Albatross

The area of distributed ledgers is a vast and quickly developing landscape. At the heart of most distributed ledgers is their consensus protocol. The consensus protocol describes the way participants in a distributed network interact with each other to obtain and agree on a shared state. While classical consensus Byzantine fault tolerant (BFT) algorithms are designed to work in closed, size-limited networks only, modern distributed ledgers -- and blockchains in particular -- often focus on open, permissionless networks. In this paper, we present a novel blockchain consensus algorithm, called \textit{Albatross}, inspired by speculative BFT algorithms. Transactions in Albatross benefit from a strong confirmation, and instant confirmations can be achieved as well. We describe the technical specification of Albatross in detail and analyse its security and performance. We conclude that the protocol is secure under regular PBFT security assumptions and has a performance close to the theoretical maximum for single-chain Proof-of-Stake consensus algorithms.