Harder. Not impossible. Harder. I don't want to make it sound like I am being disagreeable just for the sake of being disagreeable. If there is one thing the past decade has shown, it is that hacking is just a matter of time and whether a determined person is willing to direct resources at it.
Hmm. Most likely ( if not only ) way to counter that would be social hacking ( because I assume the pad is generated automatically from some source ), which seems like the best way to obtain it. Then again.. I am not an expert in this field ( but we do sometimes use parameters from link for some projects ). Is it refreshed after some time passes ( if so, maybe there is an easier way to just observe what changes )?
One-time pads have to be stored server-side. If you're going to do that, you might as well just store the data itself under a GUID server-side so you avoid network transfers and then put the GUID in the URL.