blockmindset
Lesson 2 of 514 min

Proof of Work Deep Dive

Proof of Work makes rewriting blockchain history computationally expensive and easy to verify.

Why this matters

Proof of Work explains mining, confirmations, difficulty adjustment, cumulative work, and double-spend resistance.

1

The Intuition

Miners repeatedly hash candidate block headers until one hash is below the current target. The winning hash is rare, but every node can verify it quickly.

2

See it concretely

Concrete example

Imagine a worldwide lottery where each hash attempt is a ticket. Difficulty changes how rare a winning ticket is so winners appear at a predictable average rate.

3
⚠

Tempting — but wrong

4

The precise version

A miner builds a candidate block and varies fields such as nonce, timestamp, extra nonce, and transaction ordering until the double-SHA-256 hash of the block header is below the target. Nodes select the valid chain with the most cumulative work, not simply the most blocks. Bitcoin retargets difficulty every 2016 blocks to maintain an expected ten-minute block interval.

validBlock \iff SHA256(SHA256(header)) < target

Check your understanding

Why is PoW asymmetric?

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Why do confirmations reduce double-spend risk?

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Before moving on
  • Define target, difficulty, nonce, and cumulative work.
  • Explain why mining is probabilistic.
  • Explain why the heaviest valid chain wins.
  • Connect confirmations to settlement confidence.
?Checkpoint

What makes a Proof-of-Work block valid?

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