Abstract: There is described a computer-implemented method of outputting a transmission to a second node of a blockchain, the method being performed by a first node of the blockchain, the method comprising: determining a computational power devoted by a further node to a blockchain; determining, based on the determined computational power, a parameter relating to: the influence of the further node on a consensus mechanism of the blockchain; and/or a reward for the further node; and outputting a transmission to the second node of the blockchain in dependence on the parameter.

Abstract: There is disclosed a computer-implemented method of proposing a block for addition to a first blockchain, the method comprising: identifying a block of a second blockchain; and including in a proposal block for the first blockchain a reference to the identified block of the second blockchain only when: the identified block of the second blockchain extends the second blockchain; and/or the identified block of the second blockchain exceeds a threshold probability of finality; and proposing the proposal block for addition to the first blockchain.