Wombat is using threshold cryptography. Threshold cryptosystem, works like this (in short), in order to decrypt an encrypted message a number of parties exceeding a threshold is required to cooperate in the decryption protocol. Meaning, before the election has started a threshold is set, let's say there are 4 candidates, you can agree that 3 of the candidates is enough to decrypt the votes. Also... Don't forget the paper backup, you can simply count those.