Author: Johnson Lau 2017-02-06 18:06:22
Published on: 2017-02-06T18:06:22+00:00
The bitcoin-dev mailing list has released a series of proposals for consensus changes to the Bitcoin network. These include changes to the pre-hardfork policy, sighash limitations, new transaction weight definitions, and block weight growth over time. A proposal was made to include a new extended and flexible header in the witness field of the coinbase transaction. The extended header includes space for miners to put anything they want, which bitcoin users can ignore, making it merge-mining friendly. There is also a small header space for miners to include non-consensus enforced bitcoin-related data that is useful for fee estimation. Additionally, there are proposed changes to the coinbase transaction format and the witness merkle root. Other proposed changes involve ignoring the sign bit in BIP9 and implementing a full hardfork with more drastic changes to address issues with SHA256 shortcut like ASICBoost and block withholding attacks.The hardfork signaling block is set by the sign bit of header nVersion, and at least 51% of miners are needed to build the new block format to activate it. The hard fork time is determined by a consensus of the community to prevent splitting. A special BIP9 softfork has been defined with bit-15 to relax the size limit of Header 2 and Header 3, allowing expansion without a hardfork. The latter changes would require firmware upgrades for all existing miners and light wallet upgrades, but they are not expected to happen until at least two years after the initial activation of the hardfork. An experimental implementation of these proposals can be found on GitHub, but it is still untested and not independently reviewed. It should not be used in production, although it may work fine on testnet. Finally, a new transaction weight formula encourages responsible use of UTXO, while the block size will grow linearly until a certain limit, and there is Sighash O(n^2) protection for legacy (non-segwit) outputs. Some aspects of the proposals are still under development, such as automated testing, post-hardfork support for old light wallets, and wallet support for anti-tx-replay. There is also no new p2p message to transmit secondary header and no full mining or mempool support yet.
Updated on: 2023-05-20T00:53:15.289985+00:00