Making an EXE expire after a certain date or number of days

Number of runs would be easier.
It could be done by write a value to the registry, reading it, and incrementing it.

When the program loads:
First, check to see if there is a value in the registry under you're program name.
Either read it, if it is there, or use zero
Add one to the value
Save it to the registry.
If the value is over the number of times you want it to load - Quit!

The only problem would be if you're students now about how to use the registry.

Hope it works

If you hide it in the registry, students can play around with the registry until they find the key, then change it back, allowing it to make more runs.


My suggestion:

If on or past date,

create a batch file, (on that execution) that  deletes the .exe and the .bat  Call a shell execute or fork (windows or unix) and then quit the program.
(You can write one easy enough by using normal file output.)

There's no chance for them editing the registry, no chance to roll back the system date, etc.  It will allow you to have full control over what they do.  They'll need a binary editor to change anything.  (Even if they know the termination date, the program can't be launched again because it will delete itself)  Just make sure to get the system working directory, and delete that, allowing the case if they move it to another directory.

Hope this helps.

Its always possible to back up the file, and tinker with it even after it has deleted itself :)

I've thought of this before, and never came up with a fully reasonable solution, short of being impossible.
The closest functional idea I came up with was to encapsulate the original executable inside another executable which requires an external module, such as a DLL file which is located on a server somewhere (requiring an internet connection to use).  When you want to expire the executable, simply remove the DLL and the encapsulator will fail to launch.

Of course the same fall backs still exist.  Reverse engineering, caching the DLL and spoofing the server address etc...

lets be practical, what is the expertise level of your students ? .. how long do u intend to keep the 'working-period'..
how much time do u have on ur hand before u deliver?.
lets think things like that  , and work out a resonably secure method.

talking about reverse engineering ,, well i guess its not a kids play, i hope and kind of believe that his students are not such 'experts' ,some good amount of dedication is requried to reverse engineer and hack the binary thing,  not talking abtmodifying registry or decompiling java classes , even that can be made resonably seccure from hands of casual -hackers.

sorry abt mulltiple posts .. but here is the one very widely used method....( not perfect , but resonably secure)., pardon me if u already tried this
have a string that has release date+ expiry date + some more information regarding release .. and make a decently strong hash of it(128 bit is good enough) .. use MD5 or something similar .. and make it as license key.. and deliver it with ur exec.. which on its launch will check the key and parse out the validity of the time period, and in absence of the key .. simply exits ..

Hopefully his students aren't that good... otherwise you'll probably make him consider expiring the students instead of the program hehe.

Alternatively you can limit the program's capacity. If you tear out all the unnecessary features and make all the necessary ones specific to only work on 1 thing students will find that the program can't be used for anything else.

Excuse me for being rather cryptic... I don't know what the program is supposed to do :)

I would tend to agree with akshayxx.   You wouldn't even need to to have an elaborate encryption for the keys, just something to force expiration that isn't too easily guessable.

The secret to the deletion method is to NOT tell the students.  One day they execute it, and it's just gone.  Short, sweet and to the point.  If you worried about students caching the .exe; you could use netconnection and force them connect to a server where the date is held.  It makes them authenticate, but not a big deal if your on campus and your dorms are wired for it.

.

This is an interesting topic because the intelligence required to cheat such a method is that of any average idiot with computer skills and experience.

I recommend hiding a file and encrypting the data, also be careful how you write the code because it can be detected easily with any HEX editor. Writing cryptic code is just as important as securing your data!!!

Hide a file in c:\windows with some odd extension. add about 40k to it and whalla you have an extremely un-obvious and un-obtrusive file. Then again Spy++ and other hooks can catch any data stored that isnt in the actual processes immediate memory.

Good luck

http://www.aspack.com/asprotect.html

AsProtect is a simple application protection tool that can offer several kinds of protection to this executable.

suqui:
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There are a number of valid solutions here.