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RC4 encryption in javascript and php
/*
* RC4 symmetric cipher encryption/decryption
*
* @license Public Domain
* @param string key - secret key for encryption/decryption
* @param string str - string to be encrypted/decrypted
* @return string
*/
function rc4(key, str) {
var s = [], j = 0, x, res = '';
for (var i = 0; i < 256; i++) {
s[i] = i;
}
for (i = 0; i < 256; i++) {
j = (j + s[i] + key.charCodeAt(i % key.length)) % 256;
x = s[i];
s[i] = s[j];
s[j] = x;
}
i = 0;
j = 0;
for (var y = 0; y < str.length; y++) {
i = (i + 1) % 256;
j = (j + s[i]) % 256;
x = s[i];
s[i] = s[j];
s[j] = x;
res += String.fromCharCode(str.charCodeAt(y) ^ s[(s[i] + s[j]) % 256]);
}
return res;
}
<?php
/*
* RC4 symmetric cipher encryption/decryption
*
* @license Public Domain
* @param string key - secret key for encryption/decryption
* @param string str - string to be encrypted/decrypted
* @return string
*/
function rc4($key, $str) {
$s = array();
for ($i = 0; $i < 256; $i++) {
$s[$i] = $i;
}
$j = 0;
for ($i = 0; $i < 256; $i++) {
$j = ($j + $s[$i] + ord($key[$i % strlen($key)])) % 256;
$x = $s[$i];
$s[$i] = $s[$j];
$s[$j] = $x;
}
$i = 0;
$j = 0;
$res = '';
for ($y = 0; $y < strlen($str); $y++) {
$i = ($i + 1) % 256;
$j = ($j + $s[$i]) % 256;
$x = $s[$i];
$s[$i] = $s[$j];
$s[$j] = $x;
$res .= $str[$y] ^ chr($s[($s[$i] + $s[$j]) % 256]);
}
return $res;
}
?>
@WebReflection

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WebReflection commented Sep 12, 2012

just wonder if this, or its source ... was actually inspired by this one: http://code.google.com/p/sessionstorage/source/browse/trunk/src/RC4.js

@farhadi

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Owner

farhadi commented Mar 7, 2013

Well, different implementations of the same algorithm couldn't be much different.
Actually I wrote this code about 7 years ago based on some pseudocode in an article about RC4 (which I don't remember where I found) and published it in my personal website:
http://web.archive.org/web/20060810225251/http://farhadi.ir/rc4.html

@Madhavarao

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Madhavarao commented Apr 5, 2013

Is it possible to get java compatible algorithm for the same?

@farhadi

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Owner

farhadi commented Apr 5, 2013

I'm not a Java developer but the code is simple and I think an average Java programmer can port it to Java.

@basgroot

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basgroot commented Jun 15, 2013

Javascript works, but PHP code doesn't work with unicode strings, like '€'.

@basgroot

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basgroot commented Jun 15, 2013

It looks like there is a difference in the last line of the PHP version, compared to JS:
JS: res += String.fromCharCode(str.charCodeAt(y) ^ s[(s[i] + s[j]) % 256]);
PHP: $res .= $str[$y] ^ chr($s[($s[$i] + $s[$j]) % 256]);

This is my PHP version, which works with unicode, at least on my server:

function mb_chr($char) {
return mb_convert_encoding('&#'.intval($char).';', 'UTF-8', 'HTML-ENTITIES');
}

function mb_ord($char) {
$result = unpack('N', mb_convert_encoding($char, 'UCS-4BE', 'UTF-8'));

if (is_array($result) === true) {
return $result[1];
}
return ord($char);
}

function rc4($key, $str) {
if (extension_loaded('mbstring') === true) {
mb_language('Neutral');
mb_internal_encoding('UTF-8');
mb_detect_order(array('UTF-8', 'ISO-8859-15', 'ISO-8859-1', 'ASCII'));
}

$s = array();
for ($i = 0; $i < 256; $i++) {
$s[$i] = $i;
}
$j = 0;
for ($i = 0; $i < 256; $i++) {
$j = ($j + $s[$i] + mb_ord(mb_substr($key, $i % mb_strlen($key), 1))) % 256;
$x = $s[$i];
$s[$i] = $s[$j];
$s[$j] = $x;
}
$i = 0;
$j = 0;
$res = '';
for ($y = 0; $y < mb_strlen($str); $y++) {
$i = ($i + 1) % 256;
$j = ($j + $s[$i]) % 256;
$x = $s[$i];
$s[$i] = $s[$j];
$s[$j] = $x;

$res .= mb_chr(mb_ord(mb_substr($str, $y, 1)) ^ $s[($s[$i] + $s[$j]) % 256]);

}
return $res;
}

@reyneke-vosz

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reyneke-vosz commented Jul 23, 2013

Thats exactly what i need! PHP-Decryption and JS-Encryption. In my case I had to utf8_encode the decrypted string. Works fine, thanks!

@eduardoalcantara

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eduardoalcantara commented Jul 24, 2013

I need encryption and decryption for at least PHP.

@r3wt

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r3wt commented May 14, 2014

i need php encryption and js decryption for websocket messages

@DamilolaJegede

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DamilolaJegede commented Jul 16, 2014

But this is one-way. How about the snippet for decryption?

@burn0050

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burn0050 commented Nov 11, 2014

Actually, @DamilolaJegede, this function is symmetrical. If you pass the resulting (encoded) string back into the function, you get the original string back.

@MrsSahsirao

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MrsSahsirao commented May 5, 2015

how to combine this rc4 with Message Authentication code?

@aldoemilio

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aldoemilio commented May 2, 2016

Hi Basgroot, I need to encript a series of _GET values before including them in the URL, and decript them in the target page in order to populate it, with the various _GET values. But the function does not decript the string as pairs of GET keys and values. How can I achieve this?

@weeco

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weeco commented Aug 20, 2017

Why is there no support for streaming? Or at least keeping the internal state?
Can you add that please?

RC4 is a stream cipher so there has to be support for transforming data while keeping the internal state of the encryption/decryption SBox (https://en.wikipedia.org/wiki/RC4 see: Key scheduling)

@weeco

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weeco commented Aug 20, 2017

nevermind, this one does the trick
https://www.npmjs.com/package/simple-rc4
;-)

@jesobreira

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jesobreira commented Nov 10, 2017

Here's my port to AutoIt3:

Func rc4($sKey, $sStr)
	Local $s[256], $j = 0, $x, $res, $y, $i
	Local $uBound
	For $i = 0 To 255
		$s[$i] = $i
	Next
	For $i = 0 To 255
		$j = Mod(($j + $s[$i] + Asc(StringMid($sKey, Mod($i, StringLen($sKey))+1, 1))), 256)
		$x = $s[$i]
		$s[$i] = $s[$j]
		$s[$j] = $x
	Next
	$i = 0
	$j = 0
	For $y = 0 To StringLen($sStr)-1
		$i = Mod(($i + 1), 256)
		$j = Mod(($j + $s[$i]), 256)
		$x = $s[$i]
		$s[$i] = $s[$j]
		$s[$j] = $x
		$res &= Chr(BitXOR(Asc(StringMid($sStr, $y+1, 1)), ($s[Mod(($s[$i] + $s[$j]), 256)])))
	Next
	Return $res
EndFunc
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