChanged = { }
+                        )
+                    }
+                }
+            }
+        }
+    }
+}

ui-lib/src/androidTest/java/co/electriccoin/zcash/ui/screen/restore/view/RestoreViewSecuredScreenTest.kt

@@ -0,0 +1,54 @@
+package co.electriccoin.zcash.ui.screen.restore.view
+
+import androidx.compose.runtime.CompositionLocalProvider
+import androidx.compose.ui.test.junit4.ComposeContentTestRule
+import androidx.compose.ui.test.junit4.createComposeRule
+import androidx.test.filters.MediumTest
+import cash.z.ecc.android.bip39.Mnemonics
+import co.electriccoin.zcash.test.UiTestPrerequisites
+import co.electriccoin.zcash.ui.common.LocalScreenSecurity
+import co.electriccoin.zcash.ui.common.ScreenSecurity
+import co.electriccoin.zcash.ui.design.theme.ZcashTheme
+import co.electriccoin.zcash.ui.screen.restore.state.WordList
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.test.runTest
+import org.junit.Rule
+import org.junit.Test
+import java.util.Locale
+import kotlin.test.assertEquals
+
+@OptIn(ExperimentalCoroutinesApi::class)
+class RestoreViewSecuredScreenTest : UiTestPrerequisites() {
+    @get:Rule
+    val composeTestRule = createComposeRule()
+
+    @Test
+    @MediumTest
+    fun acquireScreenSecurity() = runTest {
+        val testSetup = TestSetup(composeTestRule)
+
+        assertEquals(1, testSetup.getSecureScreenCount())
+    }
+
+    private class TestSetup(composeTestRule: ComposeContentTestRule) {
+        private val screenSecurity = ScreenSecurity()
+
+        fun getSecureScreenCount() = screenSecurity.referenceCount.value
+
+        init {
+            composeTestRule.setContent {
+                CompositionLocalProvider(LocalScreenSecurity provides screenSecurity) {
+                    ZcashTheme {
+                        RestoreWallet(
+                            Mnemonics.getCachedWords(Locale.ENGLISH.language).toSortedSet(),
+                            WordList(emptyList()),
+                            onBack = { },
+                            paste = { "" },
+                            onFinished = { }
+                        )
+                    }
+                }
+            }
+        }
+    }
+}

ui-lib/src/androidTest/java/co/electriccoin/zcash/ui/screen/seed/view/SeedViewSecuredScreenTest.kt

@@ -0,0 +1,50 @@
+package co.electriccoin.zcash.ui.screen.seed.view
+
+import androidx.compose.runtime.CompositionLocalProvider
+import androidx.compose.ui.test.junit4.ComposeContentTestRule
+import androidx.compose.ui.test.junit4.createComposeRule
+import androidx.test.filters.MediumTest
+import cash.z.ecc.sdk.fixture.PersistableWalletFixture
+import co.electriccoin.zcash.test.UiTestPrerequisites
+import co.electriccoin.zcash.ui.common.LocalScreenSecurity
+import co.electriccoin.zcash.ui.common.ScreenSecurity
+import co.electriccoin.zcash.ui.design.theme.ZcashTheme
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.test.runTest
+import org.junit.Rule
+import org.junit.Test
+import kotlin.test.assertEquals
+
+@OptIn(ExperimentalCoroutinesApi::class)
+class SeedViewSecuredScreenTest : UiTestPrerequisites() {
+    @get:Rule
+    val composeTestRule = createComposeRule()
+
+    @Test
+    @MediumTest
+    fun acquireScreenSecurity() = runTest {
+        val testSetup = TestSetup(composeTestRule)
+
+        assertEquals(1, testSetup.getSecureScreenCount())
+    }
+
+    private class TestSetup(composeTestRule: ComposeContentTestRule) {
+        private val screenSecurity = ScreenSecurity()
+
+        fun getSecureScreenCount() = screenSecurity.referenceCount.value
+
+        init {
+            composeTestRule.setContent {
+                CompositionLocalProvider(LocalScreenSecurity provides screenSecurity) {
+                    ZcashTheme {
+                        Seed(
+                            persistableWallet = PersistableWalletFixture.new(),
+                            onBack = {},
+                            onCopyToClipboard = {}
+                        )
+                    }
+                }
+            }
+        }
+    }
+}

