Tuesday, 25 September 2018

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.


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)
  • If majority of the nodes are honest, they will grow and outpace the any competing chains.
  • To modify any block
          - The attacker would have to redo all the proof of work for all the blocks from that block till the last block.
          - And catch up and surpass work of the honest nodes
  • As per the original paper of Satashi Nakamoto:
            - There is a premises that as number of blocks increase, the probability of slower attacker catching up diminishes.

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