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From: Dan Bryant <dkbryant@gmail.com>
Date: Mon, 20 Nov 2017 12:04:09 -0600
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To: bitcoin-dev@lists.linuxfoundation.org, Johnson Lau <jl2012@xbt.hk>
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Subject: Re: [bitcoin-dev] Why SegWit Anyway?
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Is there any incentive for miners to pick segwit transactions over
non-segwit transaction.  Do they require less, equal, or more compute to
process?

On Nov 20, 2017 11:46 AM, "Johnson Lau via bitcoin-dev" <
bitcoin-dev@lists.linuxfoundation.org> wrote:

We can=E2=80=99t =E2=80=9Cjust compute the Transaction ID the same way the =
hash for signing
the transaction is computed=E2=80=9D because with different SIGHASH flags, =
there
are 6 (actually 256) ways to hash a transaction.

Also, changing the definition of TxID is a hardfork change, i.e. everyone
are required to upgrade or a chain split will happen.

It is possible to use =E2=80=9Cnormalised TxID=E2=80=9D (BIP140) to fix mal=
leability issue.
As a softfork, BIP140 doesn=E2=80=99t change the definition of TxID. Instea=
d, the
normalised txid (i.e. txid with scriptSig removed) is used when making
signature. Comparing with segwit (BIP141), BIP140 does not have the
side-effect of block size increase, and doesn=E2=80=99t provide any incenti=
ve to
control the size of UTXO set. Also, BIP140 makes the UTXO set permanently
bigger, as the database needs to store both txid and normalised txid

On 21 Nov 2017, at 1:24 AM, Praveen Baratam via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

Bitcoin Noob here. Please forgive my ignorance.

From what I understand, in SegWit, the transaction needs to be serialized
into a data structure that is different from the current one where
signatures are separated from the rest of the transaction data.

Why change the format at all? Why cant we just compute the Transaction ID
the same way the hash for signing the transaction is computed?

--=20
Dr. Praveen Baratam

about.me <http://about.me/praveen.baratam>
_______________________________________________

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<div dir=3D"auto">Is there any incentive for miners to pick segwit transact=
ions over non-segwit transaction.=C2=A0 Do they require less, equal, or mor=
e compute to process?</div><div class=3D"gmail_extra"><br><div class=3D"gma=
il_quote">On Nov 20, 2017 11:46 AM, &quot;Johnson Lau via bitcoin-dev&quot;=
 &lt;<a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org">bitcoin-dev@l=
ists.linuxfoundation.org</a>&gt; wrote:<br type=3D"attribution"><blockquote=
 class=3D"quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padd=
ing-left:1ex"><div style=3D"word-wrap:break-word;line-break:after-white-spa=
ce"><div>We can=E2=80=99t =E2=80=9Cjust compute the Transaction ID the same=
 way the hash for signing the transaction is computed=E2=80=9D because with=
 different SIGHASH flags, there are 6 (actually 256) ways to hash a transac=
tion.</div><div><br></div><div>Also, changing the definition of TxID is a h=
ardfork change, i.e. everyone are required to upgrade or a chain split will=
 happen.</div><div><br></div>It is possible to use =E2=80=9Cnormalised TxID=
=E2=80=9D (BIP140) to fix malleability issue. As a softfork, BIP140 doesn=
=E2=80=99t change the definition of TxID. Instead, the normalised txid (i.e=
. txid with scriptSig removed) is used when making signature. Comparing wit=
h segwit (BIP141), BIP140 does not have the side-effect of block size incre=
ase, and doesn=E2=80=99t provide any incentive to control the size of UTXO =
set. Also, BIP140 makes the UTXO set permanently bigger, as the database ne=
eds to store both txid and normalised txid<br><div><div><br><blockquote typ=
e=3D"cite"><div class=3D"elided-text"><div>On 21 Nov 2017, at 1:24 AM, Prav=
een Baratam via bitcoin-dev &lt;<a href=3D"mailto:bitcoin-dev@lists.linuxfo=
undation.org" target=3D"_blank">bitcoin-dev@lists.<wbr>linuxfoundation.org<=
/a>&gt; wrote:</div><br class=3D"m_-2919472362485226639Apple-interchange-ne=
wline"></div><div><div class=3D"elided-text"><div dir=3D"ltr"><div><span st=
yle=3D"font-family:Verdana,arial,sans-serif;font-size:14px">Bitcoin Noob he=
re. Please forgive my ignorance.</span></div><span style=3D"font-family:Ver=
dana,arial,sans-serif;font-size:14px"><div><span style=3D"font-family:Verda=
na,arial,sans-serif;font-size:14px"><br></span></div>From what I understand=
, in SegWit, the transaction needs to be serialized into a data structure t=
hat is different from the current one where signatures are separated from t=
he rest of the transaction data.</span><div><span style=3D"font-family:Verd=
ana,arial,sans-serif;font-size:14px"><br></span></div><div><span style=3D"f=
ont-family:Verdana,arial,sans-serif;font-size:14px">Why change the format a=
t all? Why cant we just compute the Transaction ID the same way the hash fo=
r signing the transaction is computed?</span><br clear=3D"all"><div><br></d=
iv>-- <br><div class=3D"m_-2919472362485226639gmail_signature"><div style=
=3D"color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13px;backgro=
und-color:rgb(255,255,255)">Dr. Praveen Baratam</div><div style=3D"color:rg=
b(34,34,34);font-family:arial,sans-serif;font-size:13px;background-color:rg=
b(255,255,255)"><br></div><div style=3D"color:rgb(34,34,34);font-family:ari=
al,sans-serif;font-size:13px;background-color:rgb(255,255,255)"><a href=3D"=
http://about.me/praveen.baratam" style=3D"color:rgb(17,85,204)" target=3D"_=
blank">about.me</a></div></div>
</div></div></div>
______________________________<wbr>_________________<div class=3D"quoted-te=
xt"><br>bitcoin-dev mailing list<br><a href=3D"mailto:bitcoin-dev@lists.lin=
uxfoundation.org" target=3D"_blank">bitcoin-dev@lists.<wbr>linuxfoundation.=
org</a><br><a href=3D"https://lists.linuxfoundation.org/mailman/listinfo/bi=
tcoin-dev" target=3D"_blank">https://lists.linuxfoundation.<wbr>org/mailman=
/listinfo/bitcoin-<wbr>dev</a><br></div></div></blockquote></div><br></div>=
</div><br>______________________________<wbr>_________________<br>
bitcoin-dev mailing list<br>
<a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org">bitcoin-dev@lists.=
<wbr>linuxfoundation.org</a><br>
<a href=3D"https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev" =
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/mailman/listinfo/bitcoin-<wbr>dev</a><br>
<br></blockquote></div><br></div>

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