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To: Luke Dashjr <luke@dashjr.org>,
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Cc: Pieter Wuille <pieter.wuille@gmail.com>
Subject: Re: [bitcoin-dev] Taproot proposal
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Good morning Luke,


> Is there any way to use the Taproot construct here while retaining extern=
al
> script limitations that the involved party(ies) cannot agree to override?
> For example, it is conceivable that one might wish to have an uncondition=
al
> CLTV enforced in all circumstances.

Perhaps this can be enforced offchain, by participants refusing to sign a t=
ransaction unless it has an `nLockTime` of the agreed-upon "unconditional C=
LTV".
Then the CLTV need only be on branches which have a strict subset of the pa=
rticipants as signers.

>
> It may be useful to have a way to add a salt to tap branches.

Would not adding `OP_PUSH(<salt>) OP_DROP` to the leaves work?
If you enforce always salting with a 32-byte salt, that "only" saves 3 byte=
s of witness data (for the `OP_PUSHDATA1+size` and `OP_DROP` opcodes).
Or do you refer to always salting every node?
(I am uncertain, but would not adding a salt to every leaf be sufficient?)

(in any case, if you use different pubkeys for each contract, rather than r=
eusing keys, is that not enough randomization to prevent creating rainbow t=
ables of scripts?)

>
> Some way to sign an additional script (not committed to by the witness
> program) seems like it could be a trivial addition.

It seems to me the annex can be used for this, by having it contain both th=
e script and the signature somehow concatenated.

Regards,
ZmnSCPxj