[javascript]arcfour aka RC4 enc/decript function

arcfour.js

// arcfour aka RC4 enc/decrypt function
// see: http://en.wikipedia.org/wiki/RC4
arcfour = (function () {
    "use strict";
    var swap = function (a, i, j) {
        var tmp = a[i];
        a[i] = a[j];
        a[j] = tmp;
    };
    
    var ksa = function (key) {
        var buf = [];
        for (var i = 0; i < 256; i++) {
            buf[i] = i;
        }
        var j = 0;
        for (var i = 0; i < 256; i++) {
            j = (j + buf[i] + key[i % key.length]) % 256;
            swap(buf, i, j);
        }
        return buf;
    };
    
    var prga = function (buf) {
        var i = 0;
        var j = 0;
        
        return function () {
            i = (i + 1) % 256;
            j = (j + buf[i]) % 256;
            swap(buf, i, j);
            return buf[(buf[i] + buf[j]) % 256];
        };
    };
    
    return function (data, key) {
        var keybuf = ksa(key);
        var keygen = prga(keybuf);
        
        var result = [];
        for (var i = 0; i < data.length; i++) {
            result[i] = data[i] ^ keygen();
        }
        return result;
    };
})();

example.js

// run example with node.js: node example.js
require("./arcfour");
require("./utf8");

// example
var key = UTF8.toBytes("JavaScript");
var src = UTF8.toBytes("Hello Word!こんにちは世界");

var enc = arcfour(src, key);
var dec = arcfour(enc, key);

console.log(src);
console.log(enc);
console.log(dec);
console.log(UTF8.toText(dec));

utf8.js

// UTF8 codec
UTF8 = (function () {
    "use strict";
    var fromCharCode = function (code) {
	if (code <= 0x7F) return [code];
	var tail = [];
	var hmask = 0x02;
	while (code > 0x3F) {
            tail.unshift(0x80 | (0x3F & code));
            code = code >> 6;
            hmask = (hmask | 0x01) << 1;
	}
	return [hmask << (6 - tail.length) | code].concat(tail);
    };
    var toCharCode = function (buf) {
	var h = buf.shift();
	if ((0x80 & h) === 0) return h;
	var code = 0;
	var shift = 0;
	var mask = 0x3F;
	while ((0x80 & (h << (shift + 1))) !== 0) {
            code = (code << 6) | (0x3F & buf.shift());
            shift += 1;
            mask = mask >> 1;
	}
	return ((h & mask) << (6 * shift)) | code;
    };
    
    return {
	toBytes: function (text) {
	    var result = [];
	    for (var i = 0; i < text.length; i++) {
		var code = text.charCodeAt(i);
		result = result.concat(fromCharCode(code));
	    }
	    return result;
	},
	toText: function (bytes) {
	    bytes = bytes.slice();
	    var result = "";
	    while (bytes.length > 0) {
		var code = toCharCode(bytes);
		result += String.fromCharCode(code);
	    }
	    return result;
	}
    };
})();