Protect NET code from reverse engineering

Question

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

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There is a detailed comparison sheet for several  Net obfuscation tools     Screenshoot taken from obfuscators io

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

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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

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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

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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

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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

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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 nbsp 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

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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

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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

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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

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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

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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 nbsp 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

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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

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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

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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

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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

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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

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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 nbsp Overflow uses  for example  I m pretty sure that Stack nbsp 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

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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  -

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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

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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

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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

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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

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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

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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

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Obfuscate the code  There is an example in Obfuscating C  Code

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You can t fully secure any application  managed or not   If systems like the Playstation and iPad can get cracked  mdash  where the vendor even controls the hardware  mdash  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  mdash  even in a simple way  mdash  they ll also be willing to do something more difficult or dangerous like pull your application from a torrent site  mdash  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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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  -

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I can recommend using Obfuscator

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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

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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

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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

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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

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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

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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

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There is a detailed comparison sheet for several  Net obfuscation tools     Screenshoot taken from obfuscators io

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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

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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

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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 nbsp 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

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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

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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

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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

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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

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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    We have added System Runtime CompilerServices namespace deceleration  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

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It s impossible to fully secure an application  sorry

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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

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It s impossible to fully secure an application  sorry

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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    We have added System Runtime CompilerServices namespace deceleration  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

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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

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I can recommend using Obfuscator

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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

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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

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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

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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 nbsp 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

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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

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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

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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 nbsp 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

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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

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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 nbsp 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

User · Answer

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

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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

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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

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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

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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  amp  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

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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

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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

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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

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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 nbsp Overflow uses  for example  I m pretty sure that Stack nbsp 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

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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

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Obfuscate the code  There is an example in Obfuscating C  Code

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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  -

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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  amp  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

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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

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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

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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

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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

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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

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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

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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

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

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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

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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

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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

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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

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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

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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  -

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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

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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

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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

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You can t fully secure any application  managed or not   If systems like the Playstation and iPad can get cracked  mdash  where the vendor even controls the hardware  mdash  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  mdash  even in a simple way  mdash  they ll also be willing to do something more difficult or dangerous like pull your application from a torrent site  mdash  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

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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

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

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