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As far as I understand in crypto-mining you are trying to find the nonce such that the hash starts with some amount of zero's. I do not understand how this nonce is used to actually validate anything.

2 Answers 2

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In the context of your question, you can think about mining in two distinct ways:

  • the act of building block templates and 'mining' to find a valid block (this done by miners)
  • the act of validating a block that another node has told you about (this is done by network nodes)

For miners that are building blocks, the nonce isn't used to validate anything per say, it is just a piece of data that can quickly be varied to produce different hash results for an otherwise unchanged block structure. This is to say, miners can create a block template, and then quickly vary the nonce to produce many slightly different versions of the block, each of which will have a distinct hash. Hopefully they can find a block structure (which includes a specific nonce) that leads to a valid hash.

For nodes that are validating blocks, there are many rules that the block is checked against to see if it is valid. One of the rules is 'does the block header produce a valid hash?' (ie, one that is below the target value). Since the nonce is a component of the block header, you could say that the nonce is needed to validate the block.

Note though, there are many other rules for validity that the node will run through, that do not utilize the nonce in any way.

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  • could you please clarify what you mean by building block templates?
    – KoalaMaybe
    Jul 29, 2022 at 22:25
  • A 'block template' is the name for the block structure that a miner will create when trying to find a valid block. The block template will be an otherwise valid block full of whatever header and transaction data the miner chooses to add to it, and the miner will then 'mine on that template' by iterating the nonce (and 'extranonce') in the hopes of finding a hash that will be counted as a valid block on the network.
    – chytrik
    Jul 30, 2022 at 7:18
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How is crypto Mining actually validating the block?

It isn't.

Before a miner starts mining a block template, they must have already have validated the data in the block template. They must already have checked that the data in the block template is valid. That each piece of data in it already passes all the Bitcoin rules.

Mining a block successfully acts to confirm transactions in the block but confirmation of transactions is completely different to validation (AKA verification) of transactions and blocks etc.

in crypto-mining you are trying to find the nonce such that the hash starts with some amount of zero's.

That is not true for Bitcoin. In Bitcoin, miners find a set of data, including nonce and other values, whose hash is less than or equal to a target value. There is no measuring of the number of leading zeroes.

I do not understand how this nonce is used to actually validate anything.

It isn't used in the way implied by the framing of your question.

See answer by chytrik The nonce is just a meaningless number whose value can be varied by the miner in the hope of finding a value that causes the hash of the whole block to be less than the target. It is part of the block data that all other nodes hash to validate that the block data does indeed have a hash less than the target, as it should. As chytrik noted, there are a large number of other characteristics of the block contents that are also each separately validated.

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