What is Betterhash?
Matt Corallo's Betterhash is designed to 'help' with the centralization of mining scene in bitcoin (and most PoW coins) which is considered as an inevitable consequence of pools dominating it.
The main idea is improving Stratum (the protocol behind pooling) such that individual miners could have a chance to build their custom blocks by including/excluding transactions deliberately while they are using pool operator's address in the coinbase transaction as the wallet that collects the rewards. This is done by a pretty sophisticated handshake phase in which the miner receives a block template from the pool in each round instead of receiving a simple block header (which commits to a full block of pool's choice and the miner has no clue about its contents) and trying to find a nonce for it which is how things work now.
For the miner to be able to fill in the block template, building his own block, it would be necessary to run a full node and it is the first not the last thing that this protocol does for improving decentralization in bitcoin. Other strengths include:
- Resisting covert censorship (my term) threats:
Officially, Matt and proponents of Betterhash believe that it is strong mitigation for censorship as a whole but it is not exactly the case. Pools are efficient when they are large enough and large pools are subject to political and jurisdiction intervention. Betterhash leaves centralized architecture of pool/miner relationship untouched and it is more than obvious that pool operators could be forced to reject miner generated blocks/shares that do include transactions that are hypothetically supposed to be censored and Betterhash can do absolutely nothing about it.
What Betterhash can do for censorship resistance tho is making it very hard and almost impossible for pool operators to do it covertly and in accordance with their private agendas.
- Resisting hash rate hijacking
It has been observed in some occasions pool operators use the miners' hash power to mine alternative chains for political purposes, Betterhash can mitigate this attack because miners are fully engaged with what they are mining.
- Collusion resistance
More block-generators, less collusion feasibility. Given Betterhash was possible to dominate the mining scene of bitcoin it would make it bulletproof against all forms of 51% attack.
So, why not Betterhash?
Unfortunately, Matt's protocol isn't employed and won't be ever because of a basic flaw: cost/benefit justifiability problem.
Looking again at the pros listed above (and other strengths not listed) it is obvious that they all share the same property of being strategically beneficial for bitcoin and lack one simple property: bringing any tangible advantage in terms of income for miners and pools at the same time that it comes with meaningful costs for miners and huge costs for pools.
Miners costs for implementing Betterhash
Besides the obvious cost of setting up a full node, miners need a substantially better internet connection and a local proxy and will experience a more 'stale rate' than what they get with legacy Stratum because it takes more time for the pool server to validate and accept their shares.
Pools costs
Here is the bottleneck. Better hash requires pool server to do an exhaustive job each time a miner issues a share and if they want to compete with the current Stratum utility level in terms of covering the variance it is not possible to use higher target difficulties for lowering the number of shares miners are used to submit. Hence a pool server should meet a very high level of hardware and Internet bandwidth requirement for handling the same number of miners that are connected now. The situation worsens considering the migration phase in which pool servers need to have parallel capacities for both versions of Stratum.
Conclusion
Betterhash is a good but impractical idea because it is trying to compete with the optimized (still fragile) current mining protocol without offering any tangible advantage. In a decentralized, wild environment like bitcoin, actors do not pay for and commit to what is considered good for the community without getting reasonable rewards almost instantly, it is called The Tragedy Of Commons.
You are right, but any new technology is very difficult to implement. Betterhash is still very attractive.