[bitcoin-dev] [BIP Proposal] BetterHash Mining Protocol Replacements

[Matt Corallo <lf-lists@mattcorallo.com>]

Been working on this one for a while, so its already been through a few
rounds of feeback (thanks to all those who already have provided feedback)!

At a high level, this meets a few goals:

1) Replace getblocktemplate with something that is both more performant
(no JSON encoding, no full transactions sent over the wire to update a
job, hence we can keep the same CTransactionRef in Bitcoin Core making
lots of validation things way faster), more robust for consensus changes
(no need to add protocol changes to add commitments ala SegWit in the
future), and moves more block-switching logic inside of the work
provider (allowing Bitcoin Core to better optimize work switching as it
knows more than an outside pool server, specifically we can play more
games with how we do mempool eviction, empty block mining, and not
mining fresh transactions more easily by moving to a more "push" model
from the normal "pull" getblocktemplate implementation).

2) Replace Stratum with something more secure (sign messages when
applicable, without adding too much overhead to the pool), simpler to
implement (not JSON-wrapped-hex, no 32-byte-swapped-per-4-byte-byteorder
insanity), and better-defined (a clearly written spec, encompassing the
various things shoved backwards into stratum like suggested difficulty
in the password field and device identification by setting user to
"user.device") with VENDOR_MESSAGEs provided for extensibility instead
of conflicting specifications from various different vendors.

3) Provide the ability for a pool to accept work which the users of the
pool selected the transactions for, providing strong decentralization
pressure by removing the network-level centralization attacks pools can
do (or be compromised and used to perform) while still allowing them
full control of payout management and variance reduction.

While (1) and (2) stand on their own, making it all one set of protocols
to provide (3) provides at least the opportunity for drastically better
decentralization in Bitcoin mining in the future.

The latest version of the full BIP draft can be found at
https://github.com/TheBlueMatt/bips/blob/betterhash/bip-XXXX.mediawiki
and implementations of the work-generation part at
https://github.com/TheBlueMatt/bitcoin/commits/2018-02-miningserver and
pool/proxy parts at https://github.com/TheBlueMatt/mining-proxy (though
note that both implementations are currently on a slightly out-of-date
version of the protocol, I hope to get them brought up to date in the
coming day or two and make them much more full-featured. The whole stack
has managed to mine numerous testnet blocks on several different types
of hardware).

Matt