CFP'93 - Electronic Voting - Evaluating the Threat by Michael Ian Shamos,
No Receipts Allowed
If the voter is worried that the machine may not have processed her vote correctly, why doesn't it just print a receipt? After all, when I play the lottery I get a ticket, and it's that ticket alone that allows me to claim the prize.
Some candidates have figured out that it can be cheaper to pay voters
directly for their votes than to spend the money campaigning and risk losing
on Election Day. If you think about it, though, you might wonder how the
candidate could ever know whom I voted for. What a fool he would be to
pay money and never be able to verify that it had done any good. However,
if the voting system printed a receipt that recorded my choices, it would
violate the vote-buying prohibition of Commandment III, since I could redeem
the receipt for cash from an unscrupulous candidate. (I leave
it to your political imagination to determine whether any such people exist.) Without a receipt you would think he has only my word for how I voted, but even this is not true. Every card, mark-sense and electronic system can easily be used to implement vote-buying, but not on a large scale. (I won't publish how this is done, but it is absurdly simple.) Receipts would turn the practice into a virtual epidemic.
Just want to make sure that we understand the implications of such a request. :-)