Proof of Work

Proof of work (PoW) is a core concept in blockchain technology, providing a mechanism for achieving consensus in decentralized networks.


The definition of proof of work is a consensus mechanism that requires participants, known as miners, to use computational resources to solve complex cryptographic equations. These mathematical puzzles serve as a means of validating transactions and creating new blocks in the blockchain. Miners use software programs that run on computer systems called nodes.

PoW was first introduced as a solution to combat spam and denial-of-service (DoS) attacks in centralized systems. The concept was adapted for digital tokens in 2004 by US software developer Hal Finney who introduced the idea of “reusable proof of work” using the 160-bit secure hash algorithm 1 (SHA-1).

Satoshi Nakamoto, the anonymous developer of the Bitcoin (BTC) cryptocurrency, adopted the concept as the underlying consensus mechanism for the Bitcoin blockchain launched in 2009. Since then, PoW has become synonymous with security and decentralization within the cryptocurrency space.

Techopedia Explains the Meaning of Proof of Work

What is Proof of Work?

A blockchain is a decentralized, distributed ledger that records all Bitcoin transactions electronically. Peer-to-peer (P2P) transactions are completed between users who do not know or trust each other, and there is no trusted centralized intermediary such as a bank involved, so they are considered “trustless” transactions.

Consensus mechanisms such as PoW allow cryptocurrency transactions on blockchain networks to be “trustless” and decentralized while providing secure functionality to prevent errors or fraud.

To understand the meaning of proof of work, think about using a mining task as verification for a block. The miner who is first to complete the cryptographic puzzle wins the right to verify and add a block of transactions to the blockchain. In exchange for their use of resources to do this, they receive a certain amount of newly minted Bitcoin and a share of the transaction fees as a reward. The block reward is reduced by half every four years in a process known as “halving”.

One of the downsides of proof of work is that it is energy-intensive to have vast computer networks running continuously to solve cryptographic equations. Partly for that reason, engineers have developed other types of consensus mechanisms for verifying transactions, such as proof of stake (PoS), proof of authority (PoA, and Practical Byzantine Fault Tolerance (BFT).

How Does PoW Work?

Blockchain transaction data such as the amount, date and time, and sender and recipient wallet addresses are recorded and encrypted into a block header.

The block header where the information for each transaction is recorded is an encrypted hexadecimal number that the blockchain creates through its hashing function. The hash created for each block is used in the hash for the next block, creating a permanent chain of blocks that cannot be altered or tampered with. This forms the basis for a PoW’s blockchain’s security and immutability.

Proof of Work and Mining

As each block closes, the hash must be validated before a new block can be created. The hash includes a series of numbers known as the nonce, or “number used once.” Miners each generate a hash. The network sets a target, the result of a mathematical formula converted to a hexadecimal number, which dictates the mining difficulty.

Miners must generate a hash value below the target to create a new block. If a miner’s hash value is higher than the network target, the mining program adds a value of 1 to the nonce to generate a new hash. The miner that solves the hash broadcasts the solution to the network. Other miners verify that the hash value is correct, and once consensus is reached, the miner wins the right to add the block to the chain and receive the reward for their work.

Proof of Work

Mining Difficulty

The mining difficulty regulates how challenging it is for miners to solve the cryptographic equations required to create and add new blocks to the chain. The difficulty is adjusted dynamically at regular intervals – typically every few thousand blocks – to ensure that the time it takes to generate each block remains consistent at 10 minutes. The primary purpose of adjusting the difficulty is to maintain this stable rate of block creation, regardless of fluctuations in the total computational power (hash rate) of the network.

If the hash rate increases significantly, indicating that more miners are competing to solve the cryptographic equations, the difficulty will increase to make the puzzles harder to solve. Conversely, if the hash rate decreases, the difficulty will decrease to make the puzzles easier, ensuring that the smaller number of miners can still generate the blocks at the desired rate. This dynamic adjustment mechanism helps to stabilize the network, preventing rapid fluctuations in block creation times and ensuring the smooth operation of the blockchain protocol.

As the network adjusts the difficulty, it effectively changes the target value to create a valid block, making it easier or harder for miners to find a valid hash.

Additionally, the mining difficulty helps to keep the blockchain network sure, as it deters malicious actors from attempting to manipulate the blockchain by overpowering the network with computational resources.

Miners in PoW

As they are responsible for validating and adding new blocks to the PoW blockchain, miners are crucial to the proof of work mechanism. They dedicate computational resources to solve the network’s cryptographic puzzles and are rewarded with newly minted Bitcoin and transaction fees for their efforts.

The highly competitive nature of mining means that as the Bitcoin blockchain has become larger and more popular, with more miners joining the network, it has become harder for individual miners to win the race to solve cryptographic puzzles. As a result, miners have moved beyond individual computing systems to large-scale operations, and many miners have joined mining pools to increase their chances of receiving a reward.

