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phpnode.jscryptographyopensslmcrypt

Node.js: how to decipher text ciphered in php?

My PHP ciphering looks like this:

<?
$salt = '…';
$data = '…';

$iv = mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_CFB), MCRYPT_RAND);
$ciphered = trim(base64_encode(mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $salt, $data, MCRYPT_MODE_ECB,$iv)));

I'm trying to decipher the result of the code above with:

ciphered = '…';
crypto = require('crypto');
salt = crypto.createHash('md5').update('…').digest('hex');
iv = '0123456789123455';
decipher = crypto.createDecipheriv('aes-256-cbc', salt, iv);
deciphered = decipher.update(ciphered, 'base64');
deciphered += decipher.final('utf-8');

This code results in: TypeError: DecipherFinal fail

Solution

  • a couple of problems I see:

    1. mismatch of operating modes. you generate an IV for a CFB (Cipher Feedback) operating mode,you use ECB (Electronic Code Book - not recommended, just check out the image in that wiki article for why) as your mode when you actually encrypt, then try to decrypt using CBC (Cipher Block Chaining) mode. You should stick to one mode (probably CBC). To do this keep the decryption side aes-256-cbc and make the encryption side MCRYPT_MODE_CBC

    2. you pass $salt (which is actually your key) into mcrypt_encrypt without hashing it, but do hash it, and return a hex string when crypto.createDecipheriv expects a binary encoded string, per its documentation. Both keys need to be the same, and need to follow the proper encoding so that they remain the same when passed into the functions.

    3. It looks like you generate an IV on the encryption side, then use a fixed string for an IV on the decryption side. The IV (Initialization vector) needs to be communicated with the ciphertext to the decryption side (and it is okay to be transmitted in the clear along with the ciphertext).

    4. the update method on your decipher object does not accept base64 as an encoding, per its documentation. You will need to convert your base64 text to something else (probably a binary encoding) and then pass it into the update method with the proper encoding.

    5. PHP's default charset is ISO-8859-1, but you are trying to decrypt your ciphertext as a UTF-8 string. This may cause problems, especially if you use characters beyond those used in standard ASCII. you either need to make sure that your PHP side is operating in UTF-8 mode (check out this SO answer on how to do that), or ensure that your input only uses ASCII characters (ISO-8859-1 is a superset of ASCII) and use the 'ascii' output encoding.

    Most of your problems boil down to encoding issues. I don't know a lot about the various types of encoding on node.js, so you will need to research that on your own, but the issues with the cryptographic primitives should be easy to fix. make sure to read the documentation I linked and the mcrypt_encrypt documentation as well.