> For the complete documentation index, see [llms.txt](https://hub.bsvblockchain.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hub.bsvblockchain.org/wiki/mining-and-consensus/mining/proof-of-work.md). # Proof of Work A **proof of work** is a piece of data which is difficult (costly and/or time-consuming) to produce but easy for others to verify. Proof of work production usually involves a computational task that includes a random process with low probability of success, so that a lot of trial and error is required *on average* before a valid proof of work is generated. In Bitcoin the proof of work scheme is based on the SHA-256 hashing algorithm. 1. Proof of Work in Bitcoin Bitcoin uses a proof of work system in the process of mining. In order for a block to be accepted, the broadcasting node must demonstrate proof of valid work which covers all of the data in the block. The difficulty of discovering valid work outcomes is adjusted to limit the average growth rate of the blockchain to one block every 10 minutes. For a block to be valid, a nonce must be discovered that results in the double SHA-256 hash of the block header, to a value less than the current target. This indicates that the node which discovered this block is an active participant in the network. Each block header contains the hash of the block being built upon, thus creating the chain of blocks that comprise the ledger. Changing a block can only be done by making a new block, containing the same predecessor, and requires regenerating all subsequent blocks by redoing the work they contain. This protects the blockchain from tampering. 2. Summary 3. Proof of work is part of the Bitcoin consensus mechanism. 4. The Bitcoin proof of work algorithm attempts to solve a puzzle with a low probability of success per trial. 5. A Miner uses a candidate block header as the input, hashes it to check whether the hash value is below a target. If not, the Miner changes the nonce in the block header and tries again. Once the hash value is below the target, the block has been successfully mined. 6. In order for a block to be accepted by the Bitcoin network, Miners must complete a proof of work which covers all of the data in the block. The difficulty of this work is adjusted to limit the rate at which new blocks can be generated by the network to one every 10 minutes on average. Due to the very low probability of successful generation, it is impossible to predict which computer will generate the next block. 7. The low probability of successfully finding valid proof of work solutions reduces the likelihood that two or more Miners generate a block around the same time. 8. Attribution This content is based on content sourced from under [Creative Commons Attribution 3.0](https://creativecommons.org/licenses/by/3.0/). Although it may have been extensively revised and updated, we acknowledge the original authors. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://hub.bsvblockchain.org/wiki/mining-and-consensus/mining/proof-of-work.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.