this is a cut and paste from what I answered to @rocking-dave's comment:
I only have a moment as alone with the baby who is a little demanding today but, I would assume that if there was a unique key provided for a voter that was known (connected to the voter. When it is used it can be burned. But, the vote it casts randomizes the information and disconnects it from the voter. That way, it is possible to know if the key voted but, not how it voted.
There must be multiple ways to do this and it has got to be safer than being able to send a friend in to vote for you and have your name crossed off the list even though they are of the opposite sex... I am not saying that anyone I know did this of course ;)
Oh technically there are plenty of ways that it can be done. But then you have to convince the world that it's tamper proof.
To convince me, the technology would need to be open source with publicly available block chain, but then there's a lot of people that might still not be convinced...