Change/recompile my .exe at runtime

[Andrew D]

I am creating a program that will be sold as a subscription. I am trying to decide how to prevent users from passing the program to others without purchasing it. I was thinking that on the very first run, the program could pull the MAC address from the computer it is run on, and create a constant at run time. This constant is then hard wired into the program and is used for comparison every time the program is run thereafter. If the MAC address do not match, it is on a different computer.

How do I recompile my .exe to include a globally declared constant used for comparison? And how do I use this variable throughout my program?

Or is there a simpler way to create my program to require Key Codes for renewal once per year?

[!NoItAll]

node locking a program is the best approach - and I will tell you that the MAC address is a lousy way to do that. First off - if the customer changed their nic the program would no longer run. If the customer switched their wireless adapter on - your program would have a 50/50 chance of no longer running as the wireless nic MAC would now possibly be first...
There are a number of ways to do this, including getting the serial number of the disk drive, the motherboard, etc. You can even hash them together or allow one, but not both to change. A much better approach.

Dim mos As New ManagementObjectSearcher("SELECT * FROM Win32_PhysicalMedia")
 
For Each mo As ManagementObject In mos.Get()
    Dim serial As String = mo("SerialNumber").ToString()
Next
 

[Andrew D]

How do I node lock the program? I am not familiar with this and cannot find anything googling. Could you point me in the right direction?

[!NoItAll]

Node lock is really just a term, not a method or function you can call.
It means something like this in your startup code where:
MySecretlyStoredNodeNumber

is a function that fetches the nodeserial from a secret hiding place (typically some nether region of the registry)

and
GetNodeNumber

is your function that returns a serial number hashed from some hardware serial numbers you either concatenate, or add, or divide, or run some super-secret algorithm you determine will be difficult to hack.

If MySecretlyStoredNodeNumber = 0 then
   SaveMyNodeNumber
Else
   Dim NodeSerialNumber as Integer = GetNodeNumber
   If NodeSerialNumber <> MySecretlyStoredNodeNumber then
      End
   End if
End if
 

Calling End is drastic and fast and will often confuse the user so you will likely want to put up a message that tells them why you are about to end the program.

Warning:

I wrote a program many years ago for viewing images from Sony Mavica cameras and used a key to unlock the software. It took people about 5 days to post a hack on the internet so anyone could get it free.
There are enough decompilers out there that it's not that difficult to do. If you truly need to lock your program then you need to look into dongles from a company like WIBU - where an actual portion of your code resides inside the encrypted dongle so the program cannot run without it plugged into the USB drive. Cracking/Hacking that is truly impossible (ok - well NEARLY impossible). They even opened their dongles to the hacking community and offer decent prizes to anyone who can hack it. One person in the past was only able to get a program to run for a short time - that's all. They are expensive - but as you can see - well worth it if you are distributing an expensive application in China or Russia (for example).

[Andrew D]

The problem with that is that if the OS is removed, the registry is removed losing the nodeserial. If the Hard Disk is formatted, the nodeserial is lost. This method also allows the .exe file to be redistributed. Is there a way to take this hashed nodeserial and make it static in the .exe file once the file is on the users computer? Or another way to go about achieving the desired result?

[kadghar]

What we do in my company is this:

When you open an unregistered software, it shows you a 16 digit number (hex) that is nothing but the 3 first digits of your HDD's serial number, encrypted with 3DES and the key is a truncated hash of a text made with today's date and 'my secret numbers'

The user sends us those 16 digits, and we decrypt them, and encrypt them back, now using a truncated hash of today's date and another set of 'my secret numbers'

When the software recieves the 'Confirmation Code' it decrypts it and checks it vs the HDD's serial number. If it's a match, the software writes the HDD's serial number and some confirmation stuff into a class that will be converted into an XLM (using XmlSerializer), strong encrypted with Rinjindaels and stored somewere in user's hdd.

Each time the software is loaded, it checks for the 'security stuff' and for the HDD's serial number.

The problem here is that each 'security file' will work in one of each 4096 HDDs (lucky we dont have that many clients) (unlucky will say the sales guy.)

Since we trust our clients, if somehow he or she changed his or her computer, we'll send him or her as many confirmation codes as he or she wants.