'Time-locking' files

[Phreak]

Hello everyone! :wave:

Wasn't sure where to post this...
But I need some help/advice. Ok here's the deal;
A friend of me has made a cd for some of his customers. The cd
contains PDF documents, and some Excel sheets.

So he asked me if I could set a 'time-lock' on his files. So that
the files can't be opened after a specific date...

Anyone knows how i can put such a timelock on files? :confused:



Thanks,

#phreak :afrog:

[Kasracer]

Nope possible. They're files, they don't have any kind of logic that can run to check for this.

In order to do something like this, you'd have to either put them on a thumb drive with some embedded programming (which could easily be defeated if you're handy with microchips) or you'd have to create a startup program that doesn't give the user access to, perhaps, a special partition on the CD. The latter, of course, is very easily defeated and possibly not possible.

Don't do this. This is just bad design.

Besides, if a user opens them on their system, Adobe typically creates a temporary cache since the CD is read-only. What are you going to do about those? Also, if anyone decided to copy them to someplace else (something most sane people would do), then the "time-locking" would do no good.

Fyi, this should have went into the general development forum. A nice mod will come along and move it :)

[wossname]

Alternatively you could encrypt the files. Have a custom service running to periodically encrypt any file that is old.

[Kasracer]

Alternatively you could encrypt the files. Have a custom service running to periodically encrypt any file that is old.
Still wouldn't work. You could encrypt the files before they get to the user's computer but then you'll need to provide a decryptor. The decryptor could either easily be broken or, once the file is decrypted, Adobe's cache or a good old File -> Save As (or even File -> Print -> PrimoPDF or another PDF printer) and you have the file forever.

Using a service to encrypt the files seems kind of silly and would easily be defeated by holding the Shift key. After all, you can't run / install your service if I'm holding down my shift key :). Besides, in Vista your service won't install without my permission anyway :)

[wossname]

My point was that you use encryption as a means of preventing the user viewing the file once it's old.

But yes, you're right about the service. I'd forgotten about the shift key trick. I'm so glad I don't have to write code for windows any more :D

[Kasracer]

My point was that you use encryption as a means of preventing the user viewing the file once it's old.

So what you're suggesting is a service that can encrypt old files? That seems malicious as the CD would be read-only so it would have to encrypt files it thought came from the CD on the user's computer.

But yes, you're right about the service. I'd forgotten about the shift key trick. I'm so glad I don't have to write code for windows any more :D
Well in Linux and OS X CDs can't just automatically run code as well. You still have to tell it it's ok.

[si_the_geek]

Thread moved to General Developer Forum

[kleinma]

Phreak, the biggest problem you would likely face with a "time lock" is what your source of time is to compare it to.

even if you could write some code that prevented the file from being opened after a certain date, you would just be comparing it to the system time of the users computer, which they could just change. Sure I guess you could go some route of pulling time from the internet, but that crops up all kinds of other things you would have to consider.

[Phreak]

Thanks for all the replies guys! :D



Its not like the customers really cant open the files. Its for there own 'safety'...

The PDF and Excel files contain product id numbers. Like an order list, they can call/email the company and order the products with there associated product id numbers.

He wants to renew/change the PDF and Excel files every 6 months. Thats why he wants the timelock on the files. So that the customers dont order new products using the old product list...

So im looking for a simple solution to timelocking the files.. If the customer 'cracks' the timelocked file. Then he has a problem, because if he orders something from that timelocked file (which is old by then) he may order something with the wrong product id.

hehe, sorry for the bad english.. im kinda tired :lol:


edit:
So, no problem in using the system time of the computer then =)...


#phreak :thumb:

[Kasracer]

So im looking for a simple solution to timelocking the files.. If the customer 'cracks' the timelocked file. Then he has a problem, because if he orders something from that timelocked file (which is old by then) he may order something with the wrong product id.

Well, if a user orders something via an ID then you would just tell them you don't carry it anymore. You wouldn't want to re-use IDs just in case. What if my clock is 10 minutes behind yours and I order something from my file but you're using the newer one? If we're reusing IDs, then I just inadvertantly ordered something else. That's bad. I would suggest avoiding using IDs.

As for the time-lock, well it's not entirely possible. I would just suggest telling your customers to order from the newest files depending on their dates. If they don't, the only bad thing that can happen is you tell them we don't have that product.

Just like I have 3 year old Oriental Trading catalogs at home (I don't but as an example), I'm not going to call up and demand to order something from that catalog especially if there is an expiration date on it.

[Phreak]

Yep.. I told him the same Kasracer... But he wants to do it that way. I dont know why :confused:


Well.. I think the best thing to do is to make some kind of auto run menu on the CD. And from the autorun you can launch the PDF / Excel files. And just make the files on the CD hidden... :lol:

[Shaggy Hiker]

This guy needs to get with the WWW program. His basic problem is that he is sending stuff around on hard media. That's sending an item via the mail, once it's en-route, you can't touch it, alter it, maintain it, etc. With the web, he can do all of the things he is talking about, and it's kind of routine. Everybody would be working with the same set of data, which he would have control over. No issues with items going stale as long as the site is up to date.

[Kasracer]

Yep.. I told him the same Kasracer... But he wants to do it that way. I dont know why :confused:
This is the hard part of our jobs. You know better than your boss because you're doing the programming and he does not. Even though he says he still wants it, what you should do is sit down with him, talk about feasability and explain to him why it's not a good idea. If he still want to do it then you'll have to but at least you tried.

[Phreak]

Yeah.. Ill go and have a talk with him tomorrow. And if he still want to do it his way, then ill have to do that...


Thanks everyone ! :afrog:

[Hack]

As long as you get paid for it, it is irrelevent if it is stupid. :D

[Phreak]

lol.. so true :D