Blockchain Consensus

In this paper, we present a new definition of Byzantine consensus that applies to blockchains, applications that allow to transfer digital assets through transactions. More precisely, a blockchain is a distributed abstraction where participants must reach a consensus on a unique block of transactions to be appended to the chain. This new consensus definition requires a validity property based on an application-specific predicate but does not require a decided value to be proposed as long as it is valid. Its novelty is to allow to reach consensus on a value even if this value was proposed only by Byzantine processes, provided that it is considered valid by the application. The advantage of differentiating the validation of a proposed value and the nature of the proposing participant is to make the system progress by appending blocks with transactions, where other algorithms would typically abort.