I have heard that some, if not all, widely used electronic voting systems (e.g., Diebold, Sequioa, Dominion) use closed-source software. If so, how can the public be sure that a closed system isn't rigged? What is the justification for not opening their source code? Doesn't the public have a right to transparency? And how can a method of simply counting votes possibly be considered proprietary?
There are a couple of moving parts here:
What is the justification for not opening their source code?
This is more of a question to the customers (in this case - the government) than the manufacturers. I don't know any specific details about any voting system, but generally speaking, if the government purchases anything (in this case - a voting system) from a private vendor, it should publish a request for tender with the specifications of the system it wishes to purchase. If publishing the system's code as open source isn't listed there as a requirement, the vendor is free to use whatever proprietary license it wishes. In that case, the question becomes why a specific vendor chose a specific closed license for their software, which will boil down to their business model.
And how can a method of simply counting votes possibly be considered proprietary?
A voting machine does much more than applying a
++ operator to a variable - you need to develop an (administrative) way to input the candidates on the ballot, a way to record votes, handle fault tolerance (e.g., what if the power is lost?), error handling (what if someone attempts to vote for two candidates on the same ballot?), accessible interfaces (can the machine be handled by a visually impaired individual), fraud detection algorithms (hopefully!), etc.
Therefore, not having in an electronic open source election backbone that can collect all votes whether federal state or local is unforgivable. Additionally, an open source voters registry would allow a voter to audit their own submission regardless of how that submission originated (ie: scanned ballot, online entry, or voting machine.)
Naturally, certain personal data would need to remain secret, while other data is publicly available. These kinds of rules could easily be implemented by open source developers. Such developers work free of charge! There actually would be no or very low governmental investment.
I believe an open source blockchain application would be the perfect solution. There are some available.