feat(security): replace CleartextKeysetHandle with AndroidKeysetManager (#105)
- Extract PrivateKeysetStore interface for testability - Add AndroidKeystorePrivateKeysetStore (Android Keystore-backed AEAD) - Refactor E2EEKeyManager to use PrivateKeysetStore - Add legacy migration: old cleartext key is removed, forcing re-generation - Update DI module to provide AndroidKeystorePrivateKeysetStore - Adapt unit tests with FakePrivateKeysetStore + migration test Private key material no longer appears as cleartext JSON on the JVM heap. Existing devices with legacy keys will re-generate and re-upload via EnsureKeyPairUseCase on next app launch.
This commit is contained in:
Jens Reinemann
parent
10cb474906
commit
8e7352dcc4
5 changed files with 143 additions and 18 deletions
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@ -0,0 +1,40 @@
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package de.bollwerk.app.data.security
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import android.content.Context
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import com.google.crypto.tink.KeyTemplates
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import com.google.crypto.tink.KeysetHandle
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import com.google.crypto.tink.integration.android.AndroidKeysetManager
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/// Stores the private Tink keyset encrypted via Android Keystore.
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/// The raw key material never appears as cleartext on the JVM heap.
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internal class AndroidKeystorePrivateKeysetStore(
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private val context: Context
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) : PrivateKeysetStore {
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override fun hasKeyset(): Boolean {
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val prefs = context.getSharedPreferences(PREF_FILE_NAME, Context.MODE_PRIVATE)
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return prefs.contains(KEYSET_NAME)
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}
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override fun getKeysetHandle(): KeysetHandle =
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AndroidKeysetManager.Builder()
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.withSharedPref(context, KEYSET_NAME, PREF_FILE_NAME)
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.withMasterKeyUri(MASTER_KEY_URI)
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.build()
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.keysetHandle
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override fun generateAndStoreKeyset(): KeysetHandle =
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AndroidKeysetManager.Builder()
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.withSharedPref(context, KEYSET_NAME, PREF_FILE_NAME)
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.withKeyTemplate(KeyTemplates.get(KEY_TEMPLATE))
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.withMasterKeyUri(MASTER_KEY_URI)
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.build()
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.keysetHandle
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private companion object {
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const val PREF_FILE_NAME = "bollwerk_e2ee_keyset_prefs"
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const val KEYSET_NAME = "bollwerk_e2ee_private_keyset"
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const val MASTER_KEY_URI = "android-keystore://bollwerk_e2ee_master_key"
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const val KEY_TEMPLATE = "DHKEM_X25519_HKDF_SHA256_HKDF_SHA256_CHACHA20_POLY1305"
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}
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}
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@ -1,11 +1,11 @@
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package de.bollwerk.app.data.security
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import android.util.Log
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import com.google.crypto.tink.CleartextKeysetHandle
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import com.google.crypto.tink.HybridDecrypt
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import com.google.crypto.tink.HybridEncrypt
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import com.google.crypto.tink.JsonKeysetReader
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import com.google.crypto.tink.JsonKeysetWriter
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import com.google.crypto.tink.KeyTemplates
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import com.google.crypto.tink.KeysetHandle
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import com.google.crypto.tink.hybrid.HybridConfig
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import de.bollwerk.app.domain.model.SettingsKey.StringKey
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@ -16,25 +16,22 @@ import javax.inject.Singleton
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@Singleton
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internal class E2EEKeyManager @Inject constructor(
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private val privateKeysetStore: PrivateKeysetStore,
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private val secureStorage: SecureTokenStorage
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) {
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init {
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HybridConfig.register()
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migrateFromLegacyIfNeeded()
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}
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fun hasKeyPair(): Boolean =
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secureStorage.get(StringKey.E2EEPrivateKeyset.key) != null
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fun hasKeyPair(): Boolean = privateKeysetStore.hasKeyset()
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fun generateAndStoreKeyPair() {
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val template = KeyTemplates.get("DHKEM_X25519_HKDF_SHA256_HKDF_SHA256_CHACHA20_POLY1305")
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val privateHandle = KeysetHandle.generateNew(template)
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val privateKeysetJson = serializeKeysetToJson(privateHandle)
