[stuffn]

This seems like navel gazing. Under OP's constraints it wouldn't matter what the tally is. The authoritarian won't cede power because they lost by a cryptographically secure election. They'll either

A. Force the cryptography to be weak to provide plausible deniability

B. Issue more passports for "citizens" that "voted" for them

C. Refuse the count and just keep power

Leaders don't cede power because their citizens are angry. Especially not in authoritarian countries.