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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 crackable...so 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.
Thanks
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.
Conclusion
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.
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.
Update
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.
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
EDIT:
The Presentation Notes from Evading Pirates and Stopping Vampires
Some basic keypoints
Modify the LVL
Implement LVL Tamper Resistance
Use obfuscation
Add reflection
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.
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.
Piracy will always be an issue. By in large crackers are better at playing this Security Though Obscurity game than developers.
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...
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.
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 :)
Android users are just going to have accept the pain of constant phone-homes. The only secure Android app is an always-connected Android app.
This is, in large part, due to Google's refusal to lock-down the installation, like Apple has. On IOS you have to jailbreak the phone. On Android you can load any APK on a stock, factory install.
Keep some/most/all your content on the server; deliver it in chunks; validate the license/session on each call.
It will be incredibly hard to inhibit this kind ov behavior. Anything that is handled on the client-side is hackable using APK decompilation and modding, memory editing with software such as Game Guardian ect.
The only way I can see how partially getting around it, would be to make an online game instead. Or have certain functions handled online. Or if anti-tamper encryption like denuvo ever is available for Android / iOS.
Related
I implemented In app Billing in my Android application. I pretty much followed the sample (Dungeon) application to get it working. It seems to be functioning fine as of now. I now need to decide how much effort I should put into the Security portion.
I do have a server that I could use to implement the Security.java stuff. I also am currently using the standard PurchaseDatabase implementation.
As of right now I am thinking of just encrypting the .db file with a device specific key, and leaving Security.java alone.
My thinking is that my app is a pretty niche app, and I am not expecting a lot of hacking on it. If there are some people that put in the effort to save a couple bucks (each item to be purchased will only be $1), so be it.
I guess I am looking for opinions on what other people think about this...it seems there is no 100% secure implementation...just implementations that make the hacking not worth the effort. Have other people seen a lot of hacking of In App Purchases?
You got it right: you don't need to implement very complex protection features, you need to implement protection features that take too much time to be found and removed Here's a video from Google I/O 2011 about techniques to reduce "leechers": http://www.youtube.com/watch?v=TnSNCXR9fbY, I thoroughly recommend it. Some techniques you may want to try are:
use LVL;
obfuscate code;
call LVL at random times from a background thread;
insert license checks mixed with normal code;;
CRC code files;
be industrious: use reflection in JNI to check signatures;
encrypt core libraries/resources and load them on the fly.
Some of these techniques are very simple, other require a non negligible effort. The best recommendation is to be creative, hide checks where crackers do not expect them.
Another important point is to make your application degrade gracefully if you suspect piracy. For example, don't throw an "invalid license" because your license check needs network access on application start; instead, store somewhere a "valid for two months" token and randomly update it. Check it after a random number of days (say, a random integer in the 30-60 days range). Customers won't notice this check and it is hard to crack because it will not be apparent after a lot of time, much more time than crackers are willing to spend on a single application.
The tips in the Security and Design document for Android's In-app Billing state that:
In particular, attackers look for known entry points and exit
points in an application, so it is important that you modify these
parts of your code that are identical to the sample application.
Since I am going to use In-app Billing for the first time, I am very much interested in understanding what this means exactly, in terms of securing my subscription-based app:
What are exactly those "known entry/exit points"?
What do I need to modify in these parts, to make the task of an
attacker more difficult?
Given the fact that nothing can be protected from eventual reverse-engineering, is it really worth it to go to such great length to protect an
application/service?
I think that document is talking about the methods that are standard in Android for starting an application, namely the activity lifecycle methods (onCreate, etc.). These are easy for attackers to find because they aren't obfuscated (since the framework needs to be able to find them).
Given the fact that nothing can be protected from eventual
reverse-engineering, is it really worth it to go to such great length
to protect an application/service?
This is indeed an interesting question! To answer it one also has to ask: What is the expected cost of not protecting the app?
If the items sold via IAP incurr an actual cost for the provider/developer (think for instance of selling MP3s where for each download the provider might have to pay a license fee himself) this becomes even more important. This usually indicates the the possible win for an adversary and, thus, the effort he may be willing to invest in reverse engineering.
