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PoW is a mechanism to keep block chain incorruptable from malicious nodes. Now in a private block chain where all nodes are supposed to be honest, what purpose PoW would serve? Would it not be just a waste of computational power?

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    What do you try to achieve from having a blockchain? – Achala Dissanayake Oct 23 '17 at 8:11
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    Why using blockchain if all the nodes are supposed to be honest ? – Adrien Forbu Oct 23 '17 at 8:22
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    @AdrienForbu to agree on the state, if 5 companies are honest but they want to share a db, blockchain might be a good solution. of course without PoW. I know it's not where the blockchain shines but still a valid use-case imo. Honest != never make mistakes, blockchain makes sure there is global ordering of transactions and there is only 1 state they all agree. – EralpB Nov 23 '17 at 11:55
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You might want to look at this article.

To resume some of the points :

  • A private blockchain is a form of shared database
  • Different consensus protocols than Proof Of Work exist for private/permission blockchains
  • Check out Quorum and Hyperledger Fabric for enterprise blockchain solutions under active development
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Proof of work is not required on a permissioned or private blockchain.

For the more efficient operation, for example Proof-of-Authority can be used, like in Ethereum Kovan testnet.

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In general, PoW is immoral in it's waste of energy. Other consensus algorithms are available that do are more energy efficient, such as

  • PoS (Proof of Stake) used by Ethereum (winner has the most "stake" or "wealth" of some kind)
  • PBFT (Practical Byzantine Fault Tolerance) elects a leader. Does not scale due to the high number of messages between nodes.
  • Raft (which elects a leader until the leader times-out). Scales well and is efficient. Not BFT (vulnerable to bad actor nodes)
  • PoET (Proof of Elapsed Time) (which generates a random wait time and the first timer to expire wins)
  • PoS is not used by Ethereum at the moment, they have plans to upgrade in the near future though – abed Nov 8 '18 at 9:11

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