[c#] Protect .NET code from reverse engineering?

Obfuscation is one way, but it can't protect from breaking the piracy protection security of the application. How do I make sure that the application is not tampered with, and how do I make sure that the registration mechanism can't be reverse engineered?

Also it is possible to convert a C# application to native code, and Xenocode is too costly.

C# provides lot of features, and is the ideal language for my code, so writing the whole codebase again in C++ is out of the question.

Secure certificates can be easily removed from the signed assemblies in .NET.

Just to add a warning: if you are going to use obfuscation, check that everything still works! Obfuscation might change things like class- and method-names. So if you use reflection to call certain methods and/or classes (like in a plugin-architecture) your application could fail after obfuscating. Also stacktraces might be useless to track down errors.

A secret that you share with lots of people is not a secret. If you have secret stuff in your code, obfuscating it is no protection; it only has to be deobfuscated once. If you have a secret that you don't want to share with your customers, then don't share it with your customers. Write your code as a web service and keep your super secret code on your own server, where only you can see it.

Well, you cannot FULLY protect your product from being cracked, but you can maximize/enhance the security levels and make it a little bit too difficult to be cracked by newbies and intermediate crackers.

But bear in mind nothing is uncrackable, only the software on server side is well protected and cannot be cracked. Anyway, to enhance the security levels in your application, you can do some simple steps to prevent some crackers "not all" from cracking your applications. These steps will make these crackers go nuts and maybe desperate:

• Obfuscate your source code, obviously this will make your source code look like a mess and unreadable.
• Trigger several random checking routines inside your application like every two hours, 24 hours, one day, week, etc. or maybe after every action the user take.
• Save your released application's MD5 checksum on your server and implement a routine that can check the current file MD5 checksum with the real one on you server side and make it randomly triggered. If the MD5 checksum has been changed that means this copy has been pirated. Now you can just block it or release an update to block it, etc.
• Try to make a routine that can check if some of your codes (functions, classes, or specific routines) are actually have been modified or altered or even removed. I call it (code integrity check).
• Use free unknown packers to pack your application. Or, if you have the money, go for commercial solutions such as Thamida or .NET Reactor. Those applications get updated regularly and once a cracker unpack your application, you can just get a new update from those companies and once you get the new update, you just pack your program and release a new update.
• Release updates regularly and force your customer to download the latest update.
• Finally make your application very cheap. Don't make it too expensive. Believe me, you will get more happy customers and crackers will just leave your application, because it isn't worth their time to crack a very cheap application.

Those are just simple methods to prevent newbies and intermediate crackers from cracking your application. If you have more ideas to protect your application just don't be shy to implement them. It will just make crackers lives hard, and they will get frustrated, and eventually they will leave your application, because it's just doesn't worth their time.

Lastly, you also need to consider spending your time on coding a good and quality applications. Don't waste your time on coding complicated security layers. If a good cracker wants to crack your application he/she will do no matter what you do...

Now go and implement some toys for the crackers...

In my experience, making your application or library more difficult to crack hurts your honest customers whilst only slightly delaying the dishonest ones. Concentrate on making a great, low friction product instead of putting a lot of effort into delaying the inevitable.

If it's written in .NET and compiled to CIL, it can be reflected. If security is a concern and obfuscation is to be avoided, then I recommend writing your application using a non-managed language, which is, by nature, harder to reverse engineer.

Anything running on the client can be decompiled and cracked. Obfusification just makes it harder. I don't know your application, but 99% of the time I just don't think it's worth the effort.

If it's written in .NET and compiled to CIL, it can be reflected. If security is a concern and obfuscation is to be avoided, then I recommend writing your application using a non-managed language, which is, by nature, harder to reverse engineer.

Is it really worth it? Every protection mechanism can be broken with sufficient determination. Consider your market, price of the product, amount of customers, etc.

If you want something more reliable then go down the path of hardware keys, but that's rather troublesome (for the user) and more expensive. Software solutions would be probably a waste of time and resources, and the only thing they would give you is the false sense of 'security'.

Few more ideas (none is perfect, as there is no perfect one).

• AntiDuplicate
• Change the language, use the nice tricks that the authors of Skype used
• License server

And don't waste too much time on it, because the crackers have a lot of experience with the typical techniques and are few steps ahead of you. Unless you want to use a lot of resources, probably change the programming language (do it the Skype way).

• Use online update to block those unlicensed copies.

• Verify serial number from different modules of your application and do not use a single function call to do the verification (so that crackers cannot bypass the verification easily).

• Not only check serial number at startup, do the verification while saving data, do it every Friday evening, do it when user is idle ...

• Verify application file check sum, store your security check sum in different places.

• Don't go too far on these kind of tricks, make sure your application never crash/get into malfunction while verifying registration code.

• Build a useful app for users is much more important than make a
  unbreakable binary for crackers.

Just make a good application and code a simple protection system. It doesn't matter what protection you choose, it will be reversed... So don't waste too much time/money.

Apart from purchasing protection, you (or your developers) can learn to copy-protect.

These are ideas:

At first, try to write a program that writes itself to console. That's a famous problem. Primary purpose of this task is to practice writing self-referencing code.

Second, you need to develop a technology that will rewrite some code in a way dependable on other methods' CIL.

You may write a virtual machine (yet in .NET). And put some code in there. Ultimately, the virtual machine runs another virtual machine which runs the code. That's for a part of rarely-called functions for not to slow the performance too much.

Rewrite some logic into C++/CLI, and mix managed code with unmanaged. This will harden the disassembling. In this case, do not forget to provide x64 binaries too.

If you want people to able to run your code (and if you don't, then why did you write it in the first place?), then their CPU needs to be able to execute your code. In order to be able to execute the code, the CPU needs to be able to understand it.

Since CPUs are dumb, and humans aren't, this means that humans can understand the code as well.

There's only one way to make sure that your users don't get your code: don't give them your code.

This can be achieved two ways: Software as a service (SaaS), that is, you run your software on your server and only let your users access it remotely. This is the model that Stack Overflow uses, for example. I'm pretty sure that Stack Overflow doesn't obfuscate their code, yet you can't decompile it.

The other way is the appliance model: instead of giving your users your code, you give them a computer containing the code. This is the model that gaming consoles, most mobile phones and TiVo use. Note that this only works if you "own" the entire execution path: you need to build your own CPU, your own computer, write your own operating system and your own CLI implementation. Then, and only then can you protect your code. (But note that even the tiniest mistake will render all of your protections useless. Microsoft, Apple, Sony, the music industry and the movie industry can attest to that.)

Or, you could just do nothing, which means that your code will be automatically protected by copyright law.

If it's written in .NET and compiled to CIL, it can be reflected. If security is a concern and obfuscation is to be avoided, then I recommend writing your application using a non-managed language, which is, by nature, harder to reverse engineer.

Frankly, sometimes we need to obfuscate the code (for example, register license classes and so on). In this case, your project is not free. IMO, you should pay for a good obfucator.

Dotfuscator hides your code and .NET Reflector shows an error when you attempt to decompile it.

.NET Reactor

Update

Jared pointed out that de4dot claims to be able to decompile it.

.NET Reactor provides complete protection for your sensitive intellectual property by converting your .NET assemblies into unmanaged processes which cannot be understood as CIL, and which no existing tool can decompile. Hackers have no access to any intelligible form of your source.

Powerful and flexible, the .NET Reactor licensing features allow you to enforce your license conditions and protect your revenue stream by using hardware and software locks. The license manager can build trial or permanent licenses, in a matter of seconds. A fully documented software development kit (SDK), complete with examples, allows you to call the licensing system directly from your code, allowing you to create custom extensions to the licensing system.

There is a detailed comparison sheet for several .Net obfuscation tools.

Screenshoot taken from obfuscators.io

There's Salamander, which is a native .NET compiler and linker from Remotesoft that can deploy applications without the .NET framework. I don't know how well it lives up to its claims.

In my experience, making your application or library more difficult to crack hurts your honest customers whilst only slightly delaying the dishonest ones. Concentrate on making a great, low friction product instead of putting a lot of effort into delaying the inevitable.

You can't.

There are steps you can take to make it a little more difficult, but ultimately any executable on the local machine is crackable. Eventually, that code has to be converted into native machine code and every application that is runnable is vulnerable.

What you want to do is just make it difficult enough to crack to make it not worth peoples' trouble.

Some suggestions I have for you to help protect your application:

• Obfuscate your code. Dotfuscator has a free edition and comes with Visual Studio.
• Use public/private key or asymmetric encryption to generate your product licenses. This ensures that only you can generate your license codes. Even if your application is cracked, you can be sure that they won't be releasing a key generator for your application, because it is impossible to reverse the key generating algorithm.
• Use a third-party packer to pack your .NET executable into an encrypted Win32 wrapper application. Themida is one of the better ones. This stops people from reflecting your application in .NET Reflector and makes it a pain to unpack for reversing.
• Write your own custom packer. If the third-party packers are too expensive, consider writing your own. Sometimes custom packers can be very effective, because there aren't well published methods on how to unpack them. The tutorial How to write your own packer gives a ton of good information on writing your own Win32 packer.

