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I know that the PoW in Ethereum is based on Ethash and that some parameters are adjusted in order to maintain the average time between blocks to a certain value.

Now my question is: does the Ethereum protocol allow for a drastic change of the PoW algorithm ?

I know that in bitcoins changing the SHA-256 based PoW algorithm to something else — like scrypt for instance — would required a hard fork. However, we could imagine some mechanism to maintain backward compatibility with previous PoW algorithms — like accepting different algorithms until most of the clients are updated.

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  • ethereum does not has superior upgradability compared to bitcoin. ethereum uses hard and soft forks too. so no, the protocol does not allow change of consensus rules without a hard/soft fork
    – user1816
    Commented May 2, 2016 at 6:17

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In the future there will be move to a proof of stake algorithm called Casper, which will require a hard fork because such changes are not backwards compatible.

There has already been a hard fork: Homestead. Several consensus rules were changed, such as adding the DELEGATECALL opcode and increasing the price of gas for creating contracts via transactions from 21000 to 53000. But this didn't affect the Ethhash algorithm itself.

One addition during the Homestead hard-fork, EIP 8, meant that all future versions of the client will accept incoming network upgrades and handshakes. (https://ethereum-homestead.readthedocs.io/en/latest/introduction/the-homestead-release.html), but not to the core protocol.

You might be interested in this thread for more detail on how changes to the consensus protocols work: What is a hardfork?

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  • Hi, I just wonder why would you want to change ethereum mining algorithm? Isn't ethash good enough until Casper?
    – Nicolas Massart
    Commented Apr 30, 2016 at 13:34
  • The mining algorithm is still PoW until Casper. The hardfolk didn't actually change the mining algorithm itself (as far as I know).
    – Physes
    Commented Apr 30, 2016 at 15:01

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