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Many small or one bigger POST request?

I need to gather information when user sees an article. User will browse through 1-30 articles in a minute (maybe even more if user just scrolls through everything looking something specific). I was wondering which way i can keep my server costs at minimum:
At client side javascript i push article id's into an array and send it to server when there is 30-60 id's. At server i loop through all the id's and insert them into database.
Every single time when user sees an article i will send one article id to server. In some cases this can cause over 60 requests in a minute. At server i insert the id into database.

In most of the cases, there is always a trade-off. And a lot of times, the optimal solution lies somewhere in the middle. I feel you should support both and use them interchangeably depending on the situation. Please go through following scenarios:
Will your end-user have bandwidth issues? If yes, it may make sense to go with option 2 or reduce the number of articles to a number such that it can be easily fetched at lower bandwidth as well.
Assuming the user does not has bandwidth issues such that loading of 30-60 articles won't take a lot of time for user, you can go with option 1 and keep using this option for subsequent fetch as well.
A lot of times it will make sense to go with option 1 for initial fetch and then fetch a lower number of articles after that.
Regarding server cost, it will make sense to send 30-60 articles together provided user reads them all. If you feel he won't read them all, find an optimal number using your app's analytics and send those number of articles in one go, provided bandwidth won't be an issue for user.
tl;dr; In data you should trust. Use your intuition, existing app usage patterns, and bandwidth availability of the user to make an informed decision. Also, server cost is not the only thing. Experience matters more, I think.

Secure High score ladder [duplicate]

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[I know there have been similar questions about preventing cheating on high score lists, but no answer didn't really help me for JavaScript based games, so please try to think about my question, before telling me about similar posts. I ask about best practices because the JavaScript is always visible for the user and therefore it is not possible to prevent cheating completly, I just want to make it harder.]
I'm developing a JavaScript based game that works in the browser. I want to make a high score list that contains the user name and the score of all users. To achieve that the browser sends the username and the score to my server (via AJAX).
Submitting fake scores to this list would be fairly easy: One could take a look at the AJAX requests and then make an own AJAX request with a faked score. Using something like a token that has to be send with the other data is pointless, as it will be easy to discover.
My only approach, that would prevent cheating, would be to send a description of every user action to the server and calculate the score there. But this is not really practicable as it would be too much for the server.
I accepted an answer, but in case anyone has other ideas about how to make cheating harder, please create another answer!

I like to play cheat the cheater - something like using a token to authenticate the score that changes every time the update is called... but I accept the cheat score that gets posted using a duplicate token. Then I display that cheat score to only the cheater, so it appears that it worked, but now the cheater is seeing his results in a sandbox.

You pretty much answered your own question. If you want to really make it harder for users to cheat, send game log to the server, where you'll calculate the score.
You don't have to send all the events, just ones that affect result score.
There are some techniques, though, that may help you:
include signature in your request. Something like MD5(secret_key + params). Although, "secret key" will have to be in JS source, it will effectively protect you from simple request interception (see Tamper Data and Charles)
if it's a multiplayer game, accept scores calculated by clients and compare them. Cheaters will be pretty visible (assuming that the majority of users are honest).
you can set a score cap, an "unreachable" result. Everyone who posts score higher than this is a cheater. For example, speed typing game: no one can type correct text at 1500 chars/minute, even 700 is pretty damn hard (though achievable).

On score submit:
Request some token from the server, this should be time based and only valid for about 2 seconds
Only accept submits that include a valid hash of this token, some salt and the score.
This prevents manual tampering with the request as it would timeout the score. If you want to account for high-latency give it a little more time until the timeout.
The hashing function:
Scramble the hashing function inside packed code (http://dean.edwards.name/packer/ really produces nasty to read code) if you use jQuery or some other library just drop the hashing functionality inside the library file and it gets pretty bad to find, escpecially if you use a function name like "h" :)
Handling the score-variable itself:
Well everybody with a debugging console can change the variable on runtime when doing this but if you encapsulate your whole Javascript inside a function and call it nothing is in the global namespace and it's much harder to get to the variables:
(function() {
//your js code here
})();

I have had lots of thoughts about it and, eventually, decided to only have local individual highscores, so cheating is not really beneficial for player and not harmful to others. Yet my game is just a simple minesweeper, and there were people who complained about the lack of competitive table.
Option 2, is approach taken by WebSudoku - to show your place "among the people of internet". So you will not see any other results, and people wont see your results - but you can compare yourself to crowd.
p.s: And seriously - any kid with Firebug/WebInspector can easily hack your JS game and, eventually, to be able to reach very high score.

