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References: <e537e781-e10f-7299-fddb-67fab74124c0@gmail.com>
In-Reply-To: <e537e781-e10f-7299-fddb-67fab74124c0@gmail.com>
From: Kostas Karasavvas <kkarasavvas@gmail.com>
Date: Mon, 27 May 2019 10:26:21 +0300
Message-ID: <CABE6yHsCf7Mz+wDq7wPUR3YT0ua2i4O20XjF1-GZD_zJ8BXkVQ@mail.gmail.com>
To: Aymeric Vitte <vitteaymeric@gmail.com>, 
	Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
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Subject: Re: [bitcoin-dev] Two questions about segwit implementation
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On Sun, May 26, 2019 at 5:07 PM Aymeric Vitte via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> I realized recently that my segwit implementation was not correct,
> basically some time ago, wrongly reading the specs (and misleaded by
> what follows), I thought that scriptsig would go into witness data as it
> was, but that's not the case, op_pushdata is replaced by varlen
>
> Now reading correctly the specs, they seem to be not totally correct,
> then the first question is: why OP_0 is 00 in witness data and not 0100?
> Does this apply to other op_codes? This does not look logical at all
>
>
op_pushdata allows for unsigned integers and thus it uses the extra byte to
specify that.

A varint (varlen) is unsigned.  0 and anything <= 252 is one byte length,
so 00.


> The second question is: why for non segwit inputs there is a 00 length
> in segwit data, what is the rational for that? It should just be nothing
> since you don't need this to reconciliate things
>
>
Because you don't have the number of witnesses as you have for
inputs/outputs. The witness data length is assumed to be the same as the
inputs length. And then for non-segwit inputs you need the 00 to specify
that it is empty.

Hope that helps.

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<div dir=3D"ltr"><div dir=3D"ltr"><br></div><br><div class=3D"gmail_quote">=
<div dir=3D"ltr" class=3D"gmail_attr">On Sun, May 26, 2019 at 5:07 PM Aymer=
ic Vitte via bitcoin-dev &lt;<a href=3D"mailto:bitcoin-dev@lists.linuxfound=
ation.org">bitcoin-dev@lists.linuxfoundation.org</a>&gt; wrote:<br></div><b=
lockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-le=
ft:1px solid rgb(204,204,204);padding-left:1ex">I realized recently that my=
 segwit implementation was not correct,<br>
basically some time ago, wrongly reading the specs (and misleaded by<br>
what follows), I thought that scriptsig would go into witness data as it<br=
>
was, but that&#39;s not the case, op_pushdata is replaced by varlen<br>
<br>
Now reading correctly the specs, they seem to be not totally correct,<br>
then the first question is: why OP_0 is 00 in witness data and not 0100?<br=
>
Does this apply to other op_codes? This does not look logical at all<br>
<br></blockquote><div><br></div><div>op_pushdata allows for unsigned intege=
rs and thus it uses the extra byte to specify that.</div><div><br></div><di=
v>A varint (varlen) is unsigned.=C2=A0 0 and anything &lt;=3D 252 is one by=
te length, so 00.=C2=A0</div><div>=C2=A0</div><blockquote class=3D"gmail_qu=
ote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,20=
4);padding-left:1ex">
The second question is: why for non segwit inputs there is a 00 length<br>
in segwit data, what is the rational for that? It should just be nothing<br=
>
since you don&#39;t need this to reconciliate things<br>
<br></blockquote><div><br></div><div>Because you don&#39;t have the number =
of witnesses as you have for inputs/outputs. The witness data length is ass=
umed to be the same as the inputs length. And then for non-segwit inputs yo=
u need the 00 to specify that it is empty.</div><div>=C2=A0</div><div></div=
></div><div dir=3D"ltr" class=3D"gmail_signature"><div dir=3D"ltr"><div><di=
v>Hope that helps.<br></div></div><div><br></div></div></div></div>

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