[palmer]

I'm no stranger to technology. I've written proposals for various ways for people to use cryptographic mechanisms for voting. The biggest problem is registration including verification of uniqueness (isn't registered elsewhere), citizenship, etc.

It can even do a retinal scan for each vote to make sure the same person doesn’t vote twice.

That would require a federal database of retinal scans. Otherwise the same person could vote again in a nearby state. Suffice to say that privacy of the vote and safekeeping of personal information are nontrivial and sometimes conflicting.

[JediJones]

I wouldn’t expect the verification to work across state lines. I wouldn’t necessarily even expect it to work beyond that single machine. Having people registered in multiple locations is a tougher issue like you say, but it’s not the main suspect of widespread fraud. This would be trying to address fraud at the precinct level by corrupt local officials. If every vote has to be recorded by the machine and the machine would reject the same person trying to cast a second vote, then it makes it much tougher on them to create a large amount of fake votes than would just filling in a stack of blank ballots. The most they could create would be their number of machines multiplied by their number of people involved in their scheme.