Abstract: The decentralized cryptocurrency Bitcoin popularized the notion of permissionless consensus. Bitcoin's solution, now known as the Nakamoto consensus, is to build a proof-of-work (PoW) chain and treat the longest PoW chain as consensus decisions. However, this elegant solution does have limitations. In this talk, I will present techniques to improve consensus protocols on multiple fronts.
A primary drawback of Nakamoto consensus is its long latency to confirm transactions. In contrast, the classical permissioned Byzantine consensus commits consensus decisions instantly. I will present Solida, a permissionless consensus protocol based on reconfigurable Byzantine consensus. I will then present an improved protocol for synchronous and authenticated Byzantine consensus, which tolerates 1/2 malicious participants and runs in expected 4 rounds (compared to expected 24 rounds from best prior work). Finally, Bitcoin’s hash-based PoW has raised concerns about fairness and energy consumption. I will describe my work on bandwidth-hard functions and proofs of space to address these concerns.
Bio: Ling Ren is a final year graduate student at Massachusetts Institute of Technology. He received his Master's degree from Massachusetts Institute of Technology and Bachelor's degree from Tsinghua University. His research interests span cryptography, computer security, computer architecture and distributed computing. He received the best student paper award at CCS 2013.