Thursday, May 31, 2012

Android Game Keeps Getting Hacked

So we've been through this several times now, we release a game (for cheap) and someone hacks it and puts it up on a mirror. We setup Google Alerts for all our apps, so we get told daily who's doing the hacking. So far, we have implemented the licensing service as Google has suggested, our salt is randomly made each time the license is initiated with the unique device ID. We run the check service once, when the application is started for the first time. We then generate a 512 character hash for the key and the stored value that is compared against in SharedPreferences from there on out.

Now, I know that checking once is probably where the application is being blocked. Our bytecode has most likely been looked at and recompiled without the line that initiates the check.

From here, I don't want to obfuscate our code as I have seen it broken before. I want something a little more solid, and I also want to learn how to do this properly. I am more interested in learning than making money at this point since only 2% of people will ever look for a hacked version.

So far, on my own, I have come up with a random number generator that is placed in several startup areas of the game. When initiated (say, 1 out of 50 times) the license is checked. I know this would make it harder to hack because the cracker would have to eliminate each case, compile, eliminate, compile. This method however, is still what do you guys suggest? Again, I am really interested in this process of security, so please educate, don't turn this into a discussion on obfuscation or checking periodically based on a timestamp.


Source: Tips4all


  1. Taken from my solution from this post Avoid apk cracked

    Implement your own licensing library

    I'd also refer you to check out this from Google I/O 2011 YouTube recording:

    Evading Pirates and Stopping Vampires


    The Presentation Notes from Evading Pirates and Stopping Vampires

    Some basic keypoints

    Modify the LVL
    Implement LVL Tamper Resistance
    Use obfuscation
    Add reflection

  2. My idea isnt hacker proof, but might remove some of the interest for hacking the game.

    Freemium model

    1) Make the first 5-10 levels free so people can learn the game and have some fun without paying. Less will want to hack the first level and the game will spread even further by Freemium model.

    Shareware/clustered levelpacks

    2) Let part of the game levels or logic stay online. Eg. when reaching for level 5 or 10 or 15, then download small parts for the game, and every time submit the progress-log from the game and validate this against possible values + hashcodes. This could perhaps make it possible to automatically close down of hacked accounts.

    Stealth cheater protection

    3) You could also just count "small warning flags" that you place around in the game. Dont just check for the "validation" in the beginning, no build these flags into the game logic itself. Dont make it break the gameplay, because then noone will look for it.
    Then when the user reached the end of level monster, check if there were any logged warning flags. These will not show up inside the game, so the unknowing user with a hacked edition could be playing for hours/days and suddently realize that he/she couldnt finish the game or advance to next level, because the game had a "bug". What the user didnt know was that this bug only occures on hacked clients.


    Be smarter than the crackers. Fool them into thinking the job was done. Make a copyprotection and know that the more advanced crackers will be able to remove it. But they probably dont want to play 50 levels to check if the crack also works all the way.

    Once they realize this problem, they might start to crack it too. But if you break the game up into level-packs, you can still validate between each pack download. So once you receive hacked client hash data, then just execute an exeception and crash the game on the client. Whoops the game crashed. Dont tell its because its hacked. A program error can happend. :-)

    Again, its not hacker proof. But it might annoy them enough to move on to the next game. Lastly, you could also put out regular updates for the game and only the latest version should be able to "post the records" etc. so the active users would have to update to keep in the loop.

  3. I have been doing some apk decompiling and hacking for a while (not warez, but mods and hacks mostly to the google apps and the android framework, always abiding xda-developers policies).

    Once you learn to read smali, it is almost as reading the original java code (but with way more LOCs). So, any code you add to check for keys can be found and deleted or replaced. You don't even need to recompile each time to eliminate more than one (some searches do miracles to find similar pieces of code) and, even if compilation/recompilation cycles are needed to find them, it's just a matter of one or two minutes to decompile: everything is automated by apktool and even more by apkmanager.

    Having said that, my suggestion to you is to implement some sort of online scoring table or similar, and when the user looks at the score table online, you can check the hash code you implemented and compare it with the associated gmail account. That way you can report the hack to google and send a nasty message to the user of the warez, explaining why that is illegal.

    Of course, a new hack could be implemented to eliminate the scoring table, but that would reduce the interest for the warez.

    Good luck.


    After researching to answer this question: Injecting code into APK (really about the Amazon DRM mechanism), I can tell a little bit on how Amazon is protecting the apps: it includes methods for checking for the installation validity everywhere (you can see an example of how they do it in my answer to that question). This will make any attempt to hack an app not very difficult, but extremely tedious. I believe that is a strong point: hackers won't want to spend so much time doing so many repetitive tasks: it's not challenging and it's boring. The main flaw I see in that approach is the possibility to hack the Amazon app itself to always return a valid answer, of course. But, if you mix your current hash checks with some sort of online check scattered among your methods, I believe the chances of it getting hacked may be drastically reduced.

