spritz

//public domain, based on https://www.schneier.com/blog/archives/2014/10/spritz_a_new_rc.html

function spritz(key, str) {
	var s = [],
		j = 0,
		w = 17,
		k = 0,
		res = [],
		l = key.length,
		m = str.length,
		z, x, i, y;

	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++) {
		i = (i + w) % 256;
		j = (k + s[j + s[i]]) % 256;
		k = (i + k + s[j]) % 256;
		x = s[i];
		s[i] = s[j];
		s[j] = x; //swap step
		res.push(z = str.charCodeAt(y) ^ s[j + s[i + s[z + k]]]);
	}
	return String.fromCharCode.apply(0, res);
}