Ultimately though, if people want your application cracked they will. Look at all the commercial software out there that has a vast amount of resources to protect their applications and yet they are cracked before the applications are even released to the public.

A skilled reverse engineer can fire up IDA-Pro and slice through your application like butter no matter what you do. A packed application can be unpacked and obfuscation only prevents it from making it a walk in the park. All your hard work with your complex license code can be undone with a single byte patch.

You just need to accept that there is a very real chance people are going to pirate your software. There are some people who are never going to pay for your application no matter what and these are the people you don't need to worry about.

There are however, many businesses out there who would never risk a lawsuit and happily buy software licenses and many computer users who either don't want to risk it, find it wrong or are not tech savvy enough to pirate. These are your true customers, and you should focus your efforts on providing them with a good user experience and ignore the people cracking your software.

I've had my application pirated before, and I took it as a personal affront. Here I was, a small-time developer, pouring my heart and soul into an application and these people had the gall to pirate from me?! They were taking money directly from my pocket!

I immediately added in a bunch of draconian DRM code and attempted to sabotage any person using an illegitimate or cracked copy. I should of course have been working on making my application better instead of trying to stop the inevitable. Not only that, but I was hurting my true customers will all these extra protections I was putting in.

After a long battle I realized I was fighting the tides and all this time wasted was for naught. I took out all the phone-home code except for the barebones license functions and never looked back.

Unfortunately, you are not going to run away from this. Your best bet is to write your code in C and P/Invoke it.

There is a small catch-22, someone could just decompile your application to CIL and kill any verification/activation code (for example, the call to your C library). Remember that applications that are written in C are also reverse-engineered by the more persistent hackers (just look at how fast games are cracked these days). Nothing will protect your application.

In the end it works a lot like your home, protect it well enough so that it is too much effort (spaghetti code would help here) and so that the assailant just moves onto your next door neighbor (competition :) ). Look at Windows Vista, there must be 10 different ways to crack it.

There are packages out there that will encrypt your EXE file and decrypt it when the user is allowed to use it, but once again, that is using a generic solution that has no doubt been cracked.

Activation and registration mechanisms are aimed at the 'average Joe:' people who don't have enough tech savvy to bypass it (or for that matter know that they can bypass it). Don't bother with crackers, they have far too much time on their hands.

You can't.

There are steps you can take to make it a little more difficult, but ultimately any executable on the local machine is crackable. Eventually, that code has to be converted into native machine code and every application that is runnable is vulnerable.

What you want to do is just make it difficult enough to crack to make it not worth peoples' trouble.

Some suggestions I have for you to help protect your application:

• Obfuscate your code. Dotfuscator has a free edition and comes with Visual Studio.
• Use public/private key or asymmetric encryption to generate your product licenses. This ensures that only you can generate your license codes. Even if your application is cracked, you can be sure that they won't be releasing a key generator for your application, because it is impossible to reverse the key generating algorithm.
• Use a third-party packer to pack your .NET executable into an encrypted Win32 wrapper application. Themida is one of the better ones. This stops people from reflecting your application in .NET Reflector and makes it a pain to unpack for reversing.
• Write your own custom packer. If the third-party packers are too expensive, consider writing your own. Sometimes custom packers can be very effective, because there aren't well published methods on how to unpack them. The tutorial How to write your own packer gives a ton of good information on writing your own Win32 packer.

Ultimately though, if people want your application cracked they will. Look at all the commercial software out there that has a vast amount of resources to protect their applications and yet they are cracked before the applications are even released to the public.

A skilled reverse engineer can fire up IDA-Pro and slice through your application like butter no matter what you do. A packed application can be unpacked and obfuscation only prevents it from making it a walk in the park. All your hard work with your complex license code can be undone with a single byte patch.

You just need to accept that there is a very real chance people are going to pirate your software. There are some people who are never going to pay for your application no matter what and these are the people you don't need to worry about.

There are however, many businesses out there who would never risk a lawsuit and happily buy software licenses and many computer users who either don't want to risk it, find it wrong or are not tech savvy enough to pirate. These are your true customers, and you should focus your efforts on providing them with a good user experience and ignore the people cracking your software.

I've had my application pirated before, and I took it as a personal affront. Here I was, a small-time developer, pouring my heart and soul into an application and these people had the gall to pirate from me?! They were taking money directly from my pocket!

I immediately added in a bunch of draconian DRM code and attempted to sabotage any person using an illegitimate or cracked copy. I should of course have been working on making my application better instead of trying to stop the inevitable. Not only that, but I was hurting my true customers will all these extra protections I was putting in.

After a long battle I realized I was fighting the tides and all this time wasted was for naught. I took out all the phone-home code except for the barebones license functions and never looked back.

If Microsoft could come up with a solution, we will not have pirated Windows versions, so nothing is very secure. Here are some similar questions from Stack Overflow and you can implement your own way of protecting them. If you are releasing different versions then you can adopt different techniques for different version so by the time first one is cracked the second one can take over.

• Managing features on a license basis for a C++ application

• Secure a DLL file with a license file

• Licensing / protection software?

Here's one idea: you could have a server hosted by your company that all instances of your software need to connect to. Simply having them connect and verify a registration key is not sufficient -- they'll just remove the check. In addition to the key check, you need to also have the server perform some vital task that the client can't perform itself, so it's impossible to remove. This of course would probably mean a lot of heavy processing on the part of your server, but it would make your software difficult to steal, and assuming you have a good key scheme (check ownership, etc), the keys will also be difficult to steal. This is probably more invasive than you want, since it will require your users to be connected to the internet to use your software.

There's Salamander, which is a native .NET compiler and linker from Remotesoft that can deploy applications without the .NET framework. I don't know how well it lives up to its claims.

Just make a good application and code a simple protection system. It doesn't matter what protection you choose, it will be reversed... So don't waste too much time/money.

You can't fully secure any application (managed or not). If systems like the Playstation and iPad can get cracked — where the vendor even controls the hardware — what hope does your app have? Thankfully, you don't really want to. In my opinion, you need to secure your application just enough that someone can't accidentally pirate your product, and no more.

For example, if you use a per-machine license, it shouldn't just work when you install it on a new second machine. You'll want a good error message to prevent extra support calls, but don't spend extra time making it too hard to work around and don't hit users over the head with it.

Another example is a time-limited trial. Don't even worry about simple things like if users can just roll back the system clock. Someone who does that knows they are breaking your license, and as long as a user knows when they are in violation you've done enough.

You need to do this much because users don't care about your license. Licenses are made-up things that nobody cares about until they need to. No one reads them, and they really shouldn't have to. Therefore the best way to tell the user where the boundaries are is if the out-of-the-box behavior for your application complies with the license. In this first case that means either failing to install or installing in trial-version mode the second time. For the latter, it might just mean checking a plain-text date in a configuration file. Either way, make sure you handle it in an elegant, helpful, and respectful manner.

So that explains what it means do just that much. But why not go any further? Why not plug every little hole you can find? The answer is in two parts. First, if someone will cross the ethical threshold of consciously breaking your license terms — even in a simple way — they'll also be willing to do something more difficult or dangerous like pull your application from a torrent site — and there is a certain amount of danger involved in running applications downloaded from untrusted sources. Making it any harder is only a minor annoyance for these users and risks causing problems with your paying customers. Keeping it simple may prevent someone from digging into your application and releasing a more comprehensive crack. Second, you have few eyes available to look for flaws; the hackers have many, and they have more practice finding them. You only need to miss one little flaw, and your app will have the same distribution on pirate sites as if you did nothing. You have to be right every time; they only have to be lucky once. So the effort required is very high, and the likelihood of any measure of success is very low.

Ultimately, if someone wants to pirate your application (as opposed to just using it), and that is their main goal, they will. There's nothing you can do to stop them. This is the nature of software; once the files that make up your product are on a user's computer they will be able to do with them as they wish. This is especially relevant in managed environments like Java or .NET, but it definitely applies to native code as well. Time is on their side, and given enough time any digital security can be broken.

Since you can't stop users from pirating your product, your best course of action is to engage this class of user in a way the uses them to your benefit. It is often possible to get them working for you rather than against you. With that in mind, no matter what your application is, it's probably worth it to keep a free version that is almost completely functional and doesn't expire. The difference between even a US$1 price tag and free is huge, if for no other reason than that the customer doesn't have to trust you with their credit card. A free edition of your product will not only effectively kill pirated distribution (why risk a pirated version when you can be legitimate for the same price?), it has the potential to dramatically expand your audience.

The result is that you may need to increase the price of the for-pay edition, so that in the end instead of 2,000 users at $20 each you have 100,000 free users, of which 500 are willing to pay $99 for the "professional" edition. This earns you more money than if you spent a bunch of time locking up your product. More than that, you can engage these free users and leverage the relationship in several important ways.

One is support. A pessimist would take this opportunity to complain about the increased cost of supporting 100,000 free users, but something amazing happens instead: your product becomes largely self supporting. You see this all the time with large open source projects that have no money for support costs. Users will step up and make it happen.

