PHP encoding and obfuscation - php

Question

I've been trying to understand what the code below is doing. On a fundamental level I understand what the decoding process is doing however, once arriving to the for loop, It becomes a bit confusing. Basically, I'm trying to take the below and write an appropriate encoder which will allow me to reuse the decoding routine below. I'm using this for the obfuscation of a PHP script.
Would anyone be so kind as to provide assistance in the area of taking the below and providing guidance on how I'd be able to write the reverse of this (an encoder) vs the decoding method provided?
Any assistance is greatly appreciated.
<?php
$B_yhp='bCtyDEF7u+8SszsSu+kgCO5ydU+XgC8PCVdhu1jwM7cyDU6dY0V7URbSZ/';
$L_qmfd=base64_decode($B_yhp);
for($i=0; $i<strlen($L_qmfd); $i++)
{
$L_qmfd[$i]=chr(ord($L_qmfd[$i])^((91403)%256));
}
$Laz_ep=#gzinflate(strrev($L_qmfd));
//Use $Lax_ep to generate a function IE:
//create_function('$runtime',$Laz_ep);
?>
Edited:
I've tried to create the encoder using the following but I believe I'm missing / doing something wrong. The CRC values don't end up matching and the php code doesn't successfully decode to it's original state so I know I'm clearly missing a step or overlooking something here.
<?php
$hash = hash_file('crc32b', $argv[1]);
$array = unpack('N', pack('H*', $hash));
$crc32 = $array[1];
printf("CRC: %u\n",$crc32);
$content = file_get_contents($argv[1]);
$content = strrev($content);
$content = gzdeflate($content, 9);
for($i=0; $i<strlen($content); $i++)
{
$content[$i]=chr( ord($content[$i])^((91403)%256));
}
$content=base64_encode($content);
file_put_contents($argv[1]. ".packed",$content);
?>

Answer 1

You are doing the gzdeflate and strrev in the wrong order. Do the gzdeflate first, then reverse the deflated $content.
<?php
$hash = hash_file('crc32b', $argv[1]);
$array = unpack('N', pack('H*', $hash));
$crc32 = $array[1];
printf("CRC: %u\n",$crc32);
$content = file_get_contents($argv[1]);
$content = gzdeflate($content, 9); // Swapped these
$content = strrev($content); // two lines
for($i=0; $i<strlen($content); $i++)
{
$content[$i]=chr( ord($content[$i])^((91403)%256));
}
$content=base64_encode($content);
file_put_contents($argv[1]. ".packed",$content);
?>