PiLi: An Extremely Simple Synchronous Blockchain

We describe PiLi, an extremely simple synchronous blockchain that tolerates minority corruptions. The protocol description is the extremely natural and intuitive. Informally, every epoch, an eligible proposer proposes a block (tagged with the current epoch) extending the freshest notarized chain observed so far. Nodes vote on all valid proposals from eligible proposers as long as 1) the proposed block extends from a parent chain has been notarized in the node’s view; and 2) this parent is “not too stale”. When a block gains votes from the majority of nodes, it is considered notarized but not necessarily final. If a node observes a notarized chain ending with 6 blocks of consecutive epochs and no other notarized blocks of these 6 epochs have been seen, then this notarized chain except the trailing 5 blocks are considered final.