Split key concern out of storage plugin

This creates a KeyManager interface in the new core module which the storage module can use to get the key from.

app/src/main/java/com/stevesoltys/seedvault/crypto/KeyManager.kt

@@ -24,7 +24,7 @@ internal const val KEY_ALIAS_MAIN = "com.stevesoltys.seedvault.main"
 private const val KEY_ALGORITHM_BACKUP = "AES"
 private const val KEY_ALGORITHM_MAIN = "HmacSHA256"
 
-interface KeyManager {
+interface KeyManager : org.calyxos.seedvault.core.crypto.KeyManager {
     /**
      * Store a new backup key derived from the given [seed].
      *
@@ -57,14 +57,6 @@ interface KeyManager {
      * because the key can not leave the [KeyStore]'s hardware security module.
      */
     fun getBackupKey(): SecretKey
-
-    /**
-     * Returns the main key, so it can be used for deriving sub-keys.
-     *
-     * Note that any attempt to export the key will return null or an empty [ByteArray],
-     * because the key can not leave the [KeyStore]'s hardware security module.
-     */
-    fun getMainKey(): SecretKey
 }
 
 internal class KeyManagerImpl(

app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavFactory.kt

@@ -8,12 +8,10 @@ package com.stevesoltys.seedvault.plugins.webdav
 import android.annotation.SuppressLint
 import android.content.Context
 import android.provider.Settings
-import com.stevesoltys.seedvault.crypto.KeyManager
 import com.stevesoltys.seedvault.plugins.StoragePlugin
 
 class WebDavFactory(
     private val context: Context,
-    private val keyManager: KeyManager,
 ) {
 
     fun createAppStoragePlugin(config: WebDavConfig): StoragePlugin<WebDavConfig> {
@@ -27,7 +25,6 @@ class WebDavFactory(
         val androidId =
             Settings.Secure.getString(context.contentResolver, Settings.Secure.ANDROID_ID)
         return com.stevesoltys.seedvault.storage.WebDavStoragePlugin(
-            keyManager = keyManager,
             androidId = androidId,
             webDavConfig = config,
         )

app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavModule.kt

@@ -9,6 +9,6 @@ import org.koin.android.ext.koin.androidContext
 import org.koin.dsl.module
 
 val storagePluginModuleWebDav = module {
-    single { WebDavFactory(androidContext(), get()) }
+    single { WebDavFactory(androidContext()) }
     single { WebDavHandler(androidContext(), get(), get(), get()) }
 }

app/src/main/java/com/stevesoltys/seedvault/storage/SeedvaultSafStoragePlugin.kt

@@ -11,7 +11,6 @@ import com.stevesoltys.seedvault.crypto.KeyManager
 import com.stevesoltys.seedvault.getStorageContext
 import com.stevesoltys.seedvault.plugins.saf.DocumentsStorage
 import org.calyxos.backup.storage.plugin.saf.SafStoragePlugin
-import javax.crypto.SecretKey
 
 internal class SeedvaultSafStoragePlugin(
     private val appContext: Context,
@@ -24,6 +23,4 @@ internal class SeedvaultSafStoragePlugin(
     override val context: Context get() = appContext.getStorageContext { storage.safStorage.isUsb }
     override val root: DocumentFile get() = storage.rootBackupDir ?: error("No storage set")
 
-    override fun getMasterKey(): SecretKey = keyManager.getMainKey()
-    override fun hasMasterKey(): Boolean = keyManager.hasMainKey()
 }

app/src/main/java/com/stevesoltys/seedvault/storage/StorageModule.kt

@@ -5,10 +5,11 @@
 
 package com.stevesoltys.seedvault.storage
 
+import com.stevesoltys.seedvault.crypto.KeyManager
 import com.stevesoltys.seedvault.plugins.StoragePluginManager
 import org.calyxos.backup.storage.api.StorageBackup
 import org.koin.dsl.module
 
 val storageModule = module {
-    single { StorageBackup(get(), { get<StoragePluginManager>().filesPlugin }) }
+    single { StorageBackup(get(), { get<StoragePluginManager>().filesPlugin }, get<KeyManager>()) }
 }

