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In voting scemes I have seen so far that are based on homomorphic encryption, a group of partially trusted "authorities" share the task of decrypting the result.
The voter has to trust at least one of the authorities to be sure that his personal vote will not be decrypted individually. At the same time, every voter can verify that the (joined) authorities are not tampering with the result.

Is there a fundamental reason that the voters can not simulataneously all be authorities?
If this would be possible, the only way to find out the vote of A is to compute and decrypt the votes of all voters, and the votes of all voters minus A. But as A has to help decrypting, he/she can inhibit the latter.

I can only think of practical reasons:

  1. Every voter could also inhibit obtaining the overall result. I guess there should be ways to handle that. These ways may be costly.
  2. It would be too costly.

Thanks

Dieter Cyonce
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To prevent coercion and vote-selling. If the voter has the ability to itself reveal the vote to a outsider, he could be coerced or sell his vote.

Thats why you need a trusted authority, that all voters trust not to reveal personal votes, even if a single voter wants his vote revealed.

sebastian nielsen
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  • Thank you for the comment. It would help a lot if you could explain why beeing part of the authority would help the voter to reveal his vote to a coercer. In my understanding this would need the cooperation of all partial authorities. – Dieter Cyonce Sep 13 '16 at 09:29
  • Theres multiple homorpic encryptions, but they all share a common denominator: Either everyone needs to have full authority to reveal one vote, thus the voter could reveal his own vote to a coercer, OR if all authorities must cooperate to reveal the total tally, the voter could refuse to decrypt his part of the official tally, which would "DoS" the whole vote. – sebastian nielsen Sep 15 '16 at 02:02