[gnarula94]

Homomorphic encryption would allow tallying the ballots without decrypting them.

Helios [1], for instance uses an homomorphic scheme.

There are alternatives to it though which preserve voter privacy but allow vote tallying. Shuffling is one of them. Cothority [2] implements an e-voting scheme based on Neff Shuffles

1. https://heliosvoting.org/ 2. https://github.com/dedis/cothority/tree/master/evoting

P.S. I contributed to the latter