Node.js encrypting and decrypting is doubling file size

Question

I am creating a Node.js application that can encrypt and decrypt image files. However when my code is run I get varying results: Sometimes the decrypted image looks like the original at the top but the bottom half looks corrupted, sometimes the decrypted image is completely there but looks like it was heavily compressed and sometimes the decrypted image is too corrupt to open. Here is an image that demonstrates this. The only thing these results have in common is the encrypted and decrypted images are double the file size of the original image.

const fs = require('fs');
const crypto = require('crypto');

var path = 'C:\\Users\\' + windowsUserName + '\\Desktop\\image';
    var fileExtension = '.jpg';
    var password = '1234';
    var algorithm = 'aes-256-cbc';

    var image = fs.createReadStream(path + fileExtension);

    var encryptedImage = fs.createWriteStream(path + ' encrypted' + fileExtension);
    var decryptedImage = fs.createWriteStream(path + ' decrypted' + fileExtension);

    var encrypt = crypto.createCipher(algorithm, password);
    var decrypt = crypto.createDecipher(algorithm, password);

    image.pipe(encrypt).pipe(encryptedImage);
    image.pipe(encrypt).pipe(decrypt).pipe(decryptedImage);

How do I fix the image corruption and file size doubling?

AES-CBC should be used with createCipherIv not createCipher. — Luke Joshua Park
– Luke Joshua Park, Commented Sep 13, 2018 at 4:48
I don't really understand how initialization vector's work so if you could tell me more that would be great! The answer I selected seems to work so could you explain to me why I should implement them? — Settings Menu Hard to Find
– Settings Menu Hard to Find, Commented Sep 13, 2018 at 5:14
Because without them your encryption is insecure and doesn't really work. Look up ECB mode on Wikipedia and look at the penguin. — Luke Joshua Park
– Luke Joshua Park, Commented Sep 13, 2018 at 5:16
The part I really don't get is this line: "it is important that an initialization vector is never reused under the same key". If I were to change my current code to use createCipherIv instead of createCipher wouldn't I be reusing the IV all the time? — Settings Menu Hard to Find
– Settings Menu Hard to Find, Commented Sep 13, 2018 at 5:20
Yes, that's why you should always generate a new random IV every time you encrypt. Getting encryption right is difficult, it's very delicate. The code you have, with respect, is pretty mediocre. — Luke Joshua Park
– Luke Joshua Park, Commented Sep 13, 2018 at 5:34

Mark · Accepted Answer · 2018-09-13 05:02:31Z

1

You are trying to decrypt the cypher before it is finished. If you wait until the pipe is done and read the encrypted file, it should not be garbled:

const fs = require('fs');
const crypto = require('crypto');

var path = 'file path';
    var fileExtension = '.jpg';
    var password = '1234';
    var algorithm = 'aes-256-cbc';

    var image = fs.createReadStream(path + fileExtension);
    var encryptedImage = fs.createWriteStream(path + ' encrypted' + fileExtension);
    var encrypt = crypto.createCipher(algorithm, password);
    image.pipe(encrypt).pipe(encryptedImage);

    encryptedImage.on("finish", function(){
        var decrypt = crypto.createDecipher(algorithm, password);
        var decryptedImage = fs.createWriteStream(path + ' decrypted' + fileExtension);
        var encryptedImage = fs.createReadStream(path + ' encrypted' + fileExtension);
        encryptedImage.pipe(decrypt).pipe(decryptedImage);
    })

answered Sep 13, 2018 at 5:02

Mark

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1 Comment

Settings Menu Hard to Find Over a year ago

I thought I had ruled out that possibility in one of my tests but apparently I did it wrong, thanks.

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