However, my impression is that there is only a marginal "black market" for cracked/pirated/... apps, the rationale being that it is not possible to offer those cracks or cracked apps via Google's market, which is the only one that comes pre-installed on all Android phones. Regular users will never see any other source of apps.
So, if you expect to sell a bigger volume of your app, you might well live with, say, 1% fraud by "power users". If your app is somewhat special and pricey and you expect to sell only a couple dozens or hundreds, you will be more interested in securing your intellectual property.
The first step in securing will always be obfuscation, which will take your app's security pretty far with (almost) no additional effort on your side. I recommend to obfuscate every app published if there are no strong reasons against it (stacktraces, for instance, may become completely useless in an obfuscated app).
At a fairly basic high level, entry points are where the application is started and exit points are where it ends. Each of these (as mentioned above) are unprotected and also tend to make some calls which aren't made anywhere else, making them easy to find and change.
I am looking to use one of the social networks in my Android program.
Most important for me is the ability to build a continuous leadership board in which players move up and down depending their wins/loses to others.
The idea is for players to challenge others head-to-head. The winner gains points and the loser loses points.
Equally important, I want this feature to include the possibility to "charge" the player game coins.
Scoreloop includes the possibility of challenges but they are there in order to win coins off other players. In other words, they are the means to the end.
In my case I need it to be the other way around. The "ends" is to be higher in the leadership board and the "means" are to play others with coins.
Scoreloop do have a continuos leadership board but it is not accessible from the program.
I tried looking at OpenFeint but their site is a real mess. It is impossible to understand from there exactly what is and isn't available.
I signed up and tried to add my program. I ended up adding it four times and cannot delete it!
Check out Swarm, which provides a similar feature set to the others you mentioned (Scoreloop, OpenFeint), but also specifically includes a virtual goods system (coins), that you could use to have users purchase challenge attempts (which sounds like what you're looking for). The docs are extremely well written, integration is a snap :)
Create a leaderboard using either OpenFeint or Scoreloop (we started off with Openfeint but quickly moved on to scoreloop - If you want the details, I'll be happy to explain our reasons).
Once its up, make sure its a leadarboard that allows overriding scores with worse scores.
Implement an ELO rating calculator. see: http://en.wikipedia.org/wiki/Elo_rating_system
Each player starts with a certain score (I use 1500, so that ratings will resemble the chess ratings range).
On a match end, you re-calculate each user's new Elo rating, and post it to the leaderboard.
You end up with a leaderboard that ranks each user according to their skill. i.e. the more they win, the higher their score is.
EDIT: per user request - her are some of the reasons that made us move to Scoreloop:
OF documentation looks like it was ported from iOS, and very badly so. For example, the docs gives an example of initializing OF in your Application class. This will cause their "Join / Don't like fun" full screen dialog appear out of the blue, when users are busy using other applications, as android will kill and re-create your application in the background as memory availability change.
ScoreLoop automatically creates a "userId" for the user, without them having to register / login. This allowed us to post user's highscores and display their highscores without having to bother the user for logging in.
Scoreloop have an "offline" mode, which makes it much more robust, efficient, accurate and easy to use.
In flaky network situations, OF login process took a very long time, and affected the game performance. (see #3 above).
OF does not allow you to fetch a score rank. If you want to get your user's rank, you have to fetch the complete leaderboard, cycle through it until you find your user's entry. This "solution" pretty much makes this option not-available.
Scoreloop provided us with grate support. I've opened several tickets, they all got answered promptly and professionally. These guys rock.
I wrote this code a while back, so there might have been other reasons which I forget.
My main activity is basically useless without another activity (act2). act2 can be accessed from a button in the main activity. It is also available through a home screen widget, which when clicked calls my main activity and immediately calls act2.
Right now, I have it set to check license anytime the function that handles the button click is called. This covers the button press in the main activity as well as if you come from the widget.
My question is, is this too often? Is getting a cache response anymore draining than checking a variable for example?
I have tried putting it on onCreate but when it says it's not licensed, you can just close the application and open it again and it will not run through onCreate again.
Here I assume you've read all the licensing documentation, and that you're using the SDK. You said nothing, so I'm going for the "defaults". There are a few clues on the Android developers blog as well as on the Internet.
I asked myself the same question last year. Or at least something similar. So let's go one step at a time:
My question is, is this too often? Is
getting a cache response anymore
draining than checking a variable for
example?
