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From: Natanael <natanael.l@gmail.com>
Date: Wed, 25 Jan 2017 08:15:14 +0100
Message-ID: <CAAt2M1_cQTfaDyQkaixeFB5Ubi35fSOs9Ks74WZEehtFk__B3w@mail.gmail.com>
To: Johnson Lau <jl2012@xbt.hk>
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Cc: Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Anti-transaction replay in a hardfork
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Den 25 jan. 2017 08:06 skrev "Johnson Lau" <jl2012@xbt.hk>:

What you describe is not a fix of replay attack. By confirming the same tx
in both network, the tx has been already replayed. Their child txs do not
matter.


Read it again.

The validation algorithm would be extended so that the transaction can't be
replayed, because replaying it in the other network REQUIRES a child
transaction in the same block that is valid, a child transaction the is
unique to the network. By doing this policy change simultaneously in both
networks, old pre-signed transactions *can not be replayed by anybody but
the owner* of the coins (as he must spend them immediately in the child
transaction).

It means that as soon as spent, the UTXO sets immediately and irrevocably
diverges across the two networks. Which is the entire point, isn't it?

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<div dir=3D"auto"><div class=3D"gmail_extra" dir=3D"auto"><br><div class=3D=
"gmail_quote">Den 25 jan. 2017 08:06 skrev &quot;Johnson Lau&quot; &lt;<a h=
ref=3D"mailto:jl2012@xbt.hk">jl2012@xbt.hk</a>&gt;:<br type=3D"attribution"=
><blockquote class=3D"quote" style=3D"margin:0 0 0 .8ex;border-left:1px #cc=
c solid;padding-left:1ex"><div style=3D"word-wrap:break-word"><div>What you=
 describe is not a fix of replay attack. By confirming the same tx in both =
network, the tx has been already replayed. Their child txs do not matter.</=
div></div></blockquote></div></div><div dir=3D"auto"><br></div><div dir=3D"=
auto">Read it again.=C2=A0</div><div dir=3D"auto"><br></div><div dir=3D"aut=
o">The validation algorithm would be extended so that the transaction can&#=
39;t be replayed, because replaying it in the other network REQUIRES a chil=
d transaction in the same block that is valid, a child transaction the is u=
nique to the network. By doing this policy change simultaneously in both ne=
tworks, old pre-signed transactions *can not be replayed by anybody but the=
 owner* of the coins (as he must spend them immediately in the child transa=
ction).=C2=A0</div><div dir=3D"auto"><br></div><div dir=3D"auto">It means t=
hat as soon as spent, the UTXO sets immediately and irrevocably diverges ac=
ross the two networks. Which is the entire point, isn&#39;t it?=C2=A0</div>=
<div class=3D"gmail_extra" dir=3D"auto"></div></div>

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