Don't Mine, Wait in Line: Fair and Efficient Blockchain Consensus with Robust Round Robin

Abstract

Proof-of-Stake systems randomly choose, on each round, one of the\nparticipants as a consensus leader that extends the chain with the next block\nsuch that the selection probability is proportional to the owned stake.\nHowever, distributed random number generation is notoriously difficult. Systems\nthat derive randomness from the previous blocks are completely insecure;\nsolutions that provide secure random selection are inefficient due to their\nhigh communication complexity; and approaches that balance security and\nperformance exhibit selection bias. When block creation is rewarded with new\nstake, even a minor bias can have a severe cumulative effect.\n In this paper, we propose Robust Round Robin, a new consensus scheme that\naddresses this selection problem. We create reliable long-term identities by\nbootstrapping from an existing infrastructure, such as Intel's SGX processors,\nor by mining them starting from an initial fair distribution. For leader\nselection we use a deterministic approach. On each round, we select a set of\nthe previously created identities as consensus leader candidates in round robin\nmanner. Because simple round-robin alone is vulnerable to attacks and offers\npoor liveness, we complement such deterministic selection policy with a\nlightweight endorsement mechanism that is an interactive protocol between the\nleader candidates and a small subset of other system participants. Our solution\nhas low good efficiency as it requires no expensive distributed randomness\ngeneration and it provides block creation fairness which is crucial in\ndeployments that reward it with new stake.\n