BDOMDev

@Throws(Exception::class)
fun encrypt(yourKey: SecretKey, fileData: ByteArray): ByteArray {
     val data = yourKey.getEncoded()
     val skeySpec = SecretKeySpec(data, 0, data.size, "AES")
     val cipher = Cipher.getInstance("AES", "BC")
     cipher.init(Cipher.ENCRYPT_MODE, skeySpec, IvParameterSpec(ByteArray(cipher.getBlockSize())))
     return cipher.doFinal(fileData)
}

BDOMDev

 @Throws(Exception::class)
 fun generateSecretKey(): SecretKey? {
     val secureRandom = SecureRandom()
     val keyGenerator = KeyGenerator.getInstance("AES")
     //generate a key with secure random
     keyGenerator?.init(128, secureRandom)
     return keyGenerator?.generateKey()
}

BDOMDev

fun saveSecretKey(sharedPref: SharedPreferences, secretKey: SecretKey): String {
      val encodedKey = Base64.encodeToString(secretKey.encoded, Base64.NO_WRAP)
      sharedPref.edit().putString(AppConstants.secretKeyPref, encodedKey).apply()
      return encodedKey
}

BDOMDev

@Throws(Exception::class)
fun readFile(filePath: String): ByteArray {
     val file = File(filePath)
     val fileContents = file.readBytes()
     val inputBuffer = BufferedInputStream(
         FileInputStream(file)
     )

     inputBuffer.read(fileContents)
     inputBuffer.close()

BDOMDev

@Throws(Exception::class)
fun saveFile(fileData: ByteArray, path: String) {
    val file = File(path)
    val bos = BufferedOutputStream(FileOutputStream(file, false))
    bos.write(fileData)
    bos.flush()
    bos.close()
}

BDOMDev

fun encryptDownloadedFile(filePath: String) {
    val fileData = readFile(filePath)
    val secretKey = getSecretKey(sharedPref)
    val encodedData = encode(secretKey, fileData)
    saveFile(encodedData, filePath)
}

BDOMDev

fun encryptDownloadedFile() {
    try {
        val filePath = filesDir.absolutePath + "/filename"
        val fileData = readFile(filePath)

        //get secret key
        val secretKey = getSecretKey(sharedPref)
        //encrypt file
        val encodedData = encrypt(secretKey, fileData)

BDOMDev

    fun getSecretKey(sharedPref: SharedPreferences): SecretKey {

        val key = sharedPref.getString(AppConstants.secretKeyPref, null)

        if (key == null) {
            //generate secure random
            val secretKey = generateSecreKey()
            saveSecretKey(sharedPref, secretKey!!)
            return secretKey
        }

BDOMDev

@Throws(Exception::class)
fun decrypt(yourKey: SecretKey, fileData: ByteArray): ByteArray {
     val decrypted: ByteArray
     val cipher = Cipher.getInstance("AES", "BC")
     cipher.init(Cipher.DECRYPT_MODE, yourKey, IvParameterSpec(ByteArray(cipher.blockSize)))
     decrypted = cipher.doFinal(fileData)
     return decrypted
}

BDOMDev

    private fun decryptEncryptedFile(): ByteArray {
        val filePath = filesDir.absolutePath + "/filename"
        val fileData = readFile(filePath)
        val secretKey = getSecretKey(sharedPref)
        return decode(secretKey, fileData)
    }