app/src/main/java/com/stevesoltys/seedvault/storage/WebDavStoragePlugin.kt

@@ -11,7 +11,6 @@ import at.bitfire.dav4jvm.Response.HrefRelation.SELF
 import at.bitfire.dav4jvm.exception.NotFoundException
 import at.bitfire.dav4jvm.property.webdav.DisplayName
 import at.bitfire.dav4jvm.property.webdav.ResourceType
-import com.stevesoltys.seedvault.crypto.KeyManager
 import com.stevesoltys.seedvault.plugins.chunkFolderRegex
 import com.stevesoltys.seedvault.plugins.webdav.DIRECTORY_ROOT
 import com.stevesoltys.seedvault.plugins.webdav.WebDavConfig
@@ -26,12 +25,10 @@ import org.koin.core.time.measureDuration
 import java.io.IOException
 import java.io.InputStream
 import java.io.OutputStream
-import javax.crypto.SecretKey
 import kotlin.coroutines.resume
 import kotlin.coroutines.suspendCoroutine
 
 internal class WebDavStoragePlugin(
-    private val keyManager: KeyManager,
     /**
      * The result of Settings.Secure.getString(context.contentResolver, Settings.Secure.ANDROID_ID)
      */
@@ -121,9 +118,6 @@ internal class WebDavStoragePlugin(
         }
     }
 
-    override fun getMasterKey(): SecretKey = keyManager.getMainKey()
-    override fun hasMasterKey(): Boolean = keyManager.hasMainKey()
-
     @Throws(IOException::class)
     override suspend fun getChunkOutputStream(chunkId: String): OutputStream {
         val chunkFolderName = chunkId.substring(0, 2)

app/src/test/java/com/stevesoltys/seedvault/storage/WebDavStoragePluginTest.kt

@@ -5,12 +5,10 @@
 
 package com.stevesoltys.seedvault.storage
 
-import com.stevesoltys.seedvault.crypto.KeyManager
 import com.stevesoltys.seedvault.getRandomByteArray
 import com.stevesoltys.seedvault.getRandomString
 import com.stevesoltys.seedvault.plugins.webdav.WebDavTestConfig
 import com.stevesoltys.seedvault.transport.backup.BackupTest
-import io.mockk.mockk
 import kotlinx.coroutines.runBlocking
 import org.calyxos.backup.storage.api.StoredSnapshot
 import org.junit.Assert.assertArrayEquals
@@ -21,8 +19,7 @@ import java.io.IOException
 
 internal class WebDavStoragePluginTest : BackupTest() {
 
-    private val keyManager: KeyManager = mockk()
+    private val plugin = WebDavStoragePlugin("foo", WebDavTestConfig.getConfig())
-    private val plugin = WebDavStoragePlugin(keyManager, "foo", WebDavTestConfig.getConfig())
 
     private val snapshot = StoredSnapshot("foo.sv", System.currentTimeMillis())
 
@@ -85,7 +82,7 @@ internal class WebDavStoragePluginTest : BackupTest() {
             )
 
             // other device writes another snapshot
-            val otherPlugin = WebDavStoragePlugin(keyManager, "bar", WebDavTestConfig.getConfig())
+            val otherPlugin = WebDavStoragePlugin("bar", WebDavTestConfig.getConfig())
             val otherSnapshot = StoredSnapshot("bar.sv", System.currentTimeMillis())
             val otherSnapshotBytes = getRandomByteArray()
             assertEquals(emptyList<String>(), otherPlugin.getAvailableChunkIds())
@@ -110,7 +107,6 @@ internal class WebDavStoragePluginTest : BackupTest() {
     @Test
     fun `test missing root dir`() = runBlocking {
         val plugin = WebDavStoragePlugin(
-            keyManager = keyManager,
             androidId = "foo",
             webDavConfig = WebDavTestConfig.getConfig(),
             root = getRandomString(),

core/src/main/java/org/calyxos/seedvault/core/crypto/KeyManager.kt

@@ -0,0 +1,19 @@
+/*
+ * SPDX-FileCopyrightText: 2024 The Calyx Institute
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package org.calyxos.seedvault.core.crypto
+
+import java.security.KeyStore
+import javax.crypto.SecretKey
+
+public interface KeyManager {
+    /**
+     * Returns the main key, so it can be used for deriving sub-keys.
+     *
+     * Note that any attempt to export the key will return null or an empty [ByteArray],
+     * because the key can not leave the [KeyStore]'s hardware security module.
+     */
+    public fun getMainKey(): SecretKey
+}