ui-lib/src/main/java/co/electriccoin/zcash/ui/MainActivity.kt

@@ -2,17 +2,23 @@ package co.electriccoin.zcash.ui
 
 import android.os.Bundle
 import android.os.SystemClock
+import android.view.WindowManager
 import androidx.activity.ComponentActivity
 import androidx.activity.compose.setContent
 import androidx.activity.viewModels
 import androidx.annotation.VisibleForTesting
 import androidx.compose.foundation.layout.fillMaxHeight
 import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.runtime.CompositionLocalProvider
 import androidx.compose.runtime.collectAsState
 import androidx.compose.ui.Modifier
 import androidx.core.splashscreen.SplashScreen.Companion.installSplashScreen
 import androidx.lifecycle.lifecycleScope
 import androidx.navigation.NavHostController
+import co.electriccoin.zcash.spackle.EmulatorWtfUtil
+import co.electriccoin.zcash.spackle.FirebaseTestLabUtil
+import co.electriccoin.zcash.ui.common.LocalScreenSecurity
+import co.electriccoin.zcash.ui.common.ScreenSecurity
 import co.electriccoin.zcash.ui.design.compat.FontCompat
 import co.electriccoin.zcash.ui.design.component.ConfigurationOverride
 import co.electriccoin.zcash.ui.design.component.GradientSurface
@@ -23,6 +29,7 @@ import co.electriccoin.zcash.ui.screen.home.viewmodel.SecretState
 import co.electriccoin.zcash.ui.screen.home.viewmodel.WalletViewModel
 import co.electriccoin.zcash.ui.screen.onboarding.WrapOnboarding
 import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.map
 import kotlinx.coroutines.launch
 import kotlin.time.Duration
 import kotlin.time.Duration.Companion.milliseconds
@@ -73,6 +80,23 @@ class MainActivity : ComponentActivity() {
     }
 
     private fun setupUiContent() {
+        val screenSecurity = ScreenSecurity()
+        lifecycleScope.launch {
+            screenSecurity.referenceCount.map { it > 0 }.collect { isSecure ->
+                val isTest = FirebaseTestLabUtil.isFirebaseTestLab(applicationContext) ||
+                    EmulatorWtfUtil.isEmulatorWtf(applicationContext)
+
+                if (isSecure && !isTest) {
+                    window.setFlags(
+                        WindowManager.LayoutParams.FLAG_SECURE,
+                        WindowManager.LayoutParams.FLAG_SECURE
+                    )
+                } else {
+                    window.clearFlags(WindowManager.LayoutParams.FLAG_SECURE)
+                }
+            }
+        }
+
         setContent {
             Override(configurationOverrideFlow) {
                 ZcashTheme {
@@ -81,22 +105,24 @@ class MainActivity : ComponentActivity() {
                             .fillMaxWidth()
                             .fillMaxHeight()
                     ) {
-                        when (val secretState = walletViewModel.secretState.collectAsState().value) {
-                            SecretState.Loading -> {
-                                // For now, keep displaying splash screen using condition above.
-                                // In the future, we might consider displaying something different here.
-                            }
-                            SecretState.None -> {
-                                WrapOnboarding()
-                            }
-                            is SecretState.NeedsBackup -> {
-                                WrapBackup(
-                                    secretState.persistableWallet,
-                                    onBackupComplete = { walletViewModel.persistBackupComplete() }
-                                )
-                            }
-                            is SecretState.Ready -> {
-                                Navigation()
+                        CompositionLocalProvider(LocalScreenSecurity provides screenSecurity) {
+                            when (val secretState = walletViewModel.secretState.collectAsState().value) {
+                                SecretState.Loading -> {
+                                    // For now, keep displaying splash screen using condition above.
+                                    // In the future, we might consider displaying something different here.
+                                }
+                                SecretState.None -> {
+                                    WrapOnboarding()
+                                }
+                                is SecretState.NeedsBackup -> {
+                                    WrapBackup(
+                                        secretState.persistableWallet,
+                                        onBackupComplete = { walletViewModel.persistBackupComplete() }
+                                    )
+                                }
+                                is SecretState.Ready -> {
+                                    Navigation()
+                                }
                             }
                         }
                     }

