(function(){

// Shortcuts
var C = Crypto,
    util = C.util,
    charenc = C.charenc,
    UTF8 = charenc.UTF8,
    Binary = charenc.Binary;

C.PBKDF2 = function (password, salt, keylen, options) {

	// Convert to byte arrays
	if (password.constructor == String) password = UTF8.stringToBytes(password);
	if (salt.constructor == String) salt = UTF8.stringToBytes(salt);
	/* else, assume byte arrays already */

	// Defaults
	var hasher = options && options.hasher || C.SHA1,
	    iterations = options && options.iterations || 1;

	// Pseudo-random function
	function PRF(password, salt) {
		return C.HMAC(hasher, salt, password, { asBytes: true });
	}

	// Generate key
	var derivedKeyBytes = [],
	    blockindex = 1;
	while (derivedKeyBytes.length < keylen) {
		var block = PRF(password, salt.concat(util.wordsToBytes([blockindex])));
		for (var u = block, i = 1; i < iterations; i++) {
			u = PRF(password, u);
			for (var j = 0; j < block.length; j++) block[j] ^= u[j];
		}
		derivedKeyBytes = derivedKeyBytes.concat(block);
		blockindex++;
	}

	// Truncate excess bytes
	derivedKeyBytes.length = keylen;

	return options && options.asBytes ? derivedKeyBytes :
	       options && options.asString ? Binary.bytesToString(derivedKeyBytes) :
	       util.bytesToHex(derivedKeyBytes);

};

})();