How to encrypt and decrypt strings longer than 65535 characters with PHP - php

Question

Here is my problem,
I want to encrypt JSON files that may be very long in some cases. (Sometimes containing images in Base64 format).
On the following test servers, everything works:
Raspberry Pi 3
Dell Poweredge T110
IIS on Windows 10
Synology DS1815 +
On the other hand, on the following servers, (Which are intended to be used..) the encryption does not work with more than 65535 characters, the server seems to crash.
Synology RS212
Synology DS112 +
Is there a restriction on the CPU?
Can a parameter of php.ini affect?
I tested exactly the same code on multiple servers, and on both Synology mentioned, it does not work ...
Here is my class of encryption / decryption:
class PHP_AES_Cipher {
private static $OPENSSL_CIPHER_NAME = "AES-256-CBC"; //Name of OpenSSL Cipher
private static $CIPHER_KEY_LEN = 32;
static function encrypt($key, $iv, $data) {
if (strlen($key) < PHP_AES_Cipher::$CIPHER_KEY_LEN) {
$key = str_pad("$key", PHP_AES_Cipher::$CIPHER_KEY_LEN, "0");
} else if (strlen($key) > PHP_AES_Cipher::$CIPHER_KEY_LEN) {
$key = substr($str, 0, PHP_AES_Cipher::$CIPHER_KEY_LEN);
}
$encodedEncryptedData = base64_encode(openssl_encrypt($data, PHP_AES_Cipher::$OPENSSL_CIPHER_NAME, $key, OPENSSL_RAW_DATA, $iv));
$encodedIV = base64_encode($iv);
$encryptedPayload = $encodedEncryptedData.":".$encodedIV;
return $encryptedPayload;
}
static function decrypt($key, $data) {
if (strlen($key) < PHP_AES_Cipher::$CIPHER_KEY_LEN) {
$key = str_pad("$key", PHP_AES_Cipher::$CIPHER_KEY_LEN, "0");
} else if (strlen($key) > PHP_AES_Cipher::$CIPHER_KEY_LEN) {
$key = substr($str, 0, PHP_AES_Cipher::$CIPHER_KEY_LEN);
}
$parts = explode(':', $data); //Separate Encrypted data from iv.
$decryptedData = openssl_decrypt(base64_decode($parts[0]), PHP_AES_Cipher::$OPENSSL_CIPHER_NAME, $key, OPENSSL_RAW_DATA, base64_decode($parts[1]));
return $decryptedData;
}
}
I use it like this:
$data = PHP_AES_Cipher::encrypt($key, $iv, $data);
and
$data = PHP_AES_Cipher::decrypt($key, $iv, $data);
Assuming everything works on some servers, I think the code has no problems. I already checked the Apache and PHP logs, nothing to report.
I have been searching for days without understanding the cause of the problem.
In hope that someone can help me :-)

Answer 1

Chunk it,
This is what I do (Uses PHPSecLib2 )
/**
* AES encrypt large files using streams and chunking
*
* #param resource $stream
* #param resource $outputStream
* #param string $key
* #throws SecExecption
*/
function streamSymEncode($stream, &$outputStream, $key, $chunkSize = 10240){
if(!is_resource($stream)) throw new Execption('Resource expected[input]');
rewind($stream); //make sure the stream is rewound
if(!is_resource($outputStream)) throw new Execption('Resource expected[output]');
$Cipher = new AES(AES::MODE_CBC);
$Cipher->setKey($key);
//create the IV
$iv = Random::string($Cipher->getBlockLength() >> 3);
$Cipher->setIV($iv);
if(strlen($iv_base64 = rtrim(base64_encode($iv), '=')) != 22) throw new Execption('IV lenght check fail');
fwrite($outputStream, $iv_base64.'$'); //add the IV for later use when we decrypt
while(!feof($stream)){
$chunk = fread($stream, $chunkSize);
fwrite($outputStream, rtrim(base64_encode($Cipher->encrypt($chunk)),'=').':');
}
$stat = fstat($outputStream);
ftruncate($outputStream, $stat['size'] - 1); //trim off the last character, hanging ':'
}
/**
* AES decrypt large files that were previously encrypted using streams and chunking
*
* #param resource $stream
* #param resource $outputStream
* #param string $key
* #throws SecExecption
*/
function streamSymDecode($stream, &$outputStream, $key){
if(!is_resource($stream)) throw new Execption('Resource expected[input]');
rewind($stream); //make sure the stream is rewound
if(!is_resource($outputStream)) throw new Execption('Resource expected[output]');
$Cipher = new AES(AES::MODE_CBC);
$Cipher->setKey($key);
$iv = base64_decode(fread($stream, 22) . '==');
$Cipher->setIV($iv);
fread($stream, 1); //advance 1 for the $
$readLine = function(&$stream){
$line = '';
while(false !== ($char = fgetc($stream))){
if($char == ':') break;
$line .= $char;
}
return $line;
};
while(!feof($stream)){
$chunk = $readLine($stream);
$decrypted = $Cipher->decrypt(base64_decode($chunk.'=='));
if(!$decrypted) throw new Execption('Failed to decode!');
fwrite($outputStream, $decrypted);
}
}
It takes two File stream resources like what you get from fopen and a key. Then it uses the same ecryption but chunks the file into $chunkSize separates them with : and when it decodes, it splits it back into chunks and re-assembles everything.
It winds up like this (for example)
IV$firstChunk:secondChunk:thirdChunk
This way you don't run out of memory trying to encrypt large files.
Please Note this was part of a lager class I use so I had to trim some things and make a few changes, that I haven't tested.
https://github.com/phpseclib/phpseclib
Cheers.