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From: Johnson Lau <jl2012@xbt.hk>
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Date: Tue, 21 Nov 2017 01:45:18 +0800
References: <CAAQs3wuDPktHc6kiZXqTaatOheX4KP=TRgje0_-ED5h8iNs-MA@mail.gmail.com>
To: Praveen Baratam <praveen.baratam@gmail.com>,
bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org>
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Subject: Re: [bitcoin-dev] Why SegWit Anyway?
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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 =
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 with segwit =
(BIP141), BIP140 does not have the side-effect of block size increase, =
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 =
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:
>=20
> Bitcoin Noob here. Please forgive my ignorance.
>=20
> =46rom 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.
>=20
> 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
> --=20
> Dr. Praveen Baratam
>=20
> about.me =
<http://about.me/praveen.baratam>_________________________________________=
______
> bitcoin-dev mailing list
> bitcoin-dev@lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
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charset=utf-8
<html><head><meta http-equiv=3D"Content-Type" content=3D"text/html; =
charset=3Dutf-8"></head><body style=3D"word-wrap: break-word; =
-webkit-nbsp-mode: space; line-break: after-white-space;" class=3D""><div =
class=3D"">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.</div><div class=3D""><br class=3D""></div><div =
class=3D"">Also, changing the definition of TxID is a hardfork change, =
i.e. everyone are required to upgrade or a chain split will =
happen.</div><div class=3D""><br class=3D""></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 with segwit (BIP141), BIP140 does not =
have the side-effect of block size increase, 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 needs to store both txid =
and normalised txid<br class=3D""><div class=3D""><div><br =
class=3D""><blockquote type=3D"cite" class=3D""><div class=3D"">On 21 =
Nov 2017, at 1:24 AM, Praveen Baratam via bitcoin-dev <<a =
href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org" =
class=3D"">bitcoin-dev@lists.linuxfoundation.org</a>> wrote:</div><br =
class=3D"Apple-interchange-newline"><div class=3D""><div dir=3D"ltr" =
class=3D""><div class=3D""><span =
style=3D"font-family:Verdana,arial,sans-serif;font-size:14px" =
class=3D"">Bitcoin Noob here. Please forgive my =
ignorance.</span></div><span =
style=3D"font-family:Verdana,arial,sans-serif;font-size:14px" =
class=3D""><div class=3D""><span =
style=3D"font-family:Verdana,arial,sans-serif;font-size:14px" =
class=3D""><br class=3D""></span></div>=46rom 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.</span><div class=3D""><span =
style=3D"font-family:Verdana,arial,sans-serif;font-size:14px" =
class=3D""><br class=3D""></span></div><div class=3D""><span =
style=3D"font-family:Verdana,arial,sans-serif;font-size:14px" =
class=3D"">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?</span><br clear=3D"all" class=3D""><div class=3D""><br =
class=3D""></div>-- <br class=3D""><div class=3D"gmail_signature"><div =
style=3D"color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13px;b=
ackground-color:rgb(255,255,255)" class=3D"">Dr. Praveen =
Baratam</div><div =
style=3D"color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13px;b=
ackground-color:rgb(255,255,255)" class=3D""><br class=3D""></div><div =
style=3D"color:rgb(34,34,34);font-family:arial,sans-serif;font-size:13px;b=
ackground-color:rgb(255,255,255)" class=3D""><a =
href=3D"http://about.me/praveen.baratam" style=3D"color:rgb(17,85,204)" =
target=3D"_blank" class=3D"">about.me</a></div></div>
</div></div>
_______________________________________________<br class=3D"">bitcoin-dev =
mailing list<br class=3D""><a =
href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org" =
class=3D"">bitcoin-dev@lists.linuxfoundation.org</a><br =
class=3D"">https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev<=
br class=3D""></div></blockquote></div><br class=3D""></div></body></html>=
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