encryption_with_preference1.kt

companion object {
  private const val ALGORITHM = "AES"
  private const val MODE = "CBC"
  private const val PADDING = "PKCS5Padding"
}

fun savePrivateString(key: String, value: String) {
  prefs.edit().putString(key, encrypt(value)).apply()
}

fun getPrivateString(key: String): String {
  val encrypted = prefs.getString(key, "")
  return decrypt(encrypted)
}

private fun encrypt(plain: String): String {
  val cipher = initializeCipher(Cipher.ENCRYPT_MODE)
  val encrypted = cipher.doFinal(plain.toByteArray()) ?: byteArrayOf()  // TODO catch exception
  return Base64.encodeToString(encrypted, Base64.DEFAULT)
}

private fun decrypt(encrypted: String): String {
  val cipher = initializeCipher(Cipher.DECRYPT_MODE)
  val decrypted = cipher.doFinal(plain.toByteArray()) ?: byteArrayOf()  // TODO catch exception
  return String(decrypted)
}

private fun initializeCipher(mode: Int) = Cipher.getInstance("$ALGORITHM/$MODE/$PADDING").apply {
  val key = BuildConfig.CIPHER_KEY  // !!NOTICE!! Secret key is necessarry for encryption/decryption.
  val iv = BuildConfig.CIPHER_IV  // InitializationVector. 16bytes string.
  val secretKeySpec = SecretKeySpec(key.toByteArray(), ALGORITHM)
  val ivSpec = IvParameterSpec(iv.toByteArray())
  init(mode, secretKeySpec, ivSpec)
}