Online election schemes mitigate bribery and coercion by preventing voters from creating receipts that prove how they voted. In order to guarantee that ballots appear ambiguous, existing receipt-free schemes rely on problematic assumptions when voters cast ballots. We present a new receipt-free scheme that avoids these assumptions during the election. The Masked Ballot scheme only assumes the existence of one-way untappable channels for a trusted registrar to send secret masking values to voters before the election. The masking values ambiguously disguise the votes, and so voters cast ballots over completely public channels, such as the Internet. Masked Ballot achieves receipt-freeness against an adversary who corrupts a threshold of authorities and eavesdrops on all communication during the election.