I am building a client-side program that connects to a server. This client-side program needs to have the source code available to the users as part of the licencing (not an option). However, I need to ensure that when a user connects to the server with that client-side program, it's running with the original code and hasn't been altered and re-compiled.
Is there any way to check during connection to the server that they're using an unaltered version of the program?
No, there's really no way to do that.
You're basically encountering the "Trusted Client" problem. The client code runs on the user's PC, and the user has full control over that PC. He can change the bytes of the program on disk, or even in memory. If you were to try to perform a hash or checksum against the code, he could simply change the code that did that verification and make it return "unmodified".
You could try to make things a little harder on a malicious user but there's no practical way to achieve what you're hoping.
What you have described is a issue that the video game industry has been fighting for the last decade and a half. In short, how to prevent the user from modifying the client (in their case, generally to prevent cheating, though also for copyright reasons). If that effort has taught us anything, it's that preventing modifications to the client is a constant arms race that you will never decisively win. In light of that, don't even try.
Follow the standard client-server assumption that the client is in the hands of the enemy and cannot be trusted. Build your server side defensively based on that assumption and you'll be alright.
It's very very difficult and probably not worth it. But if you are interested in pursuing it you'd have to develop something that has been code signed and monitored by the Windows kernal.
A couple topics that will orient you to the scope of the problem:
Protected media path
Driver signing
Both media devices and device drivers are digitally signed by the manufacturer and continuously monitored by Windows. If anything goes out of whack, it gets shut down (that'ts the technical term). Seems very daunting. And I don't know if the technology is available for desktop software that isn't a device driver and isn't related to DRM.
Good luck!
Related
Can a running nodejs program cryptographically prove that it is the same as a published source code version in a way that could not be tampered with?
Said another way, is there a way to ensure that the commands/code executed by a nodejs program are all and only the commands and code specified in a publicly disclosed repository?
The motivation for this question is the following: In an age of highly sophisticated hackers as well as pressures from government agencies for "backdoors" that allow them to snoop on private transactions and exchanges, can we ensure that an application has been neither been hacked nor had a backdoor added?
As an example, consider an open source-based nodejs application like lesspass (lesspass/lesspass on github) which is used to manage passwords and available for use here (https://lesspass.com/#/).
Or an alternative program for a similar purpose encryptr (SpiderOak/Encryptr on github) with its downloadable version (https://spideroak.com/solutions/encryptr).
Is there a way to ensure that the versions available on their sites to download/use/install are running exactly the same code as is presented in the open source code?
Even if we have 100% faith in the integrity of the the teams behind applications like these, how can we be sure they have not been coerced by anyone to alter the running/downloadable version of their program to create a backdoor for example?
Thank you for your help with this important issue.
sadly no.
simple as that.
the long version:
you are dealing with the outputs of a program, and want to ensure that the output is generated by a specific version of one specific program
lets check a few things:
can an attacker predict the outputs of said program?
if we are talking about open source programs, yes, an attacker can predict what you are expecting to see and even can reproduce all underlying crypto checks against the original source code, or against all internal states of said program
imagine running the program inside a virtual machine with full debugging support like firing up events at certain points in code, directly reading memory to extract cryptographic keys and so on. the attacker does not even have to modify the program, to be able to keep copys of everything you do in plaintext
so ... even if you could cryptographically make sure that the code itself was not tampered with, it would be worth nothing: the environment itself could be designed to do something harmful, and as Maarten Bodewes wrote: in the end you need to trust something.
one could argue that TPM could solve this but i'm afraid of the world that leads to: in the end ... you still have to trust something like a manufacturer or worse a public office signing keys for TPMs ... and as we know those would never... you hear? ... never have other intentions than what's good for you ... so basically you wouldn't win anything with a centralized TPM based infrastructure
You can do this cryptographically by having a runtime that checks signatures before running any code. Of course, you'd have to trust that runtime environment as well. Unless you have such an environment you're out of luck - that is, unless you do a full code review.
Furthermore you can sign the build by placing a signature within the build system. The build system and developer access in turn can be audited. This is usually how secure development environments are build. But in the end you need to trust something.
If you're just afraid that a particular download is corrupted you can test against an official hash published at one or more trusted locations.
this is my first question so please be gentle...
