There are a lot of reasons why on-line voting for anything important is a really bad idea. Some of them are technological, and technological problems, given time, can often be solved. But some of the problems are based in human nature. These kinds of problems are much harder to solve.
If you're sitting at home while you vote, someone, say from the ruling party, can stand over you and force you to vote the way they want you to. If you don't think that could happen in your country, fine. Maybe you trust your political parties more than I trust mine. But I bet you can think of places where it could happen.
That's not the only situation where people could be forced to vote for certain candidates. A woman in an abusive relationship could be prevented by her husband from voting for the candidate who wants to crack down on spousal abuse. Or imagine you're a candidate running to protect people from slum-lords, when the slum-lords can make sure that anyone who votes for you gets kicked out of their apartment. What about a single mother who can only find accommodation in a "faith" based shelter, and the shelter requires her to vote for candidates who want to take away women's reproductive rights?
And then there's the simple bribe. Did you ever wonder why parties spend money on advertising, instead of simply offering you $20 for your vote? It would probably be a lot cheaper. You don't get offered a bribe for your vote because the briber has no way of knowing you actually voted the way they paid you to. Once someone can watch you vote, they will be a lot more willing to pay you to vote their way.
None of the above happens in most modern democracies because you vote in a public place. People -- other voters and election officials -- can see that no one else could see how you voted. So there's a reasonable chance that you really did vote for the candidate you preferred, and not for the one that either coerced you or paid you to vote for them.
We're taught that the secret vote is the key to legitimacy for an electoral system. But the real key is the secret vote in a public place. Once the safety of the crowd is taken away from the act of voting, bribery and coercion become effective options. And once people believe that votes can be bought or obtained by coercion, the legitimacy of the whole electoral system evaporates.
There may be answers to these problems. I don't pretend to be smart enough to come up with them. But until we have answers to these issues, the technological problems of on-line voting pale in comparison.