"Democracy is in the counting" (Tom Stoppard)
When I studied cryptographic and electronic voting schemes I rapidly came to the conclusion that all of the practicable ones (i.e. ones which could be implemented and usable in practice) had the fatal flaw that you were trusting whoever had built and designed the system to be entirely honest in reporting the results.
The essential part of a voting system is not that your own vote is reported correctly, but that everyone else's vote is. Other important features are that the returning officers should be able to prove they have not cheated. In a system of paper ballots there is always the option for a recount, and anyone wanting to subvert the election has to forge a large number of ballots. With any electronic scheme, subverting the system is more feasible, if you you have the technical capability.
The problem is that electronic election systems are chosen by politicians, and designed by large corporation whose bosses want lucrative government contracts. Anyone remember the 'hanging chads' that got George W Bush elected, and the confusing voting paper in Florida - choesen by a republican politician?
As Tom Stoppard said - Democracy is not in the vcoting, but in the counting. The NAZIs subverted the democratic process by blatantly lieing about referenda results to deny rights to Jews (see Christabel Bielenberg's "The Past is Myself"). With an electrinic voting systems it is so much easier for those in power to cheat.
<OK, rant over>