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
Related
i need to use SLGetWindowsInformation in slc.dll but i would rather implement my own version than pinvoking it 200 times on application start up and create the datatypes it need, so is it illegal to disassemble the library and write my own code that leech the behavior of this function
p.s i'm using c# so i won't inline an assembly, ill just copy the behavior
is it illegal to disassemble the library and write my own code
That depends on where you are. There are jurisdictions where reverse engineering is a protected consumer right, and so any attempt to prohibit it in a user agreement is null and void. There are jurisdictions where reverse engineering is not a protected consumer right, and therefore you may only do so if your license agreement allows it.
If you are somewhere where you can reverse engineer legally, there may still be restrictions from other laws (such as patents) on the code produced, though patents can get in the way even if you don't copy anyone and arrive at the idea in an independent manner, along with further innovations (though ironically patents were originally designed to actually encourage innovation).
Really, you're better off avoiding the issue entirely and never look at code that does something while you're trying to do the same thing, unless that code is released under a license that allows it.
i would rather implement my own version
Why not just implement your own version? If you think you can do better than someone else, do you really need to copy that someone else?
This is really a question for a lawyer and not for a programmer, but...
It all depends on the license of the library. AFAIK system dlls are subject to MS license you agree with before the installation and I bet there's a little line that forbids any kind of disassembling. Even with free libraries you should be careful, because most don't like reverse-engineering. If you need to modify a library, it should be open-source with a license, that permits it.
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).
On opening my executable file in MSIL disassembler it shows information of my application(like literals, function, properties, resources,...) even after I assigned them private.
How can I hide these information from disassembler.
You want to look for an obfuscation solution. Remember that while private members cannot be accessed by other code, they still do exist. However, obfuscation can make it more difficult to discern what your code is doing.
An obfuscater. The information will still be there but the names will be nonsense designed to be as confusing as possible.
Generally speaking you can't. Your best bet if you are worried about someone reverse engineering your code is to consider the following techniques:
Obfuscate the code
Assembly encryption (Note: I have no experience or working knowledge of this or the details of how it works).
Compile to a native assembly instead of a MSIL assembly.
The last option pretty much defeats the purpose of .NET assemblies however it will be much harder to reverse engineer from the native assembly to C# code than from MSIL to C#. The reality is though that if someone has your DLL(s) then given enough effort and/or time the original (or fairly close) source can be developed.
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.
We are about to use Code Protectors (Obsfucation as well as Native Compilation), I assume ORMs will be dependent little bit on Reflection and I am worried will Obsfucation and Native Compilation protection techniques create any problems?
Has anyone tried successful ORM and Code Protection for any good desktop application? We are having WPF Desktop Application.
Our primary language for development is C# and we are using our custom ORM but I want to evaluate any commercial ORM or ADO.NET EF etc as well.
Question is not about what is Code Protection and which one I should use, I am trying to ask about the effect of protection on ORM.
If your code is using Reflection, most probably the obfuscated assembly will not work. You will need to exclude from obfuscation those entities referenced by their original name. Take a look at Crypto Obfuscator which will analyze your code during obfuscation and show all methods and line numbers where potentially breaking methods (such as Reflection ) are called. This is a huge timer-saver since it pinpoints the exact location and helps determine the properties/classes you need to exclude from renaming.
Try .Net Reactor. Available at http://www.eziriz.com/
Its a LOT cheaper than some of the others around, and it can do a lot more. You can also disable certain options (like obfuscation, to preserve the use of reflection) and only have certain options enabled like ILDASM Suppression, which will still protect the code.
Cheers
Redgate acquired Smart Assembly not too long ago, which is what I'd look at if I had a need to do this.
A while ago I trialed CodeViel to look at obfuscating/encrypting code with some degree of success. I think if you’re serious about doing this it’s not as simple as dropping an assembly in one end and it popping out a protected assembly. You will have to consider portions of your code (ie Namespaces, Classes, Methods, Fields, Properties, Structures, Events, and Resources) which are only to be used internally, and those that need to be exposed to other resources and libraries. In the case I was looking at I was able to encrypt (or use native compilation) to hide some method implementations, but left the class definition (name, methods, properties untouched). In some cases I left whole namespaces untouched as they contained only simple POCO objects required by other libraries.
It really seems to be a careful case by case basis as to what strategy you use where, some internals you could obfuscate to make decompilation/reverse engineering hard and that would be enough. Other cases you could use the encryption/native compilation to simply hide a method implementation. And you will also get cases where you are excluding portions of an assembly from being touched at all. Most of these programs will give you some recommended defaults and options that you can start from, but you will need to tweak and change these until you can produce results that protect your core IP but don't restrict your end users.