Flash games hack, score is 49700?? How to improve

Question

I have 2 flash games (written in as3). Both the highscore value being hacked. The normal range of each game score is not more than 5000 (normal users, will only get 2000 - 3000 points). My current method of anti-hacking is:

After finish the game, flash will use post parameters send: username=mike&score=2000&hash=md5(secret . username . score). In php page, I did the check, if the hash != md5(secret . username . score), it will return error, and WONT insert data into database.

I believe this method is not enough, or my flash games would not be hacked. Is there anything I can do to improve my flash games security/anti-hacking??

How do the hackers hack? Using third-party software like, Cheat Engine, Tamper data(firefox ext), tamperIE etc??

Can you list the all the standard hack methods? (by knowing the hack methods/problems, means has solved 50% of the problems, at least I know where the problems are, and do certain pre-caution to that)

Well, my title has "49700" because both games highscore are 49700 (actually alots of this score value inserted into my database, different users thought), so I believe they are using same methods

Thanks

Answer 1

By far the easiest method, and hardest to defeat in Flash is to use CheatEngine to simply search for the memory location that stores the score, then change the value to whatever you want. All the server-submit hashing/salting/verification in the world won't fix that because your game thinks it's valid before it packages it up in a nice valid hash for submission.

You can do 'sanity checks' on the scores if they will always fall within predefined values, but even then a determined hacker could simply suss out what the maximum allowed values is and always submit that value.

You could attempt to obfuscate your score values in memory to make them harder to find with CheatEngine, for example storing them as a multiplied value, then in your getters and setters for the score value, include a multiplication/division of the values to get/set the proper score for your views and score submission widgets. Even this is only a stall tactic though.

Unless bogus scores are costing you money, either don't worry about wasting time on the .01% of people who are cheating, or just moderate your score tables manually.

The key thing to consider in preventing cheating is: 'How much does this really matter?' If you're running some kind of high score based competition with a cash prize, then it's a pretty high priority. If you're just miffed that some random person is messing up your high scores table, it's not worth your time to stop them, just check it once a week and drop the bad scores.

Answer 2

If I wanted to hack your game I could decompile your game and find out the md5 "secret". Note that I put secret in quote marks, as the fact that it is provided in your flash game binary means that it is not actually a secret.

Its probably not possible to make your scores unhackable, all you can hope to do is make it harder.

Answer 3

The cryptographic system you are using is very similar to an HMAC, but yours implementation is less secure. The md5 algorithm is a broken, however your MAC is immune to the prefixing attack to generate hash collisions because the beginning of the your secret. The attacker must be able to control the beggaring of the string in order to create a hash collision.

TamperData is a very useful hacking tool to Modify/Capture/Replay traffic that comes from the browser. So you should prevent against replay attacks by authenticating the current date and time: hmac(secret,date_time.score.username).

The hackers are probably using a SWF Decompiler to find the value of your secret in the SWF file. In order to counter this you should try and bury the secret using a SWF obfuscation such as http://www.amayeta.com/.

None of this is a "silver bullet", this just makes it more difficult for the hacker. A hacker will always be able to modify his or her score because you are trusting the client to tell you the correct score. Even if you made the recommended changes you would still be in violation of CWE-602.

Answer 4

As you said depending on what is being done to hack this there are different holes to fix. As you are sending the actual information in your message, and "secret" is contained in the code it becomes a much easier target. Some of the things you could do to improve security

• Use a different hash function, MD5 has known flaws it is possible to create messages with the same signature without knowing the content, SHA1, SHA2 offer higher security, this will prevent an attack through a weakness of MD5

• Make the 'secret' unique to each message, ie. send it from the server for each posting, this will prevent people from reusing the same hash over and over again, and make it harder to look at the code and create the hash

• Hash the result multiple times e.g. value = hash(hash(hash(...,salt),salt),salt) this won't help if people are decompiling your program but it will help if they are just trying to recreate the hash by itself.

• Look for software to protect your SWF against decompilation, i don't do much flash so I don't have any reliable links for that

Answer 5

Would not simply running the game on the server side prevent score hacking? If the game is being run as a random game then you send the random values to the user's browser there wouldn't be much sense in them attempting to cheat,even de-compiling the flash file wouldn't give them an advantage.

Answer 6

It's not really possible to make your score validation secure if it runs entirely on the client side. You have to do at least part of it on the server side for it to be even remotely secure. I see 2 ways of doing this:

• you send periodic score updates to the server and on the server side you check that the score didn't jump "too much" (to be defined in the context of your game). If it "jumped" you can safely assume the player is hacking.

• you send the entire game movement sequence (along with any random spawns or whatever ai events) to the server with the score at the end and verify that the score is actually accurate. This will obviously not work for every game, but for some games it can work. You didn't say anything specific about your game so I'll leave this here.