Particularly if you do not publicly disclose the cert you signed it with: I'd be willing to bet there's some way to make it so you can produce a signing cert that'll claim you filled in any data you wish.
E.g. have your signature data be a class of values based on vote possibilities, but have all produce the same final signature. You could produce anything for anyone that way. I'm not sure if that'd be "forward secrecy" or "deniable encryption" or what, but there are a variety of systems that do similar things.
I am not a cryptographer and I don't know any concrete implementations that would have all the properties I want, but pieces of pretty much all things you could reasonably want in a voting system do already exist. And pretty often they can be layered together. The bigger problems in practice seem to be "people won't trust it" (which is defensible), "some of the fancier crypto is too new and not thoroughly proven" (which is very true, e.g. zero-knowledge proofs), and "implementers so far have been stunningly incompetent" (undeniable).
(edit: or I guess more easily, just sign the data after encryption, and throw away your encryption key. then you can claim whatever you like - it's encrypted, they can't know, and you can still show that it wasn't changed)
E.g. have your signature data be a class of values based on vote possibilities, but have all produce the same final signature. You could produce anything for anyone that way. I'm not sure if that'd be "forward secrecy" or "deniable encryption" or what, but there are a variety of systems that do similar things.
I am not a cryptographer and I don't know any concrete implementations that would have all the properties I want, but pieces of pretty much all things you could reasonably want in a voting system do already exist. And pretty often they can be layered together. The bigger problems in practice seem to be "people won't trust it" (which is defensible), "some of the fancier crypto is too new and not thoroughly proven" (which is very true, e.g. zero-knowledge proofs), and "implementers so far have been stunningly incompetent" (undeniable).
(edit: or I guess more easily, just sign the data after encryption, and throw away your encryption key. then you can claim whatever you like - it's encrypted, they can't know, and you can still show that it wasn't changed)