One about Mining, Proof-of-Work and difficulty.

Mining and Proof-of-Work

Mining refers to the process of aggregating, verifying and recording transactions into the blockchain, without relying on a central coordinator, through use of Proof-of-Work, which is achieved by including a specific (valid) hash into a candidate block.

A valid hash acts as a Proof-of-Work, which is used to verify that the miner has expended resources while “mining” the candidate block, which is one of the four processes that make the emergent consensus possible.

In order to create a valid hash, miners take the block header from the candidate block, the set of transactions picked from a mempool and add a nonce (number used once), which is then put through a hashing function (SHA256). The objective is to create a valid hash that meets the current target, which specifies what a valid hash currently has to comply with, a valid hash would currently need to start with five zeros, for example. Since the candidate's block header can't be changed, miners use the nonce (which is a changeable random input) to rehash a block as often as necessary, up until the created hash meets the target, creating a valid hash and thus, a Proof-of-Work.

● A blockheader, amongst other data, also includes the hash from the previous valid block, thus linking earlier blocks to the next, creating a chain of blocks, hence the term “blockchain”.

This also means that once a previous block gets tampered with, the Proof-of-Work for the tampered block + all subsequent blocks would have to be redone, since the hash from the tampered block changed, thus rendering the hash of each subsequent block invalid.

The amount of miners that participate tends to fluctuate, which is where the difficulty-adjustment chimes in. The difficulty-adjustment is a mechanism which allows the target for finding a valid hash to be self-regulating, recalibrating the target every 2016 blocks, or approximately every two weeks, making the target either harder or easier to meet, ensuring that on average every ten minutes a new block is produced.

● The difficulty changes every 2016 blocks, or approximately every two weeks.