I would say that the difference is going to be "imperceptible" to "not much". First of all, the validity timestamp (VT field from extras) is stored locally, properly encrypted/obfuscated. I'm assuming you're using the ServerManagedPolicy policy, since you said nothing about it.
Depending on the kind of the app, we should notice that you may be even writing things on onPause, for example (checking for changes if applicable, of course). So, I wouldn't worry about it.
But because there is no perceptible harm does not mean you should do something. That's why I disagree with what Kerin posted:
I'm sure you'll stop loads of piracy and you aren't wasting your time at all.
More on that later. For now I say that you shouldn't need to do lots of checkings. That's what the policies are for. They handle it probably better than you and me. Anything else is indeed a waste. Personally, I only do checkings on onCreate (obviously), and also in one more situation rarely used (but very important on the app usefulness).
What you should do, however, and I say because nobody said here yet, is properly obfuscate and change the LVL library, as well as your own code side (the checkerCallbacks). Here, I changed a lot of things on the LVL library, including some simple single key cryptography (weak), and also changed how the interfaces are implemented, and how arguments are passed, and so on. Basically, I created my own LVL after posting that question here on SO.
On the opposite of what you're doing, I also customized the VT field in order to mandate a minimum time for the validity of the cached response. That's why my app is to be used in the wild, where net access is not always available. Those subtle details depend on your app, what it does, how it does, where people would be using them.
If you're a developer, it's easy to forget about the user. There is nothing worse than a legitimate user being denied access to an app he bought. So far, I didn't have problems (I check usage statistics and compare to my account), but I believe games have more trouble (it's typical of that field).
So, returning to my constructive (please, we are all trying to learn here, myself included) critic about Kerin's post, I would say that even LVL itself is not enough to "stop loads of piracy".
If you know anything about how Android works, you'd know that the apks can be easily decrypted to source code, just use dex2jar and jdgui (Google them). In fact, I always decrypt my apps before publishing to check if everything is working the way it should. And take into account that I never did computer college, I just happened to learn java and Android to create my own app that I needed and was unavailable for Android (a tide app for my country). I'm sure there are hackers and techies much smarter out there that can do even more.
People start thinking that LVL will stop piracy, and then learn the ugly truth and be disappointed. That's not what the LVL is for. Just look at the code... it was made to avoid "automated" piracy. It is to force someone to personally look into the code, see how it works, and then "switch" the proper flags, if he can make sense of them. But then again, if you use proguard, it will make the task horrible, exhaustive (believe me, that's why I use dex2jar + jdgui myself).
If your app is being sold for $1 or even around $5 or more, it will make this trouble not worth it. That's my stance on the LVL. Obviously, if you have an niche app that costs $100, for example, you probably can do it properly, server side, with public keys. But I feel that it's not the case here.
Anyway, just my 2 cents.
You can check for the license for the first time, then cache it. The next time when your app runs, read the license from the cache, and also start a Thread that gets the license from your server. If the license that you got from the server is now invalid. You can pop up a dialog box to tell the user that the license is invalid, remove the cached license, and quit the app.
Can you suggest me any good anti-crack approaches (other than a code obfuscation), considering that the paid apps on the Market are easily cracked, and the same goes for a basic server check after a PayPal transaction?
My idea is to have one (very important for the app) Java object saved on the server, and passed to the app each time when it starts. Do you think that this sounds good ?
Note that it is more like of a theoretical question, as I am not going to implement it in an app, I am more like seeking the knowledge for this rather than a concrete solution to a problem.
Any ideas would be appreciated, even ones that you are not very sure if they are good or not. Remember, the question is for Android apps. Thanks.
EDIT: I know that there can't be an unbreakable client side application, I am asking for a good option to prevent it other than a obfuscation
No. Code stored on the server and provided for execution on the device can be grabbed and stored elsewhere such as locally. (And that's probably going to be as hard for you to implement as it will be for the attacker to patch around)
Ultimately, you have to face the fact that preventing run authorization just isn't possible on a general purpose computing platform.
Unless you move actual functionality to execution on a server requiring an individually authorized account, all you can hope for with regard to code running on the user owned device is to achieve a higher than average shade of difficulty.