Free users generally have reduced support expectations to begin with, and for good reason. All you need to do is mark the free edition as only qualifying for community support and put up a user-moderated online forum for that purpose. Your support knowledge base is self-generating, and advanced users will shepherd those who need extra hand-holding on your behalf. Even more importantly, this will allow you to identify and correct bugs faster, ultimately improving the quality of your product and lowering total support costs. This wasn't possible before because your user base wasn't large enough, but when you treat the free users as customers it can work very well.

Another is feedback. By watching your forum, you learn important improvement ideas that you may never have considered otherwise. This can allow you to ultimately turn more of your free users into paid users and create a more compelling product that will attract an even larger audience.

Finally, you need to consider marketing. All these free users are now fans rather than adversaries, and they will act accordingly. Not only that, but when it comes time to release your next version these users will have all gone through your approved distribution channel, rather than some other unknown mechanism. That means for your next version you start out connected with a larger, highly interested and supportive audience.

The best features to reserve for the professional edition are tools aimed at making it easy to do corporate deployment and management. A cracker won't see these as a compelling enough reason to hack it for his own use, but for a business looking to buy 300 licenses and push it out company-wide this is a must-have. Of course, the professional edition will be pirated anyway, but again: don't sweat it because you probably wouldn't be able to sell the product to those pirates no matter what you did, so it's not costing you any revenue.

While psychologically it can be hard to give away your product this much, hopefully you can understand how it really is the best way to go. Not only that, it's the only way to go in the long term. I know someone is out there thinking that they don't want to do it this way. After all, they've got by just fine selling their locked-down $20 product for years. But that's just too bad, because if you don't do it this way, eventually someone else will. And their product will be just as good as yours, or close enough they can get away with claiming that. Then all of a sudden your pricing looks outrageous, sales drop dramatically, and there's nothing else you can do. You can opt for an additional middle tier if you must, but it's unlikely to help you.

You can't prevent people from cracking your software.

However, you can make them create cracks that will hurt your sales less. Keygenerators that can issue a valid registration code for your software are much worse than simple patches that remove registration incentives from your software. That's because a crack will work for one software version only, and will cease to work with the next software update you release. The keygenerator will continue to work until you change your registration key algorithm and that's something you don't want to do often because it will put off your honest clients.

So, if you are looking for a method to fight illegal keygenerators for your software and you do not want to use assymetric encryption because of the long registration codes this generates, you might have a look at Partial Key Verification.

Partial Key Verification makes sure that each illegal keygenerator works only for one particular release of your software. Basically what you do is to make sure that each release of your software only links with the code for checking SOME digits of the registration code. Which digits exactly is random, so crackers would have to reverse engineer many different versions of your software and combine all this into one keygenerator in order to release a keygenerator that works for all versions of your software.

If you release new software versions on a regular basis, this leads to numerous keygenerators spread on all kinds of software piracy archives which are not working anymore. Potential software pirates usually look for a crack or keygen for the latest version, so they will likely try a few of those and give up eventually.

I've used the Partial Key Verification in my (C++) newer shareware games and it has been very effective. Before we had plenty of problems with keygenerators which we could not fight. Afterewards there were lots of cracks and some few keygenerators that worked only for that particular version of the game, but no key generator that would work with all versions. We regularly released very minor updates of the game and to render all previously existing cracks useless.

There seems to be an open source .NET framework for Partial Key Verification, although I have not tried it.

Yes, .NET binaries (EXE and DLL) can be easily decompiled to nearly source code. Check the tool .NET Reflector. Just try it against any .NET binary file. The best option is to obfuscate files, they still can be decompiled by .NET Reflector, but they create an unreadable mess. I don't think that good obfuscators would be free or cheap. The one is Dotfuscator Community Edition that comes with Visual Studio.

Is it really worth it? Every protection mechanism can be broken with sufficient determination. Consider your market, price of the product, amount of customers, etc.

If you want something more reliable then go down the path of hardware keys, but that's rather troublesome (for the user) and more expensive. Software solutions would be probably a waste of time and resources, and the only thing they would give you is the false sense of 'security'.

Few more ideas (none is perfect, as there is no perfect one).

• AntiDuplicate
• Change the language, use the nice tricks that the authors of Skype used
• License server

And don't waste too much time on it, because the crackers have a lot of experience with the typical techniques and are few steps ahead of you. Unless you want to use a lot of resources, probably change the programming language (do it the Skype way).

Apart from purchasing protection, you (or your developers) can learn to copy-protect.

These are ideas:

At first, try to write a program that writes itself to console. That's a famous problem. Primary purpose of this task is to practice writing self-referencing code.

Second, you need to develop a technology that will rewrite some code in a way dependable on other methods' CIL.

You may write a virtual machine (yet in .NET). And put some code in there. Ultimately, the virtual machine runs another virtual machine which runs the code. That's for a part of rarely-called functions for not to slow the performance too much.

Rewrite some logic into C++/CLI, and mix managed code with unmanaged. This will harden the disassembling. In this case, do not forget to provide x64 binaries too.

I can recommend using Obfuscator.

You can..

Microsoft SLP ServicesInishTech's Software Potential offers the ability to help protect code without affecting the functionality of your applications.

UPDATE: (Disclosure: I work on Eazfuscator.NET) What makes Microsoft SLP ServicesSoftware Potential different is the ability to virtualize the code, so you definitely can. Several years passed since the question was originally asked; today there are more products available that also work on a similar basis such as:

• Agile.NET
• Eazfuscator.NET

Obfuscate the code! There is an example in Obfuscating C# Code.

How to make sure that the application is not tampered with, and how to make sure that the registration mechanism can't be reverse engineered.

Both have the same very simple answer: don't hand out object code to untrusted parties, such as (apparently) your customers. Whether it's feasible to host the application on your machines only depends on what it does.

If it isn't a web application, maybe you can allow for SSH login with X forwarding to an application server (or Remote Desktop Connection, I guess, for Windows).

If you give object code to nerdy type persons, and they think your program might be fun to crack, it will get cracked. No way around it.

If you don't believe me, point out a high-profile application that hasn't been cracked and pirated.

If you go with the hardware keys, it'll make production more expensive and your users are going to hate you for it. It's a real bitch to crawl around on the floor plugging and unplugging your 27 different USB thingies because software makers don't trust you (I imagine).

There are packages out there that will encrypt your EXE and decrypt it when the user is allowed to use it

Of course, the way around it is to crack the "can-I-use-it" test so that it always returns true.

A nasty trick might be to use the byte values of the opcodes that perform the test somewhere else in the program in a dirty way that'll make the program crash with high probability unless the value is just right. It makes you linked to a particular architecture, though :-(

Looks like native forever and no needs in obfuscators now; Looks like net core RT workable solutions; soon all apps will go to .net core; https://www.codeproject.com/Articles/5262251/Generate-Native-Executable-from-NET-Core-3-1-Proje?msg=5753507#xx5753507xx https://docs.microsoft.com/en-us/archive/msdn-magazine/2018/november/net-core-publishing-options-with-net-core

not tested maybe with old win .net sdk possible do similar.

There's Salamander, which is a native .NET compiler and linker from Remotesoft that can deploy applications without the .NET framework. I don't know how well it lives up to its claims.

How to make sure that the application is not tampered with, and how to make sure that the registration mechanism can't be reverse engineered.

Both have the same very simple answer: don't hand out object code to untrusted parties, such as (apparently) your customers. Whether it's feasible to host the application on your machines only depends on what it does.

If it isn't a web application, maybe you can allow for SSH login with X forwarding to an application server (or Remote Desktop Connection, I guess, for Windows).

If you give object code to nerdy type persons, and they think your program might be fun to crack, it will get cracked. No way around it.

If you don't believe me, point out a high-profile application that hasn't been cracked and pirated.

If you go with the hardware keys, it'll make production more expensive and your users are going to hate you for it. It's a real bitch to crawl around on the floor plugging and unplugging your 27 different USB thingies because software makers don't trust you (I imagine).

There are packages out there that will encrypt your EXE and decrypt it when the user is allowed to use it

Of course, the way around it is to crack the "can-I-use-it" test so that it always returns true.

A nasty trick might be to use the byte values of the opcodes that perform the test somewhere else in the program in a dirty way that'll make the program crash with high probability unless the value is just right. It makes you linked to a particular architecture, though :-(

You can't.

There are steps you can take to make it a little more difficult, but ultimately any executable on the local machine is crackable. Eventually, that code has to be converted into native machine code and every application that is runnable is vulnerable.

What you want to do is just make it difficult enough to crack to make it not worth peoples' trouble.

Some suggestions I have for you to help protect your application:

• Obfuscate your code. Dotfuscator has a free edition and comes with Visual Studio.
• Use public/private key or asymmetric encryption to generate your product licenses. This ensures that only you can generate your license codes. Even if your application is cracked, you can be sure that they won't be releasing a key generator for your application, because it is impossible to reverse the key generating algorithm.
• Use a third-party packer to pack your .NET executable into an encrypted Win32 wrapper application. Themida is one of the better ones. This stops people from reflecting your application in .NET Reflector and makes it a pain to unpack for reversing.
• Write your own custom packer. If the third-party packers are too expensive, consider writing your own. Sometimes custom packers can be very effective, because there aren't well published methods on how to unpack them. The tutorial How to write your own packer gives a ton of good information on writing your own Win32 packer.

