Add encrypted notification log storage foundation
This commit is contained in:
ajp_anton
@@ -0,0 +1,43 @@
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package se.ajpanton.notificationlog.data
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import java.security.SecureRandom
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import javax.crypto.Cipher
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import javax.crypto.SecretKey
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import javax.crypto.spec.GCMParameterSpec
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/** Small, format-neutral AES-GCM codec used for every persisted log payload. */
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class AesGcmCipher(
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private val key: SecretKey,
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private val secureRandom: SecureRandom = SecureRandom(),
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) {
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fun encrypt(plainText: ByteArray): EncryptedPayload {
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val initializationVector = ByteArray(IV_LENGTH_BYTES).also(secureRandom::nextBytes)
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val cipher = Cipher.getInstance(TRANSFORMATION)
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cipher.init(Cipher.ENCRYPT_MODE, key, GCMParameterSpec(TAG_LENGTH_BITS, initializationVector))
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return EncryptedPayload(initializationVector, cipher.doFinal(plainText))
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}
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fun decrypt(payload: EncryptedPayload): ByteArray {
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require(payload.initializationVector.size == IV_LENGTH_BYTES) {
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"Unexpected AES-GCM initialization-vector length."
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}
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val cipher = Cipher.getInstance(TRANSFORMATION)
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cipher.init(
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Cipher.DECRYPT_MODE,
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key,
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GCMParameterSpec(TAG_LENGTH_BITS, payload.initializationVector),
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)
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return cipher.doFinal(payload.cipherText)
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}
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companion object {
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private const val TRANSFORMATION = "AES/GCM/NoPadding"
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private const val IV_LENGTH_BYTES = 12
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private const val TAG_LENGTH_BITS = 128
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}
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}
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data class EncryptedPayload(
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val initializationVector: ByteArray,
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val cipherText: ByteArray,
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)
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@@ -0,0 +1,83 @@
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package se.ajpanton.notificationlog.data
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import android.content.Context
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import android.util.AtomicFile
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import se.ajpanton.notificationlog.model.NotificationLogEntry
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import java.io.BufferedInputStream
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import java.io.BufferedOutputStream
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import java.io.DataInputStream
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import java.io.DataOutputStream
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import java.io.FileNotFoundException
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/**
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* An atomically replaced encrypted event log. It keeps every persisted log field
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* encrypted, including timestamps and package names, while the app is at rest.
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*/
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class EncryptedNotificationLogStore(context: Context) {
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private val lock = Any()
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private val file = AtomicFile(context.filesDir.resolve(FILE_NAME))
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private val cipher = AesGcmCipher(LogEncryptionKeyProvider().getOrCreate())
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fun readAll(): List<NotificationLogEntry> = synchronized(lock) {
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val payload = readPayloadOrNull() ?: return emptyList()
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NotificationLogEntryJson.decode(cipher.decrypt(payload))
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}
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fun append(entry: NotificationLogEntry) = synchronized(lock) {
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val entries = (readPayloadOrNull()?.let { NotificationLogEntryJson.decode(cipher.decrypt(it)) } ?: emptyList())
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write(entries + entry)
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}
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fun replaceAll(entries: List<NotificationLogEntry>) = synchronized(lock) {
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write(entries)
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}
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fun clear() = synchronized(lock) {
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file.delete()
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}
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private fun write(entries: List<NotificationLogEntry>) {
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val payload = cipher.encrypt(NotificationLogEntryJson.encode(entries))
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val output = file.startWrite()
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try {
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DataOutputStream(BufferedOutputStream(output)).use { stream ->
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stream.writeInt(FILE_VERSION)
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stream.writeInt(payload.initializationVector.size)
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stream.write(payload.initializationVector)
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stream.writeInt(payload.cipherText.size)
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stream.write(payload.cipherText)
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}
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file.finishWrite(output)
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} catch (error: Exception) {
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file.failWrite(output)
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throw error
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}
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}
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private fun readPayloadOrNull(): EncryptedPayload? {
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val input = try {
