NodeJS Crypto equivalent in PHP? - php

Question

I'm looking for a way to decrypt a file since a few weeks. But it's impossible to recover the file intact in PHP, only with node. But I would like to do it without node.
If someone can tell me where I could be wrong... ?
I tried with openssl_encrypt/decrypt then with OPENSSL_NO_PADDING & ZERO_PADDING options. Transform the result in base64 but impossible to have the good result...
I thank you in advance I do not know what to do...
Here is my NodeJs crypto code :
decrypt(encryptedBuffer) {
const PASSPHRASE = "";
let decryptedBuffer = Buffer.alloc(encryptedBuffer.length);
let chunkSize = 2048;
let progress = 0;
while (progress < encryptedBuffer.length) {
if ((encryptedBuffer.length - progress) < 2048) {
chunkSize = encryptedBuffer.length - progress;
}
let encryptedChunk = encryptedBuffer.slice(progress, progress + chunkSize);
// Only decrypt every third chunk and only if not at the end
if (progress % (chunkSize * 3) === 0 && chunkSize === 2048) {
let cipher = crypto.createDecipheriv('bf-cbc', PASSPHRASE, Buffer.from([0, 1, 2, 3, 4, 5, 6, 7]));
cipher.setAutoPadding(false);
encryptedChunk = Buffer.concat([cipher.update(encryptedChunk), cipher.final()]);
}
decryptedBuffer.write(encryptedChunk.toString('binary'), progress, encryptedChunk.length, 'binary');
progress += chunkSize;
}
return decryptedBuffer;
}
Here in PHP
public function decrypt($encryptedBuffer)
{
ini_set('memory_limit', '1G');
$f = fopen('myfile', 'wb+');
$chunkSize = 2048;
$progress = 0;
$passphrase = "h5ihb>p9`'yjmkhf";
while ($progress > strlen($encryptedBuffer)) {
// If the buffer is if the end calculate the valid chunksize
if ((strlen($encryptedBuffer) - $progress) < 2048) {
$chunkSize = strlen($encryptedBuffer) - $progress;
}
/** Getting the encrypted chunk part */
$encryptedChunk = substr($encryptedBuffer, $progress, $progress + $chunkSize);
// Only decrypt every third chunk and only if not at the end
if ($progress % ($chunkSize * 3) === 0 && $chunkSize === 2048) {
$encryptedChunk = openssl_decrypt($encryptedChunk, 'bf-cbc', $passphrase, OPENSSL_ZERO_PADDING, '01234567');
}
fwrite($f, $encryptedChunk);
$progress += $chunkSize;
}
}

Answer 1

There are several flaws in the PHP code:
The condition in the while loop is wrong and should be:
$progress < strlen($encryptedBuffer).
$encryptedChunk is determined incorrectly because substr() expects the length in the third parameter. The correct way is:
$encryptedChunk = substr($encryptedBuffer, $progress, $chunkSize);
In the openssl_decrypt() call, too few flags are set in the fourth parameter:
Apart from disabling the padding, the default Base64 decoding has to be disabled with OPENSSL_RAW_DATA.
For key sizes smaller than 16 bytes, the padding of the key with 0x00 values to a length of 16 bytes has to be disabled with OPENSSL_DONT_ZERO_PAD_KEY. This is a PHP bug (s. here). The fix, i.e. the flag is available as of version 7.1.8.
Overall: OPENSSL_DONT_ZERO_PAD_KEY | OPENSSL_RAW_DATA | OPENSSL_ZERO_PADDING.
The wrong IV is used, correct would be: hex2bin('0001020304050607').
With these changes, decryption with the PHP code works.
Regarding security: The short block size makes Blowfish vulnerable to birthday attacks, see here. Using a static IV is generally insecure. Rather, a random IV should be generated for each encryption.