Consensus Mechanisms

In a decentralised network with no central authority, how do participants agree on the state of the ledger? Consensus mechanisms are the rules and protocols that allow distributed nodes to reach agreement on which transactions are valid and in what order they are recorded.

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Why Consensus is Needed

In a centralised database, a single administrator decides what data is valid. In a blockchain:

• There is no central authority
• Nodes may join or leave at any time
• Some nodes may be malicious (Byzantine nodes)
• Network messages may be delayed or lost

A consensus mechanism must ensure that all honest nodes eventually agree on the same ledger state, even in the presence of faulty or malicious participants.

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The Byzantine Generals Problem

The foundational challenge of distributed consensus was formalised in 1982 by Lamport, Shostak, and Pease:

Imagine several generals surrounding a city. They must agree on a battle plan (attack or retreat), but some generals may be traitors who send conflicting messages.