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How can I protect my .NET assemblies from decompilation?
(13 answers)
Closed 6 years ago.
I am writing a .NET application (a Windows class library) for implementing the licensing our product.
The problem is that the DLL can be easily disassembled by the MSIL disassembler or any other third-party tools and one can easily break the code.
I have even tried signing the assembly, but still it can be disassembled.
So how do I prevent this?
Is there any tool to available for this?
Check out the answers for this question.
You cannot achieve complete protection, but you can hinder disassembly in ways that make it more difficult for people to succeed at it. There are more ways to do this, some of them detailed in the answers to the question in my link above:
Obfuscate your code.
Use public/private key or asymmetric encryption to generate product license keys.
Use a packer to pack your .NET executable into an encrypted w32 wrapper application.
What I would add would be incremental updating, both for your core functionality and the protection code, so your users will constantly benefit from the new features while making crackers lag behind you in breaking your software. If you can release faster than they can break and distribute your software, you are in gain. Legitimate users will always have technical support and a word to say regarding new features. They are your best market, as the ones who crack your software wouldn't have payed for it anyway.
You can't, but you can use an obfuscator so that it's impossible to make sense out of your code.
For example, have a look at Dotfuscator.
The community edition of this program is included with Visual Studio.
.NET has an attribute called SuppressIldasmAttribute which prevents disassembling the code. For example, consider the following code:
using System;
using System.Text;
using System.Runtime.CompilerServices;
[assembly: SuppressIldasmAttribute()]
namespace HelloWorld
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Hello world...");
}
}
}
As you can see, there are just two differences:
We have added System.Runtime.CompilerServices namespace decleration.
We have added [assembly: SuppressIldasmAttribute()] attribute.
After building the application in Visual Studio, when we try to open the resulting EXE file in ILDASM, now we get the error message.
Anything written for the .NET framework is subject to disassembly. You cannot prevent it.
There are obfuscation tools available that will change variable names and insert other 'noise' into your IL, for instance Dotfuscator.
You might want to consider taking another approach with your licensing library, that is, using something else other than .NET, if licensing your product is absolutely necessary.
As mentioned above in the selected answer, there is no true full proof way to secure you code.
Even in something like c++, if your applications code is in your customers hands : Eg - they have physical access to the binary, that application could potentially be disassembled.
The solution would be to keep the functionality that you are licensing, out of reach of people who may want to disassemble it, let them use it, but don't let them hold it.
Consider using :
Web Services
Keep your marketable content server side and beyond the reach of your clients. They can use it, but not examine the code.
Encrypted Binaries and Online Binaries
Maybe even streaming assemblies in an encrypted format to a wrapper application. Keep your decryption keys server side to prevent offline disassembly. This might be circumvented however if someone found a way of exporting the assembly from the app domain of the application, once it has loaded it. (You cannot load an encrypted binary, so an end user might wait until your application has done the work of decryption, then exploit that to export the finished binary) (I was investigating a way to accomplish this (the exporting) - I didn't quite get it working, doesn't mean someone else wont)
The only thing to remember is that ANY code, no matter how well coded it may be, is vulnerable if it is on a users system. You have to assume the worst when you put binaries on their system. A really talented Engineer can disassemble any dll, be it c++ or c#.
Related
I've been given the task to rewrite or convert a jar program into another language like C#.
The program is like a virtual time stamper for when workers check in and out. The writer of this program made an unfinished program leaving it more or less useless if it needs an update or changing of users, cause none of the people using it is able to rewrite or edit this code.
My problem is that I have very little to no knowledge or experience with Java programming.
My question is: Would it be easier to start from scratch or could someone with good knowledge in both Java and C# look at it and maybe point in the right direction.
MY efforts: well i tried Java Eclipse but that made me more confused than before, then i tryed a program called Java Decompiler, this is when i found out the writer is not even half done with this program, there are class files for user registration and Admin panels for editing so everything would be accessible through graphic user interface.
Heres a view of the interface (note that faces and names have been whiped due to privacy, also note that some words are in danish just ignore those. "Tids registrering" means: "time registration" and "ikke til stede" means that they are not there)
The goal is to make a program able to do:
1. Save check in/check out times and date for each user.
2. Instead of saving in a *.log it should be saved in a database.
3. Graphic interface for admin access to edit add/edit/remove users
If a Java/C# programmer wants to help we can talk about it in private about how, where and when to transfer files (again due to privacy)
If you find it too difficult or time consuming to convert i could use some help to rewrite from scratch so help from just C# programmers would also be appreciated.
