To: Johnson Lau <jl2012@xbt.hk>
References: <e537e781-e10f-7299-fddb-67fab74124c0@gmail.com>
	<6DFB6C65-D123-40FD-9CE3-49FFCA81EE46@xbt.hk>
	<e342cb8f-a909-a806-bd76-91580234cd7f@gmail.com>
	<253DB697-BECF-4D68-8A1E-1549B52D5AFA@xbt.hk>
	<a7742e04-22b1-2015-440a-ef81b5fbeed4@gmail.com>
	<DD2C67C8-0DF6-4140-8427-19B7F28FA22C@xbt.hk>
From: Aymeric Vitte <vitteaymeric@gmail.com>
Openpgp: preference=signencrypt
Autocrypt: addr=vitteaymeric@gmail.com; prefer-encrypt=mutual; keydata=
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Message-ID: <6d6766da-67fb-31e1-eceb-663bffeef74a@gmail.com>
Date: Sun, 26 May 2019 23:17:30 +0200
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In-Reply-To: <DD2C67C8-0DF6-4140-8427-19B7F28FA22C@xbt.hk>
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Cc: bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org>, me@thomaskerin.io,
	Pieter Wuille <pieter.wuille@gmail.com>
Subject: Re: [bitcoin-dev] Two questions about segwit implementation
Precedence: list

Well, OK, then back to non standard stuff and bitcoin considers that an
OP_1 or empty scriptpubkey is something that can exist, sipa does not
like my questions on this list but this is a bit frightening in fact to
see that after 10 years an OP_1 scriptpubkey or empty one can be a use
case, thanks Thomas also, where all of this is clearly documented so
people don't bother the list not to produce approximative stuff remains
mysterious

Le 26/05/2019 à 19:24, Johnson Lau a écrit :
> Empty scriptSig doesn’t imply segwit input: if the previous scriptPubKey is OP_1 (which does not allow witness), it could still be spent with an empty scriptSig
>
> Similarly, a scriptSig looking like a spend of P2SH-segwit doesn’t imply segwit input: if the previous scriptPubKey is empty, it could be spent with a push of any non-zero value.
>
>> On 27 May 2019, at 1:09 AM, Aymeric Vitte <vitteaymeric@gmail.com> wrote:
>>
>> I did not phrase correctly in fact, what I meant is: if the validator
>> sees empty or witness script in scriptSig, then this is a segwit input,
>> and doing this one by one the validator can associate the correct segwit
>> data to the correct segwit input, so 00 does not look to be needed
>>
>> Le 26/05/2019 à 18:28, Johnson Lau a écrit :
>>> This is not how it works. While the transaction creator may know which inputs are segwit, the validators have no way to tell until they look up the UTXO set.
>>>
>>> In a transaction, all information about an input the validators have is the 36-byte outpoint (txid + index). Just by looking at the outpoint, there is no way to tell whether it is segwit-enabled or not. So there needs to be a way to tell the validator that “the witness for this input is empty”, and it is the “00”.
>>>
>>>> On 27 May 2019, at 12:18 AM, Aymeric Vitte <vitteaymeric@gmail.com> wrote:
>>>>
>>>> ……. for the 00 number of witness
>>>> data for non segwit inputs the one that is doing the transaction knows
>>>> which inputs are segwit or not, then parsing the transaction you can
>>>> associate the correct input to the correct witness data, without the
>>>> need of 00, so I must be missing the use case
>