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secureStorage.set(StringKey.E2EEPrivateKeyset.key, privateKeysetJson)
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val privateHandle = privateKeysetStore.generateAndStoreKeyset()
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val publicHandle = privateHandle.publicKeysetHandle
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val publicKeysetJson = serializeKeysetToJson(publicHandle)
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val publicKeysetJson = serializePublicKeyToJson(publicHandle)
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val publicKeyBase64 = Base64.getEncoder().encodeToString(
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publicKeysetJson.toByteArray(Charsets.UTF_8)
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)
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@ -49,28 +46,45 @@ internal class E2EEKeyManager @Inject constructor(
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Base64.getDecoder().decode(recipientPublicKeyBase64),
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Charsets.UTF_8
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)
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val publicHandle = deserializeKeysetFromJson(publicKeysetJson)
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val publicHandle = deserializePublicKeyFromJson(publicKeysetJson)
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val hybridEncrypt = publicHandle.getPrimitive(HybridEncrypt::class.java)
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val ciphertext = hybridEncrypt.encrypt(plaintext.toByteArray(Charsets.UTF_8), null)
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return Base64.getEncoder().encodeToString(ciphertext)
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}
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fun decryptMessage(ciphertextBase64: String): String {
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val privateKeysetJson = secureStorage.get(StringKey.E2EEPrivateKeyset.key)
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?: throw IllegalStateException("E2EE: No private key available for decryption")
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val privateHandle = deserializeKeysetFromJson(privateKeysetJson)
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val privateHandle = privateKeysetStore.getKeysetHandle()
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val hybridDecrypt = privateHandle.getPrimitive(HybridDecrypt::class.java)
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val ciphertext = Base64.getDecoder().decode(ciphertextBase64)
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val plaintextBytes = hybridDecrypt.decrypt(ciphertext, null)
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return String(plaintextBytes, Charsets.UTF_8)
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}
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private fun serializeKeysetToJson(handle: KeysetHandle): String {
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/// Detects legacy cleartext private key in SecureTokenStorage and removes it.
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/// The key cannot be imported into AndroidKeysetManager, so hasKeyPair() returns false
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/// afterwards, triggering re-generation + server upload via EnsureKeyPairUseCase.
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private fun migrateFromLegacyIfNeeded() {
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if (secureStorage.get(StringKey.E2EEPrivateKeyset.key) == null) return
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if (!privateKeysetStore.hasKeyset()) {
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Log.i(TAG, "E2EE: Legacy cleartext private key detected – will be re-generated")
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}
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// Remove legacy cleartext key regardless – it must not persist
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secureStorage.remove(StringKey.E2EEPrivateKeyset.key)
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// Remove stale public key so it gets re-generated and re-uploaded
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secureStorage.remove(StringKey.E2EEPublicKeyBase64.key)
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}
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private fun serializePublicKeyToJson(handle: KeysetHandle): String {
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val outputStream = ByteArrayOutputStream()
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CleartextKeysetHandle.write(handle, JsonKeysetWriter.withOutputStream(outputStream))
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return outputStream.toString(Charsets.UTF_8.name())
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}
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private fun deserializeKeysetFromJson(json: String): KeysetHandle =
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private fun deserializePublicKeyFromJson(json: String): KeysetHandle =
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CleartextKeysetHandle.read(JsonKeysetReader.withString(json))
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private companion object {
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const val TAG = "E2EEKeyManager"
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}
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}
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@ -0,0 +1,16 @@
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package de.bollwerk.app.data.security
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import com.google.crypto.tink.KeysetHandle
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/// Abstraction for private keyset storage.
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/// Production uses Android Keystore; tests use in-memory storage.
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internal interface PrivateKeysetStore {
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/// Returns true if a private keyset has been stored.
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fun hasKeyset(): Boolean
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/// Returns the stored keyset handle. Throws if none exists.
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fun getKeysetHandle(): KeysetHandle
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/// Generates a new keyset, stores it, and returns the handle.