If there is any grammatical and/or spelling errors in this post I'm sorry and apologist
Most likely effort to port UI from Java (either source or byte code) to C# (or any other .Net language) will be comparable or significantly higher than rewrite as frameworks are different.
For non-UI code you may be able to do direct port of most of the code either by hand or with some automated tools as languages are close enough. If original code does not have unit tests/integration tests and not written in a style you are comfortable with than cost of rewrite may be lower.
Ultimately it is your call if the porting effort worth it or not.
I want to run a thread that checks the memory image of the current executable, for protection reasons. Any ideas how to do CRC on the current memory executable (WinAPI or .NET way)? My app is written in .NET.
Signing your assemblies will give you as good verification as you can get with relation to verify CRC of .Net assembly (see Rodrigo's answer).
If you are worried that someone will patch assembly at runtime you probably worried too much. It requires better understanding of runtime to in memory patch IL for a method that is already JIT'ed compared to simply disassembling your .Net code and fixing it up (including removal of your CRC checks).
If you doing it more for fun than you shoud be able to find base address where assembly is loaded and compute CRC of some sort... or see if pages are marked as modified...
I think that's going to be quite difficult in .NET. When an executable is loaded, it can potentially be split up and loaded into several different regions in memory. You'll need to acquaint yourself with the Window's Executable format:
http://www.microsoft.com/whdc/system/platform/firmware/PECOFF.mspx
as well as the Windows executable loading process.
You'll might also want to concern yourself with depenency dlls as well. You'll be making so many native calls, that you might want to consider doing this in C.
Not much of an answer, I'm afraid.
Any runtime check you do will have the following drawbacks:
False positives. Because this is .NET, you cannot assume the runtime doesn't modify your in-memory code. You may detect a hack where there is none.
Any run-time check you make will be no more secure than the code you are trying to protect. This includes any runtime mechanism you create in your app such as periodic CRC checks, sentinel processes, or even checking with a server where the request can be faked.
You will decrease performance in your legitimate application, where the pirated version will run better without all these checks
You will do nothing to solve patching your EXE.
I understand that you are just trying to make it as hard as possible, even though it's not 100% uncrackable. But the solutions you propose (and likely any solution you can implement yourself) will do extremely little to thwart any average cracker.
Because this is such a demanded feature though, I would look for 3rd party solutions where they have put forth the effort for a sophisticated solution which can be updated as cracking techniques evolve. I cannot recommend any personally though.
I am not aware of a way to do this in .NET.
If you are interested in protecting you executables, you can generate a new key with sn and add it to AssemblyInfo.cs, so that if the application is modified at least it will not run.
Jon Skeet's Miscellaneous Utility Library contains a method to compute the Adler32 checksum on a stream. Its usage would be:
MiscUtil.Checksum.Adler32.ComputeChecksum(stream);
As for creating a memorystream out of the assembly that is currently running... I don't know if that is even possible (or advisable).
Quite a few people have really taken interest in the dll's ivé sent them, and they're not the type that should be given away for free too often...
I was just wondering, if I were to sell my components, user controls etc, how would I go about protecting them, in terms of ownership/encrypting code (if possible) etc.. What steps have you taken to help prevent people using yours without paying for them?
You can use any commercial obfuscater which encrypt your functionality and giving error if decompile.
Here i have the whole list which are available in market.
I used many of them some are just encrypt string, public method, private methods,properties and all.
Just go through it.
see the whole list and article
The only truly secure way to protect your dll is not to give it to them. Expose it instead via a web-service etc (obviously this doesn't work in all cases). Every obfuscator can be broken with patience. Think how much the games industry spends on this, and things are broken / reverse-engineered within days, sometimes hours.
"Lawyers" may serve as a layer of protection, and obfuscation will certainly discourage idle browsing. But a determined hacker (for example, for commercial illegal spying) will be able to get at your code eventually.
I guess you simply need to weigh the costs and benefits...
Well, I will definitely put my copy right,company name and production name information to my DLL. Whenever anybody use it,those information still appear on my DLL. And if possible,I will try to use Dotfuscator tool from visual Studio which helps to obfuscate my DLL.
How do I protect the dlls of my project in such a way that they cannot be referenced and used by other people?
Thanks
The short answer is that beyond the obvious things, there is not much you can do.
The obvious things that you might want to consider (roughly in order of increasing difficulty and decreasing plausibility) include:
Static link so there is no DLL to attack.
Strip all symbols.
Use a .DEF file and an import library to have only anonymous exports known only by their export ids.
Keep the DLL in a resource and expose it in the file system (under a suitably obscure name, perhaps even generated at run time) only when running.