If you are relying on the client to send the final score to the server, then there is no way (afaik) to prevent a genius from cheating. But I think you might be able to prevent stupid people (and honest people) from cheating, so that only geniuses and their friends will dominate your leaderboards.
There are two ways I can think of
1.) "security through obscurity."
Come up with an algorithm that transforms simple scores into something else (and to transform them back). Then obfuscate it. Complicate it. Write a function that multiplies it by q and divides it by ralph. Apply a bunch of functions to it, and among the 5-15 functions that do random stuff to it, include one that multiplies the number by 19 ( a prime number ). On your server, check to make sure every incoming number (or letter) is divisible by 19, and decode
You have to write a bunch of complex code that transforms simple scores into something crazy-looking. You have to write a series of functions in the least-efficient, most spaghetti-code fashion possible. Use
One thing you cold do is to have a set of disallowed values. I.e., perhaps all points awarded are even. If anyone tries to submit an odd number, they are obviously cheating (and very stupid).
2.) time
You should be able to know when the user started the game. You should have a session started and record when they requested the page. Then you should also be able to tell when they submitted their score. And you should also know what the time series is for max points. I.e. can you get 5 points per minute, 100 per minute, minute^3, etc... If user submits more points than are possible during that time, they are cheating.
You could also strike a balance between server and client processing and make the client should send progress update every x minutes by ajax. And if it fails to report, you assume it's been compromised (much like in Bond movies, when he's infiltrating the enemy's lair and he snaps some guard's neck. When the guard doesn't respond to his next 10-minutely check-in, the alarms will go off).
If you've ever played Zynga Poker, you've probably seen what happens when someone at the table has a slow internet connection.

Depending on the nature of the game, you could use other players to verify the results. In simple games this works great, on others you have to be clever and develop many aspects around this feature. E.g. sometimes is possible to replay and verify results based on logged actions. This trick works specially well for Human versus AI, as long as the model is deterministic.
Another option is redefining the score concept to be more user-centric, this is pretty easy to implement, but tends to be hard to devise, and only applies to a few categories of games.
Purely speculative approaches are also possible, it's sometimes pretty easy to know when some parameters don't fit. It would not avoid cheating, but would moderate it a lot.
The most complicated part is getting a small enough replay log, but since most data isn't random (except for player actions, which, actually aren't that random because depend on the game) it's essentially a matter of getting the design right.
Also, if gameplay is extended enough, for action games and the like you can get a lot of compression from doing some approximation, merging (e.g. motion vectors), and clipping uninteresting stuff.

Ideally you would send your entire event log to the server for checking. Perhaps you can implement a heuristic so you can easily determine if the score is within a set of bounds. For instance, if the total game time is 5 seconds you might expect a much lower score than with a much longer game time.
Alternatively, you could choose to manually check the event log for really high scores (the overall top-X, which should be fairly stable).
You will need a seeded random number generator if you're doing anything with randomness (like random events). Which might be tricky if you hadn't already thought of it.
You can find many more resources but it really just boils down to server-side checking. JavaScript is not unique in this, but likely easiest to exploit because you not only see the client-server communication but also the client-side source code!
HTML5 Multiplayer Game Security Solutions
http://lanyrd.com/2011/jsconf/sfggb/
Games like Starcraft only record the mouse clicks and key presses. The actual commands are then simulated. I expect 'Worms Armageddon' to do something similar but their random events (like the bounciness of bananas) aren't seeded properly so in the instant replay you might get a different result.
You could imagine something similar for MMORPGs. The server calculates your position based on the keypresses, the client merely tries to give a good early interpretation but you may warp around when you're lagging because the server will place you elsewhere on the map because it didn't get the keypress events timely.
If you attack something, the server will check if you're close enough and how much damage you can expect to deal with current stats and equipment.

Record key points in game, then score is submitted with these key points. When people look high scores, they can also see overview of played game, if it looks like it is impossible to play like that without cheating, then people can report these suspicious scores to admins.

I used a system using a time based request having 3 parameters
req number, curr time, score
The req number is returned from server in the response to the update score request , each time this is a new random value.
The curr time is calculated not from computer clock but from start of game and is synced with server using an ajax request.
Update score request is sent after short intervals (around 30 sec max).
Following checks are applied on the server
Time is within 10 seconds range from the server clock.
there has been not more than 40 seconds since the req number was sent.
the score change sent after 30 seconds is possible (within 2 x humanly possible range)
Score is updated only if the above checks are passed or the user gets a disconnection message :(
This is simpler than most methods and works out to eliminate all casual hackers (well, unless they read this and want to go to the trouble of updating score quickly or making a script of their own).

