Rivest invented the 3-ballot voting protocol (see https://en.wikipedia.org/wiki/ThreeBallot)

The trick to the 3-ballot voting protocol is that not everyone can validate their vote. However, when a group of voters band together, they should be able to validate that a subset of their votes (1/3) were registered with high probability.

With a sufficiently large group of voters checking results, the law of large numbers comes into play and they can statistically detect the presence of voting fraud.