Decentralizing permissioned blockchain with delay towers
Abstract
Growing excitement around permissionless blockchains is uncovering its latent
scalability concerns. Permissioned blockchains offer high transactional
throughput and low latencies while compromising decentralization. In the quest
for a decentralized, scalable blockchain fabric, i.e., to offer the scalability
of permissioned blockchain in a permissionless setting, we present L4L to
encourage decentralization over the permissioned Libra network without
compromising its sustainability. L4L employs delay towers, -- puzzle towers
that leverage verifiable delay functions -- for establishing identity in a
permissionless setting. Delay towers cannot be parallelized due to their
sequential execution, making them an eco-friendly alternative. We also discuss
methodologies to replace validators participating in consensus to promote
compliant behavior. Our evaluations found that the cost of enabling
decentralization over permissioned networks is almost negligible. Furthermore,
delay towers offer an alternative to existing permissionless consensus
mechanisms without requiring airdrops or pre-sale of tokens.
Conflict-free replicated data types (CRDTs) are popular for optimistic replication and ensuring strong eventual consistency (SEC) in distributed systems. However, reversibility is an underdeveloped functionality for CRDTs, despite its usefulness in system restoration from an erroneous state or undoing unwanted operations. In this paper, we define the concept and design of reversible CRDTs (rCRDTs). Reverse operations compensate for the effect of reversed updates, and they extend existing CRDT interfaces. Three abstractions for reversibility are proposed: reversing a single update, multiple causally related updates, and multiple logically related updates that capture the user intention behind the updates. Moreover, a replicated and distributed key-value store, rKVCRDT, is implemented as a proof of concept that integrates the support of reversible CRDTs. The rCRDTs' evaluation show that although adding …