I am working on a software which I would like to protect using some kind of licensing scheme.
A basic scheme would be to generate some "unique" key for a user. The user sends this key and a registration code when he wants to register the software and receives an activation code.
When the application runs it validates the activation code by comparing the "unique" key and a datablob received by decrypting the activation code.
This is fair and quite simple to implement, one can choose different crypto algorithms etc. however this scheme lacks two properties:
If the user manages to spoof hardware signature etc. to produce the same "unique" key on another computer he could use the same license data.
If the user decides to uninstall the application and wants to move it to another computer, there is nothing that prevents him from using the old license data again at the old computer and still obtaining new license data for the new installation.
Do you have any suggestions on how to resolve these issues?
One idea I had was to add some random data to the "unique" key, this random data would be stored in an obscure way, if the user deinstalls the application this random data would be removed, and some kind of hash with the previous random data and the license data would be generated which could be sent to me to verify that he really have uninstalled the application and made me sure that he wont be able to use the previous license data again since the random data had changed.
Over and out, for now...
EDIT:
I currently have a scheme that works, I should mention that the most common product is installed in an embedded enviroment where hardware-changes are very rare and if there is a hardware failure then most certain the machine is broken. But I could modify the hardware-key scheme to take into account and allow for some changes.
Also because of this the software will most likely not be run inside a VM, good point though and I haven't thought about that.
The application does not call out regularly, if a network connection is available the user gets the option to make a more automatic registration, otherwise he/she gets a registration key, enters it in the software and gets an installation ID which is provided to me, registration code + installation ID generates an activation key that the user gets from me which then unlocks the software.
What I am looking for is good/feasible solutions to the 2 points. Hardware spoofing, Revoking license keys i.e. to be sure the user can not use the same regcode+activationcode.
Thank you for all your feedback
It is not necessary to
First, you should make it clear what you're trying to protect. Apparently, you want to ensure that for each purchase of your application, there will only ever be one computer on which the application is installed and runnable.
You propose to use a hardware signature as part of each user's unique key. What happens if my hardware fails (e.g. my hard disk breaks)? I'm certainly not going to purchase your application if I can't go on using it after a hardware problem, so at a minimum you must be prepared to handle key change requests. You'd better respond fast, because if your application is important I want to minimize downtime. And I'm not inviting you to check that my hardware has failed, so you'll have to take my word for it. That means any user can get a free licenses from time to time by pretexting a hardware failure.
What about virtual machines? It's probably feasible to detect all currently existing virtual machine configuration, at the risk of a few false positives now and then. If you forbid virtual machines, how do you justify this to users? If you allow virtual machines, how do you prevent the user from making multiple copies of the whole VM? (This can happen even with physical machines, with hibernation).
Is the application going to call back to you every time it starts? I guess so, from your deinstallation scheme. That's a bandwidth and availabilty cost, and will also put off some users — not everyone is online, especially in sensitive environments. But then you don't need such a complex scheme: your server can keep track of how many copies of the application are running, though you do have to handle the case when the application doesn't terminate cleanly for any reason (application crash, OS crash, power failure, loss of connectivity...).
You don't discuss this in your question, but you have to protect the application executable, so that someone can't bypass the license check with a debugger.
Place your software into appliance hardware and put a padlock on the hardware. Ship the appliance to the customer.
If you believe the customer will hacksaw the appliance open to get your code, consider encrypting the storage medium.... Then they have to hacksaw the box AND find the keys. A TPM chip or secure USB token may aid with the latter.
Being a shareware author and longtime member of ASP myself i think you are going into the wrong direction with your solution. The only way to make this workable is with a hardware device as already suggested. This or constant online activations is the only way if you want to be sure and your product is so good and without competitors that your customers will still use it.
But what we (organized small ISV's) learned from practice is that you should not do what you are trying to do. Do not bind it to hardware. Sell one license per person not one license per computer. In the end you will make more sales because of the relaxed license.
Just do enough to make the honest people stay honest. So limit the trail version (i decided to terminate the application after one hour for me) and leave the final version free from all stuff. Give a separate download for payed customers and thats it. Be a nice company and not a greedy profit maximizing by legal restrictions company.
