I am having a 8GB pen drive, I need to put a PowerPoint into that and make it read only. Rest of the space should be usable for the user.
Assuming the user will be using Windows only, what are my options to do that?
I went through other answers present on SuperUser, but none could solve my problem completely.
Is partitioning the pen drive, and then making 1 partition as read only, a solution to this? If yes, then please guide me how to do that.
Best Answer
Answers to questions like this depend on the so-called "attack model" that you want to be protected from. In other words, will the user actively try to overcome your protection? Or is the protection there just to warn the user, which you trust to be honest with respect to the read-only setting and not try to overcome it?
In the second case, setting the read-only flag in the file properties should be enough. When the user will open your file, the program will tell him that the file is read-only and they cannot save it. If the user is honest, he will not do anything.
The first case is much more difficult, and actually there is very little to do about it. Giving a USB pen to someone is much like giving them a paper sheet with pencil writing on it. There is no way you can prevent your user from erasing some part of your sheet and writing again on it, no matter what you write in it (in this metaphor there is no equivalent of the pen; everything that you write on a USB pen is erasable and re-writable; if you want to have a pen equivalent, you have to write on a CD-ROM).
In this metaphor, setting the read-only flag is no different from writing (in pencil): "Please, do not erase of modify things here". If the user is honest, they do not do it. But there is no technical mean that prevents them from doing that if they are not honest.
So, in this case, the answer is basically "no".
There is a partial workaround that may or may not be applicable to your case: you can add a digital signature to the file you want to protect. The user is still able to modify the file, but thanks to the digital signature this leaves evidence that the file was modified. However this is a very broad topic, which has in turn other caveats, and it would be off-topic to discuss it here.