Ultimately though, if people want your application cracked they will. Look at all the commercial software out there that has a vast amount of resources to protect their applications and yet they are cracked before the applications are even released to the public.

A skilled reverse engineer can fire up IDA-Pro and slice through your application like butter no matter what you do. A packed application can be unpacked and obfuscation only prevents it from making it a walk in the park. All your hard work with your complex license code can be undone with a single byte patch.

You just need to accept that there is a very real chance people are going to pirate your software. There are some people who are never going to pay for your application no matter what and these are the people you don't need to worry about.

There are however, many businesses out there who would never risk a lawsuit and happily buy software licenses and many computer users who either don't want to risk it, find it wrong or are not tech savvy enough to pirate. These are your true customers, and you should focus your efforts on providing them with a good user experience and ignore the people cracking your software.

I've had my application pirated before, and I took it as a personal affront. Here I was, a small-time developer, pouring my heart and soul into an application and these people had the gall to pirate from me?! They were taking money directly from my pocket!

I immediately added in a bunch of draconian DRM code and attempted to sabotage any person using an illegitimate or cracked copy. I should of course have been working on making my application better instead of trying to stop the inevitable. Not only that, but I was hurting my true customers will all these extra protections I was putting in.

After a long battle I realized I was fighting the tides and all this time wasted was for naught. I took out all the phone-home code except for the barebones license functions and never looked back.

Is it really worth it? Every protection mechanism can be broken with sufficient determination. Consider your market, price of the product, amount of customers, etc.

If you want something more reliable then go down the path of hardware keys, but that's rather troublesome (for the user) and more expensive. Software solutions would be probably a waste of time and resources, and the only thing they would give you is the false sense of 'security'.

Few more ideas (none is perfect, as there is no perfect one).

• AntiDuplicate
• Change the language, use the nice tricks that the authors of Skype used
• License server

And don't waste too much time on it, because the crackers have a lot of experience with the typical techniques and are few steps ahead of you. Unless you want to use a lot of resources, probably change the programming language (do it the Skype way).

I see this topic in 2 major aspects.

A) Is .NET only be reverse engineered and native not ?

B) What type of programmer we are Commercial/Hobbyist ?

Title: Protect .NET code from reverse engineering

My view:

1. Least preference to make commercial application in .NET, because it will expose even your comments on the built binary after decompile. (I don't know what is the logic to include the comments also with binary) So any one can just decompile it, rename/modify/change the look and resell the application in 24 hours.

2. In native application rename/modify/change of look is not possible as easy as one could do in .NET

3. Worried part in .NET is that you could get the whole project with solution from a single binary exe/dll.

Just imagine how week it is in security. So even a lay man could reverse engineering the .NET application easily.

4. If it is native application like C++/VB6/Delphi only expert cracker who knows ASM could patch the exe and not 100% reverse engineering like .NET.

But now the whole world is running behind the .NET because it is very easy to make projects with the advance features and libraries.

5. Good News is that Microsoft seems supporting native output from .NET in 2020 which will make coders like me to consider .NET C# as a primary language.

https://www.codeproject.com/Articles/5262251/Generate-Native-Executable-from-NET-Core-3-1-Proje?msg=5755590#xx5755590xx

It's impossible to fully secure an application, sorry.

Unfortunately, you are not going to run away from this. Your best bet is to write your code in C and P/Invoke it.

There is a small catch-22, someone could just decompile your application to CIL and kill any verification/activation code (for example, the call to your C library). Remember that applications that are written in C are also reverse-engineered by the more persistent hackers (just look at how fast games are cracked these days). Nothing will protect your application.

In the end it works a lot like your home, protect it well enough so that it is too much effort (spaghetti code would help here) and so that the assailant just moves onto your next door neighbor (competition :) ). Look at Windows Vista, there must be 10 different ways to crack it.

There are packages out there that will encrypt your EXE file and decrypt it when the user is allowed to use it, but once again, that is using a generic solution that has no doubt been cracked.

Activation and registration mechanisms are aimed at the 'average Joe:' people who don't have enough tech savvy to bypass it (or for that matter know that they can bypass it). Don't bother with crackers, they have far too much time on their hands.

Broadly speaking, there are three groups of people out there.

• Those who will not buy your software and resort to cracks, or if they don't find any, not use your software at all. Don't expect to make any money from this group. They rely either on their own skills or on crackers (who tend to prioritize their time depending on your useful and how big your audience is. The more useful, the sooner a crack will be available).

• The group of legitimate users who will buy (pay for) your software, irrespective of what protection mechanism you use. Don't make life hard for your legitimate users by using an elaborate protection mechanism since they are going to pay for it in any case. A complex protection mechanism can easily spoil the user experience and you don't want this happening to this group. Personally, I'd vote against any hardware solution, which adds to the cost of your software.

• A minority who will resort to "unethical" cracking and will only pay for your software because its features are protected by a licensing mechanism. You probably don't want to make it exceedingly easy for this group to circumvent your protection. However, all that effort you spend on protecting your software will pay back, depending on how big this group of people is. This entirely depends on the type of software you're building.

Given what you've said, if you think there is a large enough minority who can be pushed into buying your software, go ahead and implement some form of protection. Think about how much money you can make from this minority versus the time you spend working on the protection, or the amount you spend on a third party protection API/tool.

If you like to implement a solution of your own, using public-key cryptography is a good way (as opposed to symmetric algorithms) to prevent easy hacks. You could for instance digitally sign your license (serial no, or license file). The only way to get around this would then be to decompile, alter and recompile the code (which you could make harder using techniques such as those suggested in Simucal's answer).

If you want people to able to run your code (and if you don't, then why did you write it in the first place?), then their CPU needs to be able to execute your code. In order to be able to execute the code, the CPU needs to be able to understand it.

Since CPUs are dumb, and humans aren't, this means that humans can understand the code as well.

There's only one way to make sure that your users don't get your code: don't give them your code.

This can be achieved two ways: Software as a service (SaaS), that is, you run your software on your server and only let your users access it remotely. This is the model that Stack Overflow uses, for example. I'm pretty sure that Stack Overflow doesn't obfuscate their code, yet you can't decompile it.

The other way is the appliance model: instead of giving your users your code, you give them a computer containing the code. This is the model that gaming consoles, most mobile phones and TiVo use. Note that this only works if you "own" the entire execution path: you need to build your own CPU, your own computer, write your own operating system and your own CLI implementation. Then, and only then can you protect your code. (But note that even the tiniest mistake will render all of your protections useless. Microsoft, Apple, Sony, the music industry and the movie industry can attest to that.)

Or, you could just do nothing, which means that your code will be automatically protected by copyright law.

Looks like native forever and no needs in obfuscators now; Looks like net core RT workable solutions; soon all apps will go to .net core; https://www.codeproject.com/Articles/5262251/Generate-Native-Executable-from-NET-Core-3-1-Proje?msg=5753507#xx5753507xx https://docs.microsoft.com/en-us/archive/msdn-magazine/2018/november/net-core-publishing-options-with-net-core

not tested maybe with old win .net sdk possible do similar.

I also made some considerataions regarding hacking security in my design and wanna add them as some of them seem not to be mentioned:

I have a scripting interface in my application. To ensure, Scripts can only call methods which are intended to be called by (python)-scripts i have a scriptvisibilityattribute and System.Dynamic.DynamicMetaObjectProvider which recognizes these attributes.

Licenses use public/private key.

ViewModels need to be unlocked giving a password to a unlock function.

CoreRoutines may be implemented on a dongle. (There are dongles around which support that)

Big solution like wrappers was not planned.

Of course this scripting/viewModel apporach doesnt make it impossible to unlock and call script-nonvisible functions from the code but it makes it a bit more difficult doing so - like with all that's related to anti-hacking-efforts.

.NET Reactor

Update

Jared pointed out that de4dot claims to be able to decompile it.

.NET Reactor provides complete protection for your sensitive intellectual property by converting your .NET assemblies into unmanaged processes which cannot be understood as CIL, and which no existing tool can decompile. Hackers have no access to any intelligible form of your source.

Powerful and flexible, the .NET Reactor licensing features allow you to enforce your license conditions and protect your revenue stream by using hardware and software locks. The license manager can build trial or permanent licenses, in a matter of seconds. A fully documented software development kit (SDK), complete with examples, allows you to call the licensing system directly from your code, allowing you to create custom extensions to the licensing system.

Just make a good application and code a simple protection system. It doesn't matter what protection you choose, it will be reversed... So don't waste too much time/money.

There is a detailed comparison sheet for several .Net obfuscation tools.

Screenshoot taken from obfuscators.io

A secret that you share with lots of people is not a secret. If you have secret stuff in your code, obfuscating it is no protection; it only has to be deobfuscated once. If you have a secret that you don't want to share with your customers, then don't share it with your customers. Write your code as a web service and keep your super secret code on your own server, where only you can see it.

