As this article is being written, Segregated Witness (SegWit) has just activated on the bitcoin network and celebratory events are being held throughout the world. This scaling solution came at a great cost–the bitcoin cash hard fork–but developers believe it will bring increased optimization, security, and scalability to the bitcoin network. However, the great bitcoin scaling debate is far from settled, and the November target date for the SegWit2x hard fork is rapidly approaching.
One of the most contentious aspects of SegWit2x (or btc1) is its current lack of replay protection, which prevents an attacker from broadcasting a transaction on multiple blockchains with a shared history.
Bitcoin Core developers and supporters argue that since SegWit2x is implementing the hard fork (and, the argument goes, creating a new altcoin), they should be the ones to add replay protection. They have even threatened legal action if a hard fork occurs without adequate replay prevention.
SegWit2x developer Jeff Garzik–who was recently kicked out of the Bitcoin Core repository–and other New York Agreement signatories have maintained that they are upgrading bitcoin, not creating a new coin.
Since, they claim, their version will have almost all the hashpower, the onus is on the “dysfunctional minority chain” to protect itself.
After much debate, Garzik has now added opt-in replay protection to btc1 on GitHub and has proposed merging it into the codebase. The code, which is based on a replay protection patch written by former Core developer Gavin Andresen, allows users to include markers in their transactions that the SegWit2x network will consider non-standard. This will give people an avenue to remain firmly on the Core-supported chain while also making it less likely that the bitcoin ecosystem will permanently split into multiple coins (again).
However, Garzik’s concession has not been met with open arms. Critics say that the opt-in method is “useless” because it is too difficult for many casual users, and users who have the technical ability to implement it already know other methods to avoid falling prey to a replay attack. They claim that the only acceptable route is opt-out protection, whereby the protection is enabled by default and users must consciously choose to forgo it.
However, opt-out implementation does not currently appear likely. In the SegWit2x August status report distributed this morning to the Bitcoin-segwit2x mailing list, BitGo CEO Mike Belshe resisted calls for opt-out protection because it would increase the likelihood of a permanent chain split:
Some opt-out replay protection schemes have been proposed, that require all wallets to upgrade. These are naive suggestions, as they will exacerbate the chain split we are trying to avoid.
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