It has to at least know who upvoted, to prevent revotes. HN has to know who voted, not which way someone voted. HN doesn't let you change your vote once its be

It has to at least know who upvoted, to prevent revotes. HN has to know who voted, not which way someone voted. HN doesn't let you change your vote once its been made, but it does let you downvote once you have enough karma.