rc4

// public domain, from wikipedia description: https://en.wikipedia.org/wiki/RC4#Spritz 

function rc4(key, str) {
	var s = [],
		j = 0,
		x, res = [],
		i, j, y, l = key.length,
		m = str.length;
	for(i = 0; i < 256; i++) s[i] = i;

	for(i = 0; i < 256; i++) {
		j = (j + s[i] + key.charCodeAt(i % l)) % 256;
		x = s[i];
		s[i] = s[j];
		s[j] = x;
	}

	for(y = 0, i = 0, j = 0; y < m; y++) {
		j = (j + s[i = (i + 1) % 256]) % 256;
		x = s[i];
		s[i] = s[j];
		s[j] = x;
		res.push(str.charCodeAt(y) ^ s[(s[i] + s[j]) % 256]);
	}
	return String.fromCharCode.apply(0, res);
}