Trial

[JoeyC]

Hi,

I have a program almost finished now. and i need to add a "Trial" to it which the program will work untill a counter reachs 200. after which it will disable a command button and popup a message box.

I wish to do this to a file or registry, but simply having "200" stored in the regisrty is stupid as anyone could change the value back to 0.

what would be the best way to do this?

[deathfxu]

Most companies "encrypt" the data, so people don't know what they are looking at. My preferred technique is to put the date the trial will end in a file like "[program name].dll", because no one will question as to why it's in the folder, and they will not think to check it for the trial ending date.

But you do not want to just store it as "4/1/2009" (or just as "30" if the trial is to be used 30 times) just in case someone figures it out. I've found it's best to store the value three times in a row, encrypted in different ways. So if they figure out one encryption and change it, you'll still know the correct date (or counter). See this for more on encryption.

There is a known issue with storing the "trial end date". If the person puts their system clock ahead a year, installs the program, then moves the system date back, they will get to use the program for a year longer than intended. So just be advised.

[RhinoBull]

You can still use registry and encrypt (using strong encryption) some frase that will include couter value.
I would recommend to look at CVMichael's encryption example.

[JoeyC]

I think i will do somthing like this, although im not doing this based on dates. its going to be upto 200 plays, which on this poker game, it would last about an hour. I think ill store it in a dll somewhere in windows/system32. with some encryption method i found here: http://www.vbforums.com/showthread.php?t=334313

it allows you to add a salt code to it.

[dee-u]

Or perhaps you can use Steganograpy where you can store text/strings into images so they are not viewed by anyone, it should be very difficult to crack.

[isnoend07]

My app can be used 8 times. The values are stored in 2 different encrypted files.With obscure names like w32sys.itr. On form load if they are not the same or 1 files is missing then a hack has been attempted. Be care if you write to the registary with Vista as a standard user and Administrator get written to different parts of the registary

[Tom Moran]

I agree with isnoend07. Do not write to the registry... multiple encryption and the dll extension are good suggestions!