Consensus: How Strangers Agree on Truth

What you'll learn

• The Byzantine Generals Problem
• Proof-of-Work in Depth
• Proof-of-Stake: The Alternative
• Other Consensus Mechanisms
• For Deeper Reading

Key terms

Consensus mechanism

The protocol by which a distributed network of computers agrees on a single shared state. Bitcoin uses proof-of-work; Ethereum uses proof-of-stake.

Byzantine Generals Problem

A 1982 formal problem in distributed computing about reaching consensus when participants may be unreliable or malicious. Proven that consensus requires more than 2/3 honest participants.

Proof-of-work (PoW)

A consensus mechanism where participants compete to solve computational puzzles, with the winner adding the next block. Used by Bitcoin. Energy-intensive but battle-tested.

Proof-of-stake (PoS)

A consensus mechanism where validators lock up cryptocurrency as collateral to earn the right to validate blocks. Used by Ethereum since September 15, 2022. Reduces energy use ~99.95% vs PoW.

Nonce

A 32-bit number that miners change repeatedly while searching for a valid block hash. The nonce is included in the block header.

Difficulty

A measure of how hard it is to find a valid block hash. Adjusts every 2,016 blocks on Bitcoin (~2 weeks) to maintain ~10-minute block times. Currently ~144.4 trillion (Feb 2026).

Slashing

The PoS penalty mechanism where misbehaving validators have their staked cryptocurrency partially destroyed. Designed to make double-signing and other attacks economically unattractive.

Finality

The point at which a transaction is considered irreversible. Bitcoin offers probabilistic finality (~6 confirmations / 1 hour). Ethereum PoS offers explicit finality after ~12.8 minutes.

Validator

A participant in a PoS network who stakes cryptocurrency to earn the right to propose and attest to blocks. Ethereum requires 32 ETH to become a validator.

The Merge

Ethereum's transition from proof-of-work to proof-of-stake on September 15, 2022. One of the largest live software upgrades in computing history.

Delegated Proof-of-Stake (DPoS)

A consensus mechanism where token holders elect a small set of validators (often 21-100). Used by EOS, Tron, Steem. Faster but more centralized than PoS.

Slot and epoch (Ethereum)

Ethereum PoS divides time into 12-second slots, with 32 slots forming an epoch (~6.4 minutes). One validator is chosen per slot to propose a block.