Anything running on the client can be decompiled and cracked. Obfusification just makes it harder. I don't know your application, but 99% of the time I just don't think it's worth the effort.

.NET Reactor

Update

Jared pointed out that de4dot claims to be able to decompile it.

.NET Reactor provides complete protection for your sensitive intellectual property by converting your .NET assemblies into unmanaged processes which cannot be understood as CIL, and which no existing tool can decompile. Hackers have no access to any intelligible form of your source.

Powerful and flexible, the .NET Reactor licensing features allow you to enforce your license conditions and protect your revenue stream by using hardware and software locks. The license manager can build trial or permanent licenses, in a matter of seconds. A fully documented software development kit (SDK), complete with examples, allows you to call the licensing system directly from your code, allowing you to create custom extensions to the licensing system.

I see this topic in 2 major aspects.

A) Is .NET only be reverse engineered and native not ?

B) What type of programmer we are Commercial/Hobbyist ?

Title: Protect .NET code from reverse engineering

My view:

1. Least preference to make commercial application in .NET, because it will expose even your comments on the built binary after decompile. (I don't know what is the logic to include the comments also with binary) So any one can just decompile it, rename/modify/change the look and resell the application in 24 hours.

2. In native application rename/modify/change of look is not possible as easy as one could do in .NET

3. Worried part in .NET is that you could get the whole project with solution from a single binary exe/dll.

Just imagine how week it is in security. So even a lay man could reverse engineering the .NET application easily.

4. If it is native application like C++/VB6/Delphi only expert cracker who knows ASM could patch the exe and not 100% reverse engineering like .NET.

But now the whole world is running behind the .NET because it is very easy to make projects with the advance features and libraries.

5. Good News is that Microsoft seems supporting native output from .NET in 2020 which will make coders like me to consider .NET C# as a primary language.

https://www.codeproject.com/Articles/5262251/Generate-Native-Executable-from-NET-Core-3-1-Proje?msg=5755590#xx5755590xx

Broadly speaking, there are three groups of people out there.

• Those who will not buy your software and resort to cracks, or if they don't find any, not use your software at all. Don't expect to make any money from this group. They rely either on their own skills or on crackers (who tend to prioritize their time depending on your useful and how big your audience is. The more useful, the sooner a crack will be available).

• The group of legitimate users who will buy (pay for) your software, irrespective of what protection mechanism you use. Don't make life hard for your legitimate users by using an elaborate protection mechanism since they are going to pay for it in any case. A complex protection mechanism can easily spoil the user experience and you don't want this happening to this group. Personally, I'd vote against any hardware solution, which adds to the cost of your software.

• A minority who will resort to "unethical" cracking and will only pay for your software because its features are protected by a licensing mechanism. You probably don't want to make it exceedingly easy for this group to circumvent your protection. However, all that effort you spend on protecting your software will pay back, depending on how big this group of people is. This entirely depends on the type of software you're building.

Given what you've said, if you think there is a large enough minority who can be pushed into buying your software, go ahead and implement some form of protection. Think about how much money you can make from this minority versus the time you spend working on the protection, or the amount you spend on a third party protection API/tool.

If you like to implement a solution of your own, using public-key cryptography is a good way (as opposed to symmetric algorithms) to prevent easy hacks. You could for instance digitally sign your license (serial no, or license file). The only way to get around this would then be to decompile, alter and recompile the code (which you could make harder using techniques such as those suggested in Simucal's answer).

Just make a good application and code a simple protection system. It doesn't matter what protection you choose, it will be reversed... So don't waste too much time/money.

You can..

Microsoft SLP ServicesInishTech's Software Potential offers the ability to help protect code without affecting the functionality of your applications.

UPDATE: (Disclosure: I work on Eazfuscator.NET) What makes Microsoft SLP ServicesSoftware Potential different is the ability to virtualize the code, so you definitely can. Several years passed since the question was originally asked; today there are more products available that also work on a similar basis such as:

• Agile.NET
• Eazfuscator.NET

According bellow question in microsoft blog :

https://blogs.msdn.microsoft.com/amb/2011/05/27/how-to-prevent-ildasm-from-disassembling-my-net-code/

How can I prevent ILDASM from disassembling an assembly?

.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:

1. We have added System.Runtime.CompilerServices namespace deceleration.

2. 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 following message :

When it comes to .NET, if you're releasing a Windows Forms application (or any application where the client has the Portable Executable file), it's able to be cracked.

If you want to stick with .NET and want to minimize the chance of having your source code taken, then you may want to consider deploying it as an ASP.NET application across a webserver, instead of making it a Windows Forms application.

Yes. It is true. .NET code is extremely easy to reverse engineer if the code is not obfuscated.

Obfuscation will add a layer of annoyance to people trying to reverse engineer your software. Depending on which version you get, you'll get different levels of protection.

Visual Studio includes a version of Dotfuscator. Since it's a bundled version, you're definitely not getting the strongest obfuscation possible. If you look at their feature lists, you'll see exactly what you're missing (and exactly what the application will do to make your code more secure).

There are a couple of other free or open source .NET obfuscators out there (but I can't comment on the quality or the various methods they use):

• Obfuscar
• Babel.NET

In the end, nothing is perfect. If somebody really wants to see how your software works, they will.

It's impossible to fully secure an application, sorry.

According bellow question in microsoft blog :

https://blogs.msdn.microsoft.com/amb/2011/05/27/how-to-prevent-ildasm-from-disassembling-my-net-code/

How can I prevent ILDASM from disassembling an assembly?

.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:

1. We have added System.Runtime.CompilerServices namespace deceleration.

2. 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 following message :

Broadly speaking, there are three groups of people out there.

• Those who will not buy your software and resort to cracks, or if they don't find any, not use your software at all. Don't expect to make any money from this group. They rely either on their own skills or on crackers (who tend to prioritize their time depending on your useful and how big your audience is. The more useful, the sooner a crack will be available).

• The group of legitimate users who will buy (pay for) your software, irrespective of what protection mechanism you use. Don't make life hard for your legitimate users by using an elaborate protection mechanism since they are going to pay for it in any case. A complex protection mechanism can easily spoil the user experience and you don't want this happening to this group. Personally, I'd vote against any hardware solution, which adds to the cost of your software.

• A minority who will resort to "unethical" cracking and will only pay for your software because its features are protected by a licensing mechanism. You probably don't want to make it exceedingly easy for this group to circumvent your protection. However, all that effort you spend on protecting your software will pay back, depending on how big this group of people is. This entirely depends on the type of software you're building.

Given what you've said, if you think there is a large enough minority who can be pushed into buying your software, go ahead and implement some form of protection. Think about how much money you can make from this minority versus the time you spend working on the protection, or the amount you spend on a third party protection API/tool.

If you like to implement a solution of your own, using public-key cryptography is a good way (as opposed to symmetric algorithms) to prevent easy hacks. You could for instance digitally sign your license (serial no, or license file). The only way to get around this would then be to decompile, alter and recompile the code (which you could make harder using techniques such as those suggested in Simucal's answer).

Frankly, sometimes we need to obfuscate the code (for example, register license classes and so on). In this case, your project is not free. IMO, you should pay for a good obfucator.

Dotfuscator hides your code and .NET Reflector shows an error when you attempt to decompile it.

• Use online update to block those unlicensed copies.

• Verify serial number from different modules of your application and do not use a single function call to do the verification (so that crackers cannot bypass the verification easily).

• Not only check serial number at startup, do the verification while saving data, do it every Friday evening, do it when user is idle ...

• Verify application file check sum, store your security check sum in different places.

• Don't go too far on these kind of tricks, make sure your application never crash/get into malfunction while verifying registration code.

• Build a useful app for users is much more important than make a
  unbreakable binary for crackers.

Apart from purchasing protection, you (or your developers) can learn to copy-protect.

These are ideas:

At first, try to write a program that writes itself to console. That's a famous problem. Primary purpose of this task is to practice writing self-referencing code.

Second, you need to develop a technology that will rewrite some code in a way dependable on other methods' CIL.

You may write a virtual machine (yet in .NET). And put some code in there. Ultimately, the virtual machine runs another virtual machine which runs the code. That's for a part of rarely-called functions for not to slow the performance too much.

Rewrite some logic into C++/CLI, and mix managed code with unmanaged. This will harden the disassembling. In this case, do not forget to provide x64 binaries too.

You can..

Microsoft SLP ServicesInishTech's Software Potential offers the ability to help protect code without affecting the functionality of your applications.

UPDATE: (Disclosure: I work on Eazfuscator.NET) What makes Microsoft SLP ServicesSoftware Potential different is the ability to virtualize the code, so you definitely can. Several years passed since the question was originally asked; today there are more products available that also work on a similar basis such as:

• Agile.NET
• Eazfuscator.NET

You can't fully secure any application (managed or not). If systems like the Playstation and iPad can get cracked — where the vendor even controls the hardware — what hope does your app have? Thankfully, you don't really want to. In my opinion, you need to secure your application just enough that someone can't accidentally pirate your product, and no more.

For example, if you use a per-machine license, it shouldn't just work when you install it on a new second machine. You'll want a good error message to prevent extra support calls, but don't spend extra time making it too hard to work around and don't hit users over the head with it.