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fun generateAndStoreKeyset(): KeysetHandle
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}
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@ -6,7 +6,9 @@ import dagger.Provides
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import dagger.hilt.InstallIn
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import dagger.hilt.android.qualifiers.ApplicationContext
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import dagger.hilt.components.SingletonComponent
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import de.bollwerk.app.data.security.AndroidKeystorePrivateKeysetStore
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import de.bollwerk.app.data.security.EncryptedPrefsTokenStorage
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import de.bollwerk.app.data.security.PrivateKeysetStore
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import de.bollwerk.app.data.security.SecureTokenStorage
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import javax.inject.Singleton
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@ -18,4 +20,9 @@ internal object SecurityModule {
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@Singleton
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fun provideSecureTokenStorage(@ApplicationContext context: Context): SecureTokenStorage =
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EncryptedPrefsTokenStorage(context)
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@Provides
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@Singleton
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fun providePrivateKeysetStore(@ApplicationContext context: Context): PrivateKeysetStore =
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AndroidKeystorePrivateKeysetStore(context)
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}
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@ -1,5 +1,11 @@
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package de.bollwerk.app.data.security
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import com.google.crypto.tink.CleartextKeysetHandle
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import com.google.crypto.tink.JsonKeysetReader
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import com.google.crypto.tink.JsonKeysetWriter
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import com.google.crypto.tink.KeyTemplates
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import com.google.crypto.tink.KeysetHandle
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import com.google.crypto.tink.hybrid.HybridConfig
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import org.junit.Assert.assertEquals
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import org.junit.Assert.assertFalse
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import org.junit.Assert.assertNotEquals
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@ -7,21 +13,25 @@ import org.junit.Assert.assertNotNull
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import org.junit.Assert.assertTrue
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import org.junit.Before
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import org.junit.Test
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import java.io.ByteArrayOutputStream
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class E2EEKeyManagerTest {
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private lateinit var storage: FakeSecureTokenStorage
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private lateinit var privateKeysetStore: FakePrivateKeysetStore
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private lateinit var keyManager: E2EEKeyManager
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@Before
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fun setUp() {
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HybridConfig.register()
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storage = FakeSecureTokenStorage()
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keyManager = E2EEKeyManager(storage)
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privateKeysetStore = FakePrivateKeysetStore()
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keyManager = E2EEKeyManager(privateKeysetStore, storage)
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}
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@Test
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fun test_hasKeyPair_noKeyStored_returnsFalse() {
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// Given: empty storage
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// Given: empty store
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// When
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val result = keyManager.hasKeyPair()
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@ -77,7 +87,8 @@ class E2EEKeyManagerTest {
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fun test_decryptMessage_wrongKey_throwsException() {
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// Given: two separate key managers with different keys
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val storage2 = FakeSecureTokenStorage()
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val otherKeyManager = E2EEKeyManager(storage2)
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val store2 = FakePrivateKeysetStore()
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val otherKeyManager = E2EEKeyManager(store2, storage2)
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keyManager.generateAndStoreKeyPair()
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otherKeyManager.generateAndStoreKeyPair()
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@ -92,6 +103,27 @@ class E2EEKeyManagerTest {
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// Then: should throw an Exception
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keyManager.decryptMessage(encryptedForOther)
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}
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@Test
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fun test_migrateFromLegacy_removesOldCleartextKey() {
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// Given: legacy cleartext key stored in SecureTokenStorage
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val legacyHandle = KeysetHandle.generateNew(
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KeyTemplates.get("DHKEM_X25519_HKDF_SHA256_HKDF_SHA256_CHACHA20_POLY1305")
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)
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val out = ByteArrayOutputStream()
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CleartextKeysetHandle.write(legacyHandle, JsonKeysetWriter.withOutputStream(out))
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storage.set("e2ee_private_keyset", out.toString(Charsets.UTF_8.name()))
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storage.set("e2ee_public_key", "old_public_key_base64")
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// When: creating a new key manager triggers migration
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val freshStore = FakePrivateKeysetStore()
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val migratedManager = E2EEKeyManager(freshStore, storage)
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// Then: legacy keys are removed, hasKeyPair is false (forces re-generation)
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assertFalse(migratedManager.hasKeyPair())
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assertEquals(null, storage.get("e2ee_private_keyset"))
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assertEquals(null, storage.get("e2ee_public_key"))
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}
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}
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private class FakeSecureTokenStorage : SecureTokenStorage {
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@ -101,3 +133,19 @@ private class FakeSecureTokenStorage : SecureTokenStorage {
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override fun set(key: String, value: String) { store[key] = value }
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override fun remove(key: String) { store.remove(key) }
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}
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private class FakePrivateKeysetStore : PrivateKeysetStore {
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private var storedKeyset: KeysetHandle? = null
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override fun hasKeyset(): Boolean = storedKeyset != null
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override fun getKeysetHandle(): KeysetHandle =
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storedKeyset ?: throw IllegalStateException("No keyset stored")
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override fun generateAndStoreKeyset(): KeysetHandle {
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val template = KeyTemplates.get("DHKEM_X25519_HKDF_SHA256_HKDF_SHA256_CHACHA20_POLY1305")
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val handle = KeysetHandle.generateNew(template)
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storedKeyset = handle
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return handle
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}
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}
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