[bitcoin-dev] Three hardfork-related BIPs

[Luke Dashjr <luke@dashjr.org>]

I've put together three hardfork-related BIPs. This is parallel to the ongoing 
research into the MMHF/SHF WIP BIP, which might still be best long-term.

1) The first is a block size limit protocol change. It also addresses three 
criticisms of segwit: 1) segwit increases the block size limit which is 
already considered by many to be too large; 2) segwit treats pre-segwit 
transactions “unfairly” by giving the witness discount only to segwit 
transactions; and 3) that spam blocks can be larger than blocks mining 
legitimate transactions. This proposal may (depending on activation date) 
initially reduce the block size limit to a more sustainable size in the short-
term, and gradually increase it up over the long-term to 31 MB; it will also 
extend the witness discount to non-segwit transactions. Should the initial 
block size limit reduction prove to be too controversial, miners can simply 
wait to activate it until closer to the point where it becomes acceptable 
and/or increases the limit. However, since the BIP includes a hardfork, the 
eventual block size increase needs community consensus before it can be 
deployed. Proponents of block size increases should note that this BIP does 
not interfere with another more aggressive block size increase hardfork in the 
meantime. I believe I can immediately recommend this for adoption; however, 
peer and community review are welcome to suggest changes.
Text: https://github.com/luke-jr/bips/blob/bip-blksize/bip-blksize.mediawiki
Code: https://github.com/bitcoin/bitcoin/compare/master...luke-jr:bip-blksize 
(consensus code changes only)

2) The second is a *preparatory* change, that should allow trivially 
transforming certain classes of hardforks into softforks in the future. It 
essentially says that full nodes should relax their rule enforcement, after 
sufficient time that would virtually guarantee they have ceased to be 
enforcing the full set of rules anyway. This allows these relaxed rules to be 
modified or removed in a softfork, provided the proposal to do so is accepted 
and implemented with enough advance notice. Attempting to implement this has 
proven more complicated than I originally expected, and it may make more sense 
for full nodes to simply stop functioning (with a user override) after the 
cut-off date). In light of this, I do not yet recommend its adoption, but am 
posting it for review and comments only.
Text: https://github.com/luke-jr/bips/blob/bip-hfprep/bip-hfprep.mediawiki

3) Third is an anti-replay softfork which can be used to prevent replay 
attacks whether induced by a hardfork-related chain split, or even in ordinary 
operation. It does this by using a new opcode (OP_CHECKBLOCKATHEIGHT) for the 
Bitcoin scripting system that allows construction of transactions which are 
valid only on specific blockchains.
Text: https://github.com/luke-jr/bips/blob/bip-noreplay/bip-noreplay.mediawiki

Luke