encryption.js

var crypto = require('crypto');

function KeyStream(key, drop) {
	this.cipher = crypto.createCipheriv('rc4', key, new Buffer(''));
	this.key    = key;

	drop = drop || 256;

	var buffer = new Buffer(drop);

	for(var i = 0; i < drop; i++) {
		buffer.writeUInt8(i, i);
	}

	this.cipher.update(buffer);
}

KeyStream.prototype.encode = function(data, append) {
	if(append !== false) {
		append = true;
	}

	var hash  = this.cipher.update(data),
		hmac  = crypto.createHmac('sha1', this.key).update(hash).digest(),
		affix = hmac.slice(0, 4);

	var buffers = append ? [hash, affix] : [affix, hash];

	return Buffer.concat(buffers, affix.length + hash.length);
};

KeyStream.prototype.decode = function(data) {
	return this.cipher.update(data.slice(4)).slice();
};

function pbkdf2(password, salt, iterations, length) {
	iterations = iterations || 16;
	length     = length || 20;

	return crypto.pbkdf2Sync(password, salt, iterations, length);
}

exports.KeyStream = KeyStream;
exports.pbkdf2    = pbkdf2;