Re: [Bitcoin-development] SIGHASH_WITHINPUTVALUE

[Alan Reiner <etotheipi@gmail.com>]

On 01/23/2015 11:05 AM, Gregory Maxwell wrote:
> On Fri, Jan 23, 2015 at 3:24 PM, Alan Reiner <etotheipi@gmail.com> wrote:
>> Unfortunately, it seems that there was no soft-fork way to achieve this
>> benefit, at least not one that had favorable properties.  Most of the
>> soft-fork variations of it required the coins being spent to have been
>> originated in a special way.  In other words, it would only work if the
>> coins had entered the wallet with some special, modified TxOut script.  So
>> it wouldn't work with existing coins, and would require senders to update
>> their software to reshape the way they send transactions to be compatible
>> with our goals.
> I think this is unreasonable. There is a straight-forward soft-fork
> approach which is safe (e.g. no risk of invalidating existing
> transactions). Yes, it means that you need to use newly created
> addresses to get coins that use the new signature type... but thats
> only the case for people who want the new capability. This is
> massively preferable to expecting _every_ _other_ user of the system
> (including miners, full nodes, etc.) to replace their software with an
> incompatible new version just to accommodate your transactions, for
> which they may care nothing about and which would otherwise not have
> any urgent need to change.
>
>


As far as I'm concerned, anything that requires the coins to originate
in the wallet with some special form is a non-starter.  The new SIGHASH
type allows you to sign transactions with *any* coins already in your
wallet, and imposes no requirements on anyone paying your cold wallet to
be compatible with your signer. 

Any proposals that require coin origination features means that 100% of
people paying you need to "be nice" and send you coins with this special
structure.  You can't spend old coins that were sent before this
proposal was implemented, and if anyone sends you coins without
respecting the new structure, then your signing devices need the
full-complexity routines to accommodate, which defeats the entire purpose.

I am happy to entertain other ideas that achieve our goals here, but I'm
fairly confident that the new SIGHASH type is the only way that would
allow devices like Trezor to truly simplify their design (and still work
securely on 100% of funds contained by the wallet).