gmp_testbit
here's a fast alternative to compute the xor-value of two bitstrings of an arbitrary (but same) length.
<?php
/**
* xor-op for bitstrings of arbitrary length
* bitstrings must have same length
*
* @param string $o1
* @param string $o2
* @return string
*/
function bitxor($o1, $o2) {
$xorWidth = PHP_INT_SIZE*8;
$o1 = str_split($o1, $xorWidth);
$o2 = str_split($o2, $xorWidth);
$res = '';
$runs = count($o1);
for($i=0;$i<$runs;$i++)
$res .= decbin(bindec($o1[$i]) ^ bindec($o2[$i]));
return $res;
}
?>
gmp_xor
(PHP 4 >= 4.0.4, PHP 5)
gmp_xor — Bitwise XOR
Description
resource gmp_xor
( resource $a
, resource $b
)
Calculates bitwise exclusive OR (XOR) of two GMP numbers.
Parameters
- a
-
It can be either a GMP number resource, or a numeric string given that it is possible to convert the latter to a number.
- b
-
It can be either a GMP number resource, or a numeric string given that it is possible to convert the latter to a number.
Return Values
A GMP number resource.
Examples
Example #1 gmp_xor() example
<?php
$xor1 = gmp_init("1101101110011101", 2);
$xor2 = gmp_init("0110011001011001", 2);
$xor3 = gmp_xor($xor1, $xor2);
echo gmp_strval($xor3, 2) . "\n";
?>
The above example will output:
1011110111000100
add a note
User Contributed Notesgmp_xor
greenone
02-Jul-2008 05:26
02-Jul-2008 05:26
kimcbrowne at hotmail dot com
04-Oct-2005 12:48
04-Oct-2005 12:48
To be unbreakable XOR encryption must have a key that is totally random and is never re-used. If you use a key a second time, it can be broken. This can be confirmed by reading the page at http://en.wikipedia.org/wiki/One-time_pad.
Although I am not an expert on cryptography, I understand that decyphering involves recognizing patterns and that it would be possible to decrypt code that was encoded using XOR with the same key if there were enough samples to examine. Maintaining unique keys for each encryption at both encryption and decryption points to ensure 100 percent unbreakability has security problems of its own - where and how are the keys stored and how are they transmitted to the decryption points?
bukaj at bukaj dot net
28-Mar-2005 11:38
28-Mar-2005 11:38
XOR encryption is an ultimate encryption algorithm. It can't be be broken. It is used to encrypt stealth submarine's orders. I cannot agree with "kid-sister" post below. If you use vast key (as long as encrypted message) which is random (space noise recorded on a cd), the encrypted message is also radnom - impossible to decrypt without key. Under those conditions, XOR is strongest encryption algorithm ever known.
patm at pureconnection dot net
07-Jan-2004 11:22
07-Jan-2004 11:22
XOR encryption only works if the key is at liest the same size as the plaintext, and the key is perfectly random. And no, rand() is not perfectly random.
mikko at entris dot net
15-Jul-2002 07:33
15-Jul-2002 07:33
The logical XOR can be used for encrypting data. Use resource A as your original text and resource B as the key. Be sure to use long enough key so that the key doesn't loop. Decryption works the same way, input encrypted text as res A and key as res B.