The TAU Programming Languages and Systems Seminar - Tortoise and Hares Consensus -- the Meshcash Framework for Incentive-Compatible, Scalable Cryptocurrencies

Abstract:

Meshcash is a new framework for cryptocurrency protocols. It combines a novel, proof-of-work based, permissionless byzantine consensus protocol (the tortoise) that guarantees eventual consensus and irreversibility, with a possibly-faulty but quick consensus protocol (the hare). The construction is modular, allowing any suitable "hare" protocol to be plugged in. The combined protocol enjoys best of both worlds properties: consensus is quick if the hare protocol succeeds, but guaranteed even if it is faulty. Unlike most existing proof-of-work based consensus protocols, our tortoise protocol does not rely on leader-election (e.g., the single miner who managed to extend the longest chain). Rather, we use ideas from asynchronous byzantine agreement protocols to gradually converge to a consensus.

Meshcash is designed to be race-free: there is no "race" to generate the next block, hence honestly-generated blocks are always rewarded. This property turns out to be useful in scaling the transaction rate (since it removes network propagation delays as a factor in reward allocation, which is one of the main impediements to accomodating a larger volume of transactions). It also helps  in analyzing rational miners' behavior: we prove that race-free blockchain protocols are incentive-compatible and satisfy linearity of rewards (i.e., a party receives rewards proportional to its computational power).

Based on joint work with Iddo Bentov, Pavel Hubáček and Asaf Nadler.