storage/demo/build.gradle.kts

@@ -69,6 +69,7 @@ android {
 }
 
 dependencies {
+    implementation(project(":core"))
     implementation(project(":storage:lib"))
 
     implementation(libs.bundles.kotlin)

storage/demo/src/main/java/de/grobox/storagebackuptester/App.kt

@@ -9,6 +9,7 @@ import android.app.Application
 import android.os.StrictMode
 import android.os.StrictMode.VmPolicy
 import android.util.Log
+import de.grobox.storagebackuptester.crypto.KeyManager
 import de.grobox.storagebackuptester.plugin.TestSafStoragePlugin
 import de.grobox.storagebackuptester.settings.SettingsManager
 import org.calyxos.backup.storage.api.StorageBackup
@@ -19,7 +20,7 @@ class App : Application() {
     val settingsManager: SettingsManager by lazy { SettingsManager(applicationContext) }
     val storageBackup: StorageBackup by lazy {
         val plugin = TestSafStoragePlugin(this) { settingsManager.getBackupLocation() }
-        StorageBackup(this, { plugin })
+        StorageBackup(this, { plugin }, KeyManager)
     }
     val fileSelectionManager: FileSelectionManager get() = FileSelectionManager()
 

storage/demo/src/main/java/de/grobox/storagebackuptester/MainActivity.kt

@@ -24,7 +24,7 @@ class MainActivity : AppCompatActivity() {
 
         KeyManager.storeMasterKey()
 
-        if (!KeyManager.hasMasterKey()) {
+        if (!KeyManager.hasMainKey()) {
             Log.e("TEST", "storing new key")
             KeyManager.storeMasterKey()
         } else {

storage/demo/src/main/java/de/grobox/storagebackuptester/crypto/KeyManager.kt

@@ -14,7 +14,7 @@ import java.security.KeyStore
 import javax.crypto.SecretKey
 import javax.crypto.spec.SecretKeySpec
 
-object KeyManager {
+object KeyManager: org.calyxos.seedvault.core.crypto.KeyManager {
 
     private const val KEY_SIZE = 256
     internal const val KEY_SIZE_BYTES = KEY_SIZE / 8
@@ -42,9 +42,9 @@ object KeyManager {
         keyStore.setEntry(KEY_ALIAS_MASTER, ksEntry, getKeyProtection())
     }
 
-    fun hasMasterKey(): Boolean = keyStore.containsAlias(KEY_ALIAS_MASTER)
+    fun hasMainKey(): Boolean = keyStore.containsAlias(KEY_ALIAS_MASTER)
 
-    fun getMasterKey(): SecretKey {
+    override fun getMainKey(): SecretKey {
         val ksEntry = keyStore.getEntry(KEY_ALIAS_MASTER, null) as KeyStore.SecretKeyEntry
         return ksEntry.secretKey
     }

storage/demo/src/main/java/de/grobox/storagebackuptester/plugin/TestSafStoragePlugin.kt

@@ -8,13 +8,10 @@ package de.grobox.storagebackuptester.plugin
 import android.content.Context
 import android.net.Uri
 import androidx.documentfile.provider.DocumentFile
-import de.grobox.storagebackuptester.crypto.KeyManager
 import org.calyxos.backup.storage.plugin.saf.SafStoragePlugin
 import java.io.IOException
 import java.io.OutputStream
-import javax.crypto.SecretKey
 
-@Suppress("BlockingMethodInNonBlockingContext")
 class TestSafStoragePlugin(
     appContext: Context,
     private val getLocationUri: () -> Uri?,
@@ -33,14 +30,6 @@ class TestSafStoragePlugin(
         }
     }
 