I used some of the better windows protection programs first but they all had serious problems with my code. And they call get cracked sooner or later. So i gave up all of them.
P.S.: I use a hardware fingerprint schema on windows where i don't restrict the program but just to keep people away from getting new trial keys every 30 days. Together with a nag screen it seems to work. The fingerprint is an xor of user name, windows installation time, modify time stamp of a system files and harddisk serial id.
Let the registration code also be the activation code.
You generate the unique registration code at point of sale, or packaged with the product. Customer registers/activates/deactivates with you (or your server) in one step using that single code. The customer's hardware doesn't have to generate any keys.
Reregistering/reactivating still requires contact with you, so you're aware of reinstall attempts.
I think that the only solution to your problem is a cryptographic hardware dongle. Usually it would be a USB-based tamper-resistant challenge-response dongle, that can be easily transferred between computers.
These devices cost less than $1 for large quantities, and not more than $10 for very small quantities. The good ones are very hard to forge, very easy to embed in your application, and usually supplied with a free EXE encryptor which also contains anti-debugging and anti-reverse-engineering functionality.
I mean in operating systems or their applications. The only way I can think of is examine binaries for the use of dangerous functions like strcpy(), and then try to exploit those. Though with compiler improvements like Visual Studio's /GS switch this possibility should mostly be a thing of the past. Or am I mistaken?
What other ways do people use to find vulnerabilities? Just load your target in a debugger, then send unexpected input and see what happens? This seems like a long and tedious process.
Could anyone recommend some good books or websites on this subject?
Thanks in advance.
There are two major issues involved with "Client Side Security".
The most common client exploited today is the browser in the form of "Drive By Downloads". Most often memory corruption vulnerabilities are to blame. ActiveX com objects have been a common path on windows systems and AxMan is a good ActiveX fuzzer.
In terms of memory protection systems the /GS is a canary and it isn't the be all end all for stopping buffer overflows. It only aims to protect stack based overflows that are attempting to overwrite the return address and control the EIP. NX Zones and canaries are a good things, but ASLR can be a whole lot better at stopping memory corruption exploits and not all ASLR implementations are made equally secure. Even with all three of these systems you're still going to get hacked. IE 8 Running on Windows 7 had all of this and it was one of the first to be hacked at the pwn2own and here is how they did it. It involved chaining together a Heap Overflow and a Dangling Pointer vulnerability.
The problem with "client side security" is CWE-602: Client-Side Enforcement of Server-Side Security are created when the server side is trusting the client with secret resources (like passwords) or to send report on sensitive information such as the Players Score in a flash game.
The best way to look for client side issues is by looking at the traffic. WireShark is the best for non-browser client/server protocols. However TamperData is by far the best tool you can use for browser based platforms such as Flash and JavaScript. Each case is going to be different, unlike buffer overflows where its easy to see the process crash, client side trust issues are all about context and it takes a skilled human to look at the network traffic to figure out the problem.
Sometimes foolish programmers will hardcode a password into their application. Its trivial to decompile the app to obtain the data. Flash decompiling is very clean, and you'll even get full variable names and code comments. Another option is using a debugger like OllyDBG to try and find the data in memory. IDA-Pro is the best decompiler for C/C++ applications.
Writing Secure Code, 2nd edition, includes a bit about threat modeling and testing, and a lot more.
My logic of APT (Anti-Paching Technology) is as follows...
1) Store on the MSSQL server the md5 hash of the executable for protection.
2) Perform an md5 comparison (within my application startup) the hash found on the server, with the executable itself.
3) If comparison fails exit application silently.
And all these above before it is finally pached!
I mean what is your best way to protected a file from being patched?
Without using ready tools (.net reactor, virtualizer etc)
Edit: Something else just came into my mind.
Is there any way of checking the application integrity on server side?
I mean my app works only online. Could i execute something on the server (my domain) that could check the application integrity?
The thing is a cracker would patch the application precisely on step 2, removing the hash check code.
So I wouldn't call that very effective against serious crackers.
EDIT: I guess your best bet is defense in depth, given that your app has to be online I'd:
Require authentication: Authenticate users, hopefully via a cryptographic key, and require a key check to receive/send data.
Obfuscation: It makes things harder for crackers.
Continued checks: Besides checking who is sending data, validate the application each time a request is sent.
