elip151: concatenate unprefixed opcode and script pubkey

[LeoComandini]

This is a breaking change but it adheres more to the ELIP.

[LeoComandini]

Currently for scriptpubkey 0014aa..aa, we hash 01ff160014aa...aa
After this we hash ff0014aa..aa

Not sure what's the appropriate thing to do here,
we can go with this MR and change the ELIP test vectors,
we can serialize in a different way,
or edit the ELIP to match the implementation.

[apoelstra]

Agreed this is better. Though would be very easy to change the ELIP to say "you have to encode 01ff" rather than "you have to encode ff".

I guess, the question is, is this used anywhere and what would be the consequence of breaking it?

[LeoComandini]

is this used anywhere and what would be the consequence of breaking it?

It is exposed by lwk but I've no evidence of anyone using this in prod.
So in theory we're in time to change this if we prefer.

[LeoComandini]

But TBH I don't have a preference,
if we prefer to change the ELIP,
I can close this and open a PR there

[apoelstra]

I have no preference and I'm not involved with lwk at all. So you need to make the call (or find somebody who will).

Just let me know.

[LeoComandini]

@apoelstra
I think minimal disruption is changing the ELIP,
opened ElementsProject/ELIPs#13
I'll close this once that is merged

[LeoComandini]

We chose to amend the ELIP, closing