ui-lib/src/main/java/co/electriccoin/zcash/ui/common/ScreenSecurity.kt

@@ -0,0 +1,38 @@
+package co.electriccoin.zcash.ui.common
+
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.DisposableEffect
+import androidx.compose.runtime.compositionLocalOf
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.asStateFlow
+import kotlinx.coroutines.flow.update
+import kotlinx.coroutines.flow.updateAndGet
+
+class ScreenSecurity {
+    private val mutableReferenceCount: MutableStateFlow<Int> = MutableStateFlow(0)
+
+    val referenceCount = mutableReferenceCount.asStateFlow()
+
+    fun acquire() {
+        mutableReferenceCount.update { it + 1 }
+    }
+
+    fun release() {
+        val after = mutableReferenceCount.updateAndGet { it - 1 }
+
+        if (after < 0) {
+            error("Released security reference count too many times")
+        }
+    }
+}
+
+val LocalScreenSecurity = compositionLocalOf { ScreenSecurity() }
+
+@Composable
+fun SecureScreen() {
+    val screenSecurity = LocalScreenSecurity.current
+    DisposableEffect(screenSecurity) {
+        screenSecurity.acquire()
+        onDispose { screenSecurity.release() }
+    }
+}

ui-lib/src/main/java/co/electriccoin/zcash/ui/screen/backup/view/BackupView.kt

@@ -22,6 +22,7 @@ import cash.z.ecc.sdk.fixture.PersistableWalletFixture
 import cash.z.ecc.sdk.model.PersistableWallet
 import co.electriccoin.zcash.spackle.model.Index
 import co.electriccoin.zcash.ui.R
+import co.electriccoin.zcash.ui.common.SecureScreen
 import co.electriccoin.zcash.ui.design.MINIMAL_WEIGHT
 import co.electriccoin.zcash.ui.design.component.Body
 import co.electriccoin.zcash.ui.design.component.CHIP_GRID_ROW_SIZE
@@ -129,6 +130,7 @@ private fun EducationRecoveryPhrase(onNext: () -> Unit) {
 
 @Composable
 private fun SeedPhrase(persistableWallet: PersistableWallet, onNext: () -> Unit, onCopyToClipboard: () -> Unit) {
+    SecureScreen()
     Column(Modifier.verticalScroll(rememberScrollState())) {
         Header(stringResource(R.string.new_wallet_3_header))
         Body(stringResource(R.string.new_wallet_3_body_1))
@@ -153,6 +155,7 @@ private fun Test(
     onNext: () -> Unit,
     onChoicesChanged: ((choicesCount: Int) -> Unit)?
 ) {
+    SecureScreen()
     val splitSeedPhrase = wallet.seedPhrase.split
 
     val currentSelectedTestChoice = selectedTestChoices.current.collectAsState().value

ui-lib/src/main/java/co/electriccoin/zcash/ui/screen/restore/view/RestoreView.kt

@@ -53,6 +53,7 @@ import androidx.compose.ui.unit.dp
 import cash.z.ecc.sdk.model.SeedPhraseValidation
 import co.electriccoin.zcash.spackle.model.Index
 import co.electriccoin.zcash.ui.R
+import co.electriccoin.zcash.ui.common.SecureScreen
 import co.electriccoin.zcash.ui.design.MINIMAL_WEIGHT
 import co.electriccoin.zcash.ui.design.component.Body
 import co.electriccoin.zcash.ui.design.component.CHIP_GRID_ROW_SIZE
@@ -114,6 +115,7 @@ fun RestoreWallet(
     paste: () -> String?,
     onFinished: () -> Unit
 ) {
+    SecureScreen()
     userWordList.wordValidation().collectAsState(null).value?.let { seedPhraseValidation ->
         if (seedPhraseValidation !is SeedPhraseValidation.Valid) {
             Scaffold(topBar = {

ui-lib/src/main/java/co/electriccoin/zcash/ui/screen/seed/view/SeedView.kt

@@ -20,6 +20,7 @@ import androidx.compose.ui.tooling.preview.Preview
 import cash.z.ecc.sdk.fixture.PersistableWalletFixture
 import cash.z.ecc.sdk.model.PersistableWallet
 import co.electriccoin.zcash.ui.R
+import co.electriccoin.zcash.ui.common.SecureScreen
 import co.electriccoin.zcash.ui.design.component.Body
 import co.electriccoin.zcash.ui.design.component.ChipGrid
 import co.electriccoin.zcash.ui.design.component.GradientSurface
@@ -52,6 +53,7 @@ fun Seed(
     onBack: () -> Unit,
     onCopyToClipboard: () -> Unit
 ) {
+    SecureScreen()
     Scaffold(topBar = {
         SeedTopAppBar(onBack = onBack)
     }) { paddingValues ->