RC4 encryption in javascript and php

rc4.js

/*
 * 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;
}

rc4.php

<?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;
}

?>

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

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;
}

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

I need encryption and decryption for at least PHP.

i need php encryption and js decryption for websocket messages

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

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

how to combine this rc4 with Message Authentication code?

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?

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)

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

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