That design is a travesty
As an electronics engineer, I wouldn't design it anything like that. Chiefly, I would not allow any communications (wifi, LAN, internet, bluetooth) with the box while voting is going on. Each box is preloaded with the registration list - a list of social security numbers pertinent to the locale - and a vote consists of
a) self identification via SS number
b) the vote itself
When voting is complete, voting data is extracted via a USB port using encrypted protocols.
That's not 100% tamper-proof, but it's pretty good.
There is no need for a complex OS. The functions described can all be done with an extremely primitive microprocessor and some flash memory.
And on a political note, dissatisfaction with all of the candidates should be available for a vote via a choice labelled "None of the above". This carries more punch than simply not voting. It means you took the trouble to point out that all the candidates are shite.