All terms
Securing a chain by making block production computationally expensive.
Miners race to find a number that makes a block hash fall below a target. Finding it takes enormous computation and verifying it takes almost none, which is the useful asymmetry.
Rewriting history means redoing all that work faster than the honest network can extend it, which is prohibitively expensive at scale.
Bitcoin adjusts difficulty every 2016 blocks to keep block times near ten minutes regardless of how much mining power joins.
That proof of work is wasteful by accident. The cost is the point: it is what makes rewriting history expensive. Whether the security is worth the energy is a real argument, and it is a different argument from the one about inefficiency.
Common questions
Is proof of work wasteful?
Could somebody attack Bitcoin with enough hardware?
Where this comes up on the site
The guides that actually use this word, rather than a list of everything we have written.
Where to go next
More technology terms
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