Decrypt a file in dart is taking an eternity to decrypt

[marcojr]

Give this simple scenario...

import 'package:dio/dio.dart';
import 'dart:io';
import 'package:flutter/material.dart';
import 'package:encrypt/encrypt.dart' as encrypt;
import 'package:path_provider/path_provider.dart';

    final dir = await getApplicationDocumentsDirectory();
    String newDir = '${dir.path}/myDir';
    await Directory(newDir).create(recursive: true);
    await Dio().download('https://www.marcojr.co.uk/tmp/encrypted.mp3', '${dir.path}/encrypted.mp3');
    final File encodedMp3File = File('${dir.path}/encrypted.mp3');
    final receivedData = await encodedMp3File.readAsBytes();
    final key1 = encrypt.Key.fromUtf8("12345678901234567890123456789012");
    final iv = encrypt.IV.fromLength(16);
    final encrypter = encrypt.Encrypter(encrypt.AES(key1, mode: encrypt.AESMode.cbc));
    debugPrint('Starting decryption... ${DateTime.now()}');
    final decrypted = encrypter.decryptBytes(encrypt.Encrypted(receivedData), iv: iv);
    debugPrint('Finished decryption... ${DateTime.now()}');

This is taking more than 10 minutes to decrypt !

I/flutter ( 4949): Starting decryption... 2020-04-06 14:16:47.041209
I/flutter ( 4949): Finished decryption... 2020-04-06 14:26:59.547053

For comparison effect, I wrote this very same code using nodeJS and this took just miliseconds.

const axios = require('axios');
const fs = require('fs');
const crypto = require('crypto');
axios({
    method: "get",
    url: "https://www.marcojr.co.uk/tmp/encrypted.mp3",
    responseType: "stream"
}).then(async function (response) {
    var writeStream = fs.createWriteStream("./encrypted.mp3");
    response.data.pipe(writeStream);
    writeStream.on('finish', function (err) {
        console.log('start decryption ' + new Date());
        const encryptedFile = fs.readFileSync('./encrypted.mp3');
        const x_iv = crypto.randomBytes(16);
        const decipher = crypto.createDecipheriv('aes-256-cbc', "12345678901234567890123456789012", x_iv);
        const result = Buffer.concat([decipher.update(encryptedFile), decipher.final()]);
        fs.writeFileSync('decrypted.mp3',result);
        console.log('finished decrypt... ' + new Date());
      });
});

[leocavalcante]

DartVM isn't suited for such task.
Related: #105 #81 #76 #40

[wujek-srujek]

Why do you say Dart is not suited for this? I don't want to sound rude or anything, I am curious, I am just beginning with Dart (with Flutter), and want to learn.

Actually, I have just tested it with https://pub.dev/packages/cryptography and while this lib (but really PointyCastle) took 40 seconds for a 1.3 mb image (encryption and decryption alike, using AES-CBC-256), the 'cryptography' takes about 50ms. I am astonished, but can verify the the encrypted / decrypted data is correct (I'm comparing against sample data from yet another, C++ based, library).

[leocavalcante]

How cool, there is a great alternative then, nice!

[devNamanG]

Why do you say Dart is not suited for this? I don't want to sound rude or anything, I am curious, I am just beginning with Dart (with Flutter), and want to learn.

Actually, I have just tested it with https://pub.dev/packages/cryptography and while this lib (but really PointyCastle) took 40 seconds for a 1.3 mb image (encryption and decryption alike, using AES-CBC-256), the 'cryptography' takes about 50ms. I am astonished, but can verify the the encrypted / decrypted data is correct (I'm comparing against sample data from yet another, C++ based, library).

Hey @wujek-srujek , i would be really greatful if you could share that encryption that you did with the Cryptography package, i too want to implement that, because, i am afraid to say, the encrypt package does encrypt files very slowly, i tested it for a pdf file of size 12.3 mb and that took 9-9.5 minutes from reading and writing, i tested that read/write only took about < 1.5 secs. I am a newbie to encryption and really would be grateful if you share some insights on how you acheived it with cryptography package. Thank you.

[wujek-srujek]

Hi @namangor04 , as far as I remember (I don't have the code any more) I didn't do anything special, just followed the docs, you can see an example here: https://pub.dev/documentation/cryptography/latest/cryptography/AesCbc-class.html.

Note: you should probably use AES-GCM (the example above is AES-CBC) as it is more secure, but I specifically needed to use CBC.

[devNamanG]

Hi @wujek-srujek , thank you for your response, I did implement that as you said, with AES-GCM and it works like a charm, thank you for your assistance. Really Appreciate your assistance. I tested it out and was able to read, encrypt, decrypt, save the same file in <7 seconds. I would still use this package for strings maybe, but thank you for your assistance brother, you saved me a lot of time (as I am on a tight 5 day deadline for the current project).