Hide all real functions behind a factory method that exchanges a secret (better, proof of knowledge of a secret) for a table of function pointers to the real methods.
Use anti-debugging techniques borrowed from the malware world to prevent reverse engineering. (Note that this will likely get you false positives from AV tools.)
Regardless, a sufficiently determined user can still figure out ways to use it. A decent disassembler will quickly provide all the information needed.
Note that if your DLL is really a COM object, or worse yet a CLR Assembly, then there is a huge amount of runtime type information that you can't strip off without breaking its intended use.
EDIT: Since you've retagged to imply that C# and .NET are the environment rather than a pure Win32 DLL written in C, then I really should revise the above to "You Can't, But..."
There has been a market for obfuscation tools for a long time to deal with environments where delivery of compilable source is mandatory, but you don't want to deliver useful source. There are C# products that play in that market, and it looks like at least one has chimed in.
Because loading an Assembly requires so much effort from the framework, it is likely that there are permission bits that exert some control for honest providers and consumers of Assemblies. I have not seen any discussion of the real security provided by these methods and simply don't know how effective they are against a determined attack.
A lot is going to depend on your use case. If you merely want to prevent casual use, you can probably find a solution that works for you. If you want to protect valuable trade secrets from reverse engineering and reuse, you may not be so happy.
You're facing the same issue as proponents of DRM.
If your program (which you wish to be able to run the DLL) is runnable by some user account, then there is nothing that can stop a sufficiently determined programmer who can log on as that user from isolating the code that performs the decryption and using that to decrypt your DLL and run it.
You can of course make it inconvenient to perform this reverse engineering, and that may well be enough.
Take a look at the StrongNameIdentityPermissionAttribute. It will allow you to declare access to your assembly. Combined with a good code protection tool (like CodeVeil (disclaimer I sell CodeVeil)) you'll be quite happy.
You could embed it into your executable, and extract and loadlibrary at runtime and call into it. Or you could use some kind of shared key to encrypt/decrypt the accompanying file and do the same above.
I'm assuming you've already considered solutions like compiling it in if you really don't want it shared. If someone really wants to get to it though, there are many ways to do it.
Have you tried .Net reactor? I recently came across it. Some people say its great but I am still testing it out.
Well you could mark all of your "public" classes as "internal" or "protected internal" then mark you assemblies with [assembly:InternalsVisibleTo("")] Attribute and no one but the marked assemblies can see the contents.
You may be interested in the following information about Friend assemblies:
http://msdn.microsoft.com/en-us/library/0tke9fxk(VS.80).aspx
i am creating my own CMS frame work, because many of the clients i have, the have same requirements, like news module, newsletter module, etc.
now i am doing it fine, the only thing that is bothering me, is if a client wants to move from my server he would ask me to gibe him his files, and of course if i do so the new person who will take it he will see all my code, use it and benefit from i, and this is so bad for me that i spend all this time on creating my system and any one can easily see the code, plus he will see all the logic for my system, and he can easily know how other clients of mine sites are working, and that is a threat to me, finally i am using third party controls that i have paid for their license, and i don't want him to take it on a golden plate.
now what is the best way to solve this ? i thought it is encrypting, but how can i do that and how efficient is it ?
-should i merge all my CS files and Dlls in bin folder to one Dll and encrypt it, and how can i do that ?
i totally appreciate all the help on this matter as it is really crucial for me.
you should read this
Best .NET obfuscation tools/strategy
How effective is obfuscation?
In my experience, this is rarely worth the effort. Lots of companies who provide libraries like this don't bother obfuscating their code (Telerik, etc).
Especially considering what you are writing (CMSes are everywhere), you'd likely see more benefit from your time spent implementing features that put your product/implementation in a competitive advantage and make companies see that the software you are capable of writing has value, rather than the code itself.
In the end, you want to ensure you are a key factor in making software work for a company, not the DLLs you give them.
You'll need to precompile your site and obfuscate dlls.
Visual Studio has something like Dotfuscator Community Edition shipped with it. You could give it a try.
Of course, HTML output, CSS declarations, database structure and stored procedures code cannot be encrypted.
You can however try to compress CSS which will also reduce its readbility by humans.
Check here: The best approach to scramble CSS definitions to a human-unreadable state throughout an ASP.NET application
One other idea would be to use a frame in your HTML and put the most of the site pages inside of it. This way, it will not be visible when doing "View source".
Or just state it clearly that you offer whatever you're doing as a service and do not provide source codes of your work. I somehow doubt salesforce would be willing to give their sources to anyone who asks.