gmp_xor

(PHP 4 >= 4.0.4, PHP 5, PHP 7)

gmp_xor — Bitwise XOR

说明

gmp_xor ( GMP $a , GMP $b ) : GMP

Calculates bitwise exclusive OR (XOR) of two GMP numbers.

参数

a: 可以是一个 GMP 数据 resouce，或一个可以转换为数值的字符串。
b: 可以是一个 GMP 数据 resouce，或一个可以转换为数值的字符串。

返回值

GMP 数值资源.

范例

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";
?>

以上例程会输出：

1011110111000100

User Contributed Notes

greenone 02-Jul-2008 12:26


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;

}

?>

kimcbrowne at hotmail dot com 03-Oct-2005 07:48


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 05:38


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 05:22


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 02:33


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.