Another example is a time-limited trial. Don't even worry about simple things like if users can just roll back the system clock. Someone who does that knows they are breaking your license, and as long as a user knows when they are in violation you've done enough.

You need to do this much because users don't care about your license. Licenses are made-up things that nobody cares about until they need to. No one reads them, and they really shouldn't have to. Therefore the best way to tell the user where the boundaries are is if the out-of-the-box behavior for your application complies with the license. In this first case that means either failing to install or installing in trial-version mode the second time. For the latter, it might just mean checking a plain-text date in a configuration file. Either way, make sure you handle it in an elegant, helpful, and respectful manner.

So that explains what it means do just that much. But why not go any further? Why not plug every little hole you can find? The answer is in two parts. First, if someone will cross the ethical threshold of consciously breaking your license terms — even in a simple way — they'll also be willing to do something more difficult or dangerous like pull your application from a torrent site — and there is a certain amount of danger involved in running applications downloaded from untrusted sources. Making it any harder is only a minor annoyance for these users and risks causing problems with your paying customers. Keeping it simple may prevent someone from digging into your application and releasing a more comprehensive crack. Second, you have few eyes available to look for flaws; the hackers have many, and they have more practice finding them. You only need to miss one little flaw, and your app will have the same distribution on pirate sites as if you did nothing. You have to be right every time; they only have to be lucky once. So the effort required is very high, and the likelihood of any measure of success is very low.

Ultimately, if someone wants to pirate your application (as opposed to just using it), and that is their main goal, they will. There's nothing you can do to stop them. This is the nature of software; once the files that make up your product are on a user's computer they will be able to do with them as they wish. This is especially relevant in managed environments like Java or .NET, but it definitely applies to native code as well. Time is on their side, and given enough time any digital security can be broken.

Since you can't stop users from pirating your product, your best course of action is to engage this class of user in a way the uses them to your benefit. It is often possible to get them working for you rather than against you. With that in mind, no matter what your application is, it's probably worth it to keep a free version that is almost completely functional and doesn't expire. The difference between even a US$1 price tag and free is huge, if for no other reason than that the customer doesn't have to trust you with their credit card. A free edition of your product will not only effectively kill pirated distribution (why risk a pirated version when you can be legitimate for the same price?), it has the potential to dramatically expand your audience.

The result is that you may need to increase the price of the for-pay edition, so that in the end instead of 2,000 users at $20 each you have 100,000 free users, of which 500 are willing to pay $99 for the "professional" edition. This earns you more money than if you spent a bunch of time locking up your product. More than that, you can engage these free users and leverage the relationship in several important ways.

One is support. A pessimist would take this opportunity to complain about the increased cost of supporting 100,000 free users, but something amazing happens instead: your product becomes largely self supporting. You see this all the time with large open source projects that have no money for support costs. Users will step up and make it happen.

Free users generally have reduced support expectations to begin with, and for good reason. All you need to do is mark the free edition as only qualifying for community support and put up a user-moderated online forum for that purpose. Your support knowledge base is self-generating, and advanced users will shepherd those who need extra hand-holding on your behalf. Even more importantly, this will allow you to identify and correct bugs faster, ultimately improving the quality of your product and lowering total support costs. This wasn't possible before because your user base wasn't large enough, but when you treat the free users as customers it can work very well.

Another is feedback. By watching your forum, you learn important improvement ideas that you may never have considered otherwise. This can allow you to ultimately turn more of your free users into paid users and create a more compelling product that will attract an even larger audience.

Finally, you need to consider marketing. All these free users are now fans rather than adversaries, and they will act accordingly. Not only that, but when it comes time to release your next version these users will have all gone through your approved distribution channel, rather than some other unknown mechanism. That means for your next version you start out connected with a larger, highly interested and supportive audience.

The best features to reserve for the professional edition are tools aimed at making it easy to do corporate deployment and management. A cracker won't see these as a compelling enough reason to hack it for his own use, but for a business looking to buy 300 licenses and push it out company-wide this is a must-have. Of course, the professional edition will be pirated anyway, but again: don't sweat it because you probably wouldn't be able to sell the product to those pirates no matter what you did, so it's not costing you any revenue.

While psychologically it can be hard to give away your product this much, hopefully you can understand how it really is the best way to go. Not only that, it's the only way to go in the long term. I know someone is out there thinking that they don't want to do it this way. After all, they've got by just fine selling their locked-down $20 product for years. But that's just too bad, because if you don't do it this way, eventually someone else will. And their product will be just as good as yours, or close enough they can get away with claiming that. Then all of a sudden your pricing looks outrageous, sales drop dramatically, and there's nothing else you can do. You can opt for an additional middle tier if you must, but it's unlikely to help you.

If it's written in .NET and compiled to CIL, it can be reflected. If security is a concern and obfuscation is to be avoided, then I recommend writing your application using a non-managed language, which is, by nature, harder to reverse engineer.

Obfuscate the code! There is an example in Obfuscating C# Code.

The best answer is the first one from the small developer speaking from his own expierence, all the anti-reversing techniques discussed above are 101 textbook cases for any serious reverse-engineer.

Some commercial DRM solutions are pretty decent, but they crack every triple AAA game with custom DRM solutions all the time within hours (or days). Only the introduction of a completely new DRM solution - sometimes - delays in inevitable for perhaps a couple of weeks.

Getting the most out of the DRM costs a lot of time & money and can easily hurt performance, reliability, compatibility/portability and customer-relations in general. Either stick with some decent commercial DRM without trying to be too smart about and take your (less) losses or just forget about it totally ...

One example of a DRM solution which dug it's own (commercial) grave: http://en.wikipedia.org/wiki/StarForce

You can't prevent people from cracking your software.

However, you can make them create cracks that will hurt your sales less. Keygenerators that can issue a valid registration code for your software are much worse than simple patches that remove registration incentives from your software. That's because a crack will work for one software version only, and will cease to work with the next software update you release. The keygenerator will continue to work until you change your registration key algorithm and that's something you don't want to do often because it will put off your honest clients.

So, if you are looking for a method to fight illegal keygenerators for your software and you do not want to use assymetric encryption because of the long registration codes this generates, you might have a look at Partial Key Verification.

Partial Key Verification makes sure that each illegal keygenerator works only for one particular release of your software. Basically what you do is to make sure that each release of your software only links with the code for checking SOME digits of the registration code. Which digits exactly is random, so crackers would have to reverse engineer many different versions of your software and combine all this into one keygenerator in order to release a keygenerator that works for all versions of your software.

If you release new software versions on a regular basis, this leads to numerous keygenerators spread on all kinds of software piracy archives which are not working anymore. Potential software pirates usually look for a crack or keygen for the latest version, so they will likely try a few of those and give up eventually.

I've used the Partial Key Verification in my (C++) newer shareware games and it has been very effective. Before we had plenty of problems with keygenerators which we could not fight. Afterewards there were lots of cracks and some few keygenerators that worked only for that particular version of the game, but no key generator that would work with all versions. We regularly released very minor updates of the game and to render all previously existing cracks useless.

There seems to be an open source .NET framework for Partial Key Verification, although I have not tried it.

How to make sure that the application is not tampered with, and how to make sure that the registration mechanism can't be reverse engineered.

Both have the same very simple answer: don't hand out object code to untrusted parties, such as (apparently) your customers. Whether it's feasible to host the application on your machines only depends on what it does.

If it isn't a web application, maybe you can allow for SSH login with X forwarding to an application server (or Remote Desktop Connection, I guess, for Windows).

If you give object code to nerdy type persons, and they think your program might be fun to crack, it will get cracked. No way around it.

If you don't believe me, point out a high-profile application that hasn't been cracked and pirated.

If you go with the hardware keys, it'll make production more expensive and your users are going to hate you for it. It's a real bitch to crawl around on the floor plugging and unplugging your 27 different USB thingies because software makers don't trust you (I imagine).

There are packages out there that will encrypt your EXE and decrypt it when the user is allowed to use it

Of course, the way around it is to crack the "can-I-use-it" test so that it always returns true.

A nasty trick might be to use the byte values of the opcodes that perform the test somewhere else in the program in a dirty way that'll make the program crash with high probability unless the value is just right. It makes you linked to a particular architecture, though :-(

• Use online update to block those unlicensed copies.

• Verify serial number from different modules of your application and do not use a single function call to do the verification (so that crackers cannot bypass the verification easily).

• Not only check serial number at startup, do the verification while saving data, do it every Friday evening, do it when user is idle ...

• Verify application file check sum, store your security check sum in different places.

• Don't go too far on these kind of tricks, make sure your application never crash/get into malfunction while verifying registration code.

• Build a useful app for users is much more important than make a
  unbreakable binary for crackers.

Bear in mind that 99%+ of your users aren't going to be interested in examining your executable to see how it works.

Given that so few people are even going to bother trying and that most obfuscators can be worked around, is it worth your time and effort?

You'd be better off investing the time into improving your product so that more people want to use it.

