Scalable Multi-Chain Coordination via the Hierarchical Longest Chain Rule

POEM: Proof of Entropy Minima

“…Another interesting consequence of using the entropy-based measurement is that unlike difficulty-based systems with subshares the tip of the chain is dictated by the most recent subshare rather than the most dominant block. This means that instead of the tip being coerced from the top down [Geo+22], the dominant chains are pulled along by the subshares and eventually come into agreement. Therefore, blocks don't really have high independent ∆S on their own but rather become canonical as the amount of entropy reduction which references them continues to increase.…”

“…As throughput is one of the primary limitations faced by current blockchain systems, many proposals have been made on scaling blockchains via sharding. A subset of these proposals is applicable to work based consensus mechanism including BlockReduce [Geo+22], treechains, fruitchains [PS17], and bitcoinNG [Met+40]. Each of these solutions propose the use of sub-chains or shares as a mechanism to asynchronously produce datasets prior to inclusion in the highest level block data structure.…”

“…However, subchains or shares make these proposals more vulnerable to withholding attacks due to block weight stratification for the various block types in the hierarchy. The Hierarchical Longest Chain Rule (HLCR) [Geo+22], an enhancement on HCR described above, proposes that a tip is chosen hierarchically such that subchain choices are restricted by the longest tip in a dominant chain. Although promising, HLCR is potentially vulnerable to withholding attacks which would cause all of the subchain blocks to be discarded up to the average block time of the most dominant chain.…”

“…The definitions and a deeper understanding of dominant chain, subchain and merged mining can be found in[Geo+22] …”