If not cheating is more important than the game itself, try to construct and present your game in a way that it looks like finding the solution to a math problem. So the server will give an instance of the problem to the client (example A: a chess board about to be won in 3 moves, example B: a geometry dash randomly generated level) and the user will have to solve it and post back a solution (example A: the winning moves, example b: the exact timestamps and intensity of jumps to avoid obstacles)
With this approach, it is key that the server doesn't send the same level twice, or else the cheater can plan and "design" his solution in advance. Also, the game information must be randomly generated in the server and not sent via seed, or else the cheater can fake the seed and design his solution with time.
The given time for valid submissions must be also tracked in the server so that they will only have "playing" time and no "designing" time. If the cheater is good enough to design a solution as fast as honest players can win the game, then they are talented enough to win the game honestly and deserve their points.
Back in the server, you will need to check that the submitted solution is valid for that instance.
Of course this approach requires lots of extra work: More instances of games (ideally infinite and non repeating), server side generation, server side validation of submissions, time caps, etc.
Note: I know these approach was already suggested in multiple solutions some years ago, I wanted to add my humble contribution.

How to secure javascript based multiplayers games

First of all, I understand this question might be off topic and not in scope of stackoverflow but I still decided to ask since I don't know any other better place.
My question is, if I make an online game based on game engines written in javascript eg CreateJS. The game code is going to be run on the clients machine and since javascript is interpreted, it is viewable by the client.
So if a mutliplayer game is being made where users can compete against each other, what measure are taken to prevent cheating. I'm asking because since the game source is viewable, anyone can simple modify the game source and potentially cheat.
Edit: For the idea of the game, lets make one up which is very simple. Imagine we are making a game like FlappyBird or a game where the further you go in a linear map, the more point you stack up.
At the end of the game, your score is submited via a http request.
Now what is stopping a user from editing the game which causes the points to stack up 10x faster? causing a higher score to be submited?
Edit 2: Or what is stopping the users from submitting a request containing false scores via cURL without ever having to play the game?

Multiplayer games prevent cheating usually by simply verifying the game steps, rather than just the complete game output. Since all other players need to know what other players do, you will have to tell the server every step of the way and let the server "simulate" the game and check if these steps are actually valid or not. The only way to cheat in this case is by writing an AI in your browser that will then produce a feasible set of steps coming to a good result.
You also will have to send these player steps to everyone else. Since in a continuous environment players can perform so many actions per second (e.g. move and turn), you want to make sure to minimize the amount of updates to be sent. E.g. when walking in a straight line, World of Warcraft,for example, only sends an update every 500ms. They might also do not necessarily simulate and verify every single step you take, but only every X steps to avoid people running through walls or jumping over entire buildings etc.
Please note that any fast-paced game will not work well when using AJAX calls. Just setting up a connection can take many times as long as just sending a packet through an established connection. That is why you want to use Websockets in that case.
Of course, minifying and obfuscating your code will put some stones in the ways of a cheater, but depending on the vulnerabilities of your system, they might do very little, since it is usually very easy to find the code that takes care of sending and receiving packets or other core aspects of your game, no matter how well obfuscated it is.

Since you cannot believe your clients, you should make an authoritative server and dumb clients model;
That articles are full of gems for who want implements an multiplayer game
the game state is managed by the server alone. Clients send their
actions to the server. The server updates the game state periodically,
and then sends the new game state back to clients, who just render it
on the screen.
From your point of view, what happened is that you pressed the right
arrow but nothing happened for a tenth of a second; then your
character finally moved one square to the right. This perceived lag
between your inputs and its consequences may not sound like much, but
it’s noticeable – and of course, a lag of half a second isn’t just
noticeable, it actually makes the game unplayable.
So you must implement a Client-side prediction and a Server reconciliation

If you develop a "multiplayer" based game, than you should persist the data on a server, centralized, accessed by ajax within your game.
And you're right, someone could potentially "cheat" by overwriting your code with firebug for example or Greasemonkey before you send your data via a http request (ajax).
In order to prevent this you could load your ajax code for saving data dynamically. You can only prevent it by making it more difficult to overwrite your code. Use for example one-way-token in a virtual session, like the token used in OAuth, like a ticket for a ajax-call. Every other call without the right token should be refuted.

Is it possible for me to prevent hackers from using a web console to call an upvote (AJAX) function repeatedly with JavaScript?