-    override fun getMasterKey(): SecretKey {
-        return KeyManager.getMasterKey()
-    }
-
-    override fun hasMasterKey(): Boolean {
-        return KeyManager.hasMasterKey()
-    }
-
     @Throws(IOException::class)
     override suspend fun getChunkOutputStream(chunkId: String): OutputStream {
         if (getLocationUri() == null) return nullStream

storage/lib/build.gradle.kts

@@ -81,6 +81,7 @@ android {
 }
 
 dependencies {
+    implementation(project(":core"))
     implementation(libs.bundles.kotlin)
     implementation(libs.androidx.core)
     implementation(libs.androidx.fragment)

storage/lib/src/main/java/org/calyxos/backup/storage/api/StorageBackup.kt

@@ -31,6 +31,7 @@ import org.calyxos.backup.storage.scanner.DocumentScanner
 import org.calyxos.backup.storage.scanner.FileScanner
 import org.calyxos.backup.storage.scanner.MediaScanner
 import org.calyxos.backup.storage.toStoredUri
+import org.calyxos.seedvault.core.crypto.KeyManager
 import java.io.IOException
 import java.util.concurrent.atomic.AtomicBoolean
 
@@ -39,6 +40,7 @@ private const val TAG = "StorageBackup"
 public class StorageBackup(
     private val context: Context,
     private val pluginGetter: () -> StoragePlugin,
+    private val keyManager: KeyManager,
     private val dispatcher: CoroutineDispatcher = Dispatchers.IO,
 ) {
 
@@ -54,13 +56,16 @@ public class StorageBackup(
     private val backup by lazy {
         val documentScanner = DocumentScanner(context)
         val fileScanner = FileScanner(uriStore, mediaScanner, documentScanner)
-        Backup(context, db, fileScanner, pluginGetter, chunksCacheRepopulater)
+        Backup(context, db, fileScanner, pluginGetter, keyManager, chunksCacheRepopulater)
     }
     private val restore by lazy {
-        Restore(context, pluginGetter, snapshotRetriever, FileRestore(context, mediaScanner))
+        val fileRestore = FileRestore(context, mediaScanner)
+        Restore(context, pluginGetter, keyManager, snapshotRetriever, fileRestore)
     }
     private val retention = RetentionManager(context)
-    private val pruner by lazy { Pruner(db, retention, pluginGetter, snapshotRetriever) }
+    private val pruner by lazy {
+        Pruner(db, retention, pluginGetter, keyManager, snapshotRetriever)
+    }
 
     private val backupRunning = AtomicBoolean(false)
     private val restoreRunning = AtomicBoolean(false)

storage/lib/src/main/java/org/calyxos/backup/storage/api/StoragePlugin.kt

@@ -8,8 +8,6 @@ package org.calyxos.backup.storage.api
 import java.io.IOException
 import java.io.InputStream
 import java.io.OutputStream
-import java.security.KeyStore
-import javax.crypto.SecretKey
 
 public interface StoragePlugin {
 
@@ -28,16 +26,6 @@ public interface StoragePlugin {
     @Throws(IOException::class)
     public suspend fun getAvailableChunkIds(): List<String>
 
-    /**
-     * Returns a [SecretKey] for HmacSHA256, ideally stored in the [KeyStore].
-     */
-    public fun getMasterKey(): SecretKey
-
-    /**
-     * Returns true if the key for [getMasterKey] exists, false otherwise.
-     */
-    public fun hasMasterKey(): Boolean
-
     @Throws(IOException::class)
     public suspend fun getChunkOutputStream(chunkId: String): OutputStream
 
@@ -48,8 +36,7 @@ public interface StoragePlugin {
 
     /**
      * Returns *all* [StoredSnapshot]s that are available on storage
-     * independent of user ID and whether they can be decrypted
+     * independent of user ID and whether they can be decrypted with the main key.
-     * with the key returned by [getMasterKey].
      */
     @Throws(IOException::class)
     public suspend fun getBackupSnapshotsForRestore(): List<StoredSnapshot>

