[Bitcoin-segwit2x] Alpha Milestone

[Chris]

On 06/14/2017 06:43 PM, Jeff Garzik via Bitcoin-segwit2x wrote:
> As far as I'm aware, there is widespread consensus inside and outside
> the WG that replay protection would be nice to have.
>
> The technical next-step question:   What is a method that (a) provides
> replay protection yet (b) does not require a wallet upgrade?
I'll repost Gavin's slack comment here for people who haven't seen it.
While not comprehensive, it does seem like a quick and easy way to add
replay protection.

[9:14]
It would be easy to add a rule that allows tx creators to create
transactions that are not valid on the segwit2x chain.  E.g. rule could
be any tx with OP_RETURN <magic_value> is considered invalid, where
magic_value is just some arbitrary constant.

[9:15]
Would that be sufficient replay protection?  It is not clear to me what
the requirements are.

[9:16]
With just that rule, an exchange could split their UTXOs by spending
them on the 1MB chain using OP_RETURN <magic>. Wait for them to confirm,
and then they're split.

[9:17]
The "wait for them to confirm on the 1MB chain" might take a very long
time, of course, because of insufficient hashpower on that chain, but
maybe that is a feature and not a bug