Back loop XOR. How?

[Nirvana77]

Hello mans! I need you help!
This is XOR encryption:

for ($i = 0; $i < $suma; ++$i)
{
  $ctxt .= $text[$i] ^ $dlina[$i % $hlam] ^ $bite ^ $dbite;
  $bite = $text[$i];
} 

$ctxt - encryption text. How decode this text in $ctext ?
I need back loop!

Thank you

[Nirvana77]

$text -> XOR encryption -> $ctext

How create back loop?

$ctext -> XOR decryption -> $text

Pleaseeee, heeeeeelllppppp

[onemorenerd]

What is XOR encryption?
http://php.net/manual/en/language.operators.bitwise.php
http://en.wikipedia.org/wiki/Stream_cipher

Next time ask google first please!

[Nirvana77]

Next time ask google first please!

for ($i = 0; $i < $suma; ++$i) 
{ 
  $ctxt .= $text[$i] ^ $dlina[$i % $hlam] ^ $bite ^ $dbite; 
  $bite = $text[$i]; 
} 

You don't understand me!
How create back loop decryption for this operation ? :-))) This operation encryption $text.

[onemorenerd]

I think I do understand you. You want a piece of code that takes $ctxt and returns the original $text. But you don't seem to know what your snippet does.

for ($i = 0; $i < $suma; ++$i) {
    $key = $dlina[$i % $hlam] ^ ($i ? $text[$i-1] : $bite) ^ $dbite;
    $ctxt .= $text[$i] ^ $key;
} 

Better now? Then go on ... XOR decryption is basically XOR encryption with XOR encrypted input.
The real problem is to compute the dynamic key. I can't help you with that because I don't know the incredients.

Btw: What are trying to crack? Is it legal?

[Nirvana77]

Btw: What are trying to crack? Is it legal?

This code write phpcoder for my mother. This encryption text writing in MySQL. My mother want viewing the original text. She asked me to create this. But I don't know how to decode this text. It's legally.

[Nirvana77]

Better now?

NO

<?php
// this POST text
$text = 'Hello man, hello man, hello man, hello man, hello man, hello man, hello man';

// encrypt XOR
$dlina = 'xGbvdeekRjQFRmyKEyX5Uan880YYEtoVmQ6JCdCNWkhd9TkKhFSaQE';
$hlam = strlen($dlina);
$but = md5($dlina);
$bite = $but[3];
$dbite = $but[1];
$suma = strlen($text);

for ($i = 0; $i < $suma; ++$i)  
{  
  $ctxt .= $text[$i] ^ $dlina[$i % $hlam] ^ $bite ^ $dbite;  
  $bite = $text[$i];  
}

echo $ctxt."<br>";

// Decrypt this XOR
$txts = $ctxt;
$sumas = strlen($txts);

for ($i = 0; $i < $sumas; ++$i) {
    $key = $dlina[$i % $hlam] ^ ($i ? $txts[$i-1] : $bite) ^ $dbite;
    $txtss .= $txts[$i] ^ $key;
} 

echo $txtss;
?>

[onemorenerd]

The code in my last post wasn't meant to decrypt. It's just a variant of the snippet you gave with the advantage that the key can be logged.

<?php
define('BR', "\n"); echo '<pre>';

// POSTed
$input = 'Hello man, hello man, hello man, hello man, hello man, hello man, hello man';


/*
 * Your XOR encryption
 */

// take raw input
$text = $input;

// incredients
$dlina = 'xGbvdeekRjQFRmyKEyX5Uan880YYEtoVmQ6JCdCNWkhd9TkKhFSaQE';
$hlam = strlen($dlina);
$but = md5($dlina);
$bite = $but[3];
$dbite = $but[1];
$suma = strlen($text);
$ctxt = '';

// encrypt XOR
for ($i = 0; $i < $suma; ++$i) {  
  $ctxt .= $text[$i] ^ $dlina[$i % $hlam] ^ $bite ^ $dbite;  
  $bite = $text[$i];  
}

echo $text . BR;
echo $ctxt . BR;
echo BR;
echo str2bin($text) . BR;
echo str2bin($ctxt) . BR;
echo BR, BR;


/*
 * My variant of the same
 */

// this POST text
$text = $input;

// incredients
$dlina = 'xGbvdeekRjQFRmyKEyX5Uan880YYEtoVmQ6JCdCNWkhd9TkKhFSaQE';
$hlam = strlen($dlina);
$but = md5($dlina);
$bite = $but[3];
$dbite = $but[1];
$suma = strlen($text);
$ctxt = '';
$keylog = '';

// encrypt XOR
for ($i = 0; $i < $suma; ++$i) {
    $key = $dlina[$i % $hlam] ^ ($i ? $text[$i-1] : $bite) ^ $dbite;
    $keylog .= $key;
    $ctxt .= $text[$i] ^ $key;
}

echo $text . BR;
echo $ctxt . BR;
echo BR;
echo str2bin($text) . BR;
echo str2bin($keylog) . BR;
echo str2bin($ctxt) . BR;
echo BR, BR;

/*
 * XOR decryption
 */

// take encrypted input
$text = $ctxt;

// incredients
$dlina = 'xGbvdeekRjQFRmyKEyX5Uan880YYEtoVmQ6JCdCNWkhd9TkKhFSaQE';
$hlam = strlen($dlina);
$but = md5($dlina);
$bite = $but[3];
$dbite = $but[1];
$suma = strlen($text);
$ctxt = '';

// decrypt XOR encrypted data
for ($i = 0; $i < $suma; ++$i) {
    $key = $dlina[$i % $hlam] ^ ($i ? $ctxt[$i-1] : $bite) ^ $dbite;
    $keylog .= $key;
    $ctxt .= $text[$i] ^ $key;
} 

echo $text . BR;
echo $ctxt . BR;
echo BR;
echo str2bin($text) . BR;
echo str2bin($keylog) . BR;
echo str2bin($ctxt) . BR;
echo BR, BR;


/**
 * Returns an ASCII string containing the binary representation of the input data .
 * Copied from PHP Manual.
 */
function str2bin($str, $mode = 0) {
    $out = false;
    for ($a = 0; $a < strlen($str); $a++) {
        $dec = ord(substr($str, $a, 1));
        $bin = '';
        for ($i = 7; $i >= 0; $i--) {
            if ($dec >= pow(2, $i)) {
                $bin .= "1";
                $dec -= pow(2, $i);
            } else {
                $bin .= "0";
            }
        }
        /* Default-mode */
        if ($mode == 0) $out .= $bin;
        /* Human-mode (easy to read) */
        if ($mode == 1) $out .= $bin ." ";
        /* Array-mode (easy to use) */
        if ($mode == 2) $out[$a] = $bin;
    }
    return $out;
}

?>

[Nirvana77]

The code in my last post wasn't meant to decrypt. It's just a variant of the snippet you gave with the advantage that the key can be logged.

You method encrypt and decrypt XOR working fine.

// decrypt XOR encrypted data
for ($i = 0; $i < $suma; ++$i) {
$key = $dlina[$i % $hlam] ^ ($i ? $cctxt[$i-1] : $bite) ^ $dbite;
$keylog .= $key;
$cctxt .= $text[$i] ^ $key;
}

Thank you very much - onemorenerd!