A method of making a decision on a blockchain is disclosed. First public keys are received from each of a plurality of participants (A, B, C), wherein each first public key represents a possible selection by a participant and is related to a corresponding first private key by a cryptographic operation having a homomorphic property. The first public keys are combined to generate second public keys, wherein each second public key represents a possible decision based on a combination of possible selections. Third public keys, corresponding to the second public keys, are communicated to the participants. A voting blockchain transaction is generated (T