CODEWITHSUNDEEP
androidnode.jscryptographyencryption
m1uan
m1uan

Reputation: 558

How to decrypt a data in Android which was crypted in nodejs

In android i get always IllegalBlockSizeException, the data are encrypted in nodejs server and looks like (node.js: encrypting data that needs to be decrypted?):

var crypto = require('crypto');
            console.log(crypto.getCiphers(), crypto.getHashes());

            var algorithm = 'aes128'; // or any other algorithm supported by OpenSSL
            var key = 'password';

            var cipher = crypto.createCipher(algorithm, key);
            var encrypted = cipher.update(data, 'utf8', 'binary') + cipher.final('binary');


        fs.writeFile(file, encrypted, function (err) {
           cb(err);
        });

android code:

private static byte[] decrypt(byte[] raw, byte[] encrypted) throws NoSuchPaddingException, NoSuchAlgorithmException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException {
        SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
        Cipher cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.DECRYPT_MODE, skeySpec);
        byte[] decrypted = cipher.doFinal(encrypted);
        return decrypted;
    }

call method from file is in input stream (is):

byte [] b = new byte[2000000];
            is.read(b, 0, 2000000);
            byte[] decryptedData = decrypt(key,"password".getBytes());
            result = new String(decryptedData, "UTF8").split("\n");

android code is inspired by : android encryption/decryption with AES where i dont use part of SecretKey with SecureRandom... which is for sure wrong, but i dont use any secure random in node.js part. The problem can be also with coding data in file.

I generaly generate a file in nodejs which is downloaded by app and stored in sdcard i'm not sure if i should be realy care about these data but will be cool have it crypted, isn't it?:-)

Thank you so much for any help or advice;-)

Upvotes: 0

Views: 1031

Answers (1)

Duncan Jones
Duncan Jones

Reputation: 69369

An IllegalBlockSizeException means that your input is not a multiple of the AES block size (16 bytes).

Your use of the decryption method looks completely wrong:

byte [] b = new byte[2000000];
is.read(b, 0, 2000000);
byte[] decryptedData = decrypt(key,"password".getBytes()); // <--- ???!

You are passing an eight byte constant value for your ciphertext. Instead, you should be passing the data you read from your input stream.

I would strongly recommend you research the correct way to read an entire input stream, because this code snippet suggests you are not handling resources correctly. You are also likely to end up with a byte array much larger than your actual data (unless your file is exactly 2000000 bytes long).

Side note: always specify the mode and padding when creating a Cipher object. For instance, if you know your JavaScript code uses CBC-mode and PKCS#7 padding, select:

Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");

This is important, because otherwise you are relying on default values that may differ between platforms.

Upvotes: 3

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