I'd look at the structure of your app if you want to do this, doing this in a meaningful way is not as easy as it looks.
I did this for a government website and strapping down all of the keystrokes for all of the browsers (for example there is little point in stopping Alt-F4 if you don't block the back/forward buttons). Not only that, but you have to force the browser to hide the address bar to prevent the user from navigating away in this manner. A lot of people (uncluding myself) wouldn't be happy navigating a website like this.
If you
must do this, you need to do it in the browser using javascript, the principle is easy enough: handle the keypress/ keydown events for the
document, and return false for the keystrokes you want to supress.
This[
^] has something to get you started. As I said above, it isn't as simple as disabling the keystrokes you mentioned, and users won't like it.
[Edit in response to OP's comment]
What you are asking for is practically impossible, I kind of alluded to this in my own English-type way in my original reply. Even if you strap the relevant keystrokes down, the likiehood is there will some you miss and there are some you just can't block anyway. This problem becomes worse if you have to strap down several browsers.
If the exam takes place on a user's PC, and you acheieve what you want, you are effectively locking the user out their own system: this is extremely bad. They can also just fire up another browser on another machine.
If the machine is in a lab, it is better to restrict the user's internet access solely to your exam site and block the user from getting to the command prompt.
There are other strategies you could consider(especially for lab-based exams), but in my view whatever your company needs, it needs a serious re-think.
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