where do programs save their secret license or install related information? I notice that often times when you uninstall a program, clear out appdata references, check registries to make sure there is no residue of any relevant information.
If you reinstall the trial program again, it seems to know it was installed before. I'm not looking to find a way to crack trial programs but actually need to implement something similar and cant find any good information on how to do this.
They save it wherever they can, secret files, secret registry keys. There are commercial products that offer this kind of protection, like asprotect, armadillo, etc.
cmd.exe -o 2010-02-09I have handled this in two ways. First, in windows apps, I put in an encrypted Registry entry which is not in a standard location so that it is not easily found. This is a good solution if you don't mind people who either a) reformat often which removes all registry entries or b) use your software on a virtual machine which can be quickly reverted to a pre-trial state (and thus your trail can be used again quickly).
The better alternative is to have an online registry component which catches the MAC address of the machine which the trial is loaded on. Whenever the trial is reloaded, the software checks against a web service to see if the MAC address has been seen before. The only way around this is again using a Virtual Machine with the ability to change the MAC address. However, if you have a user that goes to this extreme, they'll use your trial regardless.
Could also try making the file or folder hidden - most users don't know to reveal hidden files and folders. Then you can put it anywhere really. C:/WINDOWS is sometimes a good choice because of that silly window that shows up when you click it for the first time that says "DANGER! DO NOT EDIT ANYTHING IN THIS FOLDER OR YOUR OS WILL MESS UP!" This will hide most anything from the lay man, but let's face the facts, you're not hiding anything from anyone that is active on stack overflow. :)
Some products will utilize ADS (Alternate Data Streams) and hide the data in various places.
Others will leave behind "rootkits" cough SONY.
Also some will create special registry entries that cannot be delete easily, such as entries with NULLs in the name.
It sometimes depends on how scrupulous the developer is.
Probably the most foolproof way of licensing (when done right) is through something the user physically has - some kind of hardware dongle.
Of course, it has also numerous disadvantages:
if(dongle_ok()) { do_stuff() } is an invitation for crackers to patch that over to if (1) { do_stuff() }...For most programs, the disadvantages far outweigh the advantages; however, if you're making expensive, complex software (think "production plant control"), your clients are rather cavalier about licensing (in other words, "would buy a single copy (crack it if necessary) and run it on 50 machines if they could get away with it"), and lawsuits are impractical (take too long, you don't have much evidence, uncertain outcome), this may be useful. (I didn't say simple, did I?)