Tangle 2.0 Leaderless Nakamoto Consensus on the Heaviest DAG

TL;DR

Tangle 2.0 introduces a leaderless, DAG-based consensus protocol that replaces blockchain's longest chain rule with a heaviest DAG approach, enabling scalable, parallel transaction validation without miners.

Contribution

It presents a novel probabilistic leaderless consensus framework on DAGs, replacing PoW with stake-based weights and providing formal security proofs.

Findings

Achieves secure liveness and safety under various models

Supports parallel transaction validation without total ordering

Provides formal security proof assuming a common random coin

Abstract

We introduce the theoretical foundations of the Tangle 2.0, a probabilistic leaderless consensus protocol based on a directed acyclic graph (DAG) called the Tangle. The Tangle naturally succeeds the blockchain as its next evolutionary step as it offers features suited to establish more efficient and scalable distributed ledger solutions. Consensus is no longer found in the longest chain but on the heaviest DAG, where PoW is replaced by a stake- or reputation-based weight function. The DAG structure and the underlying Reality-based UTXO Ledger allow parallel validation of transactions without the need for total ordering. Moreover, it enables the removal of the intermediary of miners and validators, allowing a pure two-step process that follows the \emph{propose-vote} paradigm at the node level and not at the validator level. We propose a framework to analyse liveness and safety under different communication and adversary models. This allows providing impossibility results in some edge cases and in the asynchronous communication model. We provide formal proof of the security of the protocol assuming a common random coin.