Full Node Operators in PoW

Full node operators maintain copies of the entire blockchain and validate transactions without engaging in mining. They contribute to network security by verifying the authenticity of blocks and transactions. These copies enable the blockchain to be restored in the event of a disruption or failure.

Proof of Work vs. Proof of Stake

While PoW relies on computational power and energy consumption, proof of stake (PoS) aims to achieve consensus with lower energy consumption and higher scalability. PoS networks select validators based on the amount of cryptocurrency they hold and are willing to “stake”, or lock, on the blockchain as collateral.

As there is no need for miners to work to solve cryptographic puzzles, PoS is less energy-intensive than proof of work. Validators in PoS networks are known as stakers rather than miners, and they only receive a share of the transaction fees as a reward, not newly minted coins as well.

By selecting stakers rather than waiting for miners to solve equations, PoS blockchains can run with much faster block creation rates than PoW chains. For instance, Ethereum’s average block time, representing its block creation rate, is around 12 seconds, compared with Bitcoin’s 10 minutes. Ethereum initially operated as a PoW blockchain but made the transition to PoS to increase its scalability.

Aspect Proof of Work (PoW) Proof of Stake (PoS)
Consensus Mechanism Requires miners to solve cryptographic puzzles through computation Selects validators based on the amount of cryptocurrency they hold
Energy Consumption High, relies on computational power and consumes significant energy Lower, as it doesn’t require extensive computational power
Validators Miners Stakers
Reward System Miners receive newly minted coins as well as transaction fees Validators receive a share of transaction fees as rewards
Scalability Generally lower due to slower block creation rates Higher due to faster block creation rates

Cryptocurrencies Using Proof of Work

Several prominent cryptocurrencies use PoW as their consensus mechanism, including Bitcoin, Dogecoin, Litecoin, Monero, and Nervos Network. Their underlying blockchain networks rely on PoW to ensure transaction security and decentralization.

Example of Proof of Work

The Bitcoin blockchain was the first to use the PoW consensus mechanism to validate transactions and create new blocks. It remains the most well-known example of proof of work in operation.

On the Bitcoin blockchain, groups of transactions are validated and sent to a block, then the PoW algorithm generates a hash for the block. Bitcoin uses the SHA-256 algorithm, which always generates hashes with 64 characters. The first miner to generate a hash that is lower than the block hash adds the block of transactions to the chain and receives the Bitcoin block reward as well as a share of the transaction fees.

The Bitcoin block reward is due to be cut in half from 6.25BTC to 3,125BTC in April 2024. The halving occurs every 210,000 blocks, roughly every four years.

Pros and Cons of Proof of Work


  • Resilience against malicious attacks.
  • Distributed network of miners
  • Accessibility to mining


  • High energy consumption
  • Limitations in transaction throughput
  • Concentration of power in mining pools that potentially undermines decentralization

Limitations of Proof of Work

Energy Intensive Nature Scalability ConstraintsSpecialized Hardware RequirementCentralization Tendency51% Attacks

PoW requires significant energy consumption, making it environmentally unfriendly.

PoW networks often struggle with scalability, leading to congestion during periods of high demand.

The Bitcoin blockchain, for instance, has experienced periods of congestion during times of high demand, leading to increased transaction fees and slower confirmation times. Solving scalability issues while maintaining the security and decentralization of PoW networks remains a significant challenge for developers.

Mining in PoW networks typically requires expensive, specialized hardware, creating barriers to entry. mining typically requires specialized hardware, such as Application-Specific Integrated Circuits (ASICs), to efficiently solve cryptographic puzzles. This hardware can be expensive to acquire and operate, creating barriers to entry for individual miners and favoring larger mining operations with access to economies of scale.

Large mining operations and pools consolidate power, potentially undermining decentralization. These mining pools have the resources to control significant portions of the network’s hash rate, leading to concerns about the concentration of influence and the potential for malicious attacks or collusion.

PoW networks are vulnerable to 51% attacks, where an entity controls the majority of the network’s hash rate, enabling manipulation or disruption of the blockchain. Executing a successful 51% attack on a large, well-established PoW network like Bitcoin is theoretically possible, but it would require a significant investment in computational resources, making such an attack impractical. However, smaller PoW networks with lower hash rates may be more vulnerable to 51% attacks, highlighting the importance of network security and decentralization.

The Bottom Line

Proof of Work serves as a robust mechanism for achieving consensus in blockchain networks, ensuring transaction security and decentralization. Despite its drawbacks, PoW continues to underpin some of the most prominent cryptocurrencies, shaping the future of decentralized finance and digital economies.


What is proof of work in short terms?

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What is an example of proof of work?

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Nicole Willing
Technology Journalist

Nicole is a professional journalist with 20 years of experience in writing and editing. Her expertise spans both the tech and financial industries. She has developed expertise in covering commodity, equity, and cryptocurrency markets, as well as the latest trends across the technology sector, from semiconductors to electric vehicles. She holds a degree in Journalism from City University, London. Having embraced the digital nomad lifestyle, she can usually be found on the beach brushing sand out of her keyboard in between snorkeling trips.