These all can still be circumvented, but they make things a lot harder and might disuade some if your app is not worth that much to them.
A patched application means the 'cracker' has complete control over the machine the code is running on (at least enough control to patch the executable). So patch prevention however smart it might be is working against the flow of control.
Complicating your binary file might be enough to discourage patching so obfuscators are propably your best bet.
you can't. once someone else has your file they can do what they like with it - first thing would be to patch out your anti-patching code.
If the application is running on someone else's machine, you cannot prevent them from patching it. You can make it harder, but it's a shell game: you cannot win. Regardless of how complicated you make it, some guy somewhere will see it as an interesting challenge to break your protection, and he will succeed. Then, everyone else just has to download his version. The most extreme form of patch-protection today is Skype (that I know of). It's insanely complicated, and yet it has been broken.
Since your application apparently runs online, you can ask yourself why you want to prevent patches in the first place (maybe it's to prevent the user from entering some bad values? Or to prevent them from seeing some information that's present in the program?), and then architect your program so that whatever you want to keep hidden or checked happens on the server.
For example if it's a game and you want to prevent players from hacking the game to know where the other players are: change the server so it only sends coordinate information for the players that you can already see.
Another example: if it's an online store and you want to make sure users don't submit purchase orders with incorrect prices, check the prices at the server.
The only exception there is if you control the hardware that the program's running on. But even there, it's very hard to do it right (see: XBox, PS3, and the many other consoles that tried to do that and failed). It's probably still better to leverage the client/server architecture rather than betting on "trusted computing".
Crackers nowadays don't bother patching your executable file; they simply change your program's variables in-memory to make its behaviour more amenable to their requirements. Defending against this is very difficult and reasonably pointless; most games' crack-protection works only by searching for signatures of known crack programs (like an AV engine does).
Everyone nailed it, you can't stop someone but you can make it harder for them, you could even go off the deep end and make some in-memory validation stuff like World Of Warcrafts Warden system.
If you tell us what language you are writing in we might be able to suggest some simple obfuscation methods.
I want to view dynamic contents (flash games, online transaction...etc) offline.
For example, I finish level 1 of this cool flash RPG game.
I go offline and play the level again.
Or, I make a purchase.
And make the purchase again offline.
Of course this won't do anything. It will be strictly for demonstration purpose.
Or, I watch a video online. Go offline and watch it again.
Is this feasible? Whatever I do through browser, it has to download things.
When it downloads, it stores on disk. Then, when it is in offline mode, it routes all traffic out to local disk.
Sounds simple, but is this really possible?
Or am I missing something?
Let's say someone patched a browser to make offline mode much more powerful.
As a web developer, how can I secure my application from this
patched browser?
Let's say I charging my contents (video, game...etc)
per view/use. With this patched browser, people can pay once
and view/use it over and over again.
They might even make a tarball out of their browser cache
and share with other people online.
So, my questions are:
is this patched browser possible?
if it is possible, how can I defend my content against it?
I'm trying to find the original author of the quote: "Trying to make digital content not copyable is like trying to make water not wet."
In your question you describe several different scenarios as if they were similar. They are not. If you have a specific question, then please ask it so that people can focus on addressing the specific case that concerns you.
Let's talk about video (and audio). Essentially, without controlling the client, you can NOT stop the downloaded video from being cached and re-watched. "Patched" browsers exist. In fact, they're not patched. They don't even need to be. FireFox has any number of plug-ins such as "DownloadHelper" which make all of this possible. YouTube goes to some effort to change their system regularly to break DownloadHelper. But they know they can only slow things down.
The only way to control a video download being re-watched is insist on the user using your completely custom plugin or application. The problem is that (a) that costs you much more money, (b) it's more painful for the user.
The other cases you mention - RPG and online transaction... these are different. Often with an RPG or other game, the client portion includes only a part of the code. Some of the code resides on your server. Without a connection to the server, the game cannot be played. You don't have to write it that way, you could make it 100% client... in which case (e.g. for Flash) the SWF file can be downloaded and played again and again, without your control.
But usually those online flash games are part-server in order to do what you say, and make them playable only online and only via the game-writers site.
An online transaction ALWAYS involves a server component, usually encrypted and non-repeatable. They can be secured.