Etherions.com: Understanding Proof of Work in Blockchain Technology

A Proof of Work is a piece of data that is difficult to generate due to its high cost or time-consuming nature, but is easy for others to verify. The generation of a Proof of Work typically involves a computational task with a randomized process that has a low probability of success, so on average, a large number of iterations of trial-and-error trials are required before a valid Proof of Work can be generated. In Bitcoin, the proof-of-workload mechanism is based on the SHA-256 hashing algorithm.

Bitcoin's Proof-of-Work Bitcoin uses a proof-of-work system during the mining process. In order for a block to be accepted by the entire network, the broadcasting node must show a valid proof of workload that encompasses all the data in the block. The difficulty of mining a valid block is adjusted for the average growth rate of the blockchain, which is set to generate a block every 10 minutes.

For a node to mine a valid block, it must find a random number (nonce) that causes the block header to hash less than the current block difficulty target value under two SHA-256 operations. This indicates that the node that discovered the block is an active participant in the network.

The block header of each new block contains the hash value of the previous block, thus connecting the blocks into chains that form the blockchain ledger. If one wishes to modify a block, one must first create a new block that also contains the information from the previous sequential block, and one also needs to redo all the workload contained in all subsequent blocks. It is this mechanism that protects the blockchain and makes it less susceptible to tampering.

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