storage/lib/src/main/java/org/calyxos/backup/storage/backup/Backup.kt

@@ -19,6 +19,7 @@ import org.calyxos.backup.storage.db.Db
 import org.calyxos.backup.storage.measure
 import org.calyxos.backup.storage.scanner.FileScanner
 import org.calyxos.backup.storage.scanner.FileScannerResult
+import org.calyxos.seedvault.core.crypto.KeyManager
 import java.io.IOException
 import java.security.GeneralSecurityException
 import kotlin.time.Duration
@@ -42,6 +43,7 @@ internal class Backup(
     private val db: Db,
     private val fileScanner: FileScanner,
     private val storagePluginGetter: () -> StoragePlugin,
+    keyManager: KeyManager,
     private val cacheRepopulater: ChunksCacheRepopulater,
     chunkSizeMax: Int = CHUNK_SIZE_MAX,
     private val streamCrypto: StreamCrypto = StreamCrypto,
@@ -60,12 +62,12 @@ internal class Backup(
     private val chunksCache = db.getChunksCache()
 
     private val mac = try {
-        ChunkCrypto.getMac(ChunkCrypto.deriveChunkIdKey(storagePlugin.getMasterKey()))
+        ChunkCrypto.getMac(ChunkCrypto.deriveChunkIdKey(keyManager.getMainKey()))
     } catch (e: GeneralSecurityException) {
         throw AssertionError(e)
     }
     private val streamKey = try {
-        streamCrypto.deriveStreamKey(storagePlugin.getMasterKey())
+        streamCrypto.deriveStreamKey(keyManager.getMainKey())
     } catch (e: GeneralSecurityException) {
         throw AssertionError(e)
     }

storage/lib/src/main/java/org/calyxos/backup/storage/prune/Pruner.kt

@@ -13,6 +13,7 @@ import org.calyxos.backup.storage.crypto.StreamCrypto
 import org.calyxos.backup.storage.db.Db
 import org.calyxos.backup.storage.measure
 import org.calyxos.backup.storage.plugin.SnapshotRetriever
+import org.calyxos.seedvault.core.crypto.KeyManager
 import java.io.IOException
 import java.security.GeneralSecurityException
 import kotlin.time.ExperimentalTime
@@ -23,6 +24,7 @@ internal class Pruner(
     private val db: Db,
     private val retentionManager: RetentionManager,
     private val storagePluginGetter: () -> StoragePlugin,
+    keyManager: KeyManager,
     private val snapshotRetriever: SnapshotRetriever,
     streamCrypto: StreamCrypto = StreamCrypto,
 ) {
@@ -30,7 +32,7 @@ internal class Pruner(
     private val storagePlugin get() = storagePluginGetter()
     private val chunksCache = db.getChunksCache()
     private val streamKey = try {
-        streamCrypto.deriveStreamKey(storagePlugin.getMasterKey())
+        streamCrypto.deriveStreamKey(keyManager.getMainKey())
     } catch (e: GeneralSecurityException) {
         throw AssertionError(e)
     }

storage/lib/src/main/java/org/calyxos/backup/storage/restore/Restore.kt

@@ -19,6 +19,7 @@ import org.calyxos.backup.storage.backup.BackupSnapshot
 import org.calyxos.backup.storage.crypto.StreamCrypto
 import org.calyxos.backup.storage.measure
 import org.calyxos.backup.storage.plugin.SnapshotRetriever
+import org.calyxos.seedvault.core.crypto.KeyManager
 import java.io.IOException
 import java.io.InputStream
 import java.security.GeneralSecurityException
@@ -28,6 +29,7 @@ private const val TAG = "Restore"
 internal class Restore(
     context: Context,
     private val storagePluginGetter: () -> StoragePlugin,
+    private val keyManager: KeyManager,
     private val snapshotRetriever: SnapshotRetriever,
     fileRestore: FileRestore,
     streamCrypto: StreamCrypto = StreamCrypto,
@@ -39,7 +41,7 @@ internal class Restore(
         // so we need to get it lazily here to prevent crashes. We can still crash later,
         // if the plugin is not providing a key as it should when performing calls into this class.
         try {
-            streamCrypto.deriveStreamKey(storagePlugin.getMasterKey())
+            streamCrypto.deriveStreamKey(keyManager.getMainKey())
         } catch (e: GeneralSecurityException) {
             throw AssertionError(e)
         }

