And while we're on that subject, I'd like to say that I am not interested in mere "paper trails" or "receipts". As regular readers of The Sideshow are aware, I join with tech-savvy supporters of democracy everywhere in saying that there is only one appropriate means of making elections secure: Paper ballots, hand-counted on the night, in public.
Receipts are no use. A paper receipt can be emitted by a machine confirming that you voted for the candidate of your choice even as it tallies a vote for someone else or no one at all. There is no natural rule that prevents coding a machine to send one electronic message while printing out a different one.
For true transparency, you don't do anything that isn't visible to the naked eye. I want to be able to watch people counting ballots and see that they are tallying the real votes. I want the ballot I marked to be counted by another human being, watched by still other human beings, in the most openly non-partisan manner possible.
Receipts are meaningless unless there is a recount. You can easily avoid a recount by ensuring that your machines never allow the tally in a significant district to come close enough to trigger a recount. With no recount, no one ever knows that the receipts don't match the official tallies.
Machines can be fiddled, so don't let them count your vote.
Update: Some people seem to be unclear that not all versions of "paper trail" and "receipts" include the use of a paper ballot. I have no problem with using those with paper ballots, but the essence is still that the ballot itself must be the piece of paper that is marked and counted to get the official tally.