I recently created a website that has a voting/upvoting feature that uses jQuery's AJAX functions. The catch is: anyone can vote. I don't require visitors to be logged in, I don't track their IP, and I don't even store a long-term cookie. Normally (don't laugh), when a user votes on something, I store the ID of the item they vote for in a JavaScript array. Whenever they try to vote, the script checks if they have voted for the given item recently by checking the array for the ID. If they have, it just gives them an alert dialog. Otherwise, it casts a vote. So it goes without saying that all a user has to do to vote again is refresh the page.
I decided to see what happens if I injected some JavaScript (in the URL bar or a web console), and I wasn't really surprised to find out that voting as many times as you want very rapidly is as easy as:
for (var i = 0; i < 100; i++) { vote(itemID); }
(and that's being nice). I'm not sure why the array isn't stopping it, but that doesn't matter; it will always be easy to exploit this, right? I mean - you could even write a little HTML document with some JS that calls the voting page on my website as many times as you want.
So I want to fix this without too much trouble. Is it possible to create an immutable variable in JavaScript? A constant (though it would really help if there was such thing as a constant that could be changed only once)? The easiest way to fix this to some degree would be to keep the ID-holding array semi-constant: can't be deleted, but can be added to. Any suggestions or solutions or explanations are greatly appreciated.

No, if the users want to cheat by messing with their client-side code, they can do that. This is just like cheat patches for games.
What you are doing now is very reasonable to avoid accidental duplicate votes, if you feel that this is not enough (for example if the votes are really important), you need to take measures on the server-side. Tracking IP or setting cookies also won't work, this relies on client-side cooperation as well. You'd have to authenticate the users and mave sure everyone votes only once by storing something in your database.

I don't know why you don't track the IP, if you track the IP, then you can check if the IP voted the same item before, or if the IP voting too often.
Of course you also need to take into consideration that people might share the same IP to browse to your site.

javascript securty: an AJAX call to record the user's screen resolution, is it possible to prevent fake numbers?

This is a javascript security question: suppose a page finds out the screen resolution of the computer, such as 1024 x 768, and want to use an AJAX call to log this data into the DB.
Is there a way to actually prevent fake data from being entered into the DB? I think whatever the HTML or Javascript does, the user can reverse engineer the code so that some fake numbers get entered into the DB, or is there a way prevent it from happening totally? (100% secure).
Update: or in a similar situation... if i write a simple javascript game... is there a way for the user to send back the score by AJAX and lie about their score?

If you start with the assumption that the user you are communicating with is malicious, then no; there is nothing you can do to control what data they pass you. Certainly not with 100% certainty - in the worst case, they can use network tools to rewrite or replace any "correct" content with whatever they want.
If you just want to prevent casual maliciousness, you could obfuscate or encrypt your code and/or data. This will not deter a determined attacker.
If you actually trust the real user, but suspect that others might try to impersonate them, you can use other techniques like a dynamic canary: send the user a random number, and if they return that same number to you, you know that it really came from them. (Or you're being hit by a man-in-the-middle attack, but hey; that's what SSL is for.)

It's not possible to stop users from sending any numbers they like back from JavaScript.
I think the best you could do is do some sort of check on the server-side to make sure the numbers sent back look like a realistic resolution.
I'm not sure why someone would spend the time to spoof those numbers in the first place though.

Yes, you are correct. Since you're using client-side code, you have to tell the
user's computer (and thus the user) in one way or another, whatever encryption or obfuscation you're using. There's no way around it.

For the resolution, it would basically be impossible to determine if it's valid resolution. My resolution is usually sent to the server as 5120 x 1600, which seems pretty unrealistic, but it's because the 2 screens are often sent as 1. Otherwise, there is a such a huge variety of possibilities in screen resolutions and screen configurations, you'd probably remove a lot of valid ones, although they might be few.
For the game score, you could do additional checks that make it more complicated to check. Things like sending multiple notices of the score throughout the game and requiring X number to ensure that the score received is valid. (IE, must receive one between 200-300, 400-500, 700-800 and then the final score of 1000.) With the final score, you could also have some kind of encrypted value that can only be used once or that contains some data with a CRC on it. Basically, in the end, require receiving other data than just the score, especially for higher scores.

To attempt an answer by elaborating on comments made by Dok, and yourself, there is a clear distinction between manipulating an application to 'cheat' it out of something, whether it be an online business to get something cheaper or a MMPORG to get more experience, than manipulating it in such a way that it renders the interface incorrectly and diminishes the overall user experience for that particular (hacker?) user.
Your time would be better spent focusing on other aspects of your site. I don't recommend the users of my site manipulate the HTML to make it look funny on their machines, but I'm not going to go all out and obfuscate my server output to stop them from hurting themselves. In your case, range checking against pre-defined safe values, making use of the DB, to ensure the user is viewing with an 'allowed' resolution puts unnecessary burden on your application, and takes time to do.