storage/lib/src/test/java/org/calyxos/backup/storage/BackupRestoreTest.kt

@@ -46,6 +46,7 @@ import org.calyxos.backup.storage.restore.RestorableFile
 import org.calyxos.backup.storage.restore.Restore
 import org.calyxos.backup.storage.scanner.FileScanner
 import org.calyxos.backup.storage.scanner.FileScannerResult
+import org.calyxos.seedvault.core.crypto.KeyManager
 import org.junit.Assert.assertArrayEquals
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertTrue
@@ -71,6 +72,7 @@ internal class BackupRestoreTest {
 
     private val fileScanner: FileScanner = mockk()
     private val pluginGetter: () -> StoragePlugin = mockk()
+    private val keyManager: KeyManager = mockk()
     private val plugin: StoragePlugin = mockk()
     private val fileRestore: FileRestore = mockk()
     private val snapshotRetriever = SnapshotRetriever(pluginGetter)
@@ -87,7 +89,7 @@ internal class BackupRestoreTest {
         every { pluginGetter() } returns plugin
         every { db.getFilesCache() } returns filesCache
         every { db.getChunksCache() } returns chunksCache
-        every { plugin.getMasterKey() } returns SecretKeySpec(
+        every { keyManager.getMainKey() } returns SecretKeySpec(
             "This is a backup key for testing".toByteArray(),
             0, KEY_SIZE_BYTES, ALGORITHM_HMAC
         )
@@ -95,11 +97,11 @@ internal class BackupRestoreTest {
         every { context.contentResolver } returns contentResolver
     }
 
-    private val restore = Restore(context, pluginGetter, snapshotRetriever, fileRestore)
+    private val restore = Restore(context, pluginGetter, keyManager, snapshotRetriever, fileRestore)
 
     @Test
     fun testZipAndSingleRandom(): Unit = runBlocking {
-        val backup = Backup(context, db, fileScanner, pluginGetter, cacheRepopulater)
+        val backup = Backup(context, db, fileScanner, pluginGetter, keyManager, cacheRepopulater)
 
         val smallFileMBytes = Random.nextBytes(Random.nextInt(SMALL_FILE_SIZE_MAX))
         val smallFileM = getRandomMediaFile(smallFileMBytes.size)
@@ -236,7 +238,8 @@ internal class BackupRestoreTest {
 
     @Test
     fun testMultiChunks(): Unit = runBlocking {
-        val backup = Backup(context, db, fileScanner, pluginGetter, cacheRepopulater, 4)
+        val backup =
+            Backup(context, db, fileScanner, pluginGetter, keyManager, cacheRepopulater, 4)
 
         val chunk1 = byteArrayOf(0x00, 0x01, 0x02, 0x03)
         val chunk2 = byteArrayOf(0x04, 0x05, 0x06, 0x07)

storage/lib/src/test/java/org/calyxos/backup/storage/prune/PrunerTest.kt

@@ -26,6 +26,7 @@ import org.calyxos.backup.storage.db.Db
 import org.calyxos.backup.storage.getRandomString
 import org.calyxos.backup.storage.mockLog
 import org.calyxos.backup.storage.plugin.SnapshotRetriever
+import org.calyxos.seedvault.core.crypto.KeyManager
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertTrue
 import org.junit.Test
@@ -37,6 +38,7 @@ internal class PrunerTest {
     private val db: Db = mockk()
     private val chunksCache: ChunksCache = mockk()
     private val pluginGetter: () -> StoragePlugin = mockk()
+    private val keyManager: KeyManager = mockk()
     private val plugin: StoragePlugin = mockk()
     private val snapshotRetriever: SnapshotRetriever = mockk()
     private val retentionManager: RetentionManager = mockk()
@@ -48,11 +50,12 @@ internal class PrunerTest {
         mockLog(false)
         every { pluginGetter() } returns plugin
         every { db.getChunksCache() } returns chunksCache
-        every { plugin.getMasterKey() } returns masterKey
+        every { keyManager.getMainKey() } returns masterKey
         every { streamCrypto.deriveStreamKey(masterKey) } returns streamKey
     }
 
-    private val pruner = Pruner(db, retentionManager, pluginGetter, snapshotRetriever, streamCrypto)
+    private val pruner =
+        Pruner(db, retentionManager, pluginGetter, keyManager, snapshotRetriever, streamCrypto)
 
     @Test
     fun test() = runBlocking {