Proof of Work (PoW) is a core mechanism in blockchain technology that ensures network security and achieves consensus, widely used especially in Bitcoin. Simply put, it is like a "digital puzzle". The process of solving the puzzle not only proves the "cost incurred" but also ensures the authenticity of transaction records, allowing untrusted nodes to jointly maintain a reliable ledger.
The essence of PoW is "exchanging computing power for trust":
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Nodes in the network (such as Bitcoin miners) need to consume computing resources (computing power) to solve a complex but easily verifiable mathematical problem. This process is "doing work".
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Whoever solves the problem first gains the right to bookkeep (such as packaging new blocks) and receives corresponding rewards (like Bitcoin).
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Other nodes only need to simply verify whether the result is correct, without repeating the calculation, to recognize the "work achievement" of this node.
The core logic of this mechanism is: the cost of cheating is far higher than the benefit of honest participation. Because tampering with records requires re-solving the puzzles of all subsequent blocks, the computing power cost is so high that it is almost impossible to achieve.
Bitcoin is a typical application of the PoW mechanism, and its operation steps can be simplified as:
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Collect transactions: Miners collect transactions from the entire network in the last 10 minutes, preparing to package them into a new block.
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Calculate hash value: Miners need to calculate a hash value (a fixed-length string, similar to a "digital fingerprint") that meets the rules for this block. The rule is: the hash value must start with a specific number of 0s (for example, the first 18 digits are 0).
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Computing power competition: There is no shortcut to calculating the hash value. It can only be tried by continuously and randomly adjusting a "nonce" in the block until a result that meets the rules is obtained. The stronger the computing power (the faster the calculation speed), the higher the probability of trying out the correct result.
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Verification and consensus: When a miner calculates a hash value that meets the rules, they will broadcast the block to all nodes in the network. Other nodes can verify whether this hash value is valid in just a few seconds. If most nodes approve, the block will be added to the blockchain, and the miner will receive a reward.
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Difficulty adjustment: The Bitcoin system automatically adjusts the rules of the hash value every 2016 blocks (about 14 days) (for example, increasing the number of 0s required) to ensure that a new block is generated every 10 minutes on average and maintain network stability.
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Prevent double-spending and cheating:
Suppose someone wants to tamper with a past transaction (for example, "steal back" the Bitcoin that has been transferred to others). He needs to recalculate the hash values of the block where the transaction is located and all subsequent blocks. This requires controlling more than 51% of the computing power of the entire network (i.e., a "51% attack"), and the cost is extremely high (based on the current computing power of Bitcoin, the daily electricity cost exceeds 100 million US dollars), thus effectively curbing cheating.
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Achieve decentralized consensus:
In the absence of a central authority, PoW allows all nodes in the network to decide which block is valid through "computing power voting" — honest nodes with superior computing power can always generate blocks that meet the rules, ensuring the consistency of the ledger.
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Control the pace of currency issuance:
Like Bitcoin, through the PoW reward mechanism, the speed of new currency issuance is strictly controlled (halved every 4 years) to avoid over-issuance, which is also the basis for its "total fixed at 21 million".
Controversies over PoW: Advantages and Disadvantages Coexist
