No it's not possible. If you provide any way for an individual to verify their own vote, then they can be coerced to provide the same proof to someone else. In

No it's not possible. If you provide any way for an individual to verify their own vote, then they can be coerced to provide the same proof to someone else. In this case the coercer would just force the voter to give them their string after they vote. Now they could theoretically lie, but they'd have to be able to give a valid string that matches the preferred vote of the coercer, and that no one else has already given them. This is sufficiently hard to arrange that at least some people will not be able to do so.