Proof of Work in Block Chain

Proof of work is the concept which makes things difficult for the fraudulent note to catch up with the Ow-nest notes.

Ideally the purpose of Proof-of-work

Produce a challenge to the user / computer
The user / computer has to produce the challenge result to submit some value.
Essentially showing the Proof of Some Work Done.
And eliminate entities which are slow or not capable enough to generate the proof of work

The idea behind Proof of Work is:

Find or generate a Value which is:

- Difficult to generate (In terms of CPU Power)

- And yet easily verifiable.

BlockChain Solve Problem

For example, proof Of Work in Blockchain

Proof of Work : Block Should have n leading 0.

For example: n = 4, hash should have 4 leading zeros.

0000AB23EF23DD223432FC0390040438DF.....

How to Get Such Proof of Work ?

Generate Nonce, (may be by Bruteforce) such that :

Combination of Nonce and Block Data generates the leading zeros.
As per the difficulty of the challenge (Value of n)
More the value of n more the difficulty.

Significance of Proof of Work

Signifies that the computation required is exponential to the number of leading zeros required.
Once the CPU effort has been expended to make satisfy proof of work the block cannot be changed.
Until redoing the proof of work.
And as the blocks are chained, redoing will require entire chain to be redone.

A Validity of Proof-of-Work

Even if Attacker tries to catch up and produce the Proof-of-Work faster, the added block will be assessed again when new block is added
Chain with longest proof of work will be accepted.
Parallel chains are formed.
Other Block will be rejected (Called the Dangling)