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file.openRead()
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} catch (_: FileNotFoundException) {
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return null
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}
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DataInputStream(BufferedInputStream(input)).use { stream ->
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require(stream.readInt() == FILE_VERSION) { "Unsupported encrypted notification-log version." }
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val initializationVector = readByteArray(stream, MAX_IV_BYTES)
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val cipherText = readByteArray(stream, MAX_CIPHER_TEXT_BYTES)
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return EncryptedPayload(initializationVector, cipherText)
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}
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}
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private fun readByteArray(stream: DataInputStream, maximumLength: Int): ByteArray {
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val length = stream.readInt()
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require(length in 1..maximumLength) { "Invalid encrypted notification-log field length." }
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return ByteArray(length).also(stream::readFully)
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}
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private companion object {
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const val FILE_NAME = "notification-log.v1"
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const val FILE_VERSION = 1
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const val MAX_IV_BYTES = 32
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const val MAX_CIPHER_TEXT_BYTES = 50 * 1024 * 1024
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}
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}
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@@ -0,0 +1,34 @@
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package se.ajpanton.notificationlog.data
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import android.security.keystore.KeyGenParameterSpec
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import android.security.keystore.KeyProperties
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import java.security.KeyStore
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import javax.crypto.KeyGenerator
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import javax.crypto.SecretKey
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/** Creates a non-exportable key in Android Keystore; it is never written into app storage. */
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class LogEncryptionKeyProvider {
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fun getOrCreate(): SecretKey {
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val keyStore = KeyStore.getInstance(ANDROID_KEY_STORE).apply { load(null) }
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(keyStore.getKey(KEY_ALIAS, null) as? SecretKey)?.let { return it }
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return KeyGenerator.getInstance(KeyProperties.KEY_ALGORITHM_AES, ANDROID_KEY_STORE).run {
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init(
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KeyGenParameterSpec.Builder(
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KEY_ALIAS,
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KeyProperties.PURPOSE_ENCRYPT or KeyProperties.PURPOSE_DECRYPT,
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)
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.setBlockModes(KeyProperties.BLOCK_MODE_GCM)
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.setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_NONE)
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.setRandomizedEncryptionRequired(true)
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.build(),
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)
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generateKey()
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}
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}
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private companion object {
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const val ANDROID_KEY_STORE = "AndroidKeyStore"
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const val KEY_ALIAS = "notification_log_storage_key_v1"
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}
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}
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@@ -0,0 +1,38 @@
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package se.ajpanton.notificationlog.data
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import org.json.JSONArray
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import org.json.JSONObject
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import se.ajpanton.notificationlog.model.NotificationAction
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import se.ajpanton.notificationlog.model.NotificationLogEntry
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/** Versioned, private plaintext representation which is encrypted before it reaches disk. */
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object NotificationLogEntryJson {
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fun encode(entries: List<NotificationLogEntry>): ByteArray = JSONArray().apply {
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entries.forEach { entry ->
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put(
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JSONObject()
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.put("id", entry.id)
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.put("recordedAtEpochMillis", entry.recordedAtEpochMillis)
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.put("packageName", entry.packageName)
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.put("appName", entry.appName)
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.put("action", entry.action.name)
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.put("contents", entry.contents),
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)
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}
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}.toString().encodeToByteArray()
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fun decode(serialized: ByteArray): List<NotificationLogEntry> {
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val array = JSONArray(serialized.decodeToString())
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return List(array.length()) { index ->
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val entry = array.getJSONObject(index)
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NotificationLogEntry(
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id = entry.getString("id"),
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recordedAtEpochMillis = entry.getLong("recordedAtEpochMillis"),
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packageName = entry.getString("packageName"),
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appName = entry.getString("appName"),
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action = NotificationAction.valueOf(entry.getString("action")),
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contents = if (entry.isNull("contents")) null else entry.getString("contents"),
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)
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}
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}
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}
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