I also made some considerataions regarding hacking security in my design and wanna add them as some of them seem not to be mentioned:

I have a scripting interface in my application. To ensure, Scripts can only call methods which are intended to be called by (python)-scripts i have a scriptvisibilityattribute and System.Dynamic.DynamicMetaObjectProvider which recognizes these attributes.

Licenses use public/private key.

ViewModels need to be unlocked giving a password to a unlock function.

CoreRoutines may be implemented on a dongle. (There are dongles around which support that)

Big solution like wrappers was not planned.

Of course this scripting/viewModel apporach doesnt make it impossible to unlock and call script-nonvisible functions from the code but it makes it a bit more difficult doing so - like with all that's related to anti-hacking-efforts.

Unfortunately, you are not going to run away from this. Your best bet is to write your code in C and P/Invoke it.

There is a small catch-22, someone could just decompile your application to CIL and kill any verification/activation code (for example, the call to your C library). Remember that applications that are written in C are also reverse-engineered by the more persistent hackers (just look at how fast games are cracked these days). Nothing will protect your application.

In the end it works a lot like your home, protect it well enough so that it is too much effort (spaghetti code would help here) and so that the assailant just moves onto your next door neighbor (competition :) ). Look at Windows Vista, there must be 10 different ways to crack it.

There are packages out there that will encrypt your EXE file and decrypt it when the user is allowed to use it, but once again, that is using a generic solution that has no doubt been cracked.

Activation and registration mechanisms are aimed at the 'average Joe:' people who don't have enough tech savvy to bypass it (or for that matter know that they can bypass it). Don't bother with crackers, they have far too much time on their hands.

I can recommend using Obfuscator.

Broadly speaking, there are three groups of people out there.

• Those who will not buy your software and resort to cracks, or if they don't find any, not use your software at all. Don't expect to make any money from this group. They rely either on their own skills or on crackers (who tend to prioritize their time depending on your useful and how big your audience is. The more useful, the sooner a crack will be available).

• The group of legitimate users who will buy (pay for) your software, irrespective of what protection mechanism you use. Don't make life hard for your legitimate users by using an elaborate protection mechanism since they are going to pay for it in any case. A complex protection mechanism can easily spoil the user experience and you don't want this happening to this group. Personally, I'd vote against any hardware solution, which adds to the cost of your software.

• A minority who will resort to "unethical" cracking and will only pay for your software because its features are protected by a licensing mechanism. You probably don't want to make it exceedingly easy for this group to circumvent your protection. However, all that effort you spend on protecting your software will pay back, depending on how big this group of people is. This entirely depends on the type of software you're building.

Given what you've said, if you think there is a large enough minority who can be pushed into buying your software, go ahead and implement some form of protection. Think about how much money you can make from this minority versus the time you spend working on the protection, or the amount you spend on a third party protection API/tool.

If you like to implement a solution of your own, using public-key cryptography is a good way (as opposed to symmetric algorithms) to prevent easy hacks. You could for instance digitally sign your license (serial no, or license file). The only way to get around this would then be to decompile, alter and recompile the code (which you could make harder using techniques such as those suggested in Simucal's answer).

You can..

Microsoft SLP ServicesInishTech's Software Potential offers the ability to help protect code without affecting the functionality of your applications.

UPDATE: (Disclosure: I work on Eazfuscator.NET) What makes Microsoft SLP ServicesSoftware Potential different is the ability to virtualize the code, so you definitely can. Several years passed since the question was originally asked; today there are more products available that also work on a similar basis such as:

• Agile.NET
• Eazfuscator.NET

Is it really worth it? Every protection mechanism can be broken with sufficient determination. Consider your market, price of the product, amount of customers, etc.

If you want something more reliable then go down the path of hardware keys, but that's rather troublesome (for the user) and more expensive. Software solutions would be probably a waste of time and resources, and the only thing they would give you is the false sense of 'security'.

Few more ideas (none is perfect, as there is no perfect one).

• AntiDuplicate
• Change the language, use the nice tricks that the authors of Skype used
• License server

And don't waste too much time on it, because the crackers have a lot of experience with the typical techniques and are few steps ahead of you. Unless you want to use a lot of resources, probably change the programming language (do it the Skype way).

You can't.

There are steps you can take to make it a little more difficult, but ultimately any executable on the local machine is crackable. Eventually, that code has to be converted into native machine code and every application that is runnable is vulnerable.

What you want to do is just make it difficult enough to crack to make it not worth peoples' trouble.

Some suggestions I have for you to help protect your application:

• Obfuscate your code. Dotfuscator has a free edition and comes with Visual Studio.
• Use public/private key or asymmetric encryption to generate your product licenses. This ensures that only you can generate your license codes. Even if your application is cracked, you can be sure that they won't be releasing a key generator for your application, because it is impossible to reverse the key generating algorithm.
• Use a third-party packer to pack your .NET executable into an encrypted Win32 wrapper application. Themida is one of the better ones. This stops people from reflecting your application in .NET Reflector and makes it a pain to unpack for reversing.
• Write your own custom packer. If the third-party packers are too expensive, consider writing your own. Sometimes custom packers can be very effective, because there aren't well published methods on how to unpack them. The tutorial How to write your own packer gives a ton of good information on writing your own Win32 packer.

Ultimately though, if people want your application cracked they will. Look at all the commercial software out there that has a vast amount of resources to protect their applications and yet they are cracked before the applications are even released to the public.

A skilled reverse engineer can fire up IDA-Pro and slice through your application like butter no matter what you do. A packed application can be unpacked and obfuscation only prevents it from making it a walk in the park. All your hard work with your complex license code can be undone with a single byte patch.

You just need to accept that there is a very real chance people are going to pirate your software. There are some people who are never going to pay for your application no matter what and these are the people you don't need to worry about.

There are however, many businesses out there who would never risk a lawsuit and happily buy software licenses and many computer users who either don't want to risk it, find it wrong or are not tech savvy enough to pirate. These are your true customers, and you should focus your efforts on providing them with a good user experience and ignore the people cracking your software.

I've had my application pirated before, and I took it as a personal affront. Here I was, a small-time developer, pouring my heart and soul into an application and these people had the gall to pirate from me?! They were taking money directly from my pocket!

I immediately added in a bunch of draconian DRM code and attempted to sabotage any person using an illegitimate or cracked copy. I should of course have been working on making my application better instead of trying to stop the inevitable. Not only that, but I was hurting my true customers will all these extra protections I was putting in.

After a long battle I realized I was fighting the tides and all this time wasted was for naught. I took out all the phone-home code except for the barebones license functions and never looked back.

.NET Reflector can only open "managed code" which basically means ".NET code". So you can't use it to disassemble COM DLL files, native C++, classic Visual Basic 6.0 code, etc. The structure of compiled .NET code makes it very convenient, portable, discoverable, verifiable, etc. .NET Reflector takes advantage of this to let you peer into compiled assemblies but decompilers and disassemblers are by no means specific to .NET and have been around as long as compilers have been around.

You can use obfuscators to make the code more difficult to read, but you can't exactly prevent it from being decompiled without also making it unreadable to .NET. There are a handful of products out there (usually expensive) that claim to "link" your managed code application into a native code application, but even if these actually work, a determined person will always find a way.

When it comes to obfuscation however, you get what you pay for. So if your code is so proprietary that you must go to such great lengths to protect it, you should be willing to invest money in a good obfuscator.

However, in my 15 or so years of experience writing code I've realized that being over-protective of your source code is a waste of time and has little benefit. Just trying to read original source code without supporting documentation, comments, etc. can be very difficult to understand. Add to that the senseless variable names that decompilers come up with and the spaghetti code that modern obfuscators create - you probably don't have to worry too much about people stealing your intellectual property.

The best answer is the first one from the small developer speaking from his own expierence, all the anti-reversing techniques discussed above are 101 textbook cases for any serious reverse-engineer.

Some commercial DRM solutions are pretty decent, but they crack every triple AAA game with custom DRM solutions all the time within hours (or days). Only the introduction of a completely new DRM solution - sometimes - delays in inevitable for perhaps a couple of weeks.

Getting the most out of the DRM costs a lot of time & money and can easily hurt performance, reliability, compatibility/portability and customer-relations in general. Either stick with some decent commercial DRM without trying to be too smart about and take your (less) losses or just forget about it totally ...

One example of a DRM solution which dug it's own (commercial) grave: http://en.wikipedia.org/wiki/StarForce

Just to add a warning: if you are going to use obfuscation, check that everything still works! Obfuscation might change things like class- and method-names. So if you use reflection to call certain methods and/or classes (like in a plugin-architecture) your application could fail after obfuscating. Also stacktraces might be useless to track down errors.

There's Salamander, which is a native .NET compiler and linker from Remotesoft that can deploy applications without the .NET framework. I don't know how well it lives up to its claims.

If Microsoft could come up with a solution, we will not have pirated Windows versions, so nothing is very secure. Here are some similar questions from Stack Overflow and you can implement your own way of protecting them. If you are releasing different versions then you can adopt different techniques for different version so by the time first one is cracked the second one can take over.

• Managing features on a license basis for a C++ application

• Secure a DLL file with a license file

• Licensing / protection software?

• Use online update to block those unlicensed copies.

