Lets first get a brief idea of the POW concept;
Proof of work (POW) is a concept by which somebody can effectively prove that they have engaged in a significant amount of computational effort. Proof of work is also used beyond the concept of block chain, there are past applications which have incorporated such schemes for example denials of service attacks, here the requestor of a particular service would have to solve a very specific computational problem before being allowed to use the service. Another good example is being able to deter spam emails.
The Double Spending issues
All the more explicitly the proof of-work addresses the "double spending issue," which is trickier to tackle without a pioneer in control. On the off chance that clients can double spend their coins, this blows up the general stockpile, spoiling every other person's coins and making the cash erratic and useless. Double spending is an issue for online exchanges on the grounds that computerized activities are not difficult to repeat, which is the thing that makes it unimportant to reorder a record or send an email to more than one individual.
Proof of-work makes multiplying computerized cash incredibly, hard. It's much what it seems like: "Proof" that somebody has done a lot of calculations.
Purpose of a Proof of Work( in Steps):
1)Present a challenge to the user or Computer.
2)The user or the computer has to produce the challenge result to submit some value.
3)Essentially showing some proof of work done.
4)Eliminates entities which are slow or not capable enough to generate proof of work.
Proof-of-Work in Blockchain
Now, coming to the idea behind the proof of work in case of blockchain technology.
* The objective here is to generate a value which is very difficult to generate in terms of computational power.
* And it should be easily verifiable.
A common example of proof of work in blockchain is the n leading zero problem. For e.g.; Block hash should have n leading 0; n=4 hash should have 4 leading zeroes. Like 0000AB234EFDDDFG675….so on. So, how does one generate such proof of work:
Generate nonce such that; combination of nonce and block data generates n leading zeroes. As per the difficulty of the challenge (n value). More value of n means more computational effort.
Significance of Proof of work:
Signifies that the calculation required is enormous to the number of leading zeroes required. Once the CPU’s computational effort has been consumed to fulfil the proof of work the block can't be changed, until redoing the proof of work. And redoing means here to redo for the entire blockchain.
The Proof of work Bitcoin:
Bitcoin utilizes the hash cash framework to create blocks. Miners make blocks by figuring the answer for a proof of work challenge. They need to locate a particular hash under an objective 256-digit number. Hash cash utilizes a SHA256 to create a hash that changes fiercely with any difference in information. It is difficult to get contribution from the yield. The best way to address this test is through expensive speculating, i.e., Proof of work.
To figure the "proof of work" answer, miners take in the rundown of exchanges and add a speculation number (nonce) as contributions for the hashing capacity. Since miners openly enter and leave the organization, the trouble is changed each 2,016 squares to keep every miner’s likelihood of settling the block inside the ten-minute stretch. This decentralizes the confirmation interaction across the whole organization. This change happens by the convention consequently expanding or diminishing the objective dependent on the quantity of miners.
The first miner to locate the "proof of work" answer communicates their answer for the blockchain network. All nodes are told that a new block was added. They double check the arrangement and afterward start working on the next block. This work is repetitive; all miners compete on similar transactions generally depending on the block reward.
In the event that right, the square miner acquires the exchange expenses and a block prize. A block prize (right now at 12.5 bitcoin) is a new bitcoin that is made and credited to the miners account. This opposition shapes the understanding which synchronizes all hubs with the equivalent blockchain duplicate.
The convention just thinks about the longest chain as legitimate and real. A deceitful chain is unreasonable over the long haul in light of the fact that an miner has a low likelihood of reliably winning the block compensation to keep up the chain. After some time, different miners will broaden the substantial chain quicker than the altered chain.
Issues with Proof-of-work
Below mentioned are a few problems related to Proof-of-work:
High energy use: Bitcoin utilizes as much energy as all of Switzerland as a result of proof of-work. Furthermore, its energy use is expanding as more miners join the chase for bitcoins, however a portion of this is controlled by environmentally friendly power.
51% assaults: It is vulnerable to the 51% attack. If miner(s) take over 51% of the hashing (guessing) power, they can dictate what truth is.
Mining centralization: Proof-of-work is tied in with making a money without one single element in control. All things considered, practically speaking the framework is fairly concentrated, with only three mining pools controlling practically half of Bitcoin's computational force. Designers are endeavoring to in any event lighten this issue, in any case.