[bitcoin-dev] Two questions about segwit implementation

Johnson Lau jl2012 at xbt.hk
Sun May 26 16:28:57 UTC 2019

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 at 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

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