• Verify serial number from different modules of your application and do not use a single function call to do the verification (so that crackers cannot bypass the verification easily).

• Not only check serial number at startup, do the verification while saving data, do it every Friday evening, do it when user is idle ...

• Verify application file check sum, store your security check sum in different places.

• Don't go too far on these kind of tricks, make sure your application never crash/get into malfunction while verifying registration code.

• Build a useful app for users is much more important than make a
  unbreakable binary for crackers.

Bear in mind that 99%+ of your users aren't going to be interested in examining your executable to see how it works.

Given that so few people are even going to bother trying and that most obfuscators can be worked around, is it worth your time and effort?

You'd be better off investing the time into improving your product so that more people want to use it.

You can't prevent people from cracking your software.

However, you can make them create cracks that will hurt your sales less. Keygenerators that can issue a valid registration code for your software are much worse than simple patches that remove registration incentives from your software. That's because a crack will work for one software version only, and will cease to work with the next software update you release. The keygenerator will continue to work until you change your registration key algorithm and that's something you don't want to do often because it will put off your honest clients.

So, if you are looking for a method to fight illegal keygenerators for your software and you do not want to use assymetric encryption because of the long registration codes this generates, you might have a look at Partial Key Verification.

Partial Key Verification makes sure that each illegal keygenerator works only for one particular release of your software. Basically what you do is to make sure that each release of your software only links with the code for checking SOME digits of the registration code. Which digits exactly is random, so crackers would have to reverse engineer many different versions of your software and combine all this into one keygenerator in order to release a keygenerator that works for all versions of your software.

If you release new software versions on a regular basis, this leads to numerous keygenerators spread on all kinds of software piracy archives which are not working anymore. Potential software pirates usually look for a crack or keygen for the latest version, so they will likely try a few of those and give up eventually.

I've used the Partial Key Verification in my (C++) newer shareware games and it has been very effective. Before we had plenty of problems with keygenerators which we could not fight. Afterewards there were lots of cracks and some few keygenerators that worked only for that particular version of the game, but no key generator that would work with all versions. We regularly released very minor updates of the game and to render all previously existing cracks useless.

There seems to be an open source .NET framework for Partial Key Verification, although I have not tried it.

Yes, .NET binaries (EXE and DLL) can be easily decompiled to nearly source code. Check the tool .NET Reflector. Just try it against any .NET binary file. The best option is to obfuscate files, they still can be decompiled by .NET Reflector, but they create an unreadable mess. I don't think that good obfuscators would be free or cheap. The one is Dotfuscator Community Edition that comes with Visual Studio.

Yes. It is true. .NET code is extremely easy to reverse engineer if the code is not obfuscated.

Obfuscation will add a layer of annoyance to people trying to reverse engineer your software. Depending on which version you get, you'll get different levels of protection.

Visual Studio includes a version of Dotfuscator. Since it's a bundled version, you're definitely not getting the strongest obfuscation possible. If you look at their feature lists, you'll see exactly what you're missing (and exactly what the application will do to make your code more secure).

There are a couple of other free or open source .NET obfuscators out there (but I can't comment on the quality or the various methods they use):

• Obfuscar
• Babel.NET

In the end, nothing is perfect. If somebody really wants to see how your software works, they will.

Unfortunately, you are not going to run away from this. Your best bet is to write your code in C and P/Invoke it.

There is a small catch-22, someone could just decompile your application to CIL and kill any verification/activation code (for example, the call to your C library). Remember that applications that are written in C are also reverse-engineered by the more persistent hackers (just look at how fast games are cracked these days). Nothing will protect your application.

In the end it works a lot like your home, protect it well enough so that it is too much effort (spaghetti code would help here) and so that the assailant just moves onto your next door neighbor (competition :) ). Look at Windows Vista, there must be 10 different ways to crack it.

There are packages out there that will encrypt your EXE file and decrypt it when the user is allowed to use it, but once again, that is using a generic solution that has no doubt been cracked.

Activation and registration mechanisms are aimed at the 'average Joe:' people who don't have enough tech savvy to bypass it (or for that matter know that they can bypass it). Don't bother with crackers, they have far too much time on their hands.

Here's one idea: you could have a server hosted by your company that all instances of your software need to connect to. Simply having them connect and verify a registration key is not sufficient -- they'll just remove the check. In addition to the key check, you need to also have the server perform some vital task that the client can't perform itself, so it's impossible to remove. This of course would probably mean a lot of heavy processing on the part of your server, but it would make your software difficult to steal, and assuming you have a good key scheme (check ownership, etc), the keys will also be difficult to steal. This is probably more invasive than you want, since it will require your users to be connected to the internet to use your software.

How to make sure that the application is not tampered with, and how to make sure that the registration mechanism can't be reverse engineered.

Both have the same very simple answer: don't hand out object code to untrusted parties, such as (apparently) your customers. Whether it's feasible to host the application on your machines only depends on what it does.

If it isn't a web application, maybe you can allow for SSH login with X forwarding to an application server (or Remote Desktop Connection, I guess, for Windows).

If you give object code to nerdy type persons, and they think your program might be fun to crack, it will get cracked. No way around it.

If you don't believe me, point out a high-profile application that hasn't been cracked and pirated.

If you go with the hardware keys, it'll make production more expensive and your users are going to hate you for it. It's a real bitch to crawl around on the floor plugging and unplugging your 27 different USB thingies because software makers don't trust you (I imagine).

There are packages out there that will encrypt your EXE and decrypt it when the user is allowed to use it

Of course, the way around it is to crack the "can-I-use-it" test so that it always returns true.

A nasty trick might be to use the byte values of the opcodes that perform the test somewhere else in the program in a dirty way that'll make the program crash with high probability unless the value is just right. It makes you linked to a particular architecture, though :-(

Well, you cannot FULLY protect your product from being cracked, but you can maximize/enhance the security levels and make it a little bit too difficult to be cracked by newbies and intermediate crackers.

But bear in mind nothing is uncrackable, only the software on server side is well protected and cannot be cracked. Anyway, to enhance the security levels in your application, you can do some simple steps to prevent some crackers "not all" from cracking your applications. These steps will make these crackers go nuts and maybe desperate:

• Obfuscate your source code, obviously this will make your source code look like a mess and unreadable.
• Trigger several random checking routines inside your application like every two hours, 24 hours, one day, week, etc. or maybe after every action the user take.
• Save your released application's MD5 checksum on your server and implement a routine that can check the current file MD5 checksum with the real one on you server side and make it randomly triggered. If the MD5 checksum has been changed that means this copy has been pirated. Now you can just block it or release an update to block it, etc.
• Try to make a routine that can check if some of your codes (functions, classes, or specific routines) are actually have been modified or altered or even removed. I call it (code integrity check).
• Use free unknown packers to pack your application. Or, if you have the money, go for commercial solutions such as Thamida or .NET Reactor. Those applications get updated regularly and once a cracker unpack your application, you can just get a new update from those companies and once you get the new update, you just pack your program and release a new update.
• Release updates regularly and force your customer to download the latest update.
• Finally make your application very cheap. Don't make it too expensive. Believe me, you will get more happy customers and crackers will just leave your application, because it isn't worth their time to crack a very cheap application.

Those are just simple methods to prevent newbies and intermediate crackers from cracking your application. If you have more ideas to protect your application just don't be shy to implement them. It will just make crackers lives hard, and they will get frustrated, and eventually they will leave your application, because it's just doesn't worth their time.

Lastly, you also need to consider spending your time on coding a good and quality applications. Don't waste your time on coding complicated security layers. If a good cracker wants to crack your application he/she will do no matter what you do...

Now go and implement some toys for the crackers...

You can't prevent people from cracking your software.

However, you can make them create cracks that will hurt your sales less. Keygenerators that can issue a valid registration code for your software are much worse than simple patches that remove registration incentives from your software. That's because a crack will work for one software version only, and will cease to work with the next software update you release. The keygenerator will continue to work until you change your registration key algorithm and that's something you don't want to do often because it will put off your honest clients.

So, if you are looking for a method to fight illegal keygenerators for your software and you do not want to use assymetric encryption because of the long registration codes this generates, you might have a look at Partial Key Verification.

Partial Key Verification makes sure that each illegal keygenerator works only for one particular release of your software. Basically what you do is to make sure that each release of your software only links with the code for checking SOME digits of the registration code. Which digits exactly is random, so crackers would have to reverse engineer many different versions of your software and combine all this into one keygenerator in order to release a keygenerator that works for all versions of your software.

If you release new software versions on a regular basis, this leads to numerous keygenerators spread on all kinds of software piracy archives which are not working anymore. Potential software pirates usually look for a crack or keygen for the latest version, so they will likely try a few of those and give up eventually.

I've used the Partial Key Verification in my (C++) newer shareware games and it has been very effective. Before we had plenty of problems with keygenerators which we could not fight. Afterewards there were lots of cracks and some few keygenerators that worked only for that particular version of the game, but no key generator that would work with all versions. We regularly released very minor updates of the game and to render all previously existing cracks useless.

There seems to be an open source .NET framework for Partial Key Verification, although I have not tried it.