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;
}

?>