  4. I know you're not really into obfuscation, but I really need to react to this:

    From here, I don't want to obfuscate
    our code as I have seen it broken
    before. I want something a little more solid, and I also want to learn how to do this properly.

    ProGuard is very reliable in my experience, and this although I use a couple of advanced features such as AIDL and some native code which calls Java method.. It takes a little work to read the documentation and do things properly, but once you're there ProGuard is extremely reliable and also optimizes your app.

    Custom security/cryptographic tricks are good, but without obfuscation it's like throwing a stone in the water in my humble opinion.

    I've used ProGuard in production for many months, and it just works flawlessly.

    If you're into learning, then read the ProGuard manual carefully, experiment with it, and inspect its output logs.

  5. Chance, that there are more talented programmers then YOU (applies for all programmer), is 100%. And if that is true, you can not fix hacking. But you can spend as much time and effort on it to go bankrupt.

    If you want to make some serious money you need to do some research on your target user group, and behavioral science. You need to make users playing that bring in new money, and thats it.

    Besides, you got it all wrong. Hackers are most active members of your user base, thy just behave in a way you did not intend them to.

    Take Zynga games on Facebook for example, do you think thy get hacked? - Sure, and about +100000 players only play, because thy can use bots, that automate everything.

    Having huge active user base botnet of actual people, makes archiver type gamers want to play the game - and if thy play, and it looks cool, then Avarage Joe will also want to play. If Avarage Joe plays, then his friends might want to play, and thy probably will not care anything other, then being better then his/her friend, killing time or having something to chat about. Avarage Joe friends will most likely be willing to pay to be better then Joe, but rather thy would like to invest in something that makes them able to be better.

    Besides if the real value is playing the game for free, then users who use the free hacked version, will most likely never would have payed for it. But thy are Avarage Joes and their friends just might. So this is like the cheapest commercial you can have. If you want to make money of your large userbase, then just make new versions of the game with small changes to levels and graphics.

  6. Piracy will always be an issue. By in large crackers are better at playing this Security Though Obscurity game than developers.

  7. First, I do NOT consider myself a pro in the SW security field whatsoever, but:

    I think an important thing is to let the application be dependent in some part(s) on the signature check. Don't let it affect immediately, but let it set some flags or change some values. later on, use those flags, check them, let the absence/incorrectness of them cause an exception of some kind which will terminate the application maybe. As long as the signature check is only relevant at the moment, it is easy to bypass it, to remove the line, once it touches more areas in the code, your application becomes harder (or less easier...) to hack. Also as I see it, not all checks should call the same routine for the sanction, because this will also make it easy to find the protection mechanism and terminate it.

    Of course, the sanction to take in cases of illegal SW may vary, you might want to crash the application when used illegally, but you might as well want to keep it running, and only send message that asks the user to buy a legal copy of the application.

    If this is just what you didn't want to hear, then I'm sorry for your time :)

  8. What an interesting and disturbing question. :-) As an exercise, you might try releasing an app through Amazon; they have their own DRM mechanism; I wonder if it works any better than ProGuard...

  9. One of the key elements in my opinion is to spread out the code so it's not all in one place. If you have a function called LicenseChecker.checkLicense() which retrieves the license and checks it, you can be sure it will be disabled promptly.

    The one advantage you have is that the crackers cannot see the comments of your code (and, if you obfuscate, method/variable names), so come up with something weird. In the onCreate() of one activity, you get the license ID. In onResume(), you get another value to check it against. Maybe create a thread and do some checks there. And then, some other irrelevant piece of code (maybe the player control) might pick up the value and compare it and store the result somewhere. Then three other irrelevant pieces of code will all independently check that value and disable your application if it doesn't match.

    Now I should say upfront that this can cause headache for yourself - obviously, cluttered, nasty code is harder to debug and prone to cause errors. Worst case, you create false positives in legitimately purchased applications.

    And, of course, everything can be reverse-engineered - once the crackers find the place where the app is disabled, they trace back the value that's being read from. They could then trace back where it's being stored, and trace that back..... or, much easier, they can just disable the final check (which is why I recommended 3 different places, all triggering delayed). Security is only as good as the weakest link.

    You will not be able to stop piracy. Your best bet is to delay the spreading of a pirated copy until the initial hype about your app has calmed down.