dot net - how to create keygen using program's code

[SystemeD]

If you don't mind software updates you can patch the program to accept all serials and deploy cracked version of the program. Probably it would be a 1-byte crack.
Another option would be to code a loader for the application to fish and save the correct serial.
Personally I would go for a keygen. You can easily use decompiled .NET code to create the keygen.

Looking for quick way out. After you put in generic serial #, the program checks for a OP_EQUALITY. Is there a way to send the text to a basic MessageBox pop-up?

If so, what routine? I'll start searching now.

Found the solution.

I tricked the program into pop-ing up a MessageBox::Show(string). W00T!

Original Code

    IL_005b:  /* 03   |                  */ ldarg.1
    IL_005c:  /* 08   |                  */ ldloc.2
    IL_005d:  /* 28   | (0A)000027       */ call       bool [mscorlib]System.String::op_Equality(string,
                                                                                                 string)

I had to NOP out the ldarg.1 (bad serial I typed in) so MessageBox call would not crash.

ldloc.2 held proper serial#.

Then I byte changed the 27 to 25 (which is the reference location of MessageBox used elsewhere in the program (looking at IL dump).

So now the code reads:

    IL_005b:  /* 00   |                  */ nop
    IL_005c:  /* 08   |                  */ ldloc.2
    IL_005d:  /* 28   | (0A)000025       */ call valuetype [System.Windows.Forms]System.Windows.Forms.DialogResult [System.Windows.Forms]System.Windows.Forms.MessageBox::Show(string)

Viola. No need for keygen. Just let the program pop out the answer for you.