Finality and the two layer approach

[ataraxiaceleste]

What do you guys think about Concordium's two-layer approach?

Concordium’s finality layer can be added on top of Nakamoto-style consensus (NSC) blockchains as systems where parties participate in a form of lottery to win the right to append blocks to the chain. The probability that a certain party wins the lottery depends on how much of the required resource they have, for example computing power for proof of work systems or stake for PoS systems.

Their finality layer allows them to dynamically ‘checkpoint’ the blockchain by using Byzantine agreement to identify and then mark common blocks in the chains of honest users as final. This two-layer approach provides the best of both worlds according to their researchers.

They achieve the following in particular:

• As long as corruption is below ⅓, their finality layer declares blocks as final faster than the finality rule in a pure NSC blockchain, which is required to wait for ‘sufficiently many’ blocks.

• When corruption is between ⅓ and ½, they can still rely on their NSC blockchain and obtain the same guarantees as a pure NSC blockchain.

They also ask us to note that pure CBFT( committee-based Byzantine fault tolerant ) such as the ones used in Tendermint [Kwo14